Study Of The Influence Of Material Internal Structure On Micro-machining By EDM

The miniaturization of products is being pursued all around the world. Micro electrical discharge machining (EDM) has become a very important technology in modern manufacture industry. Micro-EDM is an electro-thermal process, in which there is no mechanical contact during material removal. It has the ability to generate not only micro-holes and micro shafts, but also three-dimensional parts of complex shapes. However, when the feature size to be machined is close to the grain size of alloy material, the difference of thermal conductivity, melting temperature and other thermal properties between grain and grain boundary may influence the machining performance in micro EDM. It is necessary to study the influence of material internal grain and grain boundary on machining performance such as material removal rate, discharge gap and tool wear rate in micro EDM.In this study, a set of micro EDM with high-precision was developed. The control system consists of manual module, contact sensing module, servo control module, spindle rotation module, data acquisition and storage module.In this thesis, Cu, Ni and Cu-Ni alloy were selected as the research objects. A thermal conduction model was used to study the influence of thermal properties of material on the material removal. The calculated results were compared with the experimental values. It was found that they agree well.To study the difference of machining performance between the grain and the grain boundary in alloy, extensive experiments were carried out in titanium alloy with equiaxed crystals and stainless steel 304. Experimental results indicated that the machining performance such as material removal rate, tool wear ratio and discharge gap is different between the grain and the grain boundary obviously when the workpiece material is titanium alloy. However, the difference is not significant in the case of stainless steel because the grain size in stainless steel is smaller than the thickness of the samples. When micro holes are drilled through the sheet of stainless steel, several grain boundary may exist inside of the sheet. This study provides a theoretical foundation for the optimization of machining parameters to improve quality and efficiency in micro EDM.