THE PERFORMANCE OF CERMET CUTTING TOOLS WHEN MACHINING AN NI-CR-MO (EN-24) STEEL

Recently developed grades of cermet cutting tool materials, physical v apor deposition (PVD)-coated and uncoated, were used to machine a high -strength and relatively difficult-to-cut steel at cutting conditions typical of finish machining. Comparative tests were carried out with c hemical vapor deposition (CVD)-coated (TiC + Al2O3) carbide inserts at similar cutting conditions. The test results show that the PVD-coated cermet tools outperformed both the uncoated cermet and CVD-coated car bide tools at higher speed conditions due to their increased mechanica l and thermal shock resistance as well as the high lubricity of the Ti N coating layer. The coated cermet tools were rejected mainly due to t he generation of poor surface finish on the machined surface after pro longed machining due to the increased tool-workpiece contact area, wit h increasing flank wear, which permits access for dislodged hard parti cles into the interface. Plastic deformation of the cutting edge of th e coated cermet tools tends to dampen the machining operation, leading to a reduction in both the cutting and feed forces.