Effect of drill meso-geometry and lubri-cooling conditions on the finish hole in DIN S700MC HSLA steel

ABSTRACT This paper presents an investigation on the behavior and effect of the machining process by drilling through a DIN S700MC steel alloy, correlating the preparation of cutting-edge geometry with different coolinglubrication conditions, and focusing on the surface finishing of the machined part. In this context, experimental tests were performed with different cooling-lubrication systems (abundance, MQL, and dry) using solid carbide twist drills, coated with titanium aluminum nitride, with or without meso-geometry preparation (roundings). As response variables were assessed the texture (roughness), the layer affected by heat throughout the hole and burr dimensional profiles. The results indicate a significant reduction of roughness values when using the rounding drill flank, face and guides. Statistically, this result was not influenced by the different cooling-lubrication systems. Regarding burr dimension generated by the process, the tool with no meso-geometry preparation presented the same values along with the application of fluid in abundance (emulsion). In the analysis of the layer affected by heat, the tool with meso-geometry preparation presented lower values of the affected layer (microstructure change) and, statistically, there were no significant variations between the application of fluid in abundance and with MQL.