EDM performance of Cr/Cu-based composite electrodes

Electrode materials for electrical discharge machining (EDM) are usually graphite, copper and copper alloys because these materials have high melting temperature, and excellent electrical and thermal conductivity. The electrodes made by using powder metallurgy technology from special powders have been used to modify EDM surfaces in recent years, to improve wear and corrosion resistance. However, electrodes are normally fabricated at high temperatures and pressures, such that fabrication is expensive. This paper proposes a new method of blending the copper powders contained resin with chromium powders to form tool electrodes. Such electrodes are made at low pressure (20 MPa) and temperature (200 °C) in a hot mounting machine. The results showed that using such electrodes facilitated the formation of a modified surface layer on the work piece after EDM, with remarkable corrosion resistant properties. The optimal mixing ratio, appropriate pressure, and proper machining parameters (such as polarity, peak current, and pulse duration) were used to investigate the effect of the material removal rate (MRR), electrode wear rate (EWR), surface roughness, and thickness of the recast layer on the usability of these electrodes. According to the experimental results, a mixing ratio of Cu–0wt%Cr and a sinter pressure of 20 MPa obtained an excellent MRR. Moreover, this work also reveals that the composite electrodes obtained a higher MRR than Cu metal electrodes; the recast layer was thinner and fewer cracks were present on the machined surface. Furthermore, the Cr elements in the composite electrode migrated to the work piece, resulting in good corrosion resistance of the machined surface after EDM.