Numerical Calculation Of Residual Stress Of Carburizing-queching And Grinding Hard Tooth Surface

Gears are the core transmission elements in machine for manufacturing.Under the same material properties,the excellent surface quality and accuracy characteristics will be in favor of improving the service characteristics and the service life of gear.It is the primarily means to adopt heat treatment and grinding to improve the surface quality and the accuracy of gear.Residual stress distribution at the tooth surface is an important factor influenced the fatigue life.The calculation and test accuracy of the residual stress will affect the contact fatigue life prediction of gear.Currently,there are many problems such as long test period,high test cost,and being easy to damage gears.To solve those problems,a numerical calculation was presented.The precise geometry model is a prerequisite for precise numerical calculations.Carburizing-quenching and grinding have a large impact on the magnitude and distribution of participating stresses when manufacturing.This paper analyzes the influence of Carburizing-quenching and grinding of the low-speed and heavy-load gear on a gear service life.Firstly,this paper investigates the generation mechanism and influencing factors on residual stress by carburizing-quenching and grinding.Secondly,this paper presents a numerical model for the thermo-elasto-plastic behaviour of an isotropic material.Thirdly,this paper presents a numerical simulation for studying the impact on the performance of gear concerning the process-related parmeters,which uses the analytical method.Finally,calculate the grinding stress of the helical gear with initial residual stress for improving the precision of grinding.The main contents are as follows:(1)A method in geometric modeling is proposed based on the helical gear form grinding.Combined with gear form grinding kinematics principles,Equations of grinding wheel profile and grinding wheel additional radial motion are derived according to tooth segmented profile modification and longitudinal modification.Since the contact line equation is a transcendental equation,the relationship between the installation angle and the shape could not be expressed by explicit functions,which made it difficult to obtain the optimal shape.This paper firstly took three evaluation parameters of the shape,shift and offset as the objective function as well as the installation angle as variables then the contact line optimization model was establish.Secondly,a Newton iteration was introduced to solve the evaluation parameters.The corrections are determined through an optimization process that targets minimization of the tooth flank errors.A numerical of gear grinding is presented.(2)A numerical calculation in heat treatment is proposed before form grinding.In this study,numerical simulations,using the general-purpose process simulation software Deform,were carried out for the design of the helical gear.Deformation of helical gear during heat treatment of carburized quenching was analyzed with a numerical method,incorporating coupled calculations of thermal conduction,carbon diffusion,phase transformation and thermal stresses.The carburizing process of the gear was simulated by taking into account the practical carburizing and quenching techniques of the gear and by solving the diffusion equation.The carbon content distribution in the carburized layer was obtained.Based on the results,the quenching process of the gear was then simulated using the metallic thermodynamics and FEM.Microstructures and stress distributions of the gear in the quenching process were simulated;it was found that the carburization remarkably affects the quenching process.With the analysis,the effect of parameters in carburizing and quenching on the deformation was investigated.Finally,establish deformation control methods for gear heat treatment.(3)Numerical calculation of forming grinding with initial residual stress is established.The study focused on the surface intergrity issues associated with grinding of gear and the structural stability of the specimen at high temperatures,mainly involving the microstructural changes and residual stress relaxation.Consider the impact of carburizing and quenching on grinding,the deformation caused by carburizing and quenching is superimposed on the grinding process in the form of initial residual stress.Using the verified correctly grinding calculation model,the stress distribution includes the tooth surface temperature field and the residual stress field are calculated after grinding with initial residual stress.The influence of process parameters on the gear performance is analyzed and the stress and deformation of the gear after grinding is obtained.