Key Engineering Materials Vols. 651-653

Abstract: A process for the production of clad steel strips by means of vertical twin-roll strip casting is under investigation at the Institute of Metal Forming (IBF). This production concept is based on the introduction of a solid strip in the casting pool in order to join it with the solidifying melt. The advantages of this concept are a shorter process chain and a higher energy efficiency compared to the existing cladding methods. The contact time and the thickness ratio between solid strip and solidifying melt, their relative position and the alloy combination are fundamental parameters to be considered in the design of this cladding process. A numerical model is used to predict the temperature increase in the solid strip and the solidification of the melt for the material combinations 1.4301/C75 and C75/Cu, and for two process configurations. Carbon steel and copper strips were introduced in the melting pool during casting experiments. Both carbon steel and copper strips could be clad without melting when positioned on the casting roll surface. This indicates that the surface temperature of the copper strip did not rise over 1084°C. Both the copper and the carbon steel strips show partial melting when introduced in a central position.

Abstract: Properties of workpieces, like residual stress in the rim zone, cannot be predicted for manufacturing technologies reproducible in advance. This lack of predictability shall be solved by a new approach, called Process Signatures. These Process Signatures will combine the material loadings forced by the manufacturing process with the change of state variables, e. g. the variation of residual stress in the surface layer. As the Process Signatures shall achieve comparability for different processes with same physical working principle, it is necessary to describe the transition from material loadings to the change of material properties in a uniform way. Consequently an energy based approach is chosen that considers these transitions by the dissipation of the several kinds of energy brought into the manufacturing process and especially in the respective working area.A first step for the development of such Process Signatures is the identification of all process specific material loadings. This paper presents several material loadings generated during the electrochemical sinking process. In a further step the contribution of the individual material loadings to the material removal process are estimated. Finally first approaches for the combination of the main material loadings and the change of material properties are presented.

Abstract: The energetic calculations of pulse energies are only very rough approximations in many publications, because some boundary conditions are not known or are not considered. In the paper is shown that problems resulting from the choice of process energy source and the supply-gap conditions. Approximations that were still considered for long pulse durations, for example, can for micro and nanoEDM no longer be accepted. The smaller the pulse energy, it can also not allow for the simulation of a linear rising enthalpy may be used. The shifts between the measured current and voltage must not be neglected. Practical tests to have shown, that the peak of the energy input is shifted in time and the maximum is lower by about 70%. The parasitic capacitances of the connection pulse unit - working gap and electrode arrangement results in the largest errors in the power calculation. It follows that the connection conditions of industrial plants may not be changed or should be recalculated.

Abstract: The desire for individualized products forces the companies to a great diversity of combinable parts. This way, the clients can compile their personalized product. As this trend is not just limited on visual parts but also for functional components, laser additive manufacturing of metals is used more and more often in manufacturing. To bring more additive manufacturing into mass production, Laser Beam Melting and Laser Metal Deposition will be qualified for the use in tool manufacturing within the Bavarian research association “ForNextGen – Next Generation Tools”. The first subproject within this research association investigates the potential of Laser Metal Deposition in the production of hot and cold forging tools. Within initial tests optimized process, parameters for the processing of the hot-work steel 1.2709 are determined by single welding beads. The achieved density and the inner structure are analyzed within cubes that were built with the investigated parameters. As forging tools are usually made of high-carbon tool steel, the processing of materials with a rising percentage of carbon will be part of further investigations.

Abstract: The quality of additive manufactured parts however depends pretty much on the workers experience to control porosity, layer linkage and surface roughness. To analyze the robustness of the Laser Beam Melting (LBM) process a Round Robin test was made in which specimens from four institutes from different countries were tested and compared. For the tests each institute built a set of specimens out of stainless steel 1.4540. The aim of this work is to analyze the influence of the process parameters on the mechanical properties. The results show that there is a high potential for additive manufacturing but also a lot of further research is necessary to optimize this technology.

Abstract: Epoxy-based shape memory (SM) foams have been produced by solid state foaming. According to this foaming technology, precursors are made by cold compaction of thermosetting powders. Subsequently, precursors foam by heating in an oven. In this study, the SM epoxy powder was mixed with multi-walled carbon nanotubes (MWCNTs) and graphene so as to produce SM composite foams. Two different filling contents were used (0.5 and 1 wt%). In order to study the effect of nano-fillers on SM properties of the epoxy foams, foam compressibility was measured at a temperature higher than the transition temperature of the SM epoxy foam (i.e. the glass transition temperature). Moreover, recovery load was measured after a 50% of memorized strain. Results show the positive effect of the fillers in functional and structural terms.

Abstract: This paper investigates the numerical simulation of the sintering stage by solid state diffusion during the metal injection molding process for micro-bi-material component based on a thermo-elasto-viscoplastic model. The physical parameters concerning very fine 316L stainless steel and copper powders with high volume loading contents involved in the sintering model have been identified in order to set up finite element simulations. The experimental tests have been carried out in a vertical dilatometer and the identification of the material parameters have been carried out with Matlab^® platform software. Then in order to predict the shrinkage and relative density after densification, a solid state diffusion model for the sintering has been implemented in finite element software to perform the simulation of the sintering stage.

Abstract: The Pulse Electrochemical Machining Process is an innovative, non-conventional process, based on the Electrochemical Machining process. Herein, pulsed current instead of constant current and a feed overlaid mechanical vibration of the tool electrode allows a higher precision and copying accuracy in contrast to the well-established ECM process. Yet, in this context the pulse-pause time and the length of the pulse on-time used in the process cause changes in the material removal while processing and therefore influences the processing result as well as cycle times and other industry relevant criteria. Understanding these pulse- and process specific changes is a key to the process design for industrial applications, since different sets and variations in parameters also change the final form and surface topography. This contribution shows, at the example of two materials 1.4301 and electrolytic copper, how a machining process can be designed and calculated based on material specific data. The way to acquire the necessary material data sets using industrial equipment, as well as the use and information which can be drawn from the data will be addressed.

Abstract: The wire electrical discharge machining is a machining method able to allow detaching parts from plates type workpieces as a consequence of electrical discharges developed between workpiece and wire tool electrode found in a motion along its axis; there is also a work motion along the contour to be obtained. There are many factors able to exert influence on the sizes of parameters of technological interest. On the other hand, there are various methods that can be used in order to establish the optimal combination of the input factors, so that obtaining of machining best results is possible. When there are many process output factors, a problem of multiobjective optimization could be formulated. The Grey relational analysis method and the Taguchi method could be applied in order to optimize the wire electrical discharge machining process, when various criteria having distinct significances are considered. An experimental research was designed and developed in order to optimize the wire electrical discharge cutting of parts made of an alloyed steel, by considering six input factors: test piece thickness, pulse on time, pulse off time, wire axial tensile, current intensity and travelling wire electrode speed. As output parameters, one took into consideration surface roughness, wire tool electrode massic wear, cutting speed along the contour to be obtained. 16 experiments were developed in accordance with the requirements specific to a Taguchi table L16. The results of experiments were processed by means of Grey relational analysis method and Taguchi method.

Abstract: Silicon carbide (SiC) is a high performance ceramic material which is increasingly used in applications which demand for high temperature stable materials. The microstructuring of this material in its sintered state is a challenge for conventional machining methods due to its extraordinary mechanical properties. To overcome these limitations the process of electrical discharge machining (EDM) was modified with a so called assisting electrode (AE) to enable the structuring of non-conductive ceramics such as SiC. This paper presents a parametric analysis of micro electrical discharge milling process of non-conductive SiC for two different tool materials, tungsten carbide (WC) and copper (Cu). A full factorial design with four factors was conducted. The significant factors are shown with main effects plots. Two sets of optimized parameters for maximum material removal rate (MRR) and minimum tool wear rate (TWR) for both tool materials are presented. Hardness and surface roughness are measured and compared to the non-machined material.