Modelling Of Three Dimensional Surface Topography And Residual Stress In Hard Milling Of H13 Steel

Mold processing is the main core technology and key process equipment of modern manufacturing industry and enterprises in China.The advantages of mold forming include high production efficiency,good quality,low cost,saving energy raw materials and so on.As a typical air-cooled hardening hot work tool steel,H13 steel(equivalent to domestic 4Cr5MoSiV1 steel)is widely used in the manufacture of hot extrusion die,hot forging die and die casting die because of its good mechanical-thermodynamic performance.Most die failures originate from the surface and are closely related to the surface quality such as the surface topography,surface roughness and surface residual stress.With the development of high speed machine tool and high performance cutting tool technology,hard cutting technology has been applied more and more widely in die industry.Therefore,the modeling and control of surface topography and residual stress by studying the mechanism of hard cutting is of great significance for the popularization and application of this technology in die manufacturing industry.Hard milling of H13 steel is taken as the research object in this thesis.Based on analytical modeling,theoretical analysis and milling experiment,a 3D surface topography model for hard milling was established and used to research the effects of cutting parameters on surface roughness and power spectral density.Besides,an analytical model of residual stress in hard milling was established.The main research contents are as follows:First,a 3D surface topography model of hard milling was established,and an optimal cutting parameter optimization scheme based on surface roughness amplitude parameters and metal removal rate was presented.By deducing the relative motion trajectories of cutting tool and workpiece in hard milling process,a mathematical model of 3D surface topography was constructed and verified by experiments.Then the model was used to carry out simulation experiments to research the effects of the product value(p)and ratio(r)of feed per tooth fz and radial depth of cut ae on surface amplitude parameters.It was found that the influences of p and r on surface roughness amplitude parameters are different using different milling methods.Under the condition of circular indexable blade milling,the surface roughness trend with p and r is similar to‘exponential function'.However,for ball-end milling,the profile of surface roughness with the change of r value is similar to the 'check function'.By introducing p and r,the surface roughness was related to the metal removal rate,and a cutting parameter optimization method considering both of them was proposed.Secondly,the effect of milling parameters on power spectral density(PSD)was researched based on the 3D surface topography model.PSD of the surface obtained by experiment and the surface constructed by the simulation model were compared.The results show that the surface topography model in this paper can be used to accurately calculate the surface PSD consistent with the actual situation.The influence of cutting parameters on the surface PSD was studied.For the 1D PSD,it was found that the first peak in step-over direction is affected by ae,and the peak in feed direction corresponds to the effect of fz,while the second peak in step-over direction is the result of the joint action of fz and ae.The wavelength in the feed direction corresponding to the peak value of the 2D PSD is approximately equal to the feed per tooth,while the wavelength in the radial cutting depth direction is only affected by the p value.The number of angular spectral peaks on machined surface is approximately equal to the number of residual heights in the 3D surface topography.The value of p has little effect on the surface energy spectrum distribution direction,and the main factor that affects the surface energy spectrum distribution direction is r.Finally,an analytical model of surface residual stress in hard milling was established based on elastic-plastic mechanics,metal cutting principle and contact mechanics.The material flow stress in the primary shear zone of hard milling process was calculated by constructing the auxiliary plane,defining the auxiliary angle,and using the non-uniformly distributed shear zone model.Modelling of cutting temperature was conducted with homogeneous coordinate transformation and surface heat source method.The temperature rise of a point in the workpiece at any time during the process of milling can be obtained by using this model.By taking the above calculation results as the input load,the process of elastic loading,plastic loading/unloading and stress release of the workpiece was realized by using the principles of elastic-plastic mechanics and contact mechanics.And the analytical model of residual stress on the surface of hard milling was constructed.The prediction accuracy of the model was verified by experiments.The research in this thesis can provide data support and theoretical basis for the characterization and research of geometric and physical mechanical characteristics in hard milling,and the selection of cutting parameters based on surface roughness,power spectral density and residual stress.