Research On The Surface Integrity Of Gear Dedendum By Ultrasonic Rolling

As a key part of the transmission system,gears play an important role in industrial production.In recent years,in the fields of aerospace,new energy vehicles and high-speed trains,gears should possess excellent fatigue resistance to satisfy the high reliability and long life under the serious conditions of complex loads caused by high speed,heavy loads,and large temperature differences.The fatigue resistance of gears is closely related to the surface integrity including the surface roughness,hardness and residual stress of the tooth surface.To improve the surface integrity of the dendum,based on theoretical analysis,experiments and simulation,the mechanism of surface integrity and optimal process parameters in ultrasonic rolling dedendum were studied.The main research contents and results were as follows:(1)Based on the force analysis of the workpiece during the ultrasonic rolling process,the rolling pressure on the dedendum during the ultrasonic rolling was decomposed into the static force and the dynamic force according to the load source,and the Hertzian contact theory and the law of conservation of energy were employed to establish the mechanical model for the ultrasonic rolling.(2)By designing a compound horn with a distinctive conical transition the constraints of the spatial geometric position was satisfied in rolling the dedendum.Based on the simulation analysis,the horn was optimized.The acoustic system to roll the dedendum was designed,and its outputs of the vibration parameters were tested.The results showed that the acoustic system satisfied the requirements in ultrasonic rolling dedendum.The acoustic system was installed in a vertical machining center to build an ultrasonic rolling platform.(3)Single-factor experiments were used to investigate the influences of the rolling processing parameters(the rolling deep,the rolling speed and the row spacing)on the surface integrity indexes(the surface roughness of dedendum,the residual stress,and the hardness)after ultrasonic rolling.The test results showed that the residual stress of the dedendum increased by 12%～28%,and the hardness increased by 13%～26%,and value of the surface roughness Ra reduced by 19%～ 47% respectively compared with the ordinary rolling under the same processing parameters.The order of the influence of rolling parameters on surface integrity was the rolling pressure,the rolling speed,and the line spacing.(4)Analytic hierarchy process was adopted to improve the algorithm of the gray correlation analysis,and the gray correlation degree was calculate based on the orthogonal test results,to establish the relationship between the surface integrity and the gray correlation degree.And the mathematical models between each rolling parameter and surface integrity index are established respectively.To optimize surface integrity,the optimal process parameters were solved.The results of the ultrasonic rolling test showed that the residual stress of the dedendum after optimization increased up to-596.12±10MPa,and the hardness increased to 604±9HV,and the value of surface roughness reduced to 0.36±0.05μm.The results show that more excellent surface roughness,hardness and residual stress index can be obtained by ultrasonic rolling,which provides an efficient new method for dedendum surface strengthening.