Effect Of Double Lubrication Methods On Cutting Performance Of (W,Ti,Ta)C-Based Cermet Tools

In recent years,with the continuous improvement of the material performance requirements of the processing and manufacturing industry,there are more and more applications of difficult-to-machining materials,and the requirements for the performance of cutting tools are getting higher and higher.In this thesis,the self-lubricating cermet tool is made by introducing nano-Ca F₂ on the basis of（W,Ti,Ta）C-based cermet cutter.combined with micro-lubrication technology,the machinability of many kinds of difficult-to-machining materials is studied under the cutting mode of double lubrication,which reduces the amount of cutting fluid in the cutting process,improves the machining efficiency and reduces the pollution to the environment.According to the three indexes to evaluate the cutting performance of the tool,namely,the workpiece surface hardening degree,the tool cutting life and the workpiece surface roughness,this thesis selects three representative difficult-to-machining materials:304 austenitic stainless steel,Cr12 high chromium cast iron and HT250 gray cast iron.Self-lubricating cermet tools combined with micro-lubrication technology were used to explore the effect of double lubrication on the cutting performance of（W,Ti,Ta）C-based cermet tools.Firstly,nano-Ca F₂ particles were introduced into（W,Ti,Ta）C-based cermet cutters,and（W,Ti,Ta）C-based self-lubricating cermet cutters were prepared by Spark Plasma Sintering,the optimum sintering parameters are 1400°C,10 min and 30 MPa,under which the Vickers hardness and bending strength of cermet tools are 20.39±0.3 GPa and1389±35 MPa respectively The intragranular nanocrystalline structure of Ca F₂ particles in ceramic grains is an important basis for self-lubrication of tool materials.The study on cutting 304 austenitic stainless steel shows that the thickness of the modified layer on the surface of the workpiece is as high as 32.7μm without any lubrication,which is 32.7%of the cutting depth,while under the cutting mode of double lubrication,the thickness of the modified layer on the surface of the workpiece is only14.7μm,which is 55.1%lower than that without any lubrication.When no lubrication is added,the machining hardening rate of the workpiece surface is 133.4%,while under the double lubrication mode,the machining hardening rate of the workpiece surface is only112.4%,which is 15.7%lower than that without any lubrication.The results show that double lubrication can effectively reduce the work hardening of 304 austenitic stainless steel.The study of cutting Cr12 high chromium cast iron shows that the effective cutting distance of（W,Ti,Ta）C-based cermet tool without any lubrication is about 11000 m,which is higher than that of cemented carbide tool（about 8000 m）.The double lubrication method can effectively slow down the wear rate of the tool in the cutting process,and the cutting life of the self-lubricating cermet tool can be effectively extended to about 13500m,and the stable wear stage of the tool under this cutting mode is about 8100 m,which is 5.4 times that of the commercial cemented carbide tool（about 1500 m）.The study of cutting HT250 gray cast iron shows that the surface roughness of workpiece machined by（W,Ti,Ta）C-based cermet tool without any lubrication is 1.12μm,which is better than that of commercial YT15 blade（about 1.43μm）,but there is also a problem that the surface roughness of workpiece fluctuates obviously after machining.The use of double lubrication can effectively improve the stability of the tool in the cutting process,and the surface roughness of the workpiece can be as low as 0.89μm,which is37.3%lower than that of dry cutting,and the fluctuation of the surface roughness of the workpiece does not exceed 10%in the whole cutting process.The analysis shows that Ca F₂,as a solid lubricant,can form a stable lubrication film in the internal friction zone of the tool,which can effectively reduce the friction between the tool surface and the chip and accelerate the chip outflow rate.The micro lubrication technology introduced into the tool external friction area can use compressed air to accurately spray the lubricating oil to the tool cutting area in the form of oil mist,reduce the friction between the chip flow and the tool external friction area,and take away a large amount of cutting heat;under the interaction between the two,it can not only protect the tool but also improve the machining quality of the workpiece.