Study on Recast Layer Thickness of Microstructures Machined in micro-EDM with Different Electrodes

Abstract

Functional-surface microstructures are widely used in industrial practice. During the fabrication of microstructures in micro-electrical discharge machining (micro-EDM), the thermal and physical characteristics of both workpieces and electrode materials at room temperature and high temperatures have an important influence on surface quality and distribution of recast layer. In order to study the influence of different electrode material characteristics on the surface integrity of microstructures machined using micro-EDM, red copper, brass, copper-tungsten and tungsten electrode were used to perform micro-EDM on both Ti-6Al-4V alloy and 304 stainless steel. In the experiment, electrode with groove arrays featuring high copying accuracy and surface quality was designed to carry out powder mixed electrical discharge machining (PMEDM) on Ti-6Al-4V alloy, and the machining results were evaluated based on four indicators: microstructure morphology, tool electrode wear (TEW), material removal rate (MRR), and recast layer thickness (RLT). Simultaneously, the surface morphology and recast layer thickness changes of 304 stainless steel workpieces machined using the above four types of electrodes, using both normal polarity and negative polarity micro-EDM were quantitatively analyzed. The results showed that copper-tungsten electrode is recommended to machine Ti-6Al-4V alloy because it has a smaller TEW (139 µm), the highest MRR (255.39 mm3/min), and a thinner recast layer thickness (3.35 µm). This was followed by copper electrode, which featured good machining performance and machinability. When machining 304 stainless steel with negative polarity, the TEW of copper electrode and tungsten electrode was the smallest, and the thickness of recast layer was able to be effectively reduced to about 3 µm.