Experimental Investigation and Multi-Response Optimization of Drilling and Milling Parameters for Sisal/Bamboo Fiber-Reinforced Hybrid Composites

Abstract

This study investigates the machining behavior of a sisal/bamboo fiber reinforced polyester matrix hybrid composite (10%/20%/70% weight ratio, unidirectional 0° orientation) through drilling and milling operations. Taguchi methods and Gray Relational Analysis (GRA) were employed to optimize machining parameters (spindle speed, feed rate, tool diameter, and depth of cut) while considering delamination, surface roughness (R_a), and material removal rate (MRR). ANOVA (analysis of variance) was utilized to analyze the influence of the parameters. Drilling results showed that spindle speed influenced entry delamination, while tool diameter significantly impacted exit delamination. Optimal drilling parameters (A₁B₃C₃: 380 rpm, 0.25 mm/rev, 10 mm) minimized delamination (DFentry = 1.10, DFexit = 1.50) while maximizing MRR (19.63 mm³/min). In milling, feed rate was the dominant factor influencing both delamination and R_a. Higher feed rates led to increased delamination and R_a. Higher spindle speeds reduced R_a. The optimal milling parameters (S₃F₃d₂: 1180 rpm, 0.06 mm/rev, 3 mm) minimized delamination (1.41) and R_a (0.17) while maximizing MRR (2548.8 mm³/min). Although feed rate showed the largest influence on MRR, none of the factors were found to be statistically significant in influencing MRR based on ANOVA. This study provided valuable insights for optimizing machining parameters to enhance performance and reduce defects in processing the biocomposite.