Research On The Performance Of PCBN Tools In Interrupted Cutting

The polycrystalline cubic boron nitride (PCBN) tool is suitable to the high-speed cutting and dry-cutting and it is used widely in the the automobile industry abroad.Currently, study on the using of PCBN tools is mainly focus on the continuous cutting, but components with interrupted surface can be met often in productive practice, such as gear and casfellated shaft, etc, which raise more requirements to the PCBN tools' performance which will be different with the types and content of binder. So it is necessary to do some research on the performance of PCBN tools in interrupted cutting. In order to provide some references and foundations for stable, safe, efficient application of PCBN tools, different kinds of PCBN were chosen for interrupted cutting austempered ductile iron (ADI) and GCr15 bearing steel in this paper, then by using the Kistler three-dimensional dynamometer and the JSM-5600LV electronic scanner microscope, the tool performance of interrupted cutting and its wear mechanism were studied deeply based on the cutting force, tool life and the micrograph of tool wear area.According to the results of interrupted cutting ADI using PCBN tools, the cutting force can be devided into static cutting force and impact force; compared with DBC50 and BN250 tools, when the DBW85 or BN700 tools which have high CBN content are used to interrupted cut ADI, the cutting speed could be chosen higher; the life of DBW85 tool is longer than that of DBC50 and the performance of DBW85 tool is better at higher speed (130m/min more or less); the main wear types of DBW85 tool are abrasive wear and adhesion-diffusion wear, while the main wear types of DBC50 tool are micro-tipping and adhesion-diffusion wear; when interrupted cutting ADI, the performace of PCBN tool is determined by its anti-fracture toughness and thermal conductivity.In the experiments of interrupted-cutting GCr15 steel, the results show that the cutting speed of DBC50 could be chosen higher, because the speed affects the cutting force of DBC50 less; DBC50 tool is better than DBW85 on the tool life; when interrupted cutting GCr15 steel, abrasive wear, adhesion-diffusion wear and chemical wear are the main reasons of PCBN tools wear, and the resistance to high temperature and anti-fracture toughness determine interrupted-cutting performance of the tool. Addition, with the increase of cutting speed, the chip morphology of GCr15 had changed from continuous chip to serrated chip in conditon of critical speed and then to squeezing chip. Besides, when tool wear reached to some extent or the cutting speed was high (>160m/min), the tools chosen in experiment all tipped badly, so it is indicated that mechanical stress causes tipping at low cutting speed, whereas thermal and mechanical stress are the reasons of tipping at high speed.