Research On High Speed Brittle Cutting Properties And Tool Optimization Of Pure Iron

Pure iron is a metal material with good plasticity,low hardness and high magnetic permeability.Its main purpose is to use its ferromagnetism to make ferromagnetic cores of instruments and meters and other equipment that requires soft magnetism.In the cutting process of pure iron,due to the high plasticity and low hardness of pure iron,problems such as difficult chip breaking,tool adhesion and machined surface hardening will occur,which have a great impact on the quality of the machined surface and tool wear.This paper mainly analyzes the high-speed brittle cutting performance of pure iron through two methods: experiment and simulation of pure iron high-speed brittle cutting,and explores ways to solve the problem of chip breaking and tool bonding in pure iron machining.Aiming at the problem of severe tool wear at high speed,a tool optimization experiment for high-speed brittle cutting of pure iron is carried out.Through the analysis of tool wear and machined surface quality and other indicators,the tool suitable for highspeed brittle cutting of pure iron is selected.The main research contents and conclusions are as follows:First,the cutting process of pure iron in the speed range of 1000-9000 m/min is realized by the way of milling instead of turning.And use ultra-depth-of-field microscope,scanning electron microscope and metallurgical microscope to observe the chip morphology,tool wear and machined surface quality at different speeds.According to the chip shape and fracture behavior,the cutting speed of pure iron under the effect of high strain rate embrittlement is judged to evaluate the possibility of pure iron cutting in the embrittlement state.The surface roughness and surface microhardness of the processed surface are measured by a white light interferometer and a microhardness meter,and the quality of the processed surface is comprehensively analyzed.The research results show that when the cutting speed is higher than 8000 m/min,granular chips formed by brittle fracture are obtained.The chip shape,chip deformation and the quality of the machined surface at different speeds are analyzed.Secondly,a pure iron fracture model based on the criterion of maximum failure strain was used to simulate pure iron cutting with a cutting speed ranging from 300 to 8000m/min.Obtain the data of stress and strain distribution in the deformation zone,temperature during the cutting process and cutting energy consumption,which are difficult to obtain in the experiment,and analyze the changes of stress,temperature and cutting energy consumption before and after the plastic brittle transition of pure iron.The results show that within the speed range of 300-7000 m/min,the stress distribution in the first deformation zone is uniform and gradually increases with the increase of cutting speed.When the cutting reaches 8000 m/min,the stress distribution is uneven,and the maximum stress appears at the tip of the tool,and the stress decreases rapidly away from the tip of the tool.The temperature of the first and second deformation zones also increased first and then decreased with the increase of cutting speed.The decrease was not obvious before 7000 m/min,and there was a significant decrease at 8000 m/min.But the temperature of the third deformation zone increases with the increase of cutting speed.The cutting energy consumption does not change much within the speed range of 300-7000 m/min,and the chip kinetic energy gradually increases.When the cutting speed reaches 8000 m/min,the kinetic energy of the chips increases,the frictional dissipation energy and the plastic dissipation energy decrease,and the overall cutting energy consumption decreases.The brittleness removal of pure iron is conducive to reducing processing energy consumption.Finally,according to the severe wear of the tool flank at high cutting speeds,cemented carbide,PCBN and ceramic tools were selected for the pure iron cutting experiment with a cutting speed of 8000 m/min.By comparing and analyzing the wear of different tools and the quality of the machined surface,the appropriate tool is selected to achieve the removal of pure iron under the brittle state.The results show that the ceramic tool has the best wear resistance.After a cutting length of 45 m,the rake face is basically not worn,and the flank is slightly worn.The rake face and flank face of PCBN tool is obviously worn,and cemented carbide tool is severely worn.The quality of the machined surface is basically the same as the wear of the tool.The surface processed by the ceramic tool is smooth,and the average roughness is 0.358?m.The microhardness test results show that the surface hardness of the workpiece after ceramic cutting tool is lower than that of cemented carbide and PCBN cutting tools.And the work hardened layer is shallow,reaching the hardness of the workpiece matrix at a depth of 150 ?m.Comprehensive analysis of the above results,ceramic tools are more suitable for the brittle removal of pure iron at high speed.