For fiber reinforced polymeric (FRP) composites, drilling is a particularly crucial operation because the strong concentrated forces produced can cause extensive damage. In addition to creating visual defects, this damage raises the possibility that the mechanical attributes of the finished part will be degraded. FRP composites are difficult to machine due to their anisotropy, inhomogeneity, and abrasiveness of the reinforcing fibers.

In the current study, based on Taguchi's L9 orthogonal array, drilling experiments were carried out on random glass fiber reinforced polyester (RGFRP) composites using drill bits manufactured of high-speed steel (HSS) to make a decision on a parametric optimization of multiple responses such as peel up delamination factor (FDup) at entry of the drilled hole, push down delamination factor (FDdown) at exit of the drilled hole and surface roughness (Ra) using grey relational-based Taguchi analysis. The selected drilling parameters are spindle speed (A), feed rate (B), and overhang ratio (H). Based on grey relational analysis (GRA), the optimum levels of parameters resulting in minimum values of the three responses were identified and significant contribution of parameters was ascertained by analysis of variance (ANOVA). The findings demonstrated that all the selected drilling parameters have a significant effect on all the measured responses with a confidence level of 95%. From the confirmation experiment carried out at the optimum drilling conditions, there has been an improvement of grey relational grade (GRG) by 1.65 %