Evaluation of drilling Al/SiC composites with cryogenically treated HSS drills

The purpose of this study was to evaluate the performance of cryogenically treated M35 high-speed steel (HSS) twist drills in the drilling of Al/SiC metal matrix composites (MMCs) produced with the hot-pressing method in terms of dimensional accuracy (Da), surface roughness (Ra) and tool life. The cutting tool (Ct), cutting speed (Vc) and feed rate (f) were taken as control factors. The Taguchi method L (18) (2(1) x 3(7)) was used for the determination of optimum control factors. Analysis of variance (ANOVA) was applied in order to determine the effects of the control factors on Da and Ra. The optimum combinations of the control factors for Da and Ra were determined as A(2)B(2)C(1) and A(2)B(1)C(1), respectively. First-order predictive models were developed with linear regression analysis, and the coefficients of correlation for Da and Ra were calculated as R (2) = 80.5 and R (2) = 79.0, respectively. The results of the conducted experiments showed that the cryogenically treated drills exhibited better performance than the untreated drills in terms of the dimensional accuracy and surface roughness of the MMCs. In the tool life experiments, when compared to the conventionally heat-treated (CHT) tools, the cryogenically treated (CT) tools gained increases in tool life of 256 and 161 % at the cutting speeds of 15 and 25 m/min, respectively. Moreover, on both cutting tools, built-up edge (BUE) on the chisel edges and flank wear on the cutting could be observed.