Investigation of thrust force in drilling polyphthalamide (PPA) composites

•Thrust force are measured for PPA composites with respect to different drills.•The optimized drilling parameters for the minimum thrust force was found by the Taguchi Method.•The degree of effectiveness of the test parameters on the thrust was found by the statistical ANOVA method.•Drill material is most effective factor on thrust force in drilling PPA composites.•Morphology of drilled hole surface are analyzed by Scanning electron microscope (SEM). In this study, the drilling process is explored on 30% glass fiber reinforced PPA composite to investigate the influence of drilling parameters on thrust force. HSS, TiN coated HSS and carbide twist drills with 5 mm diameter and 118° point angle are used to perform the drilling tests. The drilling tests were carried out in dry conditions on the 3-axis CNC milling machine. Three different cutting speeds such as 15, 20, and 25 m/min and feed rate such as 0.05, 1.0, and 1.5 mm/rev were selected as drilling conditions. Experimental results indicated that the thrust force increases with increasing the feed rate and in contrast the force decreases with increasing the cutting speed. Statistical Analysis of Variance (ANOVA) method was used to determine the effects of drilling parameters and interactions on the thrust force. According to the analysis, drill materials play the most important role on the thrust force. In addition, mathematical models were developed using the multi-linear regression method. The optical microscope and Scanning Electron Microscopic (SEM) images were used to examine the drilled hole surface of the PPA composite material. According the images of the drilled hole surfaces indicated the existence of matrix crack, fiber pull-out, and shearing of fibers. In order to obtain the best surface quality (in terms of delamination factor and surface roughness) and minimum thrust, it is recommended to use carbide drill bits at the lowest feed rate and highest cutting velocity cutting conditions.