Milling Behavior And Strengthening Mechanism Of Carbide Tools Based On Pulsed Magnetic Field

The“Fourteenth Five-Year Plan”is to implement the strategy of intelligent and green manufacturing project,and promote the development of high-end,intelligent and green manufacturing.Facing the great needs of advanced equipment manufacturing industry,cutting tools,as one of the main parts of cutting,is the critical to high-end parts manufacturing.However,China’s high-end carbide tools rely heavily on imports,which restricts the process of transformation and upgrading of high-end equipment manufacturing,so it is imperative to realize the localization of high-end carbide tools.Improving tool wear resistance and extending service life are the key to break through the development of high-end carbide tools.This paper proposes the method of using pulsed magnetic field to strengthen cemented carbide aiming to obtain high performance tools.Taking WC-12Co cemented carbide as the research object,the milling behavior of pulsed magnetic field treated carbide tools was studied,including frictional wear behavior of milling tools,tool wear,milling forces and workpiece surface roughness.The action mechanisms of magnetic field on magnetic,mechanical performances and microstructure evolution of cemented carbide were deeply investigated,and the frictional wear and milling mechanisms of pulsed magnetic field treated tools were also clarified.The following research work was carried out in this paper.（1）The frictional wear behavior of pulsed magnetic field treated carbide tool materials was investigated using 316L stainless steel with magnetic response and TC4titanium alloy without response as workpiece materials,respectively.Based on the remanence brought about by the magnetic field treatment,Fe₃O₄magnetofluid was used as the lubricating medium in friction to study the magnetic response between the magnetic lubricating medium,the workpiece material and the magnetized carbide.Pulsed magnetic field treatment of carbide improved its tribological properties against 316L stainless steel.In dry friction,the magnetic treatment reduced the average friction coefficient by 10.4%,the wear of the workpiece by 17.7%and the ball wear area by 16.4%compared to the untreated one.In addition,the application of Fe₃O₄ magnetofluid further enhanced the tribological performance,with almost no wear observed on the carbide balls,a 26.8%reduction in workpiece wear,and a 12.4%reduction in the average friction coefficient.In contrast,during the friction between the magnetically treated carbide balls and TC4,the friction coefficient did not change significantly,and the workpiece wear and ball wear during cutting fluid lubrication were reduced by 5.5%and 11.3%,respectively.When Fe₃O₄magnetofluid and magnetization treatment were applied simultaneously,the workpiece wear was reduced by 33.9%and the ball wear was reduced by 36.4%compared with the untreated balls lubricated by cutting fluid.Therefore,the pulsed magnetic field treated WC-12Co balls had a good friction reduction and anti-wear effect when rubbing 316L,but there was no friction reduction and only a slight anti-wear effect when rubbing TC4,which was enhanced with the addition of magnetic fluid.The mechanism of the pulsed magnetic field in the frictional wear process was that the remanence attracts the abrasive wear debris to form a protective layer on the surface of the workpiece,the oxidation during the friction process,and the increase of hardness due to the magnetization treatment weakens the contact degree.Under the effect of remanence,the magnetofluid will accumulate in the friction area and amplify the lubrication effect.（2）The milling behavior of pulsed magnetic field treated carbide tools for milling316L stainless steel and TC4 titanium alloy was systematically investigated.Dry milling was used for the magnetically responsive 316L stainless steel to study the effect of the pulsed magnetic field,and the non-magnetically responsive TC4 titanium alloy was supplemented with Fe₃O₄ magnetofluid to study the magnetic response in milling.The performance of the pulsed magnetic field treated tool was improved when milling 316L compared to the untreated tool.The magnetically treated tool showed a 15.90%reduction in F_x,13.29%reduction in F_y and 47.6%reduction in F_z.The magnetically treated tool has less wear,more uniform wear distribution on all four teeth,less fluctuation in the milling process,and the best surface quality of the workpiece（63.7%reduction in surface roughness）.When milling TC4,the main cutting force and tool wear of magnetic treatment at cutting fluid lubrication did not change significantly,and the feed force F_x at magnetofluid lubrication was reduced by 20.7%,and the milling tool wear was significantly reduced.It could be seen that the improvement of milling performance caused by pulsed magnetic field treated carbide tools was closely related to the magnetic response.The pulsed magnetic field treated tool reduced the adhesive wear during milling and attracts fine wear debris or magnetic fluid to make the transition from“two-body friction”to“three-body friction”at the milling interface,thus reducing the milling force,improving the stability of the machining process and improving the quality of the machined workpiece quality.（3）The effect of pulsed magnetic field on the magnetic and mechanical properties of cemented carbide was investigated,revealing the strengthening mechanism of pulsed magnetic field on cemented carbide and clarifying that the magnetic response medium was the key to improve the service performance.The“skin effect”and“tip effect”on the hard alloy surface were generated by pulsed magnetic field processing to achieve directional strengthening of the tool,and the domain motion was the reason of magnetic and mechanical properties changes.The magnetic domain rotated and merged during the magnetization process,the average size increased by 17.8%,the saturation magnetization decreased by 61.3%,and the remanence was retained after the magnetic field treatment.The remanence strength of the cemented carbide ball and the milling cutter increased from 0 m T to10.38 m T and 23.38 m T,respectively.In addition,the magnetic domain merging and domain wall migration promoted dislocation motion,which increased the hardness by7.94%and decreased the elastic modulus by 13.11%.The aligned domains are continuous chains of high thermal conductivity,increasing thermal conductivity by4.5%.The enhanced properties of cemented carbide improved the frictional wear behavior and milling behavior.Cemented carbide adsorbed magnetically responsive media（wear debris and magnetofluid）only in the presence of remanence strength;the increase in hardness and decrease in elastic modulus improved the degree of contact of the frictional substrate and attenuated the frictional contact stress of 152.8 MPa;while the increase in thermal conductivity reduced the frictional temperature by 6.2°C and the milling temperature by 16.8°C,respectively.（4）The microstructure evolution of magnetically treated cemented carbide was investigated,and the link between“microstructure-macroscopic properties-service performance”was established.The effects of pulsed magnetic field treatment on the microstructure evolution of cemented carbide such as phase transformation,dislocation density,atomic movement and layer dislocation changes were investigated by quasi-in situ EBSD,XRD and TEM,starting from the mechanism of pulsed magnetic field on the magnetic and mechanical properties of cemented carbide.The results show that the pulsed magnetic field treatment promotes the movement of Co atoms in WC-12Co,the grain surface spacing becomes larger by 2.4%,brings about lamellar dislocation changes,and triggers the conversion of about 1%of FCC-Co to HCP-Co,which improves the magnetic properties of the cemented carbide.In addition,the atomic movement of Co phase increases the dislocation density of cemented carbide by 13.3%,which improves the mechanical properties of cemented carbide.The analysis of the magnetic and mechanical properties and microstructure of pure W and pure Co clarified that the mechanism of the effect of pulsed magnetic field treatment on WC-12Co was achieved by the atomic movement,phase transformation,increase of dislocation density and merging of magnetic domains of Co phase.The“pulsed magnetic field-microstructure-magnetic and mechanical properties-frictional wear behavior-milling behavior”was constructed by combining the effects of pulsed magnetic field treatment on WC-12Co cemented carbide.So,this evolutionary relationship from“microstructure”to“macroscopic properties”to“service performance”has been established.In summary,the pulsed magnetic field treatment triggers the magnetic domain motion,the atomic movement of ferromagnetic Co phase,and the increase of grain surface spacing,which has the effect of promoting the phase change of Co phase and increasing the dislocation density on the organization of cemented carbide.This enhances the magnetic and mechanical properties of cemented carbide,which improves the frictional wear and milling performance of the tool and enables the strengthening of cemented carbide tools.The strengthening of carbide tools by pulsed magnetic field can contribute to the development of high-end carbide tool industry in China.