Investigation on tool wear mechanisms and machining tribology of hardened DC53 steel through modified CBN tooling geometry in hard turning

Abstract

DC 53 steel has emerged as a possible replacement of AISI D2 steel possessing competitive hardness and better toughness. In the current work, turning of DC 53 steel was conducted via Xcel modified inserts by varying workpiece hardness levels (40 and 60 HRC), cutting speed (130 and 160 m/min), feed rate (0.07 and 0.112 mm/rev), and depth of cut (0.07 and 0.17 mm). A two-level 4-factor full factorial design was employed entailing 16 runs. An analysis of variance (ANOVA) was conducted to statistically analyze the effect and contributions of input parameters on response variables namely tool life, surface roughness, volume of material removed, power consumption, and machining zone temperature. Results show that the tool life, surface roughness, volume of material removed, and machining zone temperature are primarily affected by the hardness of DC53 with PCRs of ~ 96%, ~ 25%, ~ 62%, and ~ 25%, respectively. At a 40 HRC hardness value, true crater wear was observed due to continuous chips sliding at the rake face while for the workpiece having a 60 HRC, discontinuous chip formation produced less prominent crater wear. SEM images revealed complete delamination of the coating from the tool surface with adhesion and attrition wear identified as the main wear mechanisms. The formation of a groove pattern was also noticed on the flank face. The minimum surface roughness was 0.90 µm-Ra for the workpiece having a 40 HRC hardness level, and the same value was obtained for 60 HRC as well. The threshold value of the feed rate for the excellent performance of these inserts was less than 0.20 mm/rev. Additionally, the turning process proved to be productive for this material along with a lower surface roughness value in comparison to the wire EDM process.