Optimization of Drilling Process on Al-SiC Composite Using Grey Relation Analysis

1. Introduction

Metal Matrix Composite (MMC) comprises a metallic matrix with one or more reinforcement materials to produce composite materials with superior properties like high temperature resistance, high wear resistance, corrosion resistance and good damping characteristics. These MMCs are primarily used in the aerospace, military and automobile industries. Cast metal matrix composites with particulates, whiskers and short fibers fabricated through stir casting technique (Thirumalai Kumaran et al., 2015; Suresh Kumar et al., 2014). Aluminum is the most frequently used matrix material due to its low density and ease of fabricability. SiC ceramic particles are often used as reinforcement within the Al matrix, because of its extreme hardness and temperature resistant properties. However, the higher hardness of these materials is one of the challenging factors for machining the engineering components to its final shape(Frank Muller & John Monaghan, 2000).In order to improve the machining efficiency and to reduce the machining cost it is important to select the optimal machining conditions(Coelho, 1995).

The surface finish determines the quality of the machined part. It is influenced mainly by the process parameters such as tool geometry and cutting conditions [cutting speed, feed rate and depth of cut. For achieving better surface finish one has to scarify the material removal rate. The increase in material removal rate decreases the production time of the component. Selection of suitable machining parameters is required for obtaining higher material removal rate without affecting the surface texture and quality of the finished product (Thirumalai Kumaran and Uthayakumar, 2014).

Gul Tosun and Mehtab Muratoglu (2004) observed that the carbide drills provide a better surface finish compared to the tools such as HSS and TiN coated HSS drills during drilling Al/17% SiCp MMC. Basavarajappa et al. (2007) suggested that better surface finish is obtained in TiN coated carbide drill than carbide tools during drilling Al-SiC MMC. This is due to hard coating present over the surface of the tool, which facilitates reduced build-up-edge formation during drilling. The increase in feed rate has a more predominant effect on surface roughness than cutting speed rate. Paulo Davim et al. (2001) and Ramalu et al.(2002) found that the predominant effect of feed rate is due to the burnishing or honing effect produced by the rubbing of small SiC particles trapped between the flank face of the tool and the work piece surface. Gul Tosun and Mehtap Muratoglu (2004) revealed that as the point angle of drills increases, the subsurface damage zone also increases leading to lower surface finish. The thrust forces during drilling increases considerably when higher feed rates and there is no predominant variation when the spindle speed is increased (Barnes, 1999). Edith Morin, et al. (1995) observed that the values of torque and thrust forces for 6061 Al alloy are very similar to that of composite and identified that the matrix is the one which controls drilling forces and not the reinforcing particles.