Study of recast layers and surface roughness on Al-7075 metal matrix composite during EDM machining

Abstract

Demand for low weight to strength ratio for exclusive application in automobile and aerospace components created scope for advance studies on Metal Matrix Composites (MMCs). However, machining of MMCs challenges for conventional machining processes due to uneven hardness, matrix of composites and undesired tool life. Electric Discharge Machining (EDM) is one of the unconventional material removal process, which offers alternatives for machining of MMCs because, being a non-contact process it can be machine excessive harder material, intricate shape with better surface finish and tool life. The evolved heat during EDM process and subsequent flushing of machined debris and rapidly resolidified layer is formed by the re-solidification of residual molten material on the machined surface during the EDM process leaves behind recast layers which is extremely hard and brittle. In the presents study optimization of process parameters to minimize the surface roughness of the rapidly resolidified layer of Al 7075 MMC while machining using EDM process is carried out using the Taguchi tequniues. The gap current, pulse on-time and pulse off-time were considered as process parameters. The formation of resolidified layers is investigated in terms of the surface roughness as response variables inside the hole and near the hole while EDM drilling.