Research On Material Removal Mechanisms And Surface Integrity For Abrasive Belt Rail Grinding

The rapid development of modern rail transit systems such as high-speed railways,heavy-haul railways,and urban subways has led to the increasing demand for track maintenance and the increasingly tight operating time.It is driving the evolution of rail grinding equipment and technology to be more efficient,intelligent and diversified.The abrasive belt manufacturing technology as well as abrasive's performances has obtained improvement and innovation in recent years.Subsequently,a novel rail grinding technology based on abrasive belt grinding technology-abrasive belt rail grinding(ABRG),emerged.ABRG includes elastic grinding,cold grinding,efficient grinding,etc.,and has shown promise in its engineering application.However,we lack solid theoretical understanding to support key technologies such as grinding equipment design,process parameters selection,and grinding pattern formulation,which greatly hinders the development and promotion of abrasive belt rail grinding technology.To address the challenge,in this paper,the material removal mechanism and surface integrity of ABRG were studied through focusing on the physical essence of belt grinding-the complex contact behavior among the contact wheel,the abrasive belt,and the workpiece.Firstly,based upon the significant difference among the elastic modulus of the contact wheel,the rail and the abrasive belt,the 3D contact problem among them was transformed into the 2D problem between an elastic sheet surrounded rigid circle and the rigid plane.Thereby,the contact model for the concave and normal contact wheel interacting with the ideal cylindrical rail surface was established.It is found that the contact spot is affected by the contact force and the curvature matching between the contact wheel and the rail,and it can be classified into three types,namely elliptical,double triangular and saddled shape.On this basis,the contact boundary and contact stress for the contact conditions,which involve arbitrary grinding positions or distinct curvature changes of rail profile,were acquired through a numerical method.The validity and accuracy of the above contact models were verified by FEM simulations and contact experiments.Furthermore,against the randomness of shape and distribution of grains,the grain's cutting edge was simplified as a cone with a hemispherical tip,based on which characteristics of the grains on belt were statistically analyzed.Then,the probability density function of the grains' protrusion height distribution was obtained.Combined with the single grain's cutting force equation,the mathematical relationship between the contact pressure per local unit area and the maximum cutting depth of grains was derived.Based on the macroscopic contact model,the material removal model of ABRG was developed through force balance equation.The material removal model was verified by the ABRG test bench.The results show that the average grinding depth error is less than 10%.It is also found that the grinding depth grows nonlinearly with a decreasing slope as the contact force rises,increases linearly as the belt speed ascends,and decreases inversely as the train speed rises.Afterwards,the abrasive belt topography was numerically created by 2D digital filtering technology.The discretization method was introduced to transform the overall belt grinding process into several localized plane-grinding processes carrying different contact pressure.The nominal grinding depths of grains on local belt at different moments were calculated,which contributed to extracting the envelope of the projection set formed from effective grains in the grinding direction.The simulation of the roughness profile of the ABRG based on the forming mechanism was realized,and the 2D roughness value was obtained.The simulation results show that the contact force has a distinct positive correlation effect on the Ra and Rsm both,and the influences of the belt speed and the train speed on that are inconspicuous.The effectiveness of the above rules and simulation method was verified by grinding experiments.Finally,through the grinding experiment,the influences of grinding process parameters on residual stress on rail surface were experimentally investigated.Tensile residual stress was found in the grinding direction,while the residual stress in the other orthogonal direction maintained mainly as compressive stress.A 3D FEM simulation of grain scratching based on thermo-mechanical coupling method was developed.Effects of contact surface friction,grain's tip radius,grain's protrusion depth,grain's cutting speed and grain's rake angle on the residual stress distribution in the rail sublayer were revealed.The formation mechanism of residual stress in belt grinding was further investigated.The FEM simulation of residual stress involving adjacent grains scratching was carried out.The variation of the residual stress field between the preceding scratching and the subsequent scratching was observed and discussed.