Advanced Materials Research Vols. 83-86

Abstract: This work aims an analysis on the functional surface integrity resulting from turning mechanical components manufactured from case hardened steel AISI 8620 with 1 millimeter average layer depth and hardness of 58-62HRC. A cBN tool with PVD coat and Wiper geometry-edge was used for continuous turning of hardened steel, the cutting conditions (Vc [m/min] and f in [mm/rev]) used were concerned to reflect large running production of mechanical components.

Abstract: Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. There are various types of products which can be produced by using the EDM such as dies and moulds. Today many parts used in aerospace and automotive industry and also final processes of surgical components can be finished by EDM process. A simple and easily understandable model was proposed for predicting the relative importance of different factors (composition of the steels and Electro Discharge Machining processing conditions) in order to obtain an efficient pieces. A detail application on the tool steels machined by EDM was given in this study. This model is based on thermal, metallurgical and mechanical and also in situ test conditions. It gives detail information on the effect of electrochemical parameters on the surface integrity and sub-surface damage of the material (Heat Affected Zone, HAZ), the level of residual stresses, and the surface texture. This approach is an efficient way to separate the responsibilities of the steel maker and machining process designer for increasing the reliability of the machined structures.

Abstract: In the present work, specimens were cut out from St-37 plates with 19 mm thickness. The thickness of plates was reduced to 12.5 mm by milling and grinding operations. Then a standard V-shaped fillet was made on one edge of the plates. Two plates were butt-welded by standard metal arc gas (MAG) welding process. Residual stresses induced by welding were measured on 20 specimens by centre hole drilling. Load controlled axial fatigue tests were carried out to determine the fatigue life of specimens. Crack growth rates were obtained from experiment. Fractography of specimens was performed. Genetic Algorithm (GA) was employed for prediction of residual stress value in weldments using the crack growth rates obtained from experiments. The results show that, by using the measured crack growth rates and GA model, residual stresses can be estimated with a good approximation.

Abstract: In order to ascertain the superior characteristics of PCBN tool for hardened material machining, to promote the cutting performance and efficiency of a mold manufacturing, to investigate the wear mechanism of the cutting tool, and to investigate the dimensional accuracy and surface finish of the machined molds, SKD11 die steel and the polycrystalline cubic boron nitride are used as the workpiece and tool materials, respectively, in this study for turning experiments. After some proper surface layers removed from the workpiece in the experiment, the tool wear was measured through the toolmaker’s microscope and the roughness of the machined surface was measured by the roughness measuring instruments. So that, the associated sampling data prepared for training pattern of a neural network can be obtained. Besides, the noise-mediator was used to detect cutting noise during each surface layer removal for the cutting performance judgment in the machining processes additionally. An assessment model of cutting process is thus developed using a neural network system if the reliable and sufficient data is taken from the experiments. Based on the developed neural network, the complicated relationships between the cutting parameters (cutting speed, depth of cut and feed rate) and the cutting performance (surface roughness, tool wear and cutting temperature) can be clearly clarified. The best surface roughness of 0.29μm Ra is obtained from these experiments under the cutting conditions of d =0.2mm, f =0.05mm/rev and V=120m/min. This surface quality is equivalent to the manufacturing process of chemical-mechanical polishing (CMP), and the surface roughness of 0.2~0.5μm Ra may be attained by CMP. The CMP is always applied to high precision surface processing such as the valve piping and connector components in semiconductor/LED manufacturing.

Abstract: The use of thermo-electric source of energy, as in electrical discharge machining (EDM), has greatly helped in machining all types of electrically conductive materials being used in different industrial applications. The present work investigates the different machining characteristics during electrical discharge machining on EN-8 steel with a rotary copper electrode. The effects of three independent machining parameters viz. peak current, pulse on time and rotational speed of tool electrode are chosen as variables for evaluating the output parameters such as metal removal rate, surface finish of work piece. The research focuses on developing empirical models for prediction of metal removal rate and surface finish during rotary electrical discharge machining process with the help of input parameters. The models are developed using linear regression analysis by applying logarithmic data transformation of non-linear equation. Analysis of results using partial and multiple correlation analysis reveals that electrical parameters have more significant effect than the non-electrical parameters on the machining characteristics during electrical discharge machining by a rotary electrode. Furthermore, when high MRR is criterion, high peak current and low RPM with low pulse duration produces better output; whereas, and when smooth surface finish is criterion, low peak current and low RPM with high pulse duration produces better output. In addition, the predictions based on the above developed models are verified with extra experiments and are found to be in good agreement with the experimental verifications.

Abstract: Mechanical alloying is one of the most successful methods for the manufacturing of metal matrix nanocomposite powders. In this study, Al/SiC metal matrix composite (MMCp) powders with volume fractions of 5, 10, and 15 percent SiC were successfully obtained after milling the powder for a period of 25 hours at a ball to powder ratio of 15:1 using high energy planetary milling. The Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were conducted to investigate the lattice strain of the matrix phase and the microstructure of the nanocomposite powders after 1, 10, and 25 hours of milling time. Also, the morphology of the Al-5%SiC nanocomposite powder was investigated using transmission electron microscopy (TEM). The results show that with the increase of both milling time and the reinforcement phase volume fraction, the lattice strain increases and the average size of aluminum phase crystallites decreases. Eventually, after 25 hours of milling, the nanocomposite powders show a spherical-like morphology and SiC particles were distributed in an aluminum matrix with appropriate order.

Abstract: Research activities in nanocomposite materials have been carried out for the last decade. Some of the objectives of these activities have been focused in increasing polymer physical properties. This has resulted in products for many fields of application, including: motor vehicle parts, packing, bottles, furniture, protective coatings and flame resistant material. The higher thermal-mechanical properties, better fire resistance characteristics and the low permeability rates present possibilities for the development of nanocomposite materials for components in oil, gas and chemical facilities as pipes, valves and tanks. This paper shows the vision of the authors in some potential uses of nanocomposite materials for manufacturing nonmetallic components and their possible features to reduce the high cost of corrosion.

Abstract: This paper presents a study of glass ceramic laser machining for cooktop appliances. Blind holes and special shape cross section blind holes can be created for functional purposes. A Q-switched Nd:YAG laser at its fundamental wavelength of 1064 nm with pulsewidths in the nanosecond range has been used. The material can be machined by focusing the laser beam at different depths under the back side of the glass panel, in such a way that blind holes of 2-6 mm diameter and 1-3 mm depth can be drilled. Several cross section shapes can be obtained using additional galvanometric mirrors to deflect the laser beam in the desired direction, controlling the incidence angle. These holes can be used for fastening directly components to the glass panel, avoiding gluing processes, or for approaching thermal sensors to the upper surface, controlling the work temperature in a better way. Several tests have been performed to check the modifications in glass ceramic mechanical properties. Thermal tests have verified the improvement in work temperature accuracy measurement.

Abstract: A new finishing method of holes that uses an effective electrode and a nonconductive roller to execute the design of synchronous processes of ultrasonic electrochemical finishing and rolling-leveling is investigated. The submitted processes can be used among the traditional techniques of various holes machining. Through simple equipment attachment, ultrasonic electrochemical finishing and rolling-leveling can follow to execute the finishing process on the same machine. Among the factors affecting finishing processes, the performance of rolling-leveling combined with ultrasonic electrochemical finishing is primarily discussed. In the experiment, the electrode is used with continuous and pulsed direct current. The controlled factors include roller material, roller geometry, chemical composition and concentration of the electrolyte, and flow rate of electrolytes. The experimental parameters are frequency and power level of ultrasonics, feed rate of electrode and roller, rotational speed of the finish-tool, die material, electrical current rating, and pulsed period. The design of the synchronous processes through rolling-leveling is the most influential parameter in this study. An adequate finish-tool rotational speed produces better finishing. The average effect of the ultrasonic is better than the pulsed current while the machining time needs not to be prolonged by the off-time. An effective and low-cost finishing process through the ultrasonic electrochemical finishing and using the rolling-leveling assistance after the process of traditional holes machining make the surface of the holes smooth and bright is presented.

Abstract: This paper develops the predicting model on surface roughness of laser beam cutting (LBC) for acrylic sheets. Box-Behnken design based on Response surface method was used to predict the effect of laser cutting parameters including the power requirement, cutting speed and tip distance on surface roughness during the machining. Response surface method (RSM) was used to minimize the number of experiments. It can be seen that from the experimental results, the effects of the laser cutting parameters with the surface roughness were investigated. It was found that the surface roughness is significantly affected by the tip distance followed by the power requirement and cutting speed. Some defects were found in microstructure such as burning, melting and wavy surface. This simulation gain more understanding of the surface roughness distribution in laser cutting. The developed model is suitable to be used in the range of (power 90 to 95, cutting speed 700 to 1100 and tip distance 3 to 9) to predict surface roughness.