Influence of cutting modes on the cutting tool life when drilling carbon-fiber reinforced polymer

In the manufacture of products made of carbon fiber reinforced plastics (CFRP), one of the most common cutting operations is drilling holes. This process is accompanied by intensive wear of the cutting tool and specific hole defects.The paper presents results of the study of the effect of cutting modes and geometric parameters of the drill on the tool life when drilling CFRP with high-speed steel twist drills. The tool life was assessed by the number of quality holes, the criterion for replacing the tool was the value of the hole delamination coefficient (the ratio of the maximum diameter of the damaged area to the nominal diameter of the drilled hole). The quality of holes using the light-optical microscopy was assessed. Empirical mathematical models were obtained using regression analysis and experimental design methods. The robust experimental design was built based on the pseudo-random LPτ numbers. The regression model and its statistical characteristics were obtained using the PRIAM software. Statistical characteristics of the model indicate its adequacy, informativeness and stability. The analysis of the degree of individual factors’ influence on the response function was carried out based on of the percentage of participation and the correlation coefficient. It was found that the spindle speed (27.7 %), the drill sharpening angle (17.8 %), and the interaction of the spindle speed and feed have the greatest influence.The analysis of the resulting model, marginal regression equations and marginal responses allowed to formulate recommendations for choosing cutting modes. It was found that for the given conditions the greatest number of quality holes can be obtained at the spindle speed of 1050 rpm and a feed rate of 0.17 mm/rev – this statement is true for all studied drill diameters (2 mm…4 mm) and for both angle options (90°, 118°), while drills with a sharpening angle of 118° demonstrate better results. The results obtained during the study can be used to optimize technological processes for drilling CFRP and for choosing proper cutting tool, which, in turn, will contribute to increasing both productivity and processing quality.