Numerical Simulation And Optimization On Rotary Forging Process Of Hollow Steering Shaft Based On Forge

The steering shaft is an important part of the steering system of the car.The function of steering shaft is to transmit the torque between the steering wheel and the steering gear.It is required to have certain rigidity,fatigue resistance and energy absorption function during the service.The traditional manufacturing process of automobile steering shaft is complicated and the material utilization rate is low.In contrast,the use of rotary forging technology to manufacture automotive hollow steering shaft can not only reduce the weight of the vehicle,but also save fuel and reduce pollutant emissions.Based on this purpose,the numerical simulation and orthogonal optimization design were used to obtain the optimal process parameters of the full hollow steering shaft through rotary forging,and the microstructure and performance of the prototype product were tested,too.Research as follows:(1)According to the drawing of automotive hollow steering shaft,the part structure and forming characteristics of hollow gear shaft were analyzed.The forging steps were worked out,and the mold used for rotary forging was designed based on the principle of volume invariance when forging.Then three-dimensional model of the blank and mold were established on the UG software.At last,importing the three-dimensional model into Forge2011 software to rotary forging numerical simulation of hollow gear shaft after setting up some related parameters.(2)In the process of numerical simulation,the effect of the relative angle of the hammer,the radial pressing of hammer,the velocity of the hammer,the axial feed of the blank on the material folding defects,hammer load,effective strain and effective stress after forming the steering shaft were studied.The results show that the load of the mold is mainly affected by the radial downward pressure.The equivalent stress of the material is obviously affected by the the radial pressing of hammer,the velocity of the hammer,the axial feed of the blank.At the same time,the impact of the radial pressing of hammer,the velocity of the hamme and the axial feed of the blank on the equivalent strain of the material is also large.There is no obvious linear relationship which the relative angle of the hammer impact on the equivalent stress and equivalent strain of the material.However,the equivalent stress and equivalent strain of material correspond to each other in variation,That is,the equivalent strain of the material is larger when the equivalent stress is larger,and the equivalent strain of the material is smaller on the contrary.(3)The optimal process parameters of the fully hollow steering shaft by the rotary forging are obtained through orthogonal test: the relative angle of the hammer head is 18°,the radial pressing of hammer 1mm,the hammer speed is 5 mm·s-1,and the axial feed of the blank is 0.5 mm.Then,the full hollow steering shaft of the automobile was formed by the numerical simulation software according to this group of process parameters.Through the analysis of the load of the mold,the equivalent strain of material,the equivalent stress of material and the folding.The results show that the stress and strain distribution of the fully hollow steering is reasonable,and there is no defect such as material folding and cracking.Therefore,the forging effect optimization of the full hollow steering shaft by orthogonal optimization method is great.(4)Finally,the steering shaft was sampled by the optimal process parameters.The sample surface of the full hollow steering shaft is smooth and round,and transition is average between each forming sections.Moreover,the quality of inner surface and the shape of the internal teeth formed by rotary forging is regular.The detection results show that the static torque of the sample is 320 N·m,and the fracture of low load fatigue is 4?105 times when the load is 35 N·m,which achieved the national standard.Then several key parts of the sample were sampled for the test of hardness and microstructure under metallographic microscope and scanning electron microscope.The results of hardness test show that the average hardness of the deformation zone is 201 HV,significantly higher than primitive area which is 178 HV.And the results of microstructure test show that,in the deformation zone the grains become finer and the material density is significantly improved by rotary forging.On the other hand,a fibrous structure with a preferred orientation is formed in the material by rotating forging,so that the structure of the deformation zone has a strong texture,which greatly improves the final performance of the product.