Surface Finish for a Case of Continuous and Interrupted OD Hard Turning

Hard turning is the process to watch in many industries, as it is a perfect candidate for the actual trends toward automation and flexible manufacturing. However, there are still many possible conjunctures created by different geometries or materials of the workpieces versus different types of cutting tools with effect on workpiece surface quality, tool wear, machine tool vibrations, etc. These insufficiently explored combinations make manufacturers hesitate to adopt hard turning as a finishing process. This paper brings new findings concerning the effect of cutting parameters and tool nose radius variations on surface finish as a result of continuous and interrupted hard turning. The considered workpieces are a camshaft made of AISI 1117 steel at 62 HRC for continuous cutting, and a spline shaft made of AISI 1137 steel at 48 HRC for interrupted cutting. Two types of PcBN cutting tools are used for both types of component parts. The investigation highlights the differences between the ideal, geometrically determined, surface roughness Ra and the experimental results, as well as the differences recorded between the continuous and interrupted cutting situations. The factorial experimentation technique was employed taking the resulting surface rughness (R_a) as a response variable. The influence of tool wear was finally considered in the analysis of the predicted values of roughness obtained through characteristic regression equations. A significant difference of roughness evolution versus tool wear was recorded for the continuous and interrupted surfaces. The analysis was completed based on profilometry and light interferometry measurements as well as optical and SEM microscopy observations.