Study On Wear Of Coated PCBN Tool In Cutting Hardened Steel

Hardened steel is widely applied in bearing,automobile and die industry.It is hardness and strength are high,and the machinability is poor,so its a typical difficult-to-machine material.PCBN tool with high hardness and wear resistance,good thermal stability and chemical stability,has became a common tool material for cutting hardened steel.However,the high thermal load and mechanical load in the machining process will reduce the service life of PCBN tool.The coated PCBN tool can effectively solve the problem of low service life in machining hardened steel.It is of great theoretical significance and practical value to study the wear of coated PCBN tools in cutting hardened steel.The main work is summarized as follows:(1)Preferable coating PCBN tool suitable for processing hardened steel and its reasonable cutting speed range.Coated PCBN tools(BNC2010,BNC2020)and uncoated PCBN tools(BN2000)were applied for cutting experiments.The results show that: under the same cutting conditions,the tool life of BNC2010 is about 30% higher than that of uncoated BN2000,while the tool life of BNC2020 is not different from that of uncoated BN2000,so BNC2010 can be used as the preferred tool material for cutting hardened steel.The influence of BNC2010 cutting tool on cutting force,surface roughness and cutting efficiency under different cutting speeds was comprehensively studied,and the cutting speed range of 103-125m/min was optimized.(2)The process of tool wear were studied by high definition optical microscope.The results show that the crater wear rate of BNC2010 tool is significantly lower than that of BNC2020 tool,and the wear value of BNC2010 tool is significantly lower than that of uncoated BN2000 tool;When the cutting speed exceeds 125 m/min,the crater boundary of the three kinds of cutting tools appears shell like tool material spalling,but BNC2010 tool appears spalling later;At low speed,the wear value of the flank increases approximately proportionally,but at high speed,when the flank is worn to a certain extent,the wear rate tends to accelerate;The tool flank wear of BNC2010 is obviously lower than that of the other two tools after cutting for a certain period of time.(3)The micro wear morphology and wear mechanism of the cutting tool were studied by SEM and EDS.The results show that hard point wear,adhesive wear,diffusion wear and oxidation wear occur in all three kinds of cutting tools;The bond wear and oxidation wear of BNC2010 tool are relatively light;The bond wear and oxidation wear of BNC2020 tool are relatively serious,and the hard point wear is intensified at high speed;With the increase of cutting speed,the degree of adhesive wear and oxidation wear become more serious,especially when the cutting speed exceeds 125 m/min.(4)DEFORM-3D software were applied to simulate the cutting temperature of the tool.The simulation results show that the cutting temperature of the coated PCBN tool is lower than that of the uncoated PCBN tool,while the cutting temperature of the Ti Al N coated PCBN tool is lower than that of the Ti CN coated PCBN tool,which proves that the coating can effectively reduce the cutting temperature of the PCBN tool and slow the tool wear.