Study of Surface Properties and Residual Stresses of Aluminium Matrix Composites after Electric Discharge Machining

Abstract

With the emergence of newer technologies, many advanced engineering applications require materials with enhanced properties and controlled coefficient of thermal expansion. One such class of materials are metal matrix composites (MMCs) that have reinforcements (such as fibers or particles) supported by binder (matrix) material. Particulate reinforced MMCs combine a conductive matrix which has been embedded with hard ceramic particles with an average size scale ranging from the molecular level to few microns. Such materials have vastly improved properties and are particularly difficult to machine with conventional machining methods. The use of traditional machinery to machine MMCs results in large tool wear due to the presence of abrasive nature of reinforcement. Electric Discharge Machining (EDM) provides an effective alternative to machine such materials especially when complex geometries are required. This research work has been conducted in three stages of experimentation. In Stage I, the experimental study was undertaken to identify the significant factors that affect the output responses while machining of 10vol%Al2O3/Al composite material. The material removal rate (MRR) and tool wear rate (TWR) have a direct relationship with current and an inverse relationship with pulse-on time. The results were optimized using Lexicographic Goal Programming (LGP) to predict the ideal parametric combinations for machining of MMCs. Optimal conditions for the significant parameters were listed depending upon the requirements of the machining process which may vary for rough machining (higher material removal rate) and finish machining (lower surface roughness). The mean thickness of the recast layer formed after machining was also studied. The results at this stage of experimentation show that all the responses (MRR, TWR, and SR) have a direct relationship with current but an inverse relationship with pulse-on time.