Optimization Of Rail Milling Parameters Based On Finite Element Method

As a tool to solve rail surface defects and control rail profile,rail milling and grinding machine is more and more widely used.In the process of rail milling repair,it is often accompanied by high milling force and milling temperature,which may affect the efficiency and quality of operation.Excessive’repair’will also lead to the decrease of rail life.Therefore,the parameters in milling repair need to be reasonably selected.In this paper,the orthogonal experiment is designed,and the finite element method is used to simulate the rail milling process.The milling force data of rail under different working conditions are obtained.Through range analysis,the optimal solution of milling speed and operating speed in milling parameters is selected.At the same time,the obtained optimal solution is taken as the determined parameter,and the combined experiments of different crack depths and milling quantities are designed.The stress field state of rail milling and wheel-rail contact model is analyzed by finite element method,and the optimal milling parameters under different crack depths are obtained.The specific research work and conclusions of this paper are as follows:(1)In this paper,the 75 kg/m heat-treated U78Cr V rail is taken as the research object.The Johnson-Cook constitutive model is selected for the finite element simulation of rail milling,and the USDFLD subroutine method is used to simulate the heat treatment layer and work hardening effect of rail.Secondly,the finite element model of rail milling with dynamic explicit algorithm is established by using the finite element simulation software,and the equivalent model of milling cutter head is designed.The initial residual stress field of rail is set according to the existing research parameters.(2)Using the mathematical model of rail milling surface roughness,the relationship between milling speed and operating speed is calculated:milling speed is not less than 16 times of operating speed to ensure that the roughness meets the standard requirements.Secondly,the selection range of milling parameters is determined according to the established parameter relationship.(3)Design single factor experiment and orthogonal experiment with 3 factors and5 levels in the range of parameters.The variation of milling force and milling temperature with milling parameters was analyzed by single factor experiment.The results show that the milling force decreases with the increase of milling speed and increases with the increase of milling speed and milling amount.Milling temperature increases with the increase of milling speed,operating speed and milling amount,but the effect of operating speed parameters on milling temperature is not obvious.The results of orthogonal experiment data were subjected to multiple linear regression,and the mathematical model of rail milling force was established and the correlation was tested.Through the range analysis of orthogonal experimental data,the primary and secondary influence of milling parameters on milling force is obtained:milling depth has the greatest influence,milling speed takes the second place,and working speed has the least influence.The optimal milling parameters are obtained as follows:milling speed v_c=3900 mm/s,working speed v_f=170 mm/s,milling amount a_p=0.4mm.(4)Taking the milling speed and operating speed in the optimal milling parameters as known parameters,the combined experiments of different crack depth and milling amount are designed.The stress field at the crack tip of rail with different crack depth under different milling conditions is analyzed.The results show that the influence depth of different milling parameters on the residual stress field distribution of rail subsurface after milling is different.Then,the wheel-rail contact model is established,and the results of all working conditions of the crack rail milling model are taken as the initial conditions for 10 times of wheel loading.The stress field at the crack tip under each working condition is analyzed,and the depth of the repairable crack under each milling amount is obtained.The milling parameters can be reasonably selected according to the condition of the rail crack disease.The results show that when the milling speed v_c=3900 mm/s and the operating speed v_f=170mm/s,the milling amounts are 0.4 mm,0.6 mm,0.8 mm and 1.1 mm,respectively.The crack tip with depth of 0.8 mm,1.1 mm,1.5 mm and 2.5 mm can be presented as compressive stress field,which inhibits crack growth.When the crack depth is larger,the stress field at the crack tip is mainly affected by the initial residual stress of rail.