Key Engineering Materials Vol. 549

Abstract: Friction Stir welding (FSW) is a solid state joining process developed by TWI (The Welding Institute) in 1991. This technology is suitable for joining different materials even considered difficult to be welded using more traditional techniques and it is appropriate to weld materials in different configurations (such as butt, lap, circumferential, T-joint etc). Recently, starting from the FSW approach, a new technology called Friction Stir Spot Welding (FSSW) was developed. In this case, instead of moving along the weld seam, the tool only indents two overlapped parts. In some applications, this technology can be considered as a valid alternative for single point joining processes like resistance spot welding (RSW) and riveting processes. This work deals with an experimental study of the FSSW process for the lap-joining of thin aluminum sheets. In particular, an experimental campaign was performed on AA6060 T6 aluminum sheets having a thickness equal to 2 mm. The FSSW process was applied on couples of overlapped sheets by varying the tool rotational speed, and by keeping fixed the other process parameters, such as axial feed rate, indentation depth, and dwell time. Welding forces distributions were recorded during the process. Preliminary tensile tests and metallurgical analyses were also performed to evaluate the quality of the joints as function of the chosen process parameters. A numerical model of the FSSW process was developed and implemented using the commercial FEM code Deform 3D. The model parameters were set according to the experimental evidence.

Abstract: Solid state bonding recurs in several manufacturing processes, as Friction Stir Welding (FSW), Linear Friction Welding (LFW), extrusion of hollow profiles and Accumulative Roll Bonding (ARB). The former processes are nowadays of particular industrial interest because of the specific advantages with respect to the classic welding technologies. In FSW the solid state bonding is obtained between an undeformed cold material, already placed in the advancing side of the joint, and the hot material flow incoming from the retreating side. Proper conditions of pressure, temperature, strain and strain rate are needed in order to get the final effective bonding. In the paper experimental tests on butt joints made out of AA6061-T6 aluminum alloys are used to identify the sets of process parameters resulting either in sound or poor joints. The same process conditions have been simulated used an already developed model in order to highlight the actual bonding line and the values of the main field variables determining the soundness of the joints. Finally a correlation between process parameters values, field variables values and joint effectiveness is made.

Abstract: The following paper describes a feasibility study of butt joining friction stir welding between aluminum alloy AA6016 and magnesium alloys AZ91 and AM50. Because of the variety of inimitable properties according to lightweight design and constructions, the interest in aluminum and magnesium alloys is increasing in many fields of industry. Due to the low solubility of aluminum in magnesium and inverse, these alloys tend to the formation of intermetallic phases during the joining process. This leads to an increasing micro hardness within the seam, which should be avoided. By the use of joining methods with low process temperatures, the formation of intermetallic phases is reduced. According to this circumstance, friction stir welding is an excellent alternative to fusion welding techniques used to join this alloys. The main welding process variables were exposed in the studies of similar butt joints of Al/Al and Mg/Mg. These were examined in connection to their transferability to the dissimilar joints and tailored blanks. Furthermore, the influence of different tool geometry on seam quality was investigated. The effect of process variables (mainly welding speed and revolution speed) were correlated to the results of tensile strength test. The welded samples were assayed in the presence of intermetallic phases.

Abstract: The recent miniaturization trend in manufacturing, has enhanced the production of new and highly sophisticated systems in various industrial fields. In recent years, machining of the so called difficult to cut materials has become an important issue in several sectors. Micro Electrical Discharge Machining (micro-EDM) thanks to its contactless nature, is one of the most important technologies for the machining of this type of materials and it can be considered as one of the most promising manufacturing technologies for the fabrication of micro components. One of the most relevant applications of micro-EDM is micro-drilling. Micro holes in fact, are widely used for example in micro-electromechanical systems (MEMS), serving as channels or nozzles to connect two micro-features, and in micro-mechanical components. The present study is about micro drilling of metal plates by means of micro-EDM technology. In particular, the aim of this work is to investigate the effects of the downsizing of the micro holes diameter on the drilling performances. The influence of the reduction of the diameters in terms of both process performances (e.g., tool wear, taper rate, diametrical overcut) and general quality of the holes was investigated. Steel plates having thickness equal to 0.8 mm were taken into account. The drilling process was carried out using a micro-EDM machine Sarix SX 200 with carbide electrodes having diameter equal to 300, 200, 100 and 50 μm. Since the standard electrodes adopted in this study had a diameter equal to 300 μm, a wire EDM unit was used to obtain the other electrodes. The relationship between the process parameters considered the most significant and the final output, was studied. Furthermore, the geometrical and dimensional properties of the micro-holes were analyzed using both optical and scanning electron microscopes. In particular, it is demonstrated that the diameter size has a significant influence on the final value of the diametrical overcut while peak current and frequency parameters have a negligible effect.

Abstract: In macro forming a DLC-coating can increase durability and decrease wear of a deep drawing tool. Due to size effects, the behavior in micro range can differ from the behavior in macro range. To investigate durability and wear in micro deep drawing a blanking and deep drawing tool combination was developed, capable of maximum stroke rate of 200 parts per minute. Experiments with copper foil (E-Cu58) of 0.05 mm thickness were performed to produce cylindrical micro cups with a diameter of 1 mm using the lubricant Lubrimax Edel C. The tool material is stainless steel (German standard 1.2379). The punch has a diameter of 0.9 mm and the die diameter is 1.06 mm. To increase durability and decrease wear in micro deep drawing a DLC-coated tool is used. DLC-coated and uncoated tools are compared in long term test regarding wear behavior. Furthermore, the die radii of the tools are measured optically and cross-sections of the tools are made to analyze the microstructure. Experiments show, that the DLC-coating starts to delaminate during the first 5000 strokes. By analyzing the cross section it can be recognized a high density of scattered carbides and pores with different sizes up to 35 μm in the tool material are visible, causing delamination. Furthermore, higher load and stress in micro forming provides delamination. Thus a high influence on the durability of the DLC-coatings base material can be reported in micro range.

Abstract: Pulsed phase thermography (PPT) is a common infrared technique for quantitative nondestructive testing and evaluation (NDT&E). PPT was initially applied in the aeronautical and aerospace engineering to the detection and quantification of defects in materials with either high or low thermal conductivity, such as aluminium and composite materials. This paper presents for the first time the application of PPT-technique for defect inspection in sheet metal parts, attempting to provide a solution for an alternative quality control rather than the traditional optical survey in the press shop. The inspected defects in this paper were produced in deep drawing cups, to effectively creating various crack lengths and depths respectively in both steel and aluminium alloys. The approach of the characterizing influence parameters is primarily based on the particular parameters of the PPT-technique. These parameters were firstly classified into various categories, and a DoE model was subsequently designed to define the required experiments for a process window analysis. According to the defined process window, more accurate conclusions of defect detecting effects were achieved. Studies in the paper present the fundamental perceptions for defect inspecting in the sheet metal parts by using PPT-technique in the press shop.

Abstract: This study focuses on quality assurance in a laser welded axisymmetric sandwich structure that functions as the body of an electric machine. The manufacturing quality of the structure was measured using destructive testing and visual inspection. The destructive tests included both fatigue and static tests in addition to a macrographic examination. The visual inspection comprised ocular estimates of the laser welded seams as well as their requirements. Compared with the real working conditions of the machine, the experimental tests were exhaustive. Nevertheless, in the tests, the bodies held up very well which shows the great strength of the structure.

Abstract: This paper reports the practical experiences made with extending the Value Stream Mapping (VSM) approach to the comprehensive design of a lean manufacturing system for the series production of sheet metal cable tray systems. The use of VSM for analyzing the production of repetitive units has proven to be successful in different industries. It is based on a classification of all products into product families and creates one current and future state map for each product family. This approach and the related guidelines for future state optimization are very helpful but not sufficient for a comprehensive manufacturing system (re) design, because the relation between product families value streams, the overall material flow optimization, as well as the segmentation and layout of factory remains unclear. Thus, the purpose of this paper is to develop a design procedure based on the investigation of an industrial case that allows the integrated optimization of the single value streams, their compilation in material-flow optimized production segments, and finally the (re) design of production logistics and factory layout. The findings of this research are limited due to the focused nature of a case study based research. However, the obtained results encourage assuming its transferability to similar problems.

Abstract: Manufacturing processes, as used for discrete part manufacturing, are responsible for a substantial part of the environmental impact of products, but are still poorly documented in terms of environmental footprint. A thorough analysis on the causes affecting the environmental impact in metal forming processes, especially the innovative but very energy intensive sheet metal forming technologies required to form light-weight products, is nowadays necessary. Therefore, this paper presents an energy consumption analysis, including a power and time study, of Single Point Incremental Forming (SPIF) processes. First, the influence of the most relevant process parameters (e.g. feed rate, step down) as well as the material forming itself are analysed regarding the power demand. Moreover, a comparative study and related energy efficiency assay are carried out on two different machine tools. As the forming time proves to be the dominant factor for the total energy consumption, from environmental point of view, the overall results show many similarities with conventional machining processes. Finally, this paper reports on some potential improvement measures to reduce the SPIF energy consumption.

Abstract: Superplastic forming of titanium is typically restricted to low volume, high value products due to the high costs inherent in the current process. Problems contributing to the high costs stem from the interactions that take place at the die/part interface and include; poor part surface finish due to the build-up of corrosion products on the die surface and part distortion due to adhesion at the die surface. This paper describes novel methods for the investigation of the build-up of corrosion products on the die using surface digitization tools with laboratory based simulations of the forming conditions and a novel method for monitoring, analyzing and quantifying the die surface condition in a production environment using a combination of thermal imaging techniques and image analysis.