Experimental Study On Lapping And Polishing Process Of Carburized And Hardened Steel 18CrNiMo7-6

With the development of domestic manufacturing industry and the development strategy of “ Made in China 2025 ”,high-end equipment manufacturing has put forward higher requirements on the surface quality and performance of key components.Lapping technology,as a precision machining process,is designed to remove the subsurface damage layer left by the previous process to achieve the desired surface quality and flatness.However,the lapping process mechanism is more complicated,and needs to be further studied in terms of material removal mechanism,process parameter optimization and control,and on-line detection.18CrNiMo7-6alloy steel is widely used in high-speed heavy-duty gears and other fields for its good mechanical properties and process performance.Therefore,it is important to study the influence of lapping and polishing processes on the surface integrity of18CrNiMo7-6 alloy steel.In this paper,18CrNiMo7-6 alloy steel before and after carburizing was used as the research object.The lapping and polishing orthogonal and single factor process tests were carried out to study the influence of the lapping process parameters such as lapping pad particle size,lapping pressure,lapping speed and lapping time etc,both the polishing process parameters such as polishing pressure,polishing speed and polishing time etc on the removal rate of 18CrNiMo7-6 alloy steel and surface integrity indexes such as surface roughness,residual stress,hardness and surface morphology,which to obtain better combination of lapping and polishing process parameters.The results show that:(1)With the particle size of the lapping pad from 400 # to 3000 #,the surface roughness of the workpiece before and after carburizing was reduced,the lowest was Ra17 nm and Ra15 nm respectively;the material removal rate of the workpiece was reduced,and the maximum material removal rate was 2.9 m/min and 1.164 m/min;the surface residual stress values increase,the surface after carburizing can be raised from the large residual compressive stress to the residual tensile stress,and the surface before carburizing still showed residual compressive stress;Surface hardnesswas slightly reduced.With the increase of lapping pressure,lapping speed and lapping time,the surface roughness value of the workpiece before and after carburizing was reduced,the surface residual compressive stress value was increased,and the surface hardness was slightly improved.Under the same conditions,the surface roughness value of the workpiece after carburizing was generally smaller than the surface roughness value of the substrate,and the residual stress value of the carburized surface was generally larger than the residual stress of the substrate surface.The hardness and wear resistance of 18CrNiMo7-6 steel after carburizing were greatly improved,and the degree of plastic deformation during grinding was an important cause of the above phenomenon.(2)With the polishing pressure from 0.1 MPa to 0.3 MPa,the material removal rate of the workpiece surface increases before and after carburizing,the maximum was 0.068 m/min and 0.058 m/min respectively;the surface roughness was reduced,the lowest was Ra12 nm and Ra8 nm;surface residual stresses increased,and all were residual compressive stresses,with maximum values of-447.07 MPa and-402.37 MPa,respectively.With the increase of abrasive grain size,the material removal rate,surface roughness and surface residual stress of the workpiece increase before and after carburizing.As the polishing speed increases,the workpiece material removal rate and surface residual stress increase,and the surface roughness of the workpiece reduces.With the prolongation of polishing time,the material removal rate of the workpiece increases first and then decreases,the surface roughness decreases,and the residual stress increases.