Engineering Innovations Volume 2

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Volume 2 of
Engineering Innovations
ISSN print 2813-0995
ISSN web 2813-1002

Full text available online at https://www.scientific.net/book/engineering-innovations-vol-2/978-3-0364-1097-5

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Table of Contents

Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

I En Lin, Tsun Yu Lee

Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

Alin Constantin Murariu, Nicuşor Alin Sîrbu, Marius Cocard, Iuliana Duma

Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

Vijay Shrinivas, Rajesh Narasimhan, Thillairajan Arumugam

Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport

Radu Cojocaru, Lia-Nicoleta Botila, Ion Aurel Perianu, Alexandru Adrian Geana

Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Miodrag Arsić, Zeljko Flajs, Sedmak Aleksandar, Emil Veg, Simon Sedmak

Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

Ion Aurel Perianu, Radu Cojocaru, Emilia-Florina Binchiciu, Gabriela-Victoria Mnerie

Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures

Jianwei Ma, Ana Evangelista, Assed Naked Haddad, Milind Siddhpura, Huifen Hao

Highlights of Earned Value Analysis in Construction Projects

Bruno B.F. da Costa, Jorge G. Farías, Mohammad Najjar, Mayara Amario, Carlos A.P. Soares, Assed Naked Haddad

Keywords Index

Authors Index

The original version of this eBook is available on https://www.scientific.net/book/engineering-innovations-vol-2/978-3-0364-1097-5

Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 1-6

doi: 10.4028/p-c74yw7

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2022-01-02

Accepted:
2022-01-13

Online:
2022-06-20

Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

I-EN Lin , Tsun-Yu Lee

1Department of Power Mechanical Engineering, National Formosa University, No.64, Wunhua Rd., Huwei Township, Yunlin County 632, Taiwan

samlin@nfu.edu.tw, 40724111@gm.nfu.edu.tw

Keywords: Tool life, tool wear, spindle current, statistical model.

Abstract

Metal cutting is the commonly used method in mechanical design, and the tool is the most important key factor in metal cutting. When the tool is severely worn, it will cause the tool to break. This article takes the current value of machining precision turret as an example to study the relationship between current value and tool wear. We used statistical mathematical models to predict tool life and used scatter diagrams to verify the timing of tool change and the actual degree of tool wear, to achieve accurate prediction and reduce tool waste. In our experiment, the core part of the indexing plate (turret) is machined by the horizontal machining center, The CCD image capture system was utilized to evaluate cutting tool wear. Three methods are analyzed to predict tool wear and current. The probability statistical mathematical model shows good match to predict the tool life. it is possible to find out the holes with poor quality caused by tool wear and calculate the exchange rate.

Introduction

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

Machine tools are a key industry in Taiwan's machinery industry. It is an indispensable mechanical equipment for manufacturing processing. An average of machining downtime is caused by cutting tool failure [1]. There are two methods in tool wear measurement: (1) Direct monitoring method: it requires cutting tool off-line observation. This method is not suitable for automated production. (2) Indirect monitoring method: it can be the collection of vibration or current signals. If one needs to collect the vibration signals from the tool, the sensor must be placed closer to the blade, which may affect the part accuracy. Altintas has shown the correlation between cutting force and spindle current [2]. Yang et. al. also used spindle current as control index in their the milling process [3]. Therefore, current signal might be the best index of tool wear [4].

Off-line human measurement is time-consuming and is not reliable due to many human factors. The turret fabrication time is 1 hour, but off-line measurement takes another 0.5 hours. In this study, we demonstrate the correlation between the current value and the precision of the finished product. The tool wear can be predicted through the probability model [5]. The correlation between the turret current value and tool wear can be used in reducing labor costs, increasing machine utilization... etc.

Experimental Setup

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

Machining Parts. Here we used fabrication a turret as a demonstration case in this study. The turret material is SCM21 nickel-chromium-molybdenum alloy steel. This turret has a total of 24 processing holes. The angle between the two holes is as shown in Fig. 1. The machining parameters are identical among 24 holes, and the ambient temperature has kept between .

Cutting Tools. There are three kinds of tools applied in machining process (in order): face milling cutter, tungsten steel milling cutter, and fine boring cutter. The fine boring tool affect final precision and therefore was used as our wear analysis.

Tool Tip Image Caption. The automatic tool image measuring instrument was applied to measure the tool length/diameter. After the cutting tool is processed, the tool wear occurs. The image first converted into a binary image through ImageJ software. By adjusting threshold values, we are able to cancel the noise and find a best tool boundary [6]. Fig. 2 shows the worn region by filling out different color and compute color area.

Figure 1. Turret as a core part of the indexing plate (schematic drawing).

Figure 1. Figure 1. Turret as a core part of the indexing plate (schematic drawing).

Figure 2. Cutting tool blade binarization with threshold setting.

Figure 2. Figure 2. Cutting tool blade binarization with threshold setting.

Measurement of Turret Inner Diameter. Use the BLUM TC-52 touch probe to touch the 4 poles of the depth and shallowness of the inner hole of the turret through online measurement, and then measure the inner diameter, roundness, segmentation accuracy and perpendicularity of the hole. According to the probe specification, the repeat accuracy is ( range).

Current Value Collection. We adopt a current sensor (OP-51675) and converted the spindle current value into a voltage signal. The current capture card collects 1000 data per second and sends them to the PLC through SMB (Smart Machine Box). The sampling frequency of the current value is 1000 hz , the total sampling time is 12.6 minutes, and the amount of converted data is about 759,000 . Because the noise signal occurred during tool change process, we all collect 1 to 753399 data for entire 24 holes process.

Current as an Index. Using averaged current to predict tool wear is a well-known method. When the tool starts to wear, the overall current will shift upward due to the increase in cutting resistance. Using current peak value to predict tool wear is also commonly used in the industry. This peak current can be correlated to average inner diameters. Here we proposed a method based on selection the current peak threshold value over 500 (user-defined value) (Fig. 3)

Figure 3. Current acquisition over machining process. Only peak current used to check with threshold.

Figure 3. Figure 3. Current acquisition over machining process. Only peak current used to check with threshold.

Experimental Results

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

Lifetime of Cutting Tools. The new fine boring cutter will have blade replacement after processing 3 to 4 turrets. The diameter of the fine boring cutter reaches 7.96 mm (initial diameter is 8.0 mm ). If we use fine boring cutter continuously, the diameter can reach 7.94 mm and decrease slowly afterward. There is no significant decrease in the length of the tool. The Fig. 4 shows entire boring tool features recording over 95 turrets. Regarding the jittering region, it is considered that there is a slight height error between the tool holder platform and the tool holder in the tool detector. Therefore, we could use tool diameter as index of tool wear.

Figure 4. Measurement of fine boring tool over 95 turrets: diameter, wear region and length.

Figure 4. Figure 4. Measurement of fine boring tool over 95 turrets: diameter, wear region and length.

Comparison of Wear Area and Tool Diameter

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

There were 95 turrets processed in this study. The cutting tool was empirical replaced for the first 48 turrets (i.e., turrets). In other words, the cutting blades were replaced after 3 to 5 turrets completed. We continuously use the same cutting blades from the to the (phase 1 ) and to the (phase 2). Figures 5 and 6 show tool diameter reduced as number of turret increases in both phases 1 and 2, respectively.

Figure 5. The relationship between tool diameter and wear area in Phase 1.

Figure 5. Figure 5. The relationship between tool diameter and wear area in Phase 1.

Figure 6. The relationship between tool diameter and wear area in Phase 2.

Figure 6. Figure 6. The relationship between tool diameter and wear area in Phase 2.

Comparison of Tool Outer Diameter AND Turret Inner Diameter

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

After processing the 64th turret, a measurement of the turret maximum inner diameter of 24 holes is shown in Fig.7. This measurement can more accurately observe the effect of tool wear on the finished product (without changing the cutting tool). The two show a proportional relationship.

Figure 7. Line chart of turret max inner hole diameter and boring tool outer diameter (OD).

Figure 7. Figure 7. Line chart of turret max inner hole diameter and boring tool outer diameter (OD).

Figure 8. Scatter diagram of average inner diameter and average current value.

Figure 8. Figure 8. Scatter diagram of average inner diameter and average current value.

Comparison Of Spindle Current Value And Inner Diameter Of Turret

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

We took measurement data in phase 2 as demonstration. The averaged current exceeds threshold 492.5 which reflect the tool diameter lower than 7.97 mm , can provide prediction quality accuracy (Fig.8). If we use peak current as an index with threshold 513 and same tool diameter 7.97 mm as criteria, it reaches prediction quality accuracy (Fig.9).

Figure 9. Scatter diagram of average inner diameter and peak current value.

Figure 9. Figure 9. Scatter diagram of average inner diameter and peak current value.

Probability Statistical Model In GO/NG Judgement

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

In phase 2, a total of 21 turrets were processed with a total of 504 holes. Two pieces were removed from analysis due to abnormal data acquisition issue, we included 456 holes in the analysis. There are 222 holes (out of 456) have an inner diameter of less than 7.97 mm . By setting up threshold current to 6650, we are able to achieve a data collection success ratio using peak current as an index (Fig.10). Applying the same threshold to samples in phase 2 sample, we can achieve correct GO/NG judgement rate. Similar threshold values can be applied in phases 1 and 2 and they are all listed in Table 1. It looks very promising in using probability model to achieve success GO/NG judgement rate as long as a proper threshold vale is set in the model.

Figure 10. Using probability statistical model provides better GO/NG judgement rate.

Figure 10. Figure 10. Using probability statistical model provides better GO/NG judgement rate.

Table 1. Results for setting various threshold current in phases 1 and 2 samples.

Phase 2 sample size=222 | Correct Counts (A) | Missing Count (B) | A+B | Success OK/NG judgement rate (A/A+B) | Data Collection Success Rate (A+B)/222
Threshold current=1200 and ID<7.97mm | 85 | 1 | 86 | 98.8% | 38%
Threshold current=1100 and ID<7.97mm | 95 | 1 | 96 | 98.9% | 43%
Threshold current=6650 and ID<7.97mm | 162 | 17 | 179 | 90% | 73%
Phase 1 sample size=256 | Correct Counts (A) | Missing Count (B) | A+B | Success OK/NG judgement rate (A/A+B) | Data Collection Success Rate (A+B)/256
Threshold current=1200 and ID<7.97mm | 145 | 1 | 146 | 99.3% | 57%
Threshold current=1100 and ID<7.97mm | 152 | 2 | 154 | 98.7% | 59%
Threshold current=6650 and ID<7.97mm | 210 | 4 | 214 | 98.1% | 82%

Conclusions

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

This study correlated the current value, tool wear, and finished product accuracy of precision turret machining. By continuing using cutting tool in machining process, we are able to collect all current information and compare against with tool outer diameter.

It has been verified that tool wear is highly related to spindle current and can be used for prediction.

With a proper selection of threshold current, we are able to get success OK/NG judgement rate up to which is under assumption that all data can be successful collected.

The current value can be used as an index to correlate product geometric accuracy (e.g., inner diameter), tool wear status, as well as estimating the tool life time.

References

The original version of this paper is available on https://www.scientific.net/EI.2.1.pdf

Kurada, S. and Bradley, C. "A review of machine vision sensor for tool condition monitoring" Computers in Industry,34:52~72, 1997

Altintas. Y., Prediction of Cutting Forces and Tool breakage in milling from feed drive current measurements, Journal of Engineering for Industry, pp.386-392, 114(4), 1992.

Yang, Min-Yang, and Lee, Taik-Min, Hybrid adaptive control based on the characteristics of CNC end milling, International Journal of Machine Tools and Manufacture. pp.489-499, Volume 42, Issue 4, 2002

Sun Weiwei, Huang Min, & Li Kang, Research on tool wear status monitoring method based on current signal. Journal of Henan Polytechnic University (Natural Science Edition), November, 2019.

Yuan Yuefeng, C., & Wuyi, G. L. Tool Materials Rapid Selection Based on Initial Wear. Chinese Journal of Aeronautics, Volume 23, pp. 386-392, 2010.

Chen Zhenghe, & Huang Yanxiang, Application of machine vision system to blade wear research. Green Technology Engineering and Application Seminar, pp. 625-626, 2013.

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/engineering-innovations-vol-2/978-3-0364-1097-5

Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 7-20

doi: 10.4028/p-4isiu8

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2021-09-27

Accepted:
2021-11-19

Online:
2022-06-20

Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

The original version of this paper is available on https://www.scientific.net/EI.2.7.pdf

MURARIU Alin Constantin , SÎRBU Nicuşor-Alin , COCARD Marius DUMA Iuliana

National R&D Institute for Welding and Material Testing - ISIM Timisoara, 30 Mihai Viteazul BIv. 300222, Timisoara, Romania

amurariu@isim.ro, asirbu@isim.ro, mcocard@isim.ro, diduma@isim.ro

Keywords: FDM, ULTRA PLA, design of experiments, optimization, mechanical properties

Abstract

Paper presents the results of factorial experiments made to establish the influence of technological parameters of 3D printing using the Fused Deposition Modeling (FDM) Technology, on the mechanical properties of the material deposited with ULTRA PLA filaments. By planning the experiments and the statistical processing of the results, mathematical relations were established regarding the dependence between the objective functions, the controllable factors and their interactions. To obtain high tensile strengths of the components made by 3D printing, regimes are required to allow the deposition of layers as thin as possible ( ) and temperatures as high as possible, close to . The choice of inappropriate values of these process parameters can lead to a significant decrease in tensile strength, reaching even up to of the maximum possible value to be reached. The experiments reveal that the printing speed does not have a major influence on the mechanical properties. Practical, the printing speed is limited by the technical characteristics of the printer used. The results of the experimental research obtained on a number of 30 process variants led to the establishment of optimal 3D printing variants that correspond to the requirements imposed on the objectively analysed functions (tensile strength, dimensional accuracy, speed of execution, surface quality).

1. Introduction

The original version of this paper is available on https://www.scientific.net/EI.2.7.pdf

Fused Deposition Modeling (FDM) additive manufacturing technology is constantly evolving. New printing possibilities is implemented, high-performance prints have been made and new materials have appeared. However, although it has been used for many years, the PLA (PolyLactic Acid) filament has not lost ground to the new materials, being one of the most used filaments in 3D printing with thermoplastic materials due to the fact that it behaves properly in the printing process. It combines mechanical characteristics with those of plasticity at an acceptable level, it is a biodegradable material, its decomposition being achieved at temperatures above in certain humidity conditions and in the presence of microorganisms that accelerate the process. The technological process of 3D printing is a complex technological system, being characterized by a relatively large number of independent variables, which requires their optimization in order to obtain high productivity and quality of products. A modern variant of industrial process optimization is the use of factorial experiments that consider the analysis of the influence of certain controllable factors on the outputs, as response functions. In this way, the necessary resources and workload can be considerably reduced, by resorting to the statistical processing of experimental results and establishing relationships of dependence between objective functions, controllable factors and their interactions.

The effect of printing parameters on the mechanical properties of parts fabricated by 3D printing is a topic of interest for specialists in the field, being known a series of previous studies [16]. It has been found that 3D printing by FDM is a complex phenomenon and the mechanical properties of the printed parts are strongly depending on the 3D printing process parameters and on the filament material composition. On the other hand, since FDM deposits material directionally, the result is a layered parts with anisotropic behaviour. Also, normally distributed errors were achieved
between the predicted and experimental values. The experiments have shown [3] that the pre-processing technologies such as vacuum-assisted FDM and laser or infrared heating could be used to improve the quality of the 3D printed parts due to positive impact on bonding between the layers. Also, the part cooling rate, environmental conditions and post-processing need to be considered as well since they have a significant effect on characteristics of the 3D printed components. Thus, research must be done to find optimal solutions [7-11] for the combinations of parameters to adapt them based on the application (since various optimal parameters could be obtained based on dimensional accuracy, printing time, flexural, impact or tensile strength as well as surface roughness).

In this paper, in order to establish the influence of technological parameters on the mechanical properties of the material deposited by printing using ULTRA PLA filament, the Design of Experiments approach (DOE) has been used [12]. Thus, a factorial experiment was designed and implemented aiming the following 5 objective functions: tensile strength, roughness of the printed surface, test piece thickness a , test piece width b and printing duration. The main factors (technological parameters) that significantly influence the results obtained are: print temperature, print speed (speed of movement of the print head relative to the printed component) and the height of the layer deposited at each pass (determined by the distance between the print head and component).

2. Experimental Work

The original version of this paper is available on https://www.scientific.net/EI.2.7.pdf

2.1 Material and methods

ULTRA filaments (PLA) were used in the experimental program on the influence of technological parameters on the mechanical properties of the material deposited by 3D printing. Table 1 shows the main characteristics of this material, according to the manufacturer's specification (Roboze).

Table 1: Main characteristics of the ULTRA (PLA)

ULTRA (PLA)
Properties | Value | STANDARD
Tensile strength | 52 MPa | ISO 527
Elongation | 20% | ISO 527
Flexural strength | 85 MPa | ISO 178
Impact strength | 22 kJ/m² | ISO 180
HDT @1.80 MPa | 65 °C | ISO 75
Density | 1,25 g/cm³ | ISO 1183
Description | Material designed to make high-definition parts, ideal for prototypes and small series that require both precision and mechanical rigidity.

In order to determine the limits of variation of the parameters specific to the 3D printing process and to design the factorial experiments, preliminary tests were performed in a first stage of the research. It was taken into account that these parameters influence the mechanical strength characteristics and the dimensions of the printed specimen, thus there is a need to establish optimal variants of 3D printing regimes depending on the different requirements for the practical applications.

Preliminary tests have established the ranges in which the main parameters called controllable factors of the 3D printing process can vary so that the process runs smoothly. The ranges of values obtained based on the results of the preliminary research carried out, are presented in Table 2.

Table 2: Controllable factors and their ranges of variation

No.
Crt.
Technological parameter
Symbol
U.M.
Ranges

1
Temperature
T
[° C]
200 – 300

2
Printing speed
v
[mm/s]
60 – 80

3
Layer height
h
[mm]
0.1 – 0.3

Simplify3D software was used to design and simulate the printing of test specimens for the experiment program. An example of a simulation is shown in Fig. 1.

Figure 1: Design and simulation of specimen printing, using Simplify3D software

Figure 1. Figure 1: Design and simulation of specimen printing, using Simplify3D software

The software allows to load from a database the 3D drawing of the component to be printed and the selection of process parameters: extrusion temperature, printing speed, layer height, how is made the "shell" of the component and selecting the mode of " filling" of the component. Also, the software can estimate the printing time of the component, the length of the filament consumed when making it, the weight of the component, as well as the cost of the material. The printing of the specimens was made with Roboze one printer (Fig. 2).

Figure 2: Printing of tensile test specimens

Figure 2. Figure 2: Printing of tensile test specimens

To evaluate the surface quality of 3D printed components, roughness measurements were performed using a Mitutoyo SJ - 201P device, Fig. 3.

Figure 3: Roughness measurements

Figure 3. Figure 3: Roughness measurements

2.2 Experimental testing program

Within the experimental program, specimens for tensile tests according to [13] were printed. The experimental program consisted in designing and implementing a order factorial experiment on 30 test pieces with 3 controllable factors with 2 levels, 3 replicas for each combination of controllable factors and 6 replicas in the central point. The following five objective functions were taken into consideration to be analysed: tensile strength , surface roughness , specimen thickness a [mm], specimen width and printing time . Based on the data obtained in the preliminary experiments, the central point of the experiment was determined, after which the process parameters for the experimental program, presented in Fig. 4 and Table 3, were established.

Figure 4: Establishing the technological parameters for the factorial experiment

Figure 4. Figure 4: Establishing the technological parameters for the factorial experiment

Table 3: Factorial experiment - printing variants

Experiment no./ sample identification | Temperature T [°C] | Printing speed v [mm/s] | Layer heigh h [mm]
1, 1', 1'' | -1 | -1 | -1
2, 2', 2'' | 1 | -1 | -1
3, 3', 3'' | -1 | 1 | -1
4, 4', 4'' | 1 | 1 | -1
5, 5', 5'' | -1 | -1 | 1
6, 6', 6'' | 1 | -1 | 1
7, 7', 7'' | -1 | 1 | 1
8, 8', 8'' | 1 | 1 | 1
9, 10, 9', 10', 9'', 10'' | 0 | 0 | 0

where: 1,0 and -1 represent the values of the upper and lower limits and respectively the average values of the analysed process parameters (Table 4).

Table 4: Parameters of the 3D printing process

Value
Temperature
T [°C]
Printing speed
v [mm/s]
Layer heigh
h [mm]

Maximal (1)
300
80
0.1

Average (0)
250
70
0.2

Minimum (-1)
200
60
0.3

Next, samples for the experimental program were printed using the parameters presented above. Before being tested, the specimens were conditioned at a temperature of and a relative humidity of for 8 hours, after which they were subjected to a mechanical tensile test using Zwick equipment with maximum load of 5 kN .

3. Results and Discussion

The original version of this paper is available on https://www.scientific.net/EI.2.7.pdf

The aspect of the 3D printed specimens, after the tensile tests, is shown in Fig. 5.

Figure 5: The appearance of 3D printed specimens, after the tensile test

Figure 5. Figure 5: The appearance of 3D printed specimens, after the tensile test

It is found that both the failure mode and the appearance of the fracture surfaces are related to the 3D printing parameters used to make the specimens. Thus, specimens 1,3 and 5 show a ductile fracture with a partial or complete tearing of the printed structure (Fig. 6). The other specimens show a brittle fracture, specimen 4 presenting the most brittle behaviour the since the failure occurred suddenly with the detachment of a portion from the specimen (Fig. 7).

Figure 6: Details of the failure mode and the appearance of the fracture surface (ductile fractures)

Figure 6. Figure 6: Details of the failure mode and the appearance of the fracture surface (ductile fractures)

Figure 7: Details of the failure mode and the appearance of the fracture surface (brittle fractures)

Figure 7. Figure 7: Details of the failure mode and the appearance of the fracture surface (brittle fractures)

Fig. 8 shows the Pareto diagram regarding the influence of and h parameters of the 3D printing process on the tensile strength . It can be observed that the temperature and the layer heigh (h), and their interaction have a significant influence on the objective function.

Figure 8: Pareto diagram - the influence of the process parameters and h on the tensile strength ( )

Figure 8. Figure 8: Pareto diagram - the influence of the process parameters and h on the tensile strength ( )

Eq. 1 describes the variation of the objective function - tensile strength with the process parameters and their interactions:

Fig. 9a and Fig. 9b presents the response surfaces regarding to the influence of printing process parameters on tensile strength ( ). Fig. 9a shows that in order to obtain the highest values of tensile strength of the printed components, it is favourable to be selected a temperature as close as possible to , correlated with the use of speeds close to the extreme values, (printing speed of ).

Fig. 9b shows the need to select the highest possible values of temperature (T), close to and a thickness of the layer heigh ( ) as small as possible, of 0.1 mm , to obtain high tensile strengths exceeding . It is also observed that in the case of lower temperature values, towards the minimum limit of and if a layer heigh close to 0.3 mm are used, a significant decrease of the tensile strength, up to can occur.

From the graphs shown in Fig. 9c and Fig. 9d, data can be obtained that confirm the information previously presented in the surface graphs. Thus, to obtain the highest possible values of tensile strength ( ), the highest possible values of the printing temperature, close to , the layers heigh as thin as possible and the printing speeds close to the extreme values should be selected.

Eq. 2 describes the variation of the objective function - surface roughness ( ) with the process parameters and their interactions:

Fig. 10 shows the Pareto diagram on the influence of the parameters and h of the 3D printing process on the tensile strength . It can be observed that the temperature . It is observed that the layer heigh ( h ) and the temperature ( T ) have a significant influence on this objective function.

Figure 10: Pareto diagram - the influence of the process parameters and on the surface roughness ( )

Figure 9. Figure 10: Pareto diagram - the influence of the process parameters and on the surface roughness ( )

Fig. 11a and Fig. 11b presents the response surfaces regarding to the influence of the printing process parameters on the surface roughness of the specimen .

To obtain the lowest possible values of surface roughness, it is recommended to choose temperatures as close as possible to , layers heigh as thin as possible, of 0.1 mm and printing speeds close to or .

From the graphs in the form of contour plots, shown in Fig. 11c and Fig. 11d, more accurate additional information can be obtained regarding to the selection of appropriate values of the process parameters, when it is desired to obtain a surface roughness as low as possible.

Thus, e.g., if the value of is to be between 10 to , it is recommended that the printing temperature be higher than and the layer height be selected less than 0.15 mm . (Fig. 11d).

Eq. 3 describes the variation of the objective function - the thickness of the test piece (a) with the process parameters and their interactions and Eq. 4 describes the variation of the objective function - the width of the test piece (b) with the process parameters and their interactions:

Fig. 12 shows the Pareto diagram regarding the influence of and h parameters of the 3D printing process on the specimen dimensions ( and ). It is observed that the layer heigh ( ) and its interaction with the temperature (T) have a significant influence on this objective functions.

In the similar way Fig. 12 and Fig. 13 presents the response surfaces and the contour plots regarding to the influence of the printing process parameters on the dimensions of the specimen (a and b).

Figure 12: Correlations between the main parameters of the 3D printing process ( and h) on the sample thickness (a)

Figure 10. Figure 12: Correlations between the main parameters of the 3D printing process ( and h) on the sample thickness (a)

It is revealed that obtaining values of the thickness of the test piece located in the range of 4.1 to 4.2 mm , requires the use of high temperature values, higher than and a thickness of the deposited layer less than 0.15 mm .

Eq. 5 describes the variation of the objective function - printing time ( ) with the process parameters and their interactions:

In this case, there is an influence on the objective function ( ) only from a smaller number of controllable factors and their interactions, in particular it can be seen that there is a decrease in printing time with increasing of printing speed and layer height.

Given that this size of the specimen needs to be as close as possible to a standardized value, in this case 10 mm , it is recommended to select as much as possible a set of parameters with lower values for temperature and layer thickness, speed printing has a relatively small influence on this objective function. In order to obtain values of the test piece width (b) in the range , it is shown that the process parameters can vary between relatively wide limits.

The optimization of the process as a whole was performed based on the mathematical models obtained for each objective function. In order to optimize the process, the following criteria have been established for each objective function:

tensile strength by - maximum value

surface roughness - minimum value

the test piece thickness a - target value of 4 mm

the test piece width - target value of 10 mm

printing time - minimum value

The optimal values of the printing process parameters for the different combinations of objective functions considered are presented in Table 5. Given some requirements that may arise in industrial practice, based on the results obtained in the experimental four other optimal variants of the printing process parameters were established as following:
a) Component quality (dimensional accuracy and superior mechanical characteristics) optimization with four objective functions ;
b) Execution speed - optimization with three objective functions ( );
c) Component strength - optimization with an objective function ;
d) Degree of surface finish - optimization with an objective function (Ra).

Table 5: Optimal parameters

Optimal variant
Temperature
T [°C]
Printing speed
v [mm/s]
Layer height
h [mm]

Optimum 1: with 5 objective
functions (Rm, Ra, a, b, tp)
300
80
0.1

Optimum 2: with 4 objective
functions (Rm, Ra, a, b)
300
60
0.1

Optimum 3: with 3 objective
functions (tp, a, b)
200
80
0.3

Optimum 4: with one objective
function (Rm)
300
60
0.1

Optimum 5: with one objective
function (Ra)
300
60
0.1

4. Conclusions

The original version of this paper is available on https://www.scientific.net/EI.2.7.pdf

A order factorial experiment was conducted on 30 test pieces taking into consideration the main process parameters of 3D printing process using 3 controllable factors ( and h ) with 2 levels, 3 replicas for each combination of controllable factors and 6 replicas in the central point.

Based on the experimental results obtained, regression models for correlation between the 3D printing process parameters and objective functions: tensile strength, surface roughness and component dimension (a and b) were obtained. Regression models can be used to select the appropriate process parameters to obtain required characteristics of 3D printed components, depending on the loading and operation conditions.

Experimentally, optimal variants of parameters were determined that correspond to minimum printing speeds, maximum tensile strength, high surface quality or high dimensional accuracy.

Acknowledgements

The original version of this paper is available on https://www.scientific.net/EI.2.7.pdf

This work was carried out as part of PN19.36.02.01 project: "Research on the development of the principle of additive manufacturing, 3D printing, by making innovative modelling equipment by ultrasonic thermoplastic extrusion", financed by the Romanian Ministry of Research, Innovation and Digitalization. The authors would like to acknowledge the support provided by the National R&D Institute for Welding and Material Testing - ISIM Timisoara, for all the facilities necessary to implement the experimental research.

References

The original version of this paper is available on https://www.scientific.net/EI.2.7.pdf

Leite M., Fernandes J., Deus M. A., Reis L., Vaz M.F.: Study of the influence of 3D printing parameters on the mechanical properties of PLA, International Conference on Progress in Additive Manufacturing (Pro-AM 2018), 14-17 May 2018, Singapore

Gebisa B.W., Lemu H.G.: Influence of 3D Printing FDM Process Parameters on Tensile Property of ULTEM 9085, Procedia Manufacturing 30, (2019), pp. 331-338,

Syrlybayev D., Zharylkassyn B., Seisekulova A., Akhmetov M., Perveen A., Talamona D.: Optimisation of Strength Properties of FDM Printed Parts - A Critical Review, Polymers (2021), 13, 1587,

Bayu K. R., Imaduddin, Ariawan F., Ubaidillah D., Zainal A.: A review on the fused deposition modeling (FDM) 3D printing: Filament processing, materials, and printing parameters, Open Engineering 11, no. 1, (2021), pp. 639-649,

El Magri A., Vanaei S., Vaudreuil S.: An overview on the influence of process parameters through the characteristic of 3D-printed PEEK and PEI parts, (2021),

M. Ouhsti M, El Haddadi B., Belhouideg S.: Effect of Printing Parameters on the Mechanical Properties of Parts Fabricated with Open-Source 3D Printers in PLA by Fused Deposition Modeling, Mechanics and Mechanical Engineering 22(4), (2018), pp. 895-907, doi:10.2478/mme-2018-0070

Wu J: Study on optimization of 3D printing parameters, IOP Conf. Series: Materials Science and Engineering 392 (2018) 062050 doi:10.1088/1757-899X/392/6/062050

Tontowi A.E., Ramdani L., Erdizon R. V., Baroroh D.K.: Optimization of 3D-Printer Process Parameters for Improving Quality of Polylactic Acid Printed Part, International Journal of Engineering and Technology 9 (2), (2017), pp. 589-600, doi: 10.21817/ijet/2017/v9i2/170902044

Abeykoon C., Sri-Amphorn P., Fernando A.: Optimization of fused deposition modeling parameters for improved PLA and ABS 3D printed structures, International Journal of Lightweight Materials and Manufacture 3 (2020), pp. 284-297

Haidiezul A.H.M, Hazwan M. H. M., Lee W.S., Gunalan, Najihah N.F., Fadhli I.: Shrinkage optimisation on the 3D printed part using Full Factorial Design (FFD) optimisation approach, IOP Conf. Series: Materials Science and Engineering 932 (2020) 012109, doi:10.1088/1757899X/932/1/012109

Novoa C., Flores A.: Optimizing the tensile strength for 3D printed PLA parts, Solid Freeform Fabrication 2019: Proceedings of the Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, (2019), pp. 745-765

Ramachandran K.M., Tsokos C.P.: Mathematical Statistics with Applications in R (Third Edition), Chapter 8 - Design of experiments, (2021), pp. 343-368

* * * SR EN ISO 527-1: 2020: Plastics - Determination of tensile properties - Part 1: General principles.

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Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 21-30

doi: 10.4028/p-wxru3h

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2022-01-17

Accepted:
2022-02-28

Online:
2022-06-20

Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

The original version of this paper is available on https://www.scientific.net/EI.2.21.pdf

Vijay Shrinivas , Rajesh Narasimhan and Thillairajan Arumugam

STEER Engineering Pvt. Ltd, Phase Peenya Industrial Estate, Bangalore, India

vijay.shrinivas@steerworld.com, rajesh.narasimhan@steerworld.com, thillairajan.arumugam@steerworld.com

Keywords: Tableting Machines, Banded carbides, Tempered Martensite, Scanning Electron Microscopy, Corrosion Fatigue

Abstract

AISI D3 material finds wide use as Dies in Tableting Machines for Pharmaceutical applications owing to its good strength, toughness and moderate corrosion resistance combined with cost effectiveness. However, 10-15% of AISI D3 Dies used in rotary Tableting Machines were found to fail within 4-6 months of service resulting in frequent disruption of regular production and loss in overall productivity besides having potential long-term risks such as metal contamination in the output product.

Visual examination of the failed Die showed crack across the top Die face with rust marks, but no such crack was found on the bottom face. Also, the crack on the top Die face had a jagged morphology and those cracks on the Outer Diameter (OD) surface oriented in the axial direction were found to be straight and sharp. Macro-examination of Die sectioned diametrically and perpendicular to the crack on the Die face revealed jagged axial cracks on the Internal Diameter (ID) surface. Cluster pitting marks centered around mid-height of the Die were observed on the ID surface and the cut open sections of the Die along the crack revealed extensive corrosion. While microstructural examination of samples taken on the ID surface showed presence of banded carbides oriented axially in tempered martensite matrix, the same examination carried out on samples taken on Die face revealed fine needle like carbides in tempered martensite matrix. Fractography analysis conducted in the cluster pitting zone on the ID surface clearly showed presence of micro-cracks having multiple points of origin with clear indications of propagation into the cross section of the Die. Scanning Electron Microscopy (SEM) carried out in the aforementioned zone near ID surface also showed the presence of multiple micro-cracks. The SEM-EDX analysis in the referred zone at specific locations in the vicinity of microcracks confirmed inadequate Chromium oxide content leading to lack of corrosion resistance in the material.

Based on the investigation & analyses and the detailed study of the Tableting Process in rotary Tableting Machines that revealed the nature of applied load to be cyclic, a comprehensive failure mechanism was arrived at, and it was inferred that the predominant mode of AISI D3 Die failure was Corrosion Fatigue. Finally, recommendation has been proposed to prevent such failures during service.

Introduction

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Tableting Machine - An overview. The Tableting Machine also known as tablet compressing machine is used to compress pharmaceutical powder formulations into uniform shaped & sized tablets. There are two broad types of tablet compression machines, as follows:

Single Punch Presses

Rotary Presses

Single Punch tablet press is the simplest equipment, which uses a single set of tooling consisting of a Die and a pair of upper & lower punches, for manufacture of tablets. The compaction force on the fill material is executed only by the upper punch while the lower punch is stationery. The single punch tableting press generally produces 60-80 tablets / minute.

Rotary tablet press is a mechanical device, which has several tooling stations that rotate to compress the powder mixture into tablets of uniform size, shape, and weight. The compaction force on the fill material is executed both by the upper and lower punches resulting in the powder granules getting compressed in the middle. The rotary tablet press was primarily developed to increase the output of the Tableting Machine. The capacity of the equipment is determined by the rotation speed (RPM) and the number of stations on the press. Rotary Tableting Machines typically give an output between 10,000 and 200,000 tablets per minute.
Tableting Process. The basic principle involved in the Tableting Process is compression of powder / granules between upper & lower punches in a Die hole through application of uniform hydraulic pressure. Following are the main stages involved in the Tableting Process:

Filling

Metering

Compression

Ejection

The filling stage involves transfer of powder / granules to the machine Die cavity and the granulation is overfilled to ensure complete filling of the punch-Die cavity. The metering stage involves removal of excess granulation or powder from the Tableting machine. The compression stage, which involves bringing together upper & lower punches under pressure within the Die hole, forms the tablet. Finally, the ejection stage involves removal of formed tablet from the lower punch station. The scraper then pushes the formed tablets away from the Tableting Machine into the collection bin through discharge chute. The schematic of the Tableting Process is shown in Fig.1.

Fig. 1. Schematic of Tableting Process

Fig. 1. Schematic of Tableting Process

Punch & Die System. In order to produce tablets, the punches move within the Die cavity thereby compressing the powder into tablets of desired shape, size and weight. The upper punch system, which is located on the upper section of the rotary system, moves vertically in and out of the Die bore. The lower punches, which are located on the lower section of the rotary system, move vertically but remain within the Die bore. Also, once compacted, the lower punch system enables ejection of the tablet from the Die hole. The sectional view of the elliptical Die are shown in Fig. 2 below.

Fig.2. Sectional view of elliptical Die

Fig.2. Sectional view of elliptical Die

The manufacturing sequence of the Dies involves cutting off the needed length from annealed rolled raw material stock of required diameter and rough machining the pieces to required dimensions followed by heat-treatment, which is generally a hardening & double tempering operation, to achieve a hardness of 60-64 HRC. Subsequently, the heat-treated pieces are subjected to grinding operation, Wire Electrical Discharge machining to form the central elleiptical or round hole and fine polishing before using them in rotary Tableting Machines. The details of the required chemistry and hardness are given below in Table 1 and that of inclusion rating of the steel is provided in Table. 2.

Table 1. Chemical composition and hardness of AISI D3 Dies

Composition | C | Mn | Si | S | P | Cr | Mo | Ni | V | W | Hardness, HRC
Specification AISI D3 (%) | Min | 2.00 | 0.10 | 0.10 |  |  | 11.0 |  |  |  |  | 60
| Max | 2.35 | 0.60 | 0.60 | 0.03 | 0.03 | 13.5 |  | 0.03 | 1.00 | 1.00 | 64
Round Die | Actual | 2.26 | 0.35 | 0.37 | 0.01 | 0.012 | 11.83 | 0.13 | 0.11 | 0.09 | 0.12 | 62
Elliptical Die | Actual | 2.10 | 0.35 | 0.38 | 0.01 | 0.014 | 11.81 | 0.12 | 0.11 | 0.09 | 0.11 | 62

Table 2. Inclusion Rating

Type | Sulphide | Alumina | Silicate | Oxides
Avg Size | Thin | Thick | Thin | Thick | Thin | Thick | Thin | Thick
| 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0.5

Site Information

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Service History. Cracking & breakage of Dies in Tableting Machines during regular operation after a service period of months was reported in both round and elliptical Dies. About of the Dies crack on a regular basis. The data collected was for the period October to December 2019.

Operating Parameters.

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(a) Material being processed
(b) Applied Load
(c) Speed of the rotary Tableting Machine
(d) Hours of operation
: Pharmaceutical formulation
: 75-80KN
: 50 Revolutions per minute
: 2 shifts ( hours / day)

Failure Signs. There are generally no prior indications or forewarnings before sudden cracking of the Dies resulting in abrupt stoppage of the rotary Tableting Machine.

Experimental

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Two AISI D3 Dies, one each round and elliptical, were received for analysis. Both were visually examined followed by Macroscopic examination with Celestron Digital Microscope Model No. 44308 and digital photographs were recorded. The Dies were then cut sectioned perpendicular to the crack observed on the Die face using Wire Electrical Discharge Machining (WEDM) method. Macro-examination was conducted on the cut-sections besides Liquid Penetrant testing, which was performed in accordance with ASTM E-165 standard. Subsequently, the cut sections were subjected to minor load using a vise to enable breakage along the crack to examine the fractured Die surfaces.

Samples were taken for chemical analysis, determination of inclusion rating, microstructural examination, and SEM Analysis. Chemical Analysis of the Dies was conducted using Spectromaxx Model No. 1433941 and inclusion contents were determined in accordance with ASTM E-45 standard. For microstructural analysis, the specimens taken from both the Die faces and along the Inner Diameter of cut sectioned pieces were mounted in cold setting mold with plastic resin and metallographically polished. The polished surfaces were then etched with Marbles reagent and the etched surfaces were viewed under Meiji Inverted Optical Microscope Model No. IM 7200.

The fractured surfaces of both the Dies were subjected to macroscopic examination using Celestron Digital Microscope Model No. 44308 and microstructural examination at high magnification using Carl Zeiss Sigma Scanning Electron Microscope (SEM). Also, Energy dispersive X-ray Analysis (EDX) was carried out to determine elemental composition. Bulk hardness measurements were taken using Rockwell Hardness tester Model A1-BAS Serial No. 233 and values were recorded.

Observation

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The results of chemical analysis & hardness survey (Table. 1) were found to conform to specification requirements. Visual examination of the round Die face showed a crack across the top face (Fig. 3) but no such crack was found on the opposite bottom face. In the case of the elliptical Die the crack was noticed on the top face along the major axis of the ellipse with minimum Die wall thickness (Fig. 4) but no such crack was noticed on the opposite bottom face.

Fig. 3. Visual Examination -round Die

Fig. 3. Visual Examination -round Die

Fig. 4. Visual Examination - elliptical Die

Fig. 4. Visual Examination - elliptical Die

Macro-examination (3-5X) revealed cracks of jagged morphology with rust marks on both the round & elliptical top Die faces (Fig. 5 & Fig.6) but sharp hairline cracks of 20 mm length connected to the those on the top faces were noticed on the outer diameter (OD) surfaces (Fig. 7 & Fig. 8). The macro-examination of the cut section of the round Die revealed jagged crack of length 19.5 mm on the Internal Diameter (ID) surface from the top face (Fig. 9) and cluster pit marks of 4 mm length around mid-height of the Die. The macroscopic observations of the elliptical Die were similar to that of the round Die (Fig, 10).

Fig.5. Macroexamination-round Die(rD) face

Fig.5. Macroexamination-round Die(rD) face

Fig.7. Macroexamination - rD OD surface

Fig.7. Macroexamination - rD OD surface

Fig. 9. Macroexamination - rD cluster pitmark

Fig. 9. Macroexamination - rD cluster pitmark

Fig. 6. Macroexamination-elliptical Die(eD) face

Fig. 6. Macroexamination-elliptical Die(eD) face

Fig. 8. Macroexamination - eD OD surface

Fig. 8. Macroexamination - eD OD surface

Fig.10. Macroexamination - eD cluster pitmark

Fig.10. Macroexamination - eD cluster pitmark

Liquid Penetrant examination on the cut sections of both the round & elliptical Dies showed excessive bleeding around mid-height on the ID surface. Also, while it revealed linear indications from mid-height to the top face along the ID surface and on the top Die faces, no such indications were noticed near the bottom face (Fig. 11 & Fig. 12). Visual examination of the fractured surfaces of the round & elliptical Dies showed evidence of corrosion ( Fig. 13 & Fig. 14) and clearly revealed the progression of corrosion into the material from the pitmarks observed on the ID surface.

Fig. 11. Dye Penetrant Test - Round Die

Fig. 11. Dye Penetrant Test - Round Die

Fig. 13. Fractured surface - Round Die

Fig. 13. Fractured surface - Round Die

Fig. 12. Dye Penetrant Test - Elliptical Die

Fig. 12. Dye Penetrant Test - Elliptical Die

Fig.14. Fractured surface - Elliptical Die

Fig.14. Fractured surface - Elliptical Die

Microstructural examination on samples taken on the top face of the round Die showed presence of needle shaped carbides randomly distributed in tempered martensite matrix (Fig. 15). Also, several micro-cracks have been observed in the vicinity of the large crack on the top face of the round Die (Fig. 16). However, the microstructural examination on samples on the ID surface in the vicinity of the crack revealed severely banded carbides oriented along the axis of the Die (Fig. 17). The fractrography of sample taken at the cluster pit mark zone of the round Die revealed several micro-cracks originating from the ID surface propagating into the cross section of the Die (Fig. 18).

Fig. 15. Microstructure 1 - Round Die face

Fig. 15. Microstructure 1 - Round Die face

Fig. 16. Microstructure2 - Round Die face

Fig. 17. Microstructure - Banded structure

Fig. 17. Microstructure - Banded structure

Fig. 18. Fractography - Clustered pit mark zone

Fig. 18. Fractography - Clustered pit mark zone

While Scanning Electron Microscopy in the cluster pit mark zone of the round Die ( Fig. 19) revealed the presence of multiple micro-cracks, SEM - EDX Analysis (Fig. 20) in the marked location close to the ID surface confirmed high content of and low content of (6.61%).

Fig. 19. SEM Analysis - Cluster pit mark zone

Fig. 19. SEM Analysis - Cluster pit mark zone

Total:

Figure 19. Total:

Fig. 20. SEM - EDX Analysis

Results & Discussion

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The compression stage of the Tableting Process involves bringing together both the upper & lower punches under high hydraulic pressure through application of vertical load [ ] resulting in compaction of the formulation material by almost to form the tablet [Fig.1]. This periodic application of load in the compression stage results in creating cyclic tensile hoop stress on the ID surface at the zone of compaction.

Owing to cyclic tensile hoop stresses generated in the Die cavity as mentioned above, the most prone region for the crack to initiate would be the zone of compaction on the ID surface for both the round & elliptical Dies. The cluster pit marks observed during macro-examination of the ID surface [Fig. 9] and the excessive bleeding noticed during Dye Penetrant examination of the ID surface [Fig. 11] at mid-height region of the Dies, confirm presence of multiple discontinuities in the said region and indicate the possibility of multiple crack initiation sites.

Since the ID surfaces of both the round & elliptical Dies had smooth machined finish, geometrical factors such as sharp corners etc. had played no role in crack initiation. Also, as the inclusion contents were very low ( Table 2) and no apparent grain boundary carbides were noticed ( Fig. 15), these microstructural features do not seem to have contributed towards crack initiation
either. However, the surfaces obtained by fracturing the Dies along the crack (Fig. 13 & Fig. 14) showed moderate to high corrosion suggesting contribution of environmental factors for the crack initiation on the ID surface.

While the presence of corrosion on the fractured surfaces (Fig. 13 & Fig. 14) indicate that some of the ingredients in the formulation had been corrosive to AISI D3 Dies, the SEM-EDX analysis (Table.3) showed low percentage of Cr 2 O 3 (6.61%) on the fractured surfaces in the cluster pit mark zone, despite the AISI D3 material having close to of Chromium. This clearly indicates depletion of available Chromium towards preferential formation of Chromium Carbides, thereby making the material susceptible to corrosion due to insufficient Cr 2 O 3 content. It can be inferred that the pit marks have been formed due to the ingredients used in tablet formulation that have been corrosive to the AISI D3 Dies getting smeared onto the ID surface at high pressure similar to that of a high pressure jet during every downward movement of the top punch in the compression stage of the Tableting process.

The microstructural analysis on sample taken on the ID surface of the round Die (Fig. 17) showed evidence of crack propagation direction along the Die axis. Presence of carbides preferentially oriented axially, known as banded carbides, could be observed. A banded structure can be defined as a segregated structure of approximately parallel bands of two different phases aligned in the working direction . One of the major metallurgical problems reported in the literature for high carbon steels having Chromium greater than is carbide banding [1]. The deleterious effects of carbide banding include reduced wear resistance, cracking along the carbides and reduction in fatigue resistance [1,5]. Parkar et. al. [3] reported that fatigue life of rolling element made from AMS 5749 [ ; ; Mo ] material reduced by four times due to carbide banding. Hence, the role of banded carbides found in the round Die along the axis, which happens to be the rolling direction, and their influence in the direction of crack propagation in the axial direction cannot be ruled out. The fractography at the cluster pit mark zone of the cut open / fractured surface (Fig 18) revealed multiple micro-cracks originating from the ID surface and propagating into the cross section of Die. Hence, it can be inferred that propagation of crack in the Die had been both in axial and transverse directions.

While it is clear from the evidence stated and the above discussion that crack origination had occurred on the ID surface in the cluster pit mark zone (Fig. 18) of the round Die, the jagged appearance of the crack of about 20 mm along the ID surface (Fig.5) and on the Die face suggests progressive nature of crack propagation. In addition, the appearance of hairline crack on the OD surfaces (Fig. 7) indicate accelerated crack propagation resulting in abrupt failure. The three phases of a typical fatigue failure [4,7] namely crack initiation, crack propagation through steady state & unsteady state and final fracture have been clearly evidenced in the Tableting Die failure.

Mechanism of Failure

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The tableting process, which involves high load compaction reduces the height of formulation product in the Dies by almost [ Fig 1], thereby squeezing out the ingredients [ water + other] and smearing them at high tensile hoop stress on the ID surface causing the formation of several minute corrosion pits in the mid-section of the Dies as the material has had insufficient corrosion resistance.

The cyclic loading [ ] applied during compaction had enabled formation of micro-cracks from the corrosion pits [8], which had acted as stress raisers. Multiple such micro-cracks so formed have had their origins in the mid-height region of the Dies. These micro-cracks had propagated both in the transverse direction i.e., perpendicular to the axis into the cross section of the Die [Fig 18] and in the axial direction on the ID surface [ Fig. 17] through the joining of multiple micro-cracks to form a linear discontinuity, which steadily progressed towards the top & bottom faces of the Dies.

Owing to high vertical load applied by the top punch onto the formulation material inside the Die at a set frequency ( cycles/sec), the tangential hoop stress experienced by the top half of the Die cavity is generally higher than that experienced by the bottom half of the Die cavity resulting in more intense crack propagation towards the top face of the Die compared to that of the bottom face. Also, the cyclic stresses experienced in the bottom half of the Die cavity were probably not sufficient to
enable crack propogation along the ID surface till the bottom face of Die. With crack propagtion along the ID surface not reaching the bottom face of the Die, no crack propagation occurred on the bottom faces of both the round and elliptical Dies.

During the initial phase, the micro-cracks had propagated in a stable mode due to application of continuous cyclic stresses during tableting process in a corrosive environment. The jagged morphology of the crack along the ID surface and on the top face clearly indicate the evidence of progressive crack propagation in a stable mode. Though in the next phase, the cracks had accelerated over time, the propagation continued to be stable. Once the cracks originating from the ID surface progressively reached the outer edges of the Die face and those propagating into the cross section of the Die reached a critical size, both the round & elliptical Dies were unable to withstand the prevailing cyclic tensile hoop stresses experienced during operation leading to unstable mode of crack propagation followed by sudden fracture [4,7].

Conclusion

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Cyclic stresses experienced during the compression stage of the Tableting Process together with the strong evidence of corrosive environment in service confirm that Corrosion Fatigue has been the predominant mode of failure for cracking of the Tableting Dies.

Recommendation

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Following is the recommendation to prevent Die failures in service both in round & elliptical Dies:

Deployment of Martensitic Stainless Steel Dies with a Cr content of with appropriate hardness in place of AISI D3 Dies.

Elimination of banded carbides observed in the microstructure through appropriate metal forming operation of Martensitic Stainless Steel material to avoid prefential orientation of grains and achieve near isotropic structure.

Acknowledgements

The original version of this paper is available on https://www.scientific.net/EI.2.21.pdf

The authors wish to thank the Chief Knowledge Officer & Managing Director Dr. Babu Padmanabhan of STEER Engineering Pvt. Ltd. for his encouragement, support and valuable guidance provided during the course of the failure analysis.

References

The original version of this paper is available on https://www.scientific.net/EI.2.21.pdf

D.W. Hetzer, W. Van Geertruyden, Crystallography and Metallography of carbides in high alloy steels, Materials characterization, 2008; 59(7); 825-841

J.D. Verhoeven, A review of micro segregation induced banding phenomena in Steels, Journal of Materials Engineering and Performance, 2000; 9(3); 286-296.

Parkar, Richard Jay, and Eric N. Bamberger, Effect of carbide distribution on rolling-element fatigue life of AMS 5749, NASA-TP-2189(1983); 1-14

Stephen D. Antolovich, Fatigue & Fracture, ASM Metals Handbook, 2007; 19; 911-929

D'Errico F, Failures Induced by Abnormal Banding in Steels, Journal of Failure Analysis and Prevention, 2010; 10(5); 351-357

Krauss G, Solidification, Segregation and Banding in Carbon and Alloy Steels, Metallurgical and Materials Transactions B., 2003; 34(6); 781-792

Totten G, Fatigue Crack Propagation, Advanced Materials and Processes, 2008; 166(5); 39

Ebara R, Corrosion Fatigue Phenomena Learned from Failure Analysis, Engineering Failure Analysis, 2006; 13(5); 516-525

Muller M, Theoretical Considerations on Corrosion Fatigue Crack Initiation, Metallurgical Transactions A., 1982; 13; 649-655

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Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 31-39

doi: 10.4028/p-o0d13z

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2021-10-27

Revised:
2022-01-27

Accepted:
2022-01-27

Online:
2022-06-20

Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport

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Radu COJOCARU , Lia-Nicoleta BOȚILĂ , Ion-Aurel PERIANU and Alexandru-Adrian Geană

¹National Research & Development Institute for Welding and Material Testing - ISIM;

Address: 30, Mihai Viteazu Blvd., Postal Code 300222, Timisoara, Romania

rcojocaru@isim.ro, botila@isim.ro, aperianu@isim.ro, ageana@isim.ro

Keywords: metal components wear, service life, urban rail transport vehicles

Abstract

The paper presents proposals for technical solutions based on the interest shown by transport companies in the country to reduce the cost of maintenance of means of transport by increasing the service life of metal components that, in traffic, are subject to a severe process of wear degradation. Specifically, the paper proposes solutions to solve these problems in the case of urban public transport by rail (tram). The results obtained by ISIM Timisoara (implemented at public transport companies in the country) in the field of reintroduction into operation of used metal components from trams are presented. It also presents new, innovative and efficient technical ideas and solutions, from the point of view of the cost / performance ratio and in compliance with the conditions for guaranteeing traffic safety. It is proposed to design and implement a flexible, complex and high-performance automated system for the reconditioning of tram wear components. The implementation of the proposed automated solutions will ensure: significantly increasing the service life of parts subject to wear, reducing the costs of loading with functional layers by increasing productivity, improving part quality due to automation of the loading process, use of constant process parameters, established, controllable during process. Innovative solutions are also proposed for: mobile automated inspection system for determining the degree of wear of tram wheel bandages; method of real-time monitoring of the welding loading process; technical solution to protect the rubber damping elements against overheating and degradation (the solution allows the tires to be reconditioned without removing them from the wheels). Accurate and efficient uses of automated systems, process programming units are specific approaches to the development and modernization of welding and reconditioning technologies by welding.

Introduction

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The current requirements at international level, to increase the efficiency in the field of material production have imposed the implementation in industrial practice of new concepts of design and economic manufacture of parts. Loading by electric welding is one of the most frequently used processes in this direction, due to the multiple advantages it confers. It extends to the production of new, standard or unique parts, but also to the activities of repairing manufacturing defects or those that have appeared in operation.

The definite and unanimously appreciated advantages of this process are well known as they generate important benefits [1-4]:

increasing the operational durability of loaded parts, by up to max. , by protecting the wear surfaces with adequate materials in correlating the characteristics of the operating stresses;

reduction of the consumption of special steels by up to by replacing them differentially in the composition of weight bearing structures with carbon steels or low-alloy steels, over which, in the area subjected to wear, welding-compatible materials are deposited meeting the base level of specific strength requirements;

reduction of energy consumption by up to by eliminating operations specific to the classical processing process;

increasing operational safety and reducing the risk of damage to loaded parts, as a result of improving the quality level;

reduction of operating costs.

The outstanding performances achieved in welding loading technologies are due to the harmonization of knowledge of metallurgy, physics, tribology, terotechnics, strength of materials, electrical engineering, chemistry, in the production of new filler materials, new manual and mechanized equipment, and currently due to mechanization and process automation.

Reconditioning and restoring the profile of worn parts, performed carefully and correctly, can lead to a significant extension of service life. Reconditioning must therefore be used after a correct understanding of its benefits and limitations. If applied effectively, it is an important tool in controlling degradation as well as reducing the total maintenance costs of public transport.

ISIM Timisoara has developed research programs [5,6] in order to find solutions for:

the reintroduction in the exploitation process of the used metallic elements, with reduced material and financial efforts and at the superior qualitative parameters;

increasing the life / operation of some metal components subject to wear, by covering the active surfaces with layers with superior characteristics to the basic material (hard, anticorrosive layers).
The research was based on the interest shown in recent years by transport companies in the country (RAT Timisoara, RAT Iasi, CTP Arad, RAT Oradea, RAT Bucharest) to reduce maintenance costs of transport by increasing the service life of metal components that, in traffic, are subjected to an accentuated process of degradation by wear.

Modernization and efficiency of welding / welding loading processes requires the application of a package of technological and organizational measures in order to increase productivity by automating technological processes, increasing the deposition rate, welding loading speed and reducing the volume of material imperfections in during the process.

Companies with a tradition in the field worldwide are preoccupied and have achievements in the field of reconditioning by mechanized welding (LINCOLN ELECTRIC - USA, CLOOS Germany, BUG-O - USA, ESAB - Sweden, etc.).

In the country, most welding work is generally carried out by the manual welding process with coated electrodes and by the manual MIG / MAG process. Some companies with activities in the field of welding have introduced a certain level of mechanization, as a result of internal and external collaborations, respectively through their own tooling activities. Automated welding does not have a very wide application area.

In order to increase the deposition productivity and the capacity of the reconditioning workshops of the worn components, the problem is to implement modern and high-performance welding loading systems, which also ensure a high level of deposition quality. In this way, the volume of work for the final mechanical processing of the loaded surfaces is reduced and thus the reconditioning activity becomes even more efficient.

In this context, ISIM Timisoara proposes the design and implementation of flexible, highperformance automated systems for the reconditioning of tram wear components.

Specifically, based on an active partnership between ISIM Timisoara and the partner applying the results, important problems can be solved from a technical and economic point of view:

reducing the costs of maintaining the means of urban public transport by rail (tram), by increasing the lifespan / operation of metal parts subjected to an accentuated process of wear during operation;

increasing traffic safety by using modern, automated execution, reconditioning and control techniques for metal parts subject to wear during operation.
The solutions approached for increasing the life of the parts subject to wear and reintroduction in the process of operation of worn metal assemblies, will comply with the conditions to guarantee traffic safety.

Necessity / Justification

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The service life of some 'active' tram components is limited, in some cases due to wear caused by metal-to-metal friction (e.g. between rails and wheels). In the case of a journey of about 200 kilometers per day (approximately per year) for a tram car, the average service life of a wheel, for example, or a pair of wheels (monobloc axle) is 12 months. As a result, some autonomous utilities and urban transport companies have adopted the solution of reconditioning used parts from the tram.

For example, in Table 1 are presented the parts that were reconditioned a few years ago at a large urban public transport company in the country and the number (approximately) / month:

Table 1 Parts of the tram that were being reconditioned

Part name | Material | Pieces/month | Welding process
Grease box | 230-450W | 32 | 111 / 135
Wheel hub | R52 4b | 92 | 111 / 135
Axle half-coupling | S355 | 30 | 111
Axle half-coupling | S355 | 20 | 111
Circular coupling | S355 | 20 | 111
Wheel bandages | B4 UIC810 | 60 | 121

The transport company owned 420 trams, of which about 320 ran daily.
Mostly used parts have been / are reconditioned by manual electric welding, except for the tram wheel rims where the process is performed with semi-mechanized machines made by ISIM Timisoara between 1993 and 1994.

Even if the technical level is no longer current, this generation of cars are still used today, the reconditioning of used elements being economically advantageous. For example, the costs of reconditioning the bandages from a bogie ( 4 pcs .) at that time was , while the replacement with new bandages cost . The prices are the ones from the moment of the analysis, the costs with the reconditioning being on average with min. smaller.

In addition to technical and comfort issues related to public transport, an important issue is noise and vibration pollution, which is one of the factors particularly harmful to human life and activity. It is also caused by the movement of road transport in general and trams in particular, being mainly due to wear and tear beyond the permissible limit of metal components in contact / movement.

A study on the noise level produced locally by trams (conducted at the Polytechnic University of Timisoara) revealed that trams generate the total levels of sound pressure shown in Table 2, (at a distance of 7-10 m from the measurement microphone with a speed of ) [7].

Table 2 Sound pressure level - generated by trams

Transport means | Total sound pressure level (dB)
TRAMS | Minimum - 79 | Average - 88 | Maximum - 93

It was found that the measured values are exceeded by for all categories of protected areas. The high values of the noise level are largely due to the following factors: wear and tear and unevenness of the rail, pronounced wear of metal parts in dynamic contact, change of direction of travel at line intersections, change of travel speed.

The vibrations and noise produced by trams are of interest in two respects: their influence on the driver of the means of transport and passengers, as well as on the environment (residential areas, schools, hospitals, etc.).

The conclusions of this study demonstrate the need for regular maintenance of public transport, one of the important ways being the reconditioning by timely welding of metal parts with a degree of wear beyond the permitted limits.
Replacement of used components involves high material and financial costs, so it is preferable to recondition them in order to ensure operational safety.

ISIM achievements in the field

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ISIM Timisoara has had close collaboration relations with urban public transport companies in the country for over 30 years. In this context, collaborations have been developed in the field of repair by welding of used metal components from trams, including the design and manufacture of specialized welding machines:

Two equipment for mechanized repair of used areas for tram bandages by flow welding process - Fig. 1a, b.

Fig. 1 a) The machine for loading the bandage on the front surfaces; b) The machine for loading the bandage on the rolling surfaces

Fig. 1. a) The machine for loading the bandage on the front surfaces; b) The machine for loading the bandage on the rolling surfaces

In order to cover the whole range of areas that could potentially have wear (Fig. 2), two constructive solutions of mechanized SAF welding machines were designed and made:

The machine for loading the bandage on the front surfaces (Fig. 1a);

The machine for loading the bandage on the rolling surfaces (Fig. 1b).

Main features:

Mechanized SAF welding process;

The tires are reconditioned and removed from the wheel to protect the rubber shock absorbers from the influence of the high process temperature specific to the SAF process;

The welding speed is continuously adjustable by adjusting the bandage rotational speed.

Important advantage: High deposition rate / high productivity, characteristic of the SAF process Major disadvantages:

due to the fact that the temperature at which the reconditioning part heats up is very high it is necessary to remove the tires on the wheels to protect the rubber shock absorbers, which requires additional labor costs;

SAF is not a "visible" and "clean" process, due to the formation of the slag layer; after making a welding bead, the repositioning of the welding head for the next bead is done manually, previously it is necessary to remove the slag and careful cleaning (of the previous deposit);

there is no possibility of tracking during the actual loading process, if the technological parameters fall within the prescribed limits;

the criteria / conditions for ensuring the principle of repeatability are not met.

The machines were made between 1993 and 1994 and are still in operation at RAT Bucharest.

- Reconditioning installation by MIG / MAG mechanized welding of used components from public transport

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ISIM Timisoara made for three transport companies in the country, installations for reconditioning by mechanized MIG / MAG welding of used metal surfaces (interior and exterior) from rolling stock components: tram wheel tires, tram axles, tram tubular half-couples, coupling engine, universal transmission joint, axle end bearing assembly. In Fig. 2 are presented other
representative parts that are reconditioned by using this type of installation, highlighting the areas prone to heavy wear.

Fig. 2 Rolling stock components that can be reconditioned by MIG / MAG welding

Fig. 2. Rolling stock components that can be reconditioned by MIG / MAG welding

In Fig. 3 the equipment is presented in the following operating / application situations: wheel tire reconditioning (a); axle shaft reconditioning (b) in the bearing mounting area and drum type reconditioning (c).

Fig. 3 MIG / MAG mechanized welding reconditioning equipment: a) wheel bandages; b) axle shaft, in the bearing mounting area; c) drum type parts

Fig. 3. MIG / MAG mechanized welding reconditioning equipment: a) wheel bandages; b) axle shaft, in the bearing mounting area; c) drum type parts

How the installation works:
Worn parts, ready for welding, are fixed to the clamping / actuating devices in the welding position. After positioning the welding head, the deposit will be made:

of a welding bead by rotating the bandage (Fig. 3) with plus (adjustable) and performing the required step manually by manual control;

of successive cords, the step (horizontal or vertical) being performed automatically.

Fig. 4 shows the areas susceptible to reconditioning and the macroscopic appearance of a specimen taken from a bandage in cross section in the direction of welding / loading.

Fig. 4 Tram wheel bandage (I-IV reconditioned areas by mechanized MIG / MAG welding)

Fig. 4. Tram wheel bandage (I-IV reconditioned areas by mechanized MIG / MAG welding)

Fig. 4 Tram wheel bandage (I-IV reconditioned areas by mechanized MIG / MAG welding)

Fig. 4. Tram wheel bandage (I-IV reconditioned areas by mechanized MIG / MAG welding)

At the time of implementation, the specialized MIG / MAG welding reconditioning installations, made and put into operation at the autonomous public transport utilities in Timisoara, Arad and Iasi, ensured the following economic effects:

the expenses with reconditioning / used part represent max. of the purchase price of a new part;

significant increase in operational safety for mechanized reconditioning compared to manual;

reduction by approx. of the labor required for reconditioning, by:

reduction of auxiliary times affected by machining operations after welding, as a result of uniform deposits;

reduction of the auxiliary times necessary to disassemble the bandages on the wheels, respectively axles;

reduction of consumption of electricity and welding materials by approx. ;

decrease (by approximately ) of the import of new components necessary for the means of transport of foreign origin.
In this generation of machines, the positioning of the welding head for each deposit, depending on the lip profile of the bandage is done manually, being dependent on the experience and physical condition of the welder operator. For this reason there have been cases in which the inadequate positioning of the welding head favors the formation of defects according to Fig. 5 (Marked areas have defects such as lack of melting, cracks and voids).

Obs.: The loading of the bandage from which the sample was taken was made at CTP Arad. After loading by welding the bandage was processed by cutting at the prescribed dimensions.
If, with the technique currently used, the costs of reconditioning a bandage are lower by approx. compared to the cost of a new bandage, we estimate that by automating the process and eliminating the disassembly / assembly operations of the wheel tires these costs could reach 50% (from the cost of a new bandage).
Fig. 5 Highlight bandage areas with possible defects
Given the limitations of the techniques presented, we consider it very useful to implement new solutions for automation, control and monitoring of the welding process.

Proposals for High-Performance Automated Welding Loading System

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The current requirements that are manifested at international level have as objective the implementation in industrial practice of new concepts of design and economic manufacture of parts. Charging by electric welding is one of the commonly used processes in this direction. The process extends both in the production of new parts, series or unique, and in the activities of remodeling manufacturing defects or in operation.

In order to increase the productivity of deposition and the expressive capacity of the workshops of reconditioning of used components, the problem is to make modern and high-performance welding equipment, automated, to ensure a high level of deposition. In this way, the volume of work for the final mechanical processing of the loaded surfaces is reduced and thus the reconditioning activity becomes even more efficient.

Solutions are proposed for the realization of the following systems / methods / technical solutions:

automated, flexible and efficient system for reconditioning the wear components of the trams;

mobile automated inspection system for determining the degree of wear of the tram wheel tires;

method of real-time monitoring of the welding loading process;

technical solution to protect the rubber damping elements against overheating and degradation.

Flexible automated system for welding loading, which performs and controls (in automated mode) the welding loading process and automatically generates at the end of the loading sequence a process sheet with details on compliance and consistency of prescribed parameters and its final result. This will include information on the evolution of the technological process (sampled values of the main process parameters): welding current; welding voltage; shielding gas flow; welding speed; the load ratio, to validate the conformity of the configuration and the dimensions obtained in
comparison with those prescribed. Within the flexible automated system, five action drives will be implemented for the actual welding program.

The system must ensure:

loading by automated welding of a wide range of parts (bandages, axles, wheel hubs, halfcouplings, etc.) with different configurations, of different sizes and with different loading surfaces (circular or flat);

spatial, continuous, programmed deposition of several rows, respectively layers;

a very high precision in operation, in order to avoid the appearance of shape or structural defects that can be formed due to two causes (related to the automated system):

errors of positioning of the welding head in relation to the reconditioning surfaces;

deviations from the technological parameters prescribed for loading;

Monitoring and control system of the welding process, which must detect in real time the appearance of defects (pores, cracks) and their positioning in the deposited layer; it is proposed to research and test the possibilities of using infrared thermography in real-time monitoring of the process.

Recent research, conducted by ISIM Timisoara has shown that infrared thermography can be a viable method for monitoring automatic or semi-automatic welding processes [8-10]. The use of the method can provide information on process stability, constancy of welding parameters, induction of imperfections and / or defects, respectively analysis of the quality of welded joints by thermal imaging, as well as adjustment and optimization of welding parameters by feedback connections. The verification of the method in terms of identifying imperfections in welding, revealed that they can be highlighted by the thermographic method as it is a thermal barrier that prevents heat from spreading inside the examined object according to its thermal characteristics, imperfections having different thermal conductivity in relative to the homogeneous material.

The method was verified experimentally at ISIM Timisoara, when using the friction stir welding (FSW) process, at which the temperatures developed in the welding materials during the welding process was (depending on the plasticizing temperature of the alloys to be welded) [911].

Given the positive results obtained, it is proposed to use the method for electric arc welding, where the process / process conditions are completely different (temperatures of up to are reached in the investigated area).

The mobile automated inspection system must determine as accurately as possible the degree of wear of the tram wheel tires; the data obtained from the inspection process are saved and used to program the operating cycle of the automated system for loading by welding; an inspection sheet is generated, based on the data obtained from the inspection process as well as the related recommendation (whether or not it is necessary to recondition the respective part).

The mobile automated inspection system will use laser sensors to measure distances, using a process without direct contact, offering a number of important advantages: This type of sensors offers resolutions of the order of millimeters and allow high measurement rates. The sensors are specially designed for industrial use, suitable for a wide range of applications such as: measuring depths, precision measurements, without direct contact, distances and thicknesses, positioning, etc.

Mobile automated inspection system presents the following innovative solutions:

Mobility is the main innovative element of the system and its major advantage, allowing easy use directly at the beneficiary's premises and identification of parts that need reconditioning without the need to disassemble them for inspection, thus reducing the time required and eliminating costs related to labor procedures for disassembly / assembly of part as well as replacement of related consumables;

Wear analysis algorithms are also an innovative element, which is based on the analysis of data obtained from precision measurements of laser sensors used to determine the size of the bandage, its thickness and the characteristics of damaged areas (dimensions, depths etc.) thus allowing much faster and more accurate identification of parts that require reconditioning.

Wheel cooling system - in the case of tram wheel belt, which are reconditioned without being removed from the wheel assembly or the wheel train, respectively. The system will ensure the control and maintenance of the bandage temperature during the loading process at values that do not affect the integrity of the rubber shock absorbers and the prescribed properties of the base material deposited material assembly.

The cooling method of the bandage will allow to obtain important labor savings (disassembly / assembly of the bandages on the wheels is avoided, an operation that represents of the total cost of reconditioning).

The main reason why it is important to implement automated solutions is due to the expected results: significantly increase the life of parts subject to wear, reduce loading costs with functional layers by increasing productivity, and improve part quality due to automation of loading process, use of established constant process parameters, controllable during the process.

Also, by using the automated system, the quality of the deposits does not depend on the physical condition of the welder operator, his training and experience (in the field of welding) can be of medium level. In this case the exhaust systems become more efficient from the point of view of the health of the welder operator, the control of the automated system being made from a distance (23 m from the area where the charging is actually done by electric arc welding).

Manual welding requires good professional training and experience, physical effort and concentration for a long time, inhalation of noxious substances resulting from the process (even if there are exhaust installations).

Conclusions

The original version of this paper is available on https://www.scientific.net/EI.2.31.pdf

The main reasons for the regular maintenance of means of transport are: increased operational safety, safety and comfort of passengers, reduction of noise, increase the life of wear components, reduction of malfunctions;

Rehabilitation by welding of used components allows to reduce the operating costs of public transport;

The use of automated welding loading systems ensures a uniform deposition of the layers, which has the effect of reducing by the labor for post-welding operations (machining to restore the profile of the reconditioned parts to the prescribed dimensions).

With the technologies and techniques used so far in the reconditioning of used parts, a saving of approximately can be made compared to the purchase of new parts;

Increasing productivity through automation, compared to manual / mechanized processes, improving the quality of deposits (reducing defects and making uniform layers), eliminating the disassembly / assembly of bandages in the case of tram wheels, will ensure lower prices for reconditioning used parts, in average by about compared to new parts;

Reconditioning and restoring the profile of worn parts, performed carefully and correctly, can lead to a significant extension of service life. Reconditioning should be used after a proper understanding of its benefits and limitations. If applied effectively, it is an important tool in controlling degradation as well as in reducing the total maintenance costs of public transport.

References

The original version of this paper is available on https://www.scientific.net/EI.2.31.pdf

B. Dahl, B. Mogard, Repair of rails on site by welding, Svetsaren, special issue, 2000, June., p. 102-105;

K. Cramer, Instandsetzung durch Schweißen, Der Praktiker - Schweißtechnik und mehr, 2002, No. 8, p. 284-286;

V. Georgescu; E. Constatin, Instalaţie de recondiţionare a pieselor conice uzate, folosind sudarea automată sub strat de flux, Reconditioning installation for used conical parts, using automatic submerged arc welding, Sudura, 2001, No. 1, pp. 23-26;

ELMA-TECHNIK GmbH Aachen: "Schweißen mit Präzision. MIG / MAG - Schweiß Stromquelle ELMA-ANALOG C400P und C600P". Prospect.

National research project 2C10, Program AMTRANS (2002-2004), Reintroducing in exploitation process of the worn metallic assembly from public transportation vehicles, using reconditioning by mechanized MIG/MAG welding, in conditions of guaranteeing traffic safety, 2002-2004

L.N. Boțilă, R.Cojocaru, Reconditioning of the used components from transportation devices using mechanized MIG/MAG welding procedure, Annals of the Faculty of Engineering Hunedoara, Tome II, Fascicole 3/2004, pp. 171-178, ISSN 1584-2673, categ. B+, CNCSIS, BDI,

M. Toader, L. Brîndeu, V. Bacria, N. Herişanu, C. Ştefan - "Noise and vibration produced by trams", National Conference "Installations for construction and environmental comfort", Timisoara, Aprilie 2002

A. Mihai: Termografia in infrarosu - fundamente. 2005. ISBN: 973-31-2258-0;

A. C. Murariu, A. V. Bîrdeanu, R. Cojocaru, V. Safta, D. Dehelean, L. N. Boţilă, C. Ciucă Application of Thermography in Materials Science and Engineering, Chapter in the book "Infrared Thermography", pp.27-52, available at /books/infraredthermography, ISBN: 978-953-51-0242-7, Publisher InTech, March, 2012;

R. Cojocaru, L.N. Boțilă, C. Ciucă, Infrared thermographic technique - viable alternative for monitoring of friction processing processes, Welding & Material Testing, No.1/2020, pp. 3-9, year XXIX, B+, BDI,

C. Ciucă, a.o., Possibilities of joining steel S235 using the friction stir welding process assisted by TIG, Welding& Material Testing, No.1/2019, pp.3-7, ISSN 1453-0392, Year XXVIII, B+, BDI, 2019, .

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/engineering-innovations-vol-2/978-3-0364-1097-5

Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 41-48

doi: 10.4028/p-15iqnw

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2021-11-15

Revised:
2021-11-22

Accepted:
2021-11-22

Online:
2022-06-20

Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

The original version of this paper is available on https://www.scientific.net/EI.2.41.pdf

Miodrag Arsić , Željko Flajs , Aleksandar Sedmak , Emil Veg , Simon Sedmak*3,e

Institute for Materials Testing, Bulevar Vojvode Mišića 43, Belgrade, Serbia

Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, 11120 Belgrade, Serbia

Innovation Center of the Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade, Serbia

miodrag.arsic@institutims.rs, zeljko.flajs@institutimas.rs, asedmak@mas.bg.ac.rs, eveg@mas.bg.ac.rs, *esimon.sedmak@yahoo.com

Keywords: bucket-wheel excavator boom, damage, NDT, tensometry

Abstract

Causes of damage occurrence in vital components of welded structures of the bucket-wheel excavator boom (DU1) at the coal landfill of the thermal power plant 'Nikola Tesla A' in Obrenovac (Serbia) are investigated. Bucket-wheel excavator was produced by French company 'Ameco' and it moves along the circular track. Taking into account lack of technical documentation, all tests and were carried out under the assumption that welded structures were made of structural steels S355 and S235. Investigation of causes of damage occurrence are based on results of non-destructive tests (NDT) and tensometric measurements.

Introduction

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There are 2 bucket-wheel excavators at the coal landfill of the thermal power plant 'Nikola Tesla A' in Obrenovac (Serbia), designated by DU1 and DU2, and produced in France. These bucket-wheel excavators move along the circular track (widely known as polar track). Taking into account the long period of operation under severe working conditions (dynamic loading with varying amplitudes), as well as the fact that during their design there were practically no possibilities to carry out the detailed stress - strain analysis, the most loaded elements and their connections have to be checked continuously [1-12]. This especially refers to welded joints and welded structures [3,4,7,8].

Bucket-wheel excavator with designation DU1 is presented in figure 1. Considering the fact that there was no technical documentation, all tests and researches presented in this paper were carried out under the assumption that welded structures were made of structural steels S355 and S235 [13].

Figure 1. Bucket-wheel excavator DU1 at the coal landfill of the thermal power plant 'Nikola Tesla A'

Figure 1. Figure 1. Bucket-wheel excavator DU1 at the coal landfill of the thermal power plant 'Nikola Tesla A'

Damages at Vital Sections of the Welded Lattice Structure of the Bucket-Wheel Boom

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Damage was detected mainly through visual testing (VT) of parent material and welded joints. No defects were detected with other non-destructive testing methods, as well as no deviations from expected results during hardness testing. In figure 2 the reinforcements in the damaged support structure of the cylinder, which role is to enable the moving of the bucket-wheel boom, are shown, while in figure 3 the reinforcements that were embedded in the damaged section of one of the vital girders of the structure are shown. Sections of the vital structure in the upper zone of the bucket-wheel boom with damage in the area of welded joints are shown in figure 4.

Figure 2. Reinforcements (blue) embedded in the damaged structure of the cylinder

Figure 2. Figure 2. Reinforcements (blue) embedded in the damaged structure of the cylinder

Figure 3. Reinforcements embedded in the damaged section of a vital girder at the boom structure

Figure 3. Figure 3. Reinforcements embedded in the damaged section of a vital girder at the boom structure

Figure 4. Sections at the vital structure of the upper zone of the bucket-wheel boom of the excavator DU1

Figure 4. Figure 4. Sections at the vital structure of the upper zone of the bucket-wheel boom of the excavator DU1

Stress state of Vital Structures of Bucket-Wheel Boom Based on Measured Local Strains

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Stresses were determined on the basis of tensometric measurements of local strains in the areas of parent material and welded joints at the lattice structure of the bucket-wheel boom of the excavator with designation DU1. Measurements were executed through the use of electro-resistant extensometers - measurement gauges TML PL-10 and TML PL-20. Measurement equipment for detection and processing of signals from measurement gauges to readable strain values is shown in figure 5.

Figure 5. Measurement equipment for registration and processing of electric signals

Figure 5. Figure 5. Measurement equipment for registration and processing of electric signals

Cylinder and Support Structure

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Stresses were calculated on the basis of tensometric measurements of local strains in different positions of the bucket-wheel boom during the operation of the bucket-wheel excavator DU1 (figure 1), in order to check if there is a possibility of appearance of initial cracks due to fatigue that occurs at vital structures of the cylinder, which enables the movement of the bucket-wheel boom. Measurements were carried out through the use of a large number of measurement gauges TML PL20. Certain number of measurement locations at damaged vital structure in the area of the cylinder and at the support structure of the cylinder itself are presented in figures 6 and 7. On the basis of results of measured local strains and calculated stresses it was determined that the above-mentioned structures are subjected to the highest variable stresses, when bucket-wheel excavator DU1 is in the lowest position of exploitation. Allowable tensile stresses for structural steels S235 and S355 for safety level are and respectively, with note that compressive stresses do not have the same effect on the propagation of the initial crack and structural integrity.

Figure 6. Measurement locations at the vital structure in the area of the cylinder which enables the movement of the bucket-wheel boom

Figure 6. Figure 6. Measurement locations at the vital structure in the area of the cylinder which enables the movement of the bucket-wheel boom

Figure 7. Measurement locations at the support structure of the cylinder

Figure 7. Figure 7. Measurement locations at the support structure of the cylinder

Vital Structure of the Bucket-Wheel Boom

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Stresses have been calculated in order to check if there is a possibility of occurrence of initial cracks due to fatigue at the vital structures of the cylinder, which enables the movement of the bucketwheel boom, on the basis of tensometric measurements of strains at the vital section of the structure for two positions of the boom ( and ) during the operation of the bucket-wheel excavator DU1. Measurements have been carried out through the use of a large number of measurement gauges TML PL-10. Measurement areas and measurement locations at the vital lattice structure of the bucketwheel boom, which is an integral part of excavator DU1 are presented in figures 8-10. Results of stresses calculated on the basis of measured strains are presented in tables , where maximum values are marked in red and bold.

Figure 8. Measurement locations at the vital structures of the bucket-wheel boom

Figure 8. Figure 8. Measurement locations at the vital structures of the bucket-wheel boom

Figure 9. Measurement locations at the vital structures of the bucket-wheel boom

Figure 9. Figure 9. Measurement locations at the vital structures of the bucket-wheel boom

Figure 10. Measurement locations at the vital structures of the bucket-wheel boom (cross-section 11)

Figure 10. Figure 10. Measurement locations at the vital structures of the bucket-wheel boom (cross-section 11)

Table 1. Stresses at the vital structure of bucket-wheel boom (cross-section 0, Fig. 8), maximum values marked in bold

Loads at the bucket-wheel excavator DU1 | Measurement locations
| M₁ | M₂ | M₃ | M₄ | M₅ | M₆ | M₇ | M₈
σD - Measured stress for boom position at 0⁰, MPa | - | - | 15.2 | 16.0 | 32.8 | 32.4 | 31.2 | 31.2
σD - Measured stress for boom position at 12⁰30`, MPa | - | - | 28 | 19.0 | 21.2 | 22 | 19.2 | 17.2

Table 2. Stresses at the vital structure of bucket-wheel boom (cross-section 0, Fig. 9), maximum values marked in bold

Loads at the bucket-wheel excavator DU1 | Measurement locations
| M₉ | M₁₀ | M₁₁ | M₁₂ | M₁₃ | M₁₄ | M₁₅ | M₁₆
σD- Measured stress for boom position at 0⁰, MPa | 32.8 | 27.6 | 31.2 | 30.8 | 28.4 | 27.2 | 30.0 | 29.6
σD- Measured stress for boom position at 12⁰30`, MPa | 20.4 | 18.0 | 20.0 | 19.2 | 18.0 | 19.2 | 16.8 | 16.4

Table 3. Stresses at the vital structure of bucket-wheel boom (cross-section 11, Fig. 10), maximum values marked in bold

Loads at the bucket-wheel excavator DU1 | Measurement locations
| M₁₇ | M₁₈ | M₁₉ | M₂₀ | M₂₁ | M₂₂
σD- Measured stress for boom position at 0°, MPa | 41.2 | 44.4 | 44.4 | 41.2 | 20.4 | 20.4
σD- Measured stress for boom position at 12°30', MPa | 31.2 | 31.2 | 30.0 | 30.4 | 12.0 | 12.4

Analysis of Causes of Damage in Vital Components of the Bucket-Wheel Boom

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Based on the analysis of results of non-destructive tests executed at vital structures of the bucketwheel boom, it can be concluded that initial cracks within welded joints can propagate until they reach the critical length, which confirms the assumption that damages at vital structures occurred due to inadequate welding technologies during the manufacture of the bucket-wheel excavator and/or during previous repairs performed on parent material and welded joints, figures 2-4. Significant presence of defects in the area of welded joints, figure 4, is caused by complex geometry, figure 11.

Figure 11. Node at the welded structure and locations at which fatigue cracks mainly occur

Figure 11. Figure 11. Node at the welded structure and locations at which fatigue cracks mainly occur

In accordance with recommendations [14], it was adopted that critical value of fatigue safety is . Tensile strength of the weld metal is determined by the following expressions [15]:

where:
minimum tensile strength of filler material (electrode EVB 50),
minimum tensile strength of parent material S 235, [13],
minimum tensile strength of parent material S 355, [13].
It is obvious that in both representative combinations of static stresses (figure 12), measured stresses in critical areas of vital components of the bucket-wheel (tables 1-3) lie beneath the limit line which connects fatigue strength and tensile strength of weld metal, which proves that damages at vital components of welded lattice structure of the bucket-wheel boom occurred due to the application of inadequate welding technologies during the manufacture of the bucket-wheel excavator and/or during the previous repairs.

One should notice that stresses, calculated here on the basis measured strains, are in good agreement with the numerical results, obtaing by the FEM, as shown in [16].

Fig. 12. Modified Goodman diagram

Fig. 12. Modified Goodman diagram

Conclusion

The original version of this paper is available on https://www.scientific.net/EI.2.41.pdf

Results of tensometric measurements showed that welded structure of the bucket-wheel boom was designed in complete agreement with its function and operational loads with low service stresses which could not produce damage shown in this investigation. Therefore, it is clear that damage at vital components of welded lattice structure of the bucket-wheel boom occurred due to the application of inadequate welding processes and/or procedures during the manufacture and/or during the previous repairs.

Acknowledgements

The original version of this paper is available on https://www.scientific.net/EI.2.41.pdf

This work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (Contracts No. 451-03-9/2021-14/200012, 451-03-9/2021-14/200105 and 451-03-9/2021-14/200213).

References

The original version of this paper is available on https://www.scientific.net/EI.2.41.pdf

S. Sedmak, A. Sedmak, M. Arsić, J. Tuma, An Experimental Verification of Numeralical Models for the Fracture and Fatigue of Welded Structures, Materials and technology, 41 (2007) 173-178.

M. Arsić, M. Mladenović, A. Veljović, M. Rakin, Z. Radaković, Reliability of Critical Welded Joints in Responsible Support Structures of Bucket Wheel Excavator, XIX International Conference on Material handling, constructions and logistics - MHCL '09, Belgrade, 2009, 133-138.

S. Bošnjak, N. Zrnić, A. Simonović, D. Momčilović, Failure analysis of the end eye connection of the bucket wheel excavator portal tie-rod support, Engineering Failure Analysis, 16 (2009) 740-50.

E. Rusiński, J. Czmochowski, A. Iluk, M. Kowalczyk, An analysis of the causes of a BWE counterweight boom support fracture, Engineering Failure Analysis, 17 (2010) 179-91.

M. Arsić, S. Bošnjak, N. Zrnić, A. Sedmak, N. Gnjatović, Bucket wheel failure caused by residual stresses in welded joints, Engineering Failure Analysis, 18 (2011) 700-712

S. Bošnjak, M. Arsić, N. Zrnić, M. Rakin, M. Pantelic, Bucket wheel excavator: Integrity assessment of the bucket wheel boom tie-rod welded joint, Engineering Failure Analysis, 18 (2011) 212-222.

M. Savković, M. Gašić, M. Arsić, R. Petrović, Analysis of the axle fracture of the bucket wheel excavator, Engineering Failure Analysis, 18 (2011) 433-441.

D. Arsić, N. Gnjatović, S. Simon, A. Arsić, M. Uhničak, Integrity Assessment and Determination of Residual Fatigue Life of Vital Parts of Bucket-Wheel Excavator Operating Under Dynamic Loads, Engineering Failure Analysis, 105 (2019) 182-195.

D. Danicic, S. Sedmak, I. Blacic, S. Kirin, Scenario of fracture development in bucket wheel excavator, Structural integrity and life, 13 (2013) 189-196

S. Kirin, M. Božic, M. Brzakovic, I. Vucetic, Challenges of future research in the area of industrial safety. Structural integrity and life, 15 (2015) 71-78.

S. Kirin, P. Stanojevic, I. Miljanovic, A. Sedmak, T. Peric, P. Ilic, Influence of the human factor on risks in an open-pit mine, Structural integrity and life, 15 (2015), 117-128

S. Bošnjak, Z. Petković, P. Matejić, N. Zrnić, S. Petrić, A. Simonović, Analysis of Stress-Strain State of Bucket Wheel Excavator Revolving Platform Structure - Fundament of Efficient Reconstruction, Sructural Integrity and Life, 5 (2005) 129-142

EN 10025-2: Hot rolled products of structural steels - Part 2: Technical delivery conditions for non-alloy structural steels, European Committee Standardization, 2004.

A.F. Hobbacher, Recommendations for fatigue design of welded joints and components. IIW Document XIII-2151r3-07/XV-1254r3-07. International Institute of Welding; 2008.

B.G. Mellor, R.C.T. Rainey, N.E. Kirk, The static strength of end and T fillet weld connections. Materials & Design, 20 (1999) 193-205.

M. Arsić, Ž. Flajš, A. Sedmak, E, Veg, S. Sedmak, Structural integrity assessment and repair of welded structures of the bucket-wheel boom, Structural Integrity and Life, 21 (2021) 201-206

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Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 49-57

doi: 10.4028/p-40ya00

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2021-10-29

Revised:
2021-11-22

Accepted:
2021-11-22

Online:
2022-06-20

Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Ion-Aurel PERIANU , Radu COJOCARU , Emilia-Florina BINCHICIU , Gabriela MNERIE

National Research & Development Institute for Welding and Material Testing - ISIM;

Address: 30, Mihai Viteazu Blvd., Postal Code 300222, Timisoara, Romania

aperianu@isim.ro, rcojocaru@isim.ro, ebinchiciu@isim.ro, gmnerie@isim.ro

Keywords: waterjet, abrasive waste, disposal

Abstract

Due to the extraordinary qualities established and imposed worldwide, the water jet cutting process is increasingly used in current industrial applications. It is well known that the process can be applied to a wide range of materials: metallic and non-metallic alloys, polymeric materials, ceramic materials, glass, stone, marble, wood, rubber, etc. An important challenge in the conception and design of water jet cutting equipment is the removal of used abrasive material from the discharge tank during or after water jet cutting operations. The paper presents innovative solutions proposed and developed worldwide for the evacuation / extraction from the tank of water jet cutting machines of used abrasive particles and / or particles resulting from materials subjected to the cutting process.

General Considerations

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The water jet cutting process (figure 1) has demonstrated its special utility and efficiency by implementing for the processing of a wide range of materials.

Figure 1. Abrasive-water jet cutting process of a 10 mm steel plate on ISIM Timisoara equipment

Figure 1. Figure 1. Abrasive-water jet cutting process of a 10 mm steel plate on ISIM Timisoara equipment

The water jet cutting process consists in directing a high-pressure water jet ( ) and high speed ( ) to the cutting site. The high pressure of water jet exerts compressive stresses on the material, as a result of local shearing and erosion, the material is removed and the cutting angle is achieved. The cutting process causes a deformation of the cut surface, the angle of the striations (wrinkles) depends on the correlation between the cutting speed (translation of the part) and the power of the jet. As the cutting speed increases at a constant jet power (a constant water jet pressure and a constant abrasive flow) the inclination of the risers increases to the point of lack of penetration over the entire thickness of the material. The width of the cutting angle depends on the cutting variant
(without or with abrasive) being between , the resulting surface roughness between 0.1 .

Advantages, with an emphasis on application possibilities:

no heat is generated when cutting with a water jet - this is very important, especially when cutting materials where excessive heat could change the properties of the cut part;

the joint resulting from the cutting has a small value and the material losses are small accordingly;

it can be used to obtain prototype or unique parts. An operator can program the dimensions of the part, in the control station, and the equipment "cuts" the part according to the programming;

It is less expensive and the necessary processing times are reduced compared to the usual procedures that involve making execution drawings for parts and then making parts by successive processing. [1]

Limitations as well as applicability / disadvantages:

only certain categories of materials can be cut with economic advantages; although it is technically possible to cut tool steels and other hard materials, the cutting speed is significantly reduced, the time required to cut a single piece being quite long compared to cutting using other processes.

because of the above mentioned disadvantage, cutting can have higher costs and the benefits do not compensate enough for the price of the operation;

it is not possible to cut very thick parts without losing dimensional accuracy; if the piece is large, the water jet may dissipate, the cut may deviate diagonally, and the width of the resulting joint shall be greater at the bottom than at the top. [2]

Considering special qualities, but also the economic impact through implementation in production activities, of approx. 12 years the water jet cutting process is part of the scientific program but also the industrial services program of ISIM Timisoara.

Water jet cutting equipment - general specification

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The main components of a cutting machine are:

hydraulic pump;

water filtration system;

hydraulic amplifier and accumulator;

rigid and flexible connecting pipes;

cutting head;

abrasive supply system;

part positioning system - cutting head;

pressure relief and recovery unit;

process control and command system. [3]

The schematic representation for a basic abrasive waterjet cutting unit is presented in Figure 2 A , respectively an abrasive waterjet cutting machine front view, property of ISIM Timisoara, is presented in Figure 2 B.

A - schematic representation of a water and abrasive jet cutting equipment

Figure 2. A - schematic representation of a water and abrasive jet cutting equipment

Figure 2. ISIMs water and abrasive jet cutting equipment [3]

In the case of water jet and abrasive cutting, an important component of the machine with major effects on the efficiency of the process is the exhaust abrasive systems in the exhaust tank. These systems must ensure a minimal influence on the actual operating time of the machine.

Modern solutions of waste disposal (used abrasive) for water and abrasive jet cutting equipment

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

The material from the discharge tank resulted from a water jet and abrasive cutting process consists mainly of:

used abrasives;

residues from the material subjected to the cutting process;

other small particles resulting from the operation of the equipment.

The way in which the used abrasive is evacuated and possibly recovered is very important from two points of view, namely:

limiting to a minimum the non-use times in optimal conditions of the machine;

the use of exhaust systems to allow the application of a technical solution for the easy separation of materials from the component of the abrasive material used (useful for example for cutting special metals / precious metals).
Water jet cutting equipment can be made in several variants of constructive solutions regarding the management of resulting particles during the water and abrasive jet cutting process.
In the following the authors present a series of waste removal or recovery systems that are currently used in the industrial sector, or/and are solutions provided by international scientists as patented solutions or patent request.

A. Abrasive removal system by directing the suspension of abrasive particles into a centrifugal filtration system. [4]

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Figure 3. A. system for extracting particulate matter from a liquid body - centrifugal filtration system.

Figure 3. Figure 3. A. system for extracting particulate matter from a liquid body - centrifugal filtration system.

Figure 3. B. - perspective view of the system for extracting particulate matter from a body of liquid

Figure 4. Figure 3. B. - perspective view of the system for extracting particulate matter from a body of liquid

Figure 3. Abrasive removal system [4]

The system shown in Figures 3 A + B, includes a cylindrical tank with a cavity, having an upper end and a lower end, a separator with transverse flow rigidly fixed to the upper end of the cylindrical tank, the fluid communicating with the empty cavity, an inlet pipe connected to the transverse flow separator, an outlet pipe connected to the transverse flow separator, a pump in communication with the outlet pipe and a fluid reservoir in fluid communication with the inlet. The method includes capturing particles and liquid in a tank, partially separating the particles and liquid in the tank, channeling the separated particles and liquid to a cross-flow separator positioned above the tank separating the partially separated particles and the liquid in the separator stream and capturing the particles in the tank.

The centrifugal filtration system separates the water particles by pumping the particle suspension through a centrifugal separator. A capture tank collects the used particles and the water separated from the abrasive particles can then be disposed of or recirculated to the capture tank to repeat the process of cleaning the abrasive particle suspension in the centrifugal filtration system.

B. Continuous abrasive cleaning system (GRS type), by means of automatic abrasive removal installations from the cutting machine tank. [5]

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Figure 4. A. Garnet disposal system. [5]

Figure 5. Figure 4. A. Garnet disposal system. [5]

Figure 4. B. Sanitary system for abrasive sweeping / removing installations. [5]

Figure 6. Figure 4. B. Sanitary system for abrasive sweeping / removing installations. [5]

Figure 4. C. Abrasive removal / removal system. [5]

Figure 7. Figure 4. C. Abrasive removal / removal system. [5]

The Garnet Disposal System (GRS), shown in Figure 4 A, is designed to remove spent abrasive waste from the capture tank of a continuous water jet cutting equipment, thus eliminating downtime for cleaning, maximizing at the same time production.

System of sanitary sweeping / abrasive removal installations shown in figure 4 B - specially designed to fit dimensionally with the capture tank. The system of abrasive removal sanitary installations incorporates several educators / blowers, with a ratio of 4: 1. The educators intensify the water flow and keep the abrasive in suspension, pushing it towards the system with suction holes.

Abrasive removal / disposal system, shown in Figure 4 C - used abrasive waste is stored in a 1000 kg bag at the same speed as it enters the capture tank. Used abrasive waste is relatively clean and has no cutouts or pieces larger than in diameter. The abrasive bag for used waste is easy to manage and is easily lifted from the disposal hopper with a fork after which it is disposed of.

C. Water jet and abrasive cutting equipment, with built-in abrasive tank assembly. [6]

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Figure 5. A. Front view of the water jet and abrasive cutting equipment incorporating the catchment tank assembly, including an enclosure where the abrasive water jet and the catchment tank assembly are located, including the recirculation system and filtration system; [6]

Figure 8. Figure 5. A. Front view of the water jet and abrasive cutting equipment incorporating the catchment tank assembly, including an enclosure where the abrasive water jet and the catchment tank assembly are located, including the recirculation system and filtration system; [6]

Figure 5. B. Overview of the capture tank; [6]

Figure 9. Figure 5. B. Overview of the capture tank; [6]

Figure 5. C. Abrasive removal / removal system. [6]

Figure 10. Figure 5. C. Abrasive removal / removal system. [6]

The system shown in Figure 5, A, B, C refers to a reservoir for capturing water jet and abrasive cutting equipment, which is equipped with a system that facilitates the recovery of used abrasive materials and metal residue resulting from the operation of a water jet and abrasive cutting equipment. The used material collection tank assembly includes a side and bottom clamping tank for collecting a fluid and includes a recirculation system for recirculating the fluid in the capture tank.
The spent material collection tank also includes connections to a filtration system for removing spent abrasive material and metal residue from the resulting fluid. The collection tank includes removable, consumable "wear-resistant support plates" that dissipate the residual energy resulting from the abrasive water jet, thus reducing damage to the tank. The wear plates are spaced above the bottom of the tank, thus dividing the tank into two compartments, an upper one that receives the abrasive water jet and a lower compartment, which is continuously washed, removing used abrasive materials and metal residues from the tank.
The recirculation system is designed to prevent the storage / agglomeration of used abrasive materials, scrap metal or other waste in the capture tank; including a general flow of water from the upper area to the lower area and also a scattered flow of water in the lower area. The liquid is discharged from the lower compartment in a drain through pipes leading to the filtration system. In the preferred version, the tank is portable and includes fork lift channels and quick disconnections that facilitate movement. The tank also includes leveling support legs as well as vibration isolation supports to reduce the vibration transmission to the module that generates the abrasive water jet from the water jet cutting equipment.

D) Waste abrasive drainage system with water recirculation. [7]

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Figure 6. A. Front view of water jet and abrasive cutting equipment. [7]

Figure 11. Figure 6. A. Front view of water jet and abrasive cutting equipment. [7]

Figure 6. B. Front view of the capture tank; [7]

Figure 12. Figure 6. B. Front view of the capture tank; [7]

The "dirty" end of the aluminum tank is positioned under the overflow of the machine. Sediments and oil / grease are trapped in the first compartments, while allowing relatively clean water to be recycled through the pump and attached hoses. Oil and grease can be decanted using the separator hose attached. It is then removed periodically, along with solids that have accumulated over time. The water and material suspension is recycled inside the appliance; Additional water is introduced into the pool during use. This extra water drains the spillway on the side or back of the car, taking with it used materials and oil / grease from parts.
The recirculation tank allows water to be recycled and eliminates the need to be attached to the water supply network. It also means that any chemical additives will not be diluted by use. That is, cost savings and an environmentally friendly configuration.
The recirculation tank offers the advantage of low water costs; and can create a complete closed loop system that can be positioned where water supply is not available. The only water loss is by evaporation.
E) Mobile waste disposal systems. [8]

Figure 7. Water recirculation system with tank [8]

Figure 13. Figure 7. Water recirculation system with tank [8]

Water recirculation system with 200 L tank, recirculation pump with flow higher than 3LPM, filter at the pump outlet, adjustable bypass valve, two fixed deflectors attached to the bottom of the tank to form 2 dams over which water flows and two removable baffles attached to the top of the tank to force water to run under the baffles, widen the flow path and improve sedimentation of used material.

The unit has a stainless-steel tank and two 3 mm stainless steel deflectors. Also, in addition a stainlesssteel lid with pipe-type legs, which fit on four positioning pins mounted in the upper corners of the tank. The pump requires a 240 V 10 A single phase supply.

The pump unit is usually installed next to the grinder with a hose or water connection. Because the pump unit is on wheels, it can be rotated outwards for cleaning, etc. A sludge removal tool is provided.

A locking device is installed between the pump and the grinding motor so that the pump motor is stopped when the abrasive water jet activation motor is stopped.

F) Exhaust systems with vacuum pumps [9].

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Figure 8. A. is a schematic perspective view of an embodiment of the disclosed liquid suction and filtration device, shown connected to a compressed air source and in which the interior of the container is partially broken to reveal the internal components; [9]

Figure 14. Figure 8. A. is a schematic perspective view of an embodiment of the disclosed liquid suction and filtration device, shown connected to a compressed air source and in which the interior of the container is partially broken to reveal the internal components; [9]

Figure 8. B. is a detail of the device in the adjacent figure, showing the tank lid and broken to show the inside of the container; [9]

Figure 15. Figure 8. B. is a detail of the device in the adjacent figure, showing the tank lid and broken to show the inside of the container; [9]

Suction devices have been developed in a variety of models, each to perform a specific task or set of tasks. A common configuration of a suction device is a portable vacuum in which a container, which may be a drum or other closed container, is used to collect the material to be sucked. A flexible hose that ends in a rigid rod or other instrument is connected to the canister, and the rod is placed in or near the material to be collected. Such devices typically include a vacuum pump that lowers the pressure in the sealed container below ambient level, and the pressure difference causes the material to be sucked through the collection hose and collected inside the container. Such portable devices can be used for vacuuming and collecting dry, fluid particles or a combination of particular fluids and materials.

Certain types of suction devices may be adjusted to a suction configuration, in which the particulate material, a fluid or a combination thereof, is drawn through the collection hose and retained in the container, or to a discharge configuration, in which the operation of the vacuum pump is reversed to pressurize the inside of the container over ambient pressure. The pressurized interior forces the collected material, usually a fluid, to pass through the collection hose or, in some embodiments, through a second hose, thus emptying the contents of the container.
The liquid suction and filtration device may include a sealed container, a reversible vacuum pump that communicates with the inside of the container, a two-way valve mounted on the container, a flexible hose connected to the valve, a filter positioned inside the container and connected to valve and a stand pipe connected to the valve and extending inside the container. In one aspect, the vacuum pump may be a reversible pneumatic pump. When the reversible air pump and valve are adjusted to a filling configuration and the flexible hose is placed in or in a fluid containing particulate material, the pump discharges air from inside the container to create ambient pressure inside the container. This partial vacuum can cause the fluid to be sucked through the flexible hose, the valve and the filter inside the container. The inside of the container is filled with fluid and the filter can catch and collect the particulate material which has been suspended in the fluid or introduced through the hose together with the fluid.
The described reversible vacuum pump and valve can be adjusted to a discharge configuration in which the reversible vacuum pump pressurizes the inside of the container to a pressure above ambient
temperature. In this configuration, the valve can be adjusted to create a fluid flow channel through the pipe inside the container, through the valve and through the flexible hose. The above ambient pressure inside the container can cause the fluid inside to flow through this channel and be discharged through the hose.

ISIM proposed technical solution for abrasive waste disposal

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

The proposed solution takes into account the need to periodically displace the used abrasive so that it does not clog. Thus, the work tank is equipped with a number of parts through which pressurized water is drained into the tank, thus activating all the existing water mass together with the sand (used abrasive) obtained from the cutting processing. It is a water circuit connected to a power pump that ensures the required flow. This pipe is provided with a number of connecting elements, equipped with nozzles through which the pressurized water flows which will be discharged into the tank through the holes on the surface of the tank, resulting in controlled agitation of the mixture created, respectively water and abrasive.
This mixture will be discharged through a number of holes drilled in the bottom of the tank, on its horizontal surface.
Figure 9 A shows a drawing for the real-time evacuation system of used abrasive material, implemented in a water jet and abrasive cutting machine, in portal construction with two longitudinal guideways and a beam with transverse trolley, for performing combined cutting movements.
Figure 9 B schematically shows the location of the water agitation / homogenization system (by means of a pressurized water circuit) and used abrasive, in the working tank of a water jet and abrasive cutting installation.

Figure 9 A Schematic for the real-time evacuation system of used abrasive material

Figure 16. Figure 9 A Schematic for the real-time evacuation system of used abrasive material

Figure 9 B Waste abrasive cleaning solution principle

Figure 17. Figure 9 B Waste abrasive cleaning solution principle

Conclusions

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Water and abrasive jet cutting processes are important technological processes for industrial processing. These are rather new but mature processes with possibilities for expansion, as information of technological nature regarding different cutting applications and different materials to be processed are developed. It is a current process with extraordinary qualities and versatility in application.

By implementing into production an abrasive removal system we can achieve the following benefits:

Maximizes productivity - eliminating the time required to clean the capture tank;

Reduces the possibility of thermal distortion - by removing the abrasive from the table, the heat resulting from the machining process is dissipated;

Reduces consumable costs in a closed loop system - by removing abrasive from wastewater, the filtration system can maximize water treatment rather than removing abrasive;

Abrasive sweepers are part of the removal system and are designed to prevent abrasive from dispersing into all areas of the capture tank.
By mounting a recirculation tank on an industrial water and abrasive jet cutting equipment the following advantages can be obtained:

Makes the system completely "closed" and able to operate in industrial conditions and with minimum down times;

Environmentally friendly, minimizes waste production and reduces waste disposal indirect costs;

Filters oil / grease for easy settling and disposal;

Detachable baffles for easy cleaning;

Stores and filters "used abrasive" and prepares it for disposal;

Allows water to be recycled back into the machine, which means there is no water loss;

No dilution of chemical additives inside the machine, which leads to savings in casting.

A very important aspect for the efficiency of the process is the continuity of the effective cutting time. From this point of view, a factor with major influence is the way in which management of the used abrasive is solved; presented solutions can be applied to this end.

References

The original version of this paper is available on https://www.scientific.net/EI.2.49.pdf

Jayakrishna Kandasamy, (2017), Sustainability studies on abrasive water jet cutting process, International Conference on Waste Management - RECYCLE 2016, At: IIT Guwahati;

Ludmila Volgina, Stanislav Sergeev, (2020), Water jet cutting resistance, IOP Conference Series Materials Science and Engineering, Volume 869, NEW CONSTRUCTION TECHNOLOGIES, July 2020, doi:10.1088/1757-899X/869/7/072035.

I.A. Perianu, D. Ionescu, V. Verbițchi, "Method of measuring the abrasive-water jet diameter, for cutting process control", Welding and Material Testing - BID, no.1/2017.

http:

&cntry=US&patno_fg=PAN

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Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 59-65

doi: 10.4028/p-ke9dc5

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2022-02-17

Accepted:
2022-02-28

Online:
2022-06-20

Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures

The original version of this paper is available on https://www.scientific.net/EI.2.59.pdf

Jianwei Ma , Ana Evangelista , Assed Haddad , Milind Siddhpura , Huifen Hao

Engineering Institute of Technology, Australia

Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil

Deakin University, Australia

Kelley Covey Group, Australia

12155@student.eit.edu.au ana.evangelista@eit.edu.au assed@poli.ufrj.br, milind.siddhpura@eit.edu.au juneH@kelleycovey.com.au

Keywords: Pin connection; Long-span; Experimental study; Truss-column connection; FEA

Abstract

A pin-connected joint, which was intended to accommodate a certain in-plane rotation and resist the shear forces, was introduced in this paper. Pinned-connections were applied on Truss-Column joints to support the heavy-loaded floors and roofs in a long-span steel structure. The Pinned-connection was designed in accordance with European code, and compared with other standards such as America standard and Australia standard. To better understand the behavior of materials and structure of this pin-connection structural system, four specimens, including two full-scale pin-connections and two truss connections, were tested to investigate the performance under both monotonic and cyclic loads. The load-displacement curves, hysteretic curve and ultimate loads were obtained, and the failure mode, capacity and ductility were discussed. The experimental and numerical results indicated that the pin-connection behaved good ductility, load transfer ability and capacity.

Introduction

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The pin-connected joints have been widely used in bridges and mechanical engineering. Pin-connection transfers vertical and horizontal shear loads and cannot resist any bending or moment forces, so it is often regarded as a complete hinge joint in structural designs. In recent years, pinned connections have been adopted in building structures such as supports, beam-to-column joints and bracing system [1]. Li Jiawu [2] provided a systematic study on the design of pin connections and discussed the design details. With the rapid development of contact problem analysis methods and calculation software, the application of numerical solution methods such as finite element method in these types of connections have made significant progress [3]. Some scholars [4] implemented finite element software Ansys to establish a full-size model of the typical pin connection of the building structure to study the contact force distribution, and conducted a theoretical analysis of several major factors affecting the pin contact force distribution.

The experimental study on pin-connection, which has been carried out over decades, has generally been relatively limited in mechanical area. David Duerr [5] built a comprehensive test program to investigate the behaviour of pin plates under static loading and proposed a set of solutions for calculating the strength. Dayi Ding [6] applied pin connections for truss-column in a commercial steel structure, and studied the material performance of the pin shafts and ear plates as well as full-scale experimental test under static loading and cyclic loading; Jianwei Ma [7] analyzed pin-connected joints for truss-columns connections of large-span steel structures to support heavy-loaded floor by finite element method, and carried out experimental research on pin-connections.

In this paper, a novel pin-connection joint was proposed for truss-column connection to support floor system subject to heavy loads in long-span steel structures, because typical welded and bolted
connections were unable to meet the design criterias (see Figure 1). This pin-connected joint was designed to meet some requirements such as simple, durable and achievable with higher construction speed and less on-site weldings. Moreover, the proposed joint aimed to match the development trend of "green buildings", which was an energy saving and eco-friendly policy introduced by local authorities towards lowering carbon footprint[8].

However, although pin connection has a large number of applications in China, there are few specifications prescribed on this type of connections, and the experimental and analytical study data are limited[9]. Besides, standards from other countries, including European[10], American [11]and Australia standards [12], are recommended in the design of pin-connections. Therefore, it is necessary to conduct a detailed research to investigate the static and seismic performances of this connection and provide provisions for the design of pinned connections..

Fig. 1. Application of Pin-connected Joints

Fig. 1. Application of Pin-connected Joints

Structure of the Joints

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In order to study the behaviour, four specimens including two full-scale and two large-scale models were designed as per current Europe design code and tests were conducted under static and quasi-static loads. The test results would be compared with the corresponding finite element analyses. For the construction, pin-connection joints consisted of ear plates and pin shafts which were welded together in the factory; the trusses and columns were connected by pin-connections on-site by high-strength shafts[13].

Experimental Study

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Specimen Design. Four pinned connection specimens called as JD1-JD4 were constructed and tested under monotonic and cyclic loadings. Test scales were determined as 1/2-scale on JD3 and JD4 and full-scale specimens on JD1 and JD2, since the strength constraints and geometric of existing laboratory conditions. The details of the pinned connection specimens are shown in Figure 2.

Fig. 2. Details of the Test Specimens

Fig. 2. Details of the Test Specimens

Loading Plan. Specimens JD1, JD2 and JD3 were subjected to constantly monotonic static loads at the top; cyclic loads were imposed on specimens JD4. The axial load was applied and maintained constantly by a hollow-core-hydraulic jack and reaction frame of which capacity is 2000 kN . All tests were carried out at a laboratory atmosphere of room temperature and relative humidity. The test instruments are seen in Figure 3.

Fig. 3. Test Setup for JD1, JD2, JD3 and JD4

Fig. 3. Test Setup for JD1, JD2, JD3 and JD4

Loading System. This test has two kinds of loading systems: specimens JD1-JD3 were subjected to monotonic tensile loading; the specimen JD4 was subjected to cyclic loading.

Monotonic Loading. Monotonic loading was adopted for the static tests with the load at a level until the specimen failed. Monotonic loading, the load control method, was divided into three stages of loading: Nominal load increasing by to ; ultimate load increasing by to ; fail load increasing 150%~200% nominal load until failure.

Cyclic Loading. According to Chinese standard test method, the quasi-static loading procedure adopted the method of double controlling: the whole loading process was controlled by loading before yield and displacement after yield. But because the test specimens were special, there was a gap for the pin connection, so it was very difficult to control the displacement. Therefore, load control method was applied during the whole test loading. Figure 8 shows the loading system as follows:
(1) test could no longer be carried if sudden damage occurred or sudden loss of stability occurred;
(2) the load of each level in the elastic stage was 200 KN with 2 cycles ;
(3) the load of each level in the plastic stage was 200 KN with 2 cycles until the specimen failed.

Experimental Results

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The yield load , the ultimate load , the yield displacement , and the ultimate displacement at the loading points were obtained by the results of the test. The four specimens' failure modes were familiar, which include three types: weld fracture of the ear plates, buckling at the chord members, and deformation of the shaft.
(1) Specimen JD1

This specimen was designed to be tested under a pull load only. The elastic deformation was approximately 3.7 mm , and the plastic deformation was around 8.3 mm . Damage occurred in the ear plate weld (see Figure 4). The pin shaft deformation was about 1.2 mm when the ear plate cracked. During the test if the ear plate welding pin was not destroyed, the ultimate bearing capacity could be improved. It can be seen from Figure11 that the ultimate load of Specimen JD1 is 9297 KN that is 2.21 times of design value. The load-displacement curve of the loading point is given in Figure 4.

Fig. 4. Failure, Shaft Deformation and Load-displacement Curve for Specimen JD1

Fig. 4. Failure, Shaft Deformation and Load-displacement Curve for Specimen JD1

(2) Specimen JD2

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This specimen was designed to be tested under a push load only. The behavior of the specimen was completely different under push loading. The maximum push loads were 5.82 times of design value. The capacity under pull loading was much larger than it was under push loading. Specimen JD2 showed different mechanisms to resist the pull and push loads. No apparent damages occurred in this specimen. The maximum displacement of pin shaft was approximately 12 mm when the ear plate touched the steel plate of members (as shown in Figure 5).

The load-displacement curve of the loading point is presented in Figure 5.

Fig. 5. Shaft Damage, Deformation and Load-displacement Curve for Specimen JD2

Fig. 5. Shaft Damage, Deformation and Load-displacement Curve for Specimen JD2

(3)Specimens JD3

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The bearing capacity was determined in specimens JD3 which was a part of the whole truss under the monotonic loading. It can be seen from Figure 6 that the ultimate carrying capacity of Specimen JD3 outperformed Specimen JD1 and JD2. The ductility performance of the specimens did not significantly reduce its carrying capacity in term of non-elastic deformation capacity. The weld quality significantly affected the ductilityof the joints as well as energy dissipation. When Specimen JD3 reached the ultimate load, the carrying capacity had little reduction. It was clear that the existence of truss members improves the ductility of the pinned connection.

The load-displacement curve of the specimen JD3 is illustrated in Figure 6. Specimens JD3 was not damaged mainly because of limited loading device, as shown in Figure 6. The maximum displacement of pin shaft reached 5.6 mm .

Fig. 6. Shaft Damage, Deformation and Load-displacement Curve for Specimen JD3

Fig. 6. Shaft Damage, Deformation and Load-displacement Curve for Specimen JD3

(4)Specimens JD4

The experimental lateral load-displacement curve, which represents the seismic behavior of structures, is a very important factor under cyclic loading. The area, surrounded by this curve, represents the energy-dissipation ability of the structure.

It can be seen from the test results, the specimen loading showed obvious asymmetry, especially after entering the plastic phase. The reason was the significant deformation of some components out of plane. But the test studied the tensile behavior of the member, the hysteretic curve of the tensile loading was very full, smooth, which indicated that they had better ductility and energy dissipation. Table 1 gives the main results.

Table 1. Measure Results

Sample
Load
(KN)
(+)
Dis.
(mm)
(+)
Load
(KN)
(-)
Dis.
(mm)
(-)
Load
(KN)
(+)
Dis.
(mm)
(+)
Load
(KN)
(-)
Dis.
(mm)
(-)

JD4
200
5.5
200
3.87
200
4.95
200
3.53

400
6.3
400
6.42
400
7.11
400
5.39

600
8.97
600
7.35
600
9.59
600
7.05

800
14.9
800
9.25
800
14.01
800
0.02

1000
22.7
1000
12.94
1000
22.97
1000
13.13

1200
33.0
1200

The hysteretic curve is provided in Figure 7.The damage of specimens JD4 occurred in the 1200 kN load cycle on second lap for the buckling of member's winging, as seen in Figure 7. The maximum displacement of pin shaft reached 1.5 mm .

Fig. 7. Shaft Damage, Deformation and Load-displacement Curve for Specimen JD4

Fig. 7. Shaft Damage, Deformation and Load-displacement Curve for Specimen JD4

Conclusions

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The behavior of pinned-connection joints subject to monotonic static loading and cyclic loading was investigated. Four pinned-connection specimens were studied in the tests and finite element analysis. Finite element analysis results were compared with those of experimental results. The main conclusions are summarized as follows:
(1) The welding seams between the chord members and the ear plates significantly affected the failure mode and various mechanical properties of the pinned-connection joints. Sudden fractures of the welding seams resulted in a decrease in the plastic deform ability of the pinned-connection joints. To obtain seismic energy dissipation requirements, strengthen the ear-plate thickness was recommended and increased the lengths of the welding seams to avoid generating cracks under load.
(2) The hysteretic curve shapes were full and smooth, and the load-displacement curves, which represent suitable ductility and energy dissipation ability, had gently descending stages, the pinned-connection joints showed good seismic performance, ductile performance and energy dissipation capacity.
(3) The results of the simplified calculation formulas proposed in the Europe code got along well with that of the model test and the finite element analysis. The formulas could be used to describe the strength of joint under static load and cyclic load. The results indicate that the proposed pin connection is viable and can be applied to truss-column joint in long-span steel structures.
Further studies, such as response of the whole structure and multi-scale modelling, may be required although this structural system had been used in practice. However, research on the dynamic behavior of pinned-connection joints systems as well as study to improve the details will be carried out by the author for further investigation.

References

The original version of this paper is available on https://www.scientific.net/EI.2.59.pdf

Ma, J.W., Chen Z, Hao H: Review of application of spherical plain bearing joints in steel structures. Building Structure, 2018, 48(23), p. 92-100.

Li J.: Finite Element Calculation and Research of Typical Pin Shaft. Construction Mechanization, 2005,26(10):50-51.

Wand D.: The Application of ANSYS for Bearing Contact. Bearing, 2002(9):14-16.

Zhu Hao: The Research of Contact Forcedistribution of Pin Connection for Large Steel Structure Joint. Wuhan University of Technology, 2011.

Ding, D.Y: Experimental Study on Bearing Capacity of Beam-Column Pin Joints in Long-Span Steel Structure Under Heavy Load. Journal of Tianjin University:Science and Technology, 2015,48(Suppl):53-59.

David Duerr, P.E., M.ASCE: Pinned connection strengthand behavior. Journal of Structural Engineering, 2006,132(2): 182-193.

Ma, J.W., Chen Z, Hao H: Experimental study on pin-connected support joints between large-span steel truss and steel column. Building Structure, 2016, 46(12), p. 91-97.

Liu X.C. 2015: Static and seismic experiment for welded joints in modularized prefabricated steel structure. Journal of Constructional Steel Research, 112 (2015) :183-195.

Ding Dayi, Wang Meng: Experimental and analytical investigations on a large floor truss pinned connection. Advances in Structural Engineering, 2017, Vol. 20(7) 1007-1023.

Eurocode 3 Design of Steel Structures-1993-1-8:Design of joints[S]. London: SETO,2000.

American Institute of Steel ANSI/AISC 360-05 Specification for Structural Steel Building. Chicago:American Institute of Steel Construction. Inc,2005.

Steel Structures: AS 4100-2020 . NSW: Standard Australia,2020.

J. Ma, X. Wang, H. Hao: Design and Finite Element Analysis of Truss-Column Pin-Connected Joints in Long-span Steel Structures. Journal of Tianjin University:Science and Technology, 2016, 49(Suppl): 97-103.

Wang,Z&Wang,X.D..Experimental and numerical Study On strut Up-Joint with Radial Spherical Plain Bearing. Journal of Building Structure,2013,34 (11):70-75.

Guojun Sun, Mingze Wu, Yuan Yang: Mechanical properties of radial spherical plain bearing (RSPB) joint with an inserted plate for building structural application-An experimental study. Structures, Volume 33, 2021, p. 2140-2151.

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The original version of this eBook is available on https://www.scientific.net/book/engineering-innovations-vol-2/978-3-0364-1097-5

Engineering Innovations, ISSN: 2813-1002, Vol. 2, pp 67-73

doi: 10.4028/p-6emexf

© 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2022-02-17

Accepted:
2022-02-28

Online:
2022-06-20

Highlights of Earned Value Analysis in Construction Projects

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Bruno B.F.da Costa , Jorge G. Farías , Mohammad Najjar , Mayara Amario , Carlos A.P. Soares , Assed N. Haddad

Universidade Federal do Rio de Janeiro, Athos da Silveira Ramos, 149 - Ilha do Fundão - Centro de Tecnologia - Bloco D, 207 - Cidade Universitária - 21.941-909 - Rio de Janeiro - RJ - Brasil.

Programa de Pós-Graduação em Engenharia Civil, Universidade Federal Fluminense, Rua Passos da Pátria 156, Bloco D, São Domingos, 24210-020 Niterói, RJ - Brasil.

ªbruno.barzellay@macae.ufrj.br, bjorgemariogf12@gmail.com, cmnajjar@poli.ufrj.br, mayara_amario@poli.ufrj.br, capsoares@id.uff.br,

Keywords: Earned value analysis; Construction; Project management; Performance indicators

Abstract

Construction projects are typically carried out under high-risk conditions and managers are forced to handle a great deal of uncertainty during the construction process. The Earned-Value Analysis is a control technique that provides early warnings of performance by quantitative measures, enabling timely corrective actions to ensure project success. This method was developed to control and adjust the project's baseline during execution. The objective of this article is to discuss the main implications of using EVA in construction projects through a case study. Results proved the applicability of the method in the construction industry. The various indicators generated allow managers to make forecasts for optimistic, realistic, and pessimistic scenarios, having the opportunity to correct any deviations in advance. In addition to forecasts, benchmarking data can be generated for the planners or companies responsible for the project, thus increasing the accuracy of future projects.

Introduction

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The construction industry stands out as one of the most relevant sectors of the economy [1], especially in developing countries, which depend directly on its services for the evolution of national infrastructure. The large capital traditionally invested in the sector, mostly employed in the execution phase [2], and the size of the real state developments, which demand intensive labor for their construction, contribute significantly to the progress of nations. However, construction projects are typically carried out under high-risk conditions [3], and, considering the heterogeneous and unique nature of most developments [4], managers are forced to handle a great deal of uncertainty during the construction process [5]. As a result, it is not uncommon for scope changes to occur during project development. A project is considered successful when it achieves all the objectives defined in its initial planning, that is, it has achieved the desired performance, according to the schedule and with predetermined costs [4]. However, in the real world, results achieved through the process begin to gradually deviate from the approved schedule and cost baselines [2] and need to be realigned to it. Delays and cost overruns are the main effects of projects whose implementation has not been properly managed [1,2,5]. According to Vanhoucke and Shtub [6], "the best plan is based on forecasts and is subject to forecast errors" and, therefore, the adoption of a systematic monitoring and control technique capable of dealing with the uncertainties inherent to the construction activity is essential.

Currently, different project control tools are used in the construction industry, and even so, projects run over budget and behind schedule [7]. This is because traditional methodologies are based only on comparative analysis between two parameters, the planned and the current [5], but do not report any current performance trends to forecast future performance. The Earned-Value Analysis (EVA) is a control technique that provides early warnings of performance by quantitative measures, enabling timely corrective actions to ensure project success [7-9]. This method was developed to control and adjust the project's baseline during execution [10]. For this reason, it is also called deviation analysis, and it is currently considered one of the most advanced techniques for tracking the progress of projects [5,7,11-13]. Therefore, the purpose of this article is to discuss the main
implications of using EVA in construction projects. Considering that most of the literature on the subject is theoretical, it was decided to use a case study, aiming to demonstrate the applicability of the method in real construction work. The remainder of this paper is structured as follows: Section 2 presents the conceptual background of the research, based on a review of the previous studies on EVA. Section 3 describes the case study approach employed in this paper. Section 4 presents the research findings and discusses research implications. Finally, Section 5 summarizes the conclusions and exposes work limitations and directions for further research.

Earned Value Analysis

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The concept of Earned Value was formally introduced as a cost control tool by the US Department of Defense (DoD) in the late 1960s [8]. The development of the methodology was sponsored by government agencies, to improve the management of war projects [14]. In 1967, an approach of thirty-five criteria was developed and entitled Cost/Schedule Control Systems Criteria (C/SCSC), which were used to ensure consistency in performance reports prepared for ongoing projects. In 1996, it was revised and renamed Earned Value Analysis [2]. Since then, the technique has been applied without major changes, not only in government and defense agencies but also in several other sectors, such as oil and gas, manufacturing, pharmaceutical, construction, among others [2,14].

Many authors have dedicated themselves to the study of the practical application of EVA in these different industries. De Marco and Narbaev [15], conducted a study in the European construction industry and concluded that the technique is not yet fully developed in this region. Bagherpour [16], proposed the use of fuzzy logic to deal with the uncertainties inherent in the process of forecasting future scenarios, improving the accuracy of the results. Moslemi-Naeni et al. [17], developed a new Fuzzy-EVA model for the same purpose. Table 1 defines each of these variables and expresses their respective formulas. Table 2 summarize the meanings of the numerical results of each indicator.

Table 1 - EVA parameters information

Shortcut - Definition | Formula | Shortcut - Definition | Formula
PV - Planned Value | ------- | BAC - Budget at Completion | -------
AC - Actual Cost | ------- | TCPI - To Complete Performance Index | TCPI = (BAC − EV) / (BAC − AC)
EV - Earned Value | ------- | EACo - Estimate at Completion − Optimistc Scenario | EACo = BAC − EV
CV - Cost Variance | CV = EV − AC | EACr - Estimate at Completion − Realistic Scenario | EACr = (BAC − EV) / CPI
SV - Schedule Variance | SV = EV − PV | EACp - Estimate at Completion − Pessimistic Scenario | EACp = (BAC − EV) / (CPI × SPI)
CPI - Cost Performance Index | CPI = EV/AC | ETC - Estimate to Complete | ETC = EAC − AC
SPI - Schedule Performance Index | SPI = EV/PV | VAC - Variance at Completion | VAC = BAC − EAC

Table 2 - Meaning of the numerical results of CV, SV, CPI and SPI

Variances | < 0 | = 0 | > 0
CV | cost is over budget | cost is right on planned | cost is under budget
SV | ahead of schedule | schedule is right as planned | behind schedule
Index | < 1 | = 1 | > 1
CPI | spending more than planned | on budget | spending less than planned
SPI | performing less than planned | on schedule | performing more than planned

Methods

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The methodological approach considered in this paper was a case study referring to the construction of a residential building. Initially, the planning of activities was carried out, taking into account the executive sequence of services and the resources necessary for their execution, thus creating the Work Breakdown Structure (WBS). Based on the WBS and the actual budget developed for the work, the resources contained in the budget were allocated on schedule using MS Project software, resulting in a complete schedule. To simulate the physical progress of the construction services execution, a random number generator was applied. For this purpose, the RANDBETWEEN function of the Microsoft Excel software was used, which generates random numbers for a given range of values. The results of using this function, after being properly weighted, will correspond to the percentage of progress for each task (Tables 3 and 4).

Table 3 - Weight table

Random Values | 1 to 2 | 3 to 11 | 12 to 20 | 21 to 35 | 36 to 80 | 81 to 95 | 96 to 100
Corresponding Percentage | 0% | 40% | 65% | 85% | 100% | 110% | 120%

Table 4 - Simulation result and percentage progress after weighting

Stage 1 | SR | WP | Stage 2 | SR | WP | Stage 3 | SR | WP | Stage 4 | SR | WP
Week 1 | 37 | 100% | Week 16 | 82 | 110% | Week 32 | 56 | 100% | Week 47 | 86 | 110%
Week 2 | 54 | 100% | Week 17 | 27 | 85% | Week 33 | 82 | 110% | Week 48 | 89 | 110%
Week 3 | 12 | 65% | Week 18 | 30 | 85% | Week 34 | 97 | 120% | Week 49 | 96 | 120%
Week 4 | 35 | 85% | Week 19 | 5 | 40% | Week 35 | 44 | 100% | Week 50 | 95 | 110%
Week 5 | 54 | 100% | Week 20 | 25 | 85% | Week 36 | 35 | 85% | Week 51 | 39 | 100%
Week 6 | 9 | 40% | Week 21 | 37 | 100% | Week 37 | 53 | 100% | Week 52 | 6 | 40%
Week 7 | 93 | 110% | Week 22 | 70 | 100% | Week 38 | 85 | 110% | Week 53 | 16 | 65%
Week 8 | 40 | 100% | Week 23 | 94 | 110% | Week 39 | 79 | 100% | Week 54 | 47 | 100%
Week 9 | 36 | 100% | Week 24 | 98 | 120% | Week 40 | 85 | 110% | Week 55 | 22 | 85%
Week 10 | 15 | 65% | Week 25 | 52 | 100% | Week 41 | 91 | 110% | Week 56 | 94 | 110%
Week 11 | 68 | 100% | Week 26 | 64 | 100% | Week 42 | 82 | 110% | Week 57 | 64 | 100%
Week 12 | 10 | 40% | Week 27 | 52 | 100% | Week 43 | 46 | 100% | Week 58 | 33 | 85%
Week 13 | 69 | 100% | Week 28 | 78 | 100% | Week 44 | 31 | 85% | Week 59 | 86 | 110%
Week 14 | 17 | 65% | Week 29 | 10 | 40% | Week 45 | 97 | 120% | Week 60 | 9 | 40%
Week 15 | 72 | 100% | Week 30 | 68 | 100% | Week 46 | 46 | 100% | Week 61 | 80 | 100%
|  |  | Week 31 | 25 | 85% |  |  |  | Week 62 | 93 | 110%
Average |  | 85% |  |  | 91% |  |  | 104% |  |  | 93%

Notes: SR - Simulation Results; WP - Weighted Progress
The correct analysis of the project was possible with the development of a cost baseline in Microsoft Project software. It was developed by adding all the costs allocated for each month of work and distributing it over the expected period and is graphically represented in the form of an S-curve. This curve will be used to monitor the current and future project performance [2]. The data from the EVA analysis is then typically put into graphical form to facilitate the communication progress. Considering that during the development of a project, at any time, some activities are completed, some have not yet started and others have already started but have not yet been completed [9], the EVA was then applied in four steps, simulating the construction stages at and of the expected duration, and the data and indicators generated were analyzed.

Results and Discussion

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Stage 1-25% of expected duration - The analysis takes place at the end of the 15th week, during the 4th month when the work should have an evolution of and costs . However, what was actually found was progress and . The EV in the period was . It is noticed that the variation between the AC and the EV is derisory in the fourth month. Although the values are below the PV, this does not mean that the work is saving, on the contrary, it illustrates a CV of and an SV of . These values represent that more was spent than foreseen in the budget for the services carried out in the period, and of the planned work was not carried out. The delay in general did not generate a greater loss in terms of cost, because activities planned for the period (earth and foundation works) have a low cost about the work as a whole. But as these activities are part of the critical path, the impact on time was perceived. Performance indicators reveal that the project is spending more than it should at this stage, and the cost projections for the three scenarios considered indicated that: in an optimistic scenario the project will cost , in a realistic scenario it will cost , and in a pessimistic scenario it will cost . For the schedule forecast, the number of days remaining was considered, divided by the SPI on the date, and added to the end of the measured week. In this case, 350 days were left, which when divided by the SPI of 0.89 , results in 370 days remaining to completion. As 15 weeks have passed, the end is scheduled for the 68th week of the 16th month.

Stage of expected duration - The analysis takes place at the end of the 31st week, during the 7 th month. During this period, the average progress was , better than the first one ( ), but still lower than the previously forecast. In the simulation, the progress continued below and, therefore, the physical progress was against of the expected. In this stage, the project spent when an expenditure of was expected, and the EV of the performed tasks was . The variations remain the same as in the previous stage, and the . However, during this period the variances increased, CV dropped to and SV dropped to . Indicators show that the loss concerning the initial budget has decreased compared to the previous stage, as well as the CPI is slightly lower than the TCPI, indicating that cost recovery is possible. On the other hand, SV increased considerably. With of the estimated time already elapsed, the project points to a delay. It is interesting to point out that the activities contained in the period have a higher cost in relation to the previous period, but as the average evolution was higher, the cost difference was not so marked. The difference regarding the deadline was once more perceived, due to delay in critical path activities. The cost projections for the three scenarios considered indicated that: in an optimistic scenario, the project will cost , in a realistic scenario it will cost , and in a pessimistic scenario it will cost . It can be seen that the pessimistic forecast is quite exaggerated due to the very low SPI. The finish forecast was calculated in the same way as in the previous stage, and the result is an estimated finish for the 70th week of the 16th month.

Stage of expected duration - The analysis takes place at the end of the 46th week, during the 11th month. During this period, the random average progress was , and for the first time during this simulation, the progress in the period exceeded what was planned. Even so, it was not possible to compensate for the delay in the physical progress of the works, which resulted in carried out against planned for the period. An amount of was spent, against the forecasted , but EV was , which means that what has been produced has cost less than it should have, pointing out possible savings concerning the budgeted amount. Fig. 1b illustrates that during the eleventh month, for the first time, the CPI surpasses the TCPI. The explanation for the increase in CPI is because the third stage of the expected duration is the period in which most of the project's expenses are concentrated. As the actual evolution was better than planned, it was possible to recover the loss in relation to the budgeted amount in previous periods. Performance indicators reveal that SPI increased again until 0,759 . The cost projections for the three scenarios considered indicated that: in an optimistic scenario, the project will cost , in a realistic scenario it will cost , and in a pessimistic scenario it will cost . Due to the recovery of the CPI, both the Realistic and the Pessimistic
scenarios decreased significantly, approaching the Optimistic one. The forecast now indicates an estimated completion for the 68th week.

Fig. 1 - Perfomance indicators

Fig. 1. - Perfomance indicators

Stage of expected duration - The 100% predicted duration milestone would occur on week 62 during the 15th month. However, due to the accumulation of delays related to past stages, the work was not completed on time, requiring a new simulation. The results were properly weighted according to Table 3. On the expected completion date, physical progress was , and reached , according to the new simulation, in two more weeks, totaling 64 weeks of the project. Until week 62, the project presented an AC of and an EV of (Fig. 1a). PV is equal to the total value foreseen in the budget, as the project should have finished in this period. EV remains above the AC, which shows savings in the services performed. Furthermore, it is very close to BAC, with an absolute SV of R$-14,735.63 indicating that there is little work to be done. In this final step, some indicators are no longer needed since SPI tends to 1 and TCPI tends to 0 at the end of the project. Therefore, CPI was plotted alone to best show the economy, which was R . This value represents a percentage CV of (Fig. 1b).

At the end of the project, comparisons can be made to show the differences and problems highlighted by the various indicators. A total duration of 311 days was estimated in the initial planning of the project, but in practice, it was 320 days, a delay of . These two extra weeks would generate several problems for the construction company, whose evaluation was not part of the scope of this work, such as the dissatisfaction of potential buyers of the property, who will receive the apartments after the agreed deadline. The cost projections made each month throughout the project, for the three scenarios considered. Due to a very low SPI until week 11, the pessimistic forecast is very different from the others, and it is not possible to consider it as a possible value. As the work showed economy, it was to be expected that the forecast that came closest during the entire period would be Optimistic.

Conclusions

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This study aimed to demonstrate the use of EVA for a real construction project, simulating the progress of the services performed. The results proved the applicability of the method to control projects in the construction industry. The various indicators generated allow managers to make forecasts for optimistic, realistic, and pessimistic scenarios, having the opportunity to correct any deviations in advance. In addition to forecasts, benchmarking data can be generated for the planners or companies responsible for the project, thus increasing the accuracy of future projects. However, it is important to emphasize that the positive aspects generated by the technique are only reliable if preceded by well-detailed budgets, adequate planning, and well-defined scope.

Although EVA models can effectively provide reliable forecasts, some authors have been reporting some limitations that should be considered, and some may serve as a stimulus for future work. Tzaveas et al. [10], concluded that EVA has not been as successful in assessing schedule
performance, since when the schedule is about complete, EVA schedule performance metrics become unreliable. Zhong and Wang [11] stated that EVA ignores the difference between critical and non-critical activities and the restraints of the critical activities in the whole project, distorting the indicators. Then, the integration of EVA with other methods, such as fuzzy logic, logarithm linear transformation, and non-linear cost profiling is encouraged to investigate which one best fits the criteria in question. Current research can be extended in several directions to approaches the methodology to real-life EVA applications in the construction industry. However, one of the most promising lines of research is the integration of EVA with Building Information Modeling (BIM), in its 4D and 5D dimensions. This application can improve the efficiency of monitoring project cost and deadline control and should be incorporated in future work.

References

The original version of this paper is available on https://www.scientific.net/EI.2.67.pdf

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Keywords Index

A

Abrasive Waste Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

B

Banded Carbides Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

Bucket-wheel Excavator Boom Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

C

Corrosion Fatigue Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

D

Damage Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Design Of Experiments Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

Disposal Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

E

Earned Value Analysis; Construction; Project Management; Performance Indicators Highlights of Earned Value Analysis in Construction Projects

F

Fdm Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

M

Mechanical Properties Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

Metal Components Wear Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport

N

Ndt Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

O

Optimization Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

P

Pin Connection; Long-span; Experimental Study; Truss-column Connection; Fea Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures

S

Scanning Electron Microscopy Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

Service Life Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport

Spindle Current Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

Statistical Model Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

T

Tableting Machines Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

Tempered Martensite Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

Tensometry Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Tool Life Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

Tool Wear Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

U

Ultra Pla Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

Urban Rail Transport Vehicles Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport

W

Waterjet Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

Authors Index

A

Aleksandar, S. Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Amario, M. Highlights of Earned Value Analysis in Construction Projects

Arsić, M. Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Arumugam, T. Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

B

Binchiciu, E. Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

Botila, L. Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport

C

Cocard, M. Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

Cojocaru, R. Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport; Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

Costa, B. Highlights of Earned Value Analysis in Construction Projects

D

Duma, I. Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

E

Evangelista, A. Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures

F

Farías, J. Highlights of Earned Value Analysis in Construction Projects

Flajs, Z. Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

G

Geana, A. Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport

H

Haddad, A. Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures; Highlights of Earned Value Analysis in Construction Projects

Hao, H. Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures

L

Lee, T. Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

Lin, I. Investigation on the Correlation between CNC Spindle Current Value and Tool Wear

M

Ma, J. Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures

Mnerie, G. Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

Murariu, A. Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

N

Najjar, M. Highlights of Earned Value Analysis in Construction Projects

Narasimhan, R. Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

P

Perianu, I. Considerations Regarding the Extension of the Service Life of Metal Wear Components from Urban Means of Rail Transport; Innovative Solutions for Waste Removal (Used Abrasive) Resulted from Water Jet Cutting Process

S

Sedmak, S. Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Shrinivas, V. Failure Investigation & Analyses of AISI D3 Dies used in Tableting Machines for Pharmaceutical Application

Siddhpura, M. Experimental Study on Truss-Column Pinned Connections in Large-Span Steel Structures

Soares, C. Highlights of Earned Value Analysis in Construction Projects

Sîrbu, N. Influence of 3D Printing Parameters on Mechanical Properties of the PLA Parts made by FDM Additive Manufacturing Process

V

Veg, E. Damage Occurrence in Welded Structures of the Bucket-Wheel Boom