Tool wear, surface quality, and chip formation in continuous and interrupted hard turning

The machining of hardened steel components with Polycrystalline Cubic Boron Nitride (PcBN) inserts having a geometrically defined cutting edge has gained substantially in importance due to improvements in the performance of such modern cutting tool materials. Thus, hard turning is increasingly a profitable alternative to finish grinding. However, there is still much reluctance in adopting hard turning as a finishing process because of insufficiently explored aspects related to workpiece surface quality, tool wear, chip formation, and other machining outcomes, for so many possible combinations created by different geometries or materials of the workpieces versus different types of cutting tools.; This dissertation brings new findings concerning tool wear, surface quality and chip formation in hard turning for a combination of workpiece materials and tool types not yet considered in hard machining investigations to our best knowledge. The dissertation also proposes a new two-dimensional model of chip formation based on finite element methods using the commercially available software MARC Mentat. The model can predict the effect of tool material, tool edge preparation, and cutting speed on cutting temperature, stress distribution, strain and strain-rates.; The main workpieces considered for this research are camshafts made of AISI 1117 steel at 62 HRC, and spline shafts made of AISI 1137 steel at 48 HRC. These types of steels are widely used for component parts in the automotive industry in a hardened state; however, they were not yet considered on a large scale for hard turning investigations. The cutting tools selected for this research are PcBN inserts that were relatively new on the American market when this research was initiated: Amborite DBC50 and Amborite DBN45. Thus, new findings related to tool flank wear evolution, wear mechanism and tool life, as well as surface quality versus cutting regime, tool geometry, and tool wear are presented.; The research also involved materials that were previously considered for hard turning studies: M50 steel was employed for tool life trials while AISI 52100 was used for refinement and validation of the numerical model of chip formation. However, different cutting conditions and different geometries were adopted from those in already published work.