Experimental Investigations of Drilling Process Parameters for Hemp Polyester Composites

The development of polymer composites with natural fibers offers a cost-effective alternative for applications in the aviation and automotive industries. The synthetic fibers possess impressive mechanical properties; they are more expensive than natural fibers. This has led to increased interest in hybrid composite materials combining both types. Researchers are focused on creating new fiber-reinforced composites to expand their applications. However, machining these composites can be challenging due to their heterogeneity and issues like delamination, influenced by both the fiber type and cutting parameters. In the current research, the hemp-polyester composites were developed using hemp fibre and as reinforcement and isophthalic polyester resin as a matrix material employing the hand layup technique. This study aims to analyze how speed, feed and tool geometry affect delamination and Thrust Force (TF). Drilling tests were conducted using a full factorial Design of Experiments (DoE) approach, considering various feed rates (0.09, 0.19, 0.29 mm/rev), spindle speeds (700, 2700, 4700 rpm), and tool geometries (plexi point, twist, parabolic). Analysis of Variance (ANOVA) was employed to evaluate their interactions and percentage contribution of machining parameters on thrust force and delamination. The results showed that spindle speed has little effect on delamination and that tool geometry and feed rate are the main determinants. Major Findings: The investigations conclude that drill geometry and feed rate effectively influence the hole drilling in hemp polyester composites. The plexi point and parabolic tool reduced thrust force and delamination compared to standard twist drill. The feed rate directly increased thrust force and delamination factor, spindle speed had no prominent effect on thrust force.