In this paper, an investigation has been made to explore the thrust force, torque and surface roughness that contain important information related to the quality of the hole produced during the drilling of hybrid aluminum metal matrix composites-Al7075/Al2O3p/Grp using low cost HSS twist drill bits. These composites are increasingly being used in aerospace, marine, automobile and mineral processing industries owing to their superior mechanical and wear properties. In this study, hybrid composites were reinforced with the hard ceramic (0 and 3 wt. % of Al2O3) and soft solid lubricant (2, 4 and 6 wt. % of graphite) of particle sizes 40μm. These composites with varying percentages of Al2O3 and graphite were fabricated by using stir casting method in a controlled atmosphere. Uniform distribution of reinforcing particles was confirmed by optical microscopy and SEM views. The experiments were designed using Taguchi's L18 orthogonal array (21 x 34) to examine the machinability of these composites during drilling. The drilling experiments were carried out at various speeds (244, 445, 890 rpm), point angles (108°, 114° and 118°), and chisel point thickness (2, 1.7, 1.4mm) to study their effect and reinforcing particles on thrust force, torque and surface roughness,. Analysis of variance and main effects plots were used to analyze the experimental data and find the optimal combinations of various input parameters. The results based on these analyses showed that thrust force is mainly affected by point angles of drill bit. Torque is mainly affected by wt% of graphite and point angles. The thrust force and torque have similar effects of point angles. The surface roughness decreased with increase of wt% of alumina and increases with increase of the speed.
Al7075 composites, drilling, thrust force, torque, surface roughness
