Influence Of Material Microstructure On Processing Performances Of Micro EDM

In modern industry, traditional machining technology faces more and more challenges due to the increasing requirements of product minimization. Non-traditional machining methods provide solutions to generate micro features such as micro holes and cavities in super alloy and ceramics. Micro electrical discharge machining (EDM) is one of them. Micro EDM is based on energy in the form of heat generated by pulsed electrical discharges between two electrodes. In micro EDM, there is no mechanical contact and macro force. Therefore, micro EDM can process any electrically conductive material regardless of its hardness. However, the microstructure of workpiece has to be considered when the size of micro feature is of the same order as the microstructure of workpiece material. In this paper, single crystal copper and porous stainless steel304are selected to study the effect of different material microstructures on the machining performance of micro EDM, such as material removal rate, tool wear rate and discharge gap.In this study, a control system of micro EDM is developed, which is consist of manual module, automatic processing module, contact detection module, spindle rotation module and so on. The set of micro EDM is modified on the basis of the former device in laboratory. The device is controlled by Pmac card. Some libraries of motion control functions are programmed using LabVIEW software such as velocity function, moving function, coordinate display function.In this thesis, the anisotropy of the physical characteristics of single crystal copper, such as thermal conductivity and electrical conductivity, is discussed. Extensive experiments are carried out on single crystal copper with different crystal orientation,<100>,<110> and<111>. The material removal ratio, the tool wear ratio and the discharge gap are calculated after experiment. It was found that the crystalline orientation has no effect on the machining performance of micro EDM.To understand the machining characteristics of porous structure of material by micro EDM, micro holes are drilled in porous stainless steel304and solid stainless steel304. Three pore sizes of stainless steel,1μm,5μm and10μm, are used in experiments. Experimental results show that the signals of short circuit during drilling a micro hole in a solid sheet are much more than those of sheets with pores. Another two samples with the pore sizes of15μm and20μm are drilled respectively. The results indicate that the material removal ratio increases with an increase of pore size when the pore size is less than the discharge gap. However, when the pore size is larger than the discharge gap, the material removal rate decreases. The results of this study is helpful to understand the influence of micro structure of material on the machining performance of micro EDM, even on other micro machining processes.