Recast layer removal of 304 stainless steel by combining micro-EDM with negative polarity micro-EDM

Electrical discharge machining (EDM) has been widely used in the machining of mechanical parts. However, the parts obtained by EDM have recast layers and micro-cracks on their surface, which seriously affect their mechanical properties. In order to remove the recast layers and micro-cracks resulted from EDM, this paper proposed to combine micro-EDM with negative polarity micro-EDM. First, the mechanical part was machined using conventional EDM, after which the surface of the part had a distinct recast layer and micro-cracks. As the conventional EDM was nearing completion, the power supply was replaced by a micro-EDM power supply and then the part was processed by micro-EDM to reduce the thickness of the recast layer. After micro-EDM, the part was processed by negative polarity micro-EDM, which can remove the recast layer and the micro-cracks on the surface of the part. Conventional EDM was performed on 304 stainless steel using a copper electrode with voltage of 250 V, pulse width of 7 ms, and pulse interval of 5 ms. The experimental results showed that the recast layer and micro-cracks on the surface of the part were obvious and the surface quality of the part was poor. After that, the same part was sequentially subjected to micro-EDM and negative polarity micro-EDM with voltage of 110 V, pulse width of 0.5 μs, and pulse interval of 15 μs. The experimental results showed that the recast layer and micro-cracks on the surface of the part were almost invisible and the surface quality of the part was greatly improved.