Intermittent machining of hardened steels with different types of PcBN cutting tools

Abstract

The paper discusses the results of the experimental investigation of the performance of several grades of PcBN cutting composites in conditions of the interrupted machining of hardened steel. Both BH and BL types of PcBN indexable inserts with additions of Si3N4, TiC, and TiCN were tested, and cutting speed varied to assess the possibility of applying these cutting tools in different conditions. It has been shown that BL PcBN can be utilized for turning with shock loads in case of high cutting speed and low depth of cut (0,2 mm). While in the range of comparatively low cutting speeds BL cutting tools are actually inoperable, and because of microchipping of polycrystalline fragments and brittle destruction of the cutting edge, an increase of the cutting speed to 210 m/min changes wear pattern and formation of the wear land. As well as this, measurement of the form and values of the cutting forces impulses revealed the effect of their peak growth by up to 40%. The danger of shock impulses was analyzed by FEM modeling, and it was demonstrated that during impacts, the maximal value of the third Principal stress exceeds the average level of compressive stresses during continuous cutting by 1.6 times, which can cause damage to the cutting tool. The data on the estimation of tool fracture probability depending on loading conditions are presented, and the possibility of reducing such probability is shown.