In the tool matching model established by Niu Jiahui, polycrystalline cubic boron nitride (PCBN) tool ranks third among the tools suitable for machining vermicular graphite cast iron, second only to alumina and titanium carbide tools. The poor initial property and high cost of PCBN tools limit its application in the machining of vermicular graphite cast iron. In recent years, with the development of tool manufacturing technology, with the selection of suitable hard phase and high purity CBN single crystal, the tool compactness can be improved and the manufacturing cost can be reduced. The demand for vermicular graphite cast iron increases, which puts forward higher requirements for cutting efficiency, wear resistance and life of cutting tools. When machining vermicular graphite cast iron at high speed, the tool life of cemented carbide tools decreases sharply, while PCBN tools can meet the above requirements. Weichai Power Company’s vermicular graphite cast iron diesel engine processing, the most commonly used tool is PCBN, the use of PCBN cutting tools can improve machining efficiency and machining surface quality to meet the needs of orders. Machining vermicular graphite cast iron with PCBN tool will be an important direction in the future. at this stage, there are few researches on the cutting performance and tool wear mechanism of vermicular graphite cast iron machined by PCBN cutter. therefore, this study is necessary. This chapter selects the integral PCBN tool whose metal bond is aluminum, the metal bond will reduce its hardness, but the initial property has been strengthened to be suitable for high-speed intermittent machining of vermicular graphite cast iron with pearlite content more than 90%.
The cutting force, cutting temperature, tool wear and surface integrity of PCBN tool in milling vermicular graphite cast iron were studied.
The main results are as follows: (1) the cutting force changes obviously with the feed, which is basically consistent with the cutting temperature. Under the condition of small feed rate, the cutting force and cutting temperature increase with the increase of cutting speed, but the change is not obvious at large feed rate.
(2) the tool failure form of PCBN high speed milling vermicular graphite cast iron is flank wear, and the tool life decreases with the increase of feed rate and speed, but the material removal volume under the condition of large feed rate is larger than that under the condition of small feed rate.
(3) the tool wear mechanism of high speed milling vermicular graphite cast iron with PCBN cutter is mainly bond wear, including oxide bonding. The Si element in the workpiece can be seen in almost all energy spectra, which indicates that there is diffusion wear in the milling process.
(4) the cutting speed has little effect on the machined surface morphology and surface roughness, while the feed rate has a great influence on the machined surface morphology and surface roughness.
(5) the microhardness increases with the increase of feed rate, and increases continuously with the increase of cutting speed under the condition of small feed, but under the condition of large feed, due to the resistance of thermal softening effect and the influence of tool wear, as a result, the microhardness increases at first and then decreases and then increases with the increase of cutting speed.