Optimization of hybrid Al-MMC drilling using a new RAMS-RATMI-based approach

This paper presents parametric analysis and optimization of a drilling operation on hybrid aluminium metal matrix composites (Al-MMCs), consisting of Al 7075 as the base material, and 2% SiC and 2.5% (fly ash + bagasse ash) as the reinforcements. Based on Taguchi's orthogonal array, 27 experiments are conducted, and the main effects and interaction effects of spindle speed, feed rate and drill diameter on material removal rate (MRR), delamination factor and conicity of the machined holes are studied. It is noticed that higher values of all the three drilling parameters would result in higher MRR. On the other hand, lower delamination damage can be achieved at lower values of spindle speed and feed rate, and moderate drill diameter. Lower spindle speed and drill diameter, and moderate feed rate are responsible for minimum conicity. This paper proposes application of two recently developed multi-criteria decision making (MCDM) tools, i.e. ranking alternatives by median similarity (RAMS) and ranking alternatives by trace to median index (RATMI) to solve the corresponding multi-objective parametric optimization problem of the said drilling operation. It can be interestingly noted that both these approaches identify the optimal parametric combination as spindle speed = 170 rpm, feed rate = 41 mm/min and drill diameter = 10 mm yielding maximum MRR of 7.473 g/min, and minimum delamination and conicity of 1.0416 and 0.00002 respectively. The metallurgical characterization of the developed hybrid Al-MMCs is also performed with the help of scanning electron microscopic images which show good bonding between the matrix and the reinforcement particles. It is noticed that the average hardness of Al-MMCs increases with addition of SiC + flyash + bagasse ash as the reinforcement particles. A comparative analysis of the derived results against other popular MCDM tools proves the efficacy of RAMS and RATMI methods in optimizing the considered drilling operation on the hybrid Al-MMCs.