Fundamental Research on Thermal Cracks of Cemented Carbide Hob in Hobbing

Abstract

This paper deals with the state of the thermal crack development on the rake face of cemented carbide hob material, P30, whose flank face was coated with TiN and (Ti,Al)N films when changing the hob feed in the cases of dry and MQL system in hobbing. Experiments were carried out by simulating hobbing by fly tool cutting on a milling machine. As a consequence, the following points were clarified: (1) The number of thermal cracks obtained with MQL system is smaller than that obtained in dry when using both TiN- and (Ti,Al)N-coated tools, irrespective of changing the hob feed. In the case of MQL system, however, the delamination occurs on the thermal crack. (2) The thermal cracks begin to appear at a distance of contact length with chip from cutting edge, which develop toward the cutting edge. The thermal cracks also occur almost perpendicular to the top cutting edge, the roundish portion and the side cutting edge. (3) The occurrence directions of thermal cracks agree approximately with the directions of chips which flowed out perpendicular to the three cutting edges of hob tooth.