Analysis And Control Method Of Elastic Deformation Behavior Of Die During Helical Gear Precision Forming

Helical gears are one of the more widely used components in mechanical transmission.The tooth profile with helix angle is advantageous for achieving a smoother transmission and a higher transmission efficiency.At present,the production method of helical gears is mainly machining,and this traditional production method generally has the shortcomings of material waste,cutting off metal flow lines,,and low efficiency of production.The characteristics of precision forging technology that utilizes the plasticity of metal to form the workpiece just can solve the above problems and get better performance gear parts.However,due to the complex geometry of the helical gear,the forming load is too large which resulting in die elastic deformation.And the excessive forming force makes excessive elastic deformation energy to accumulate on the surface of the workpiece,which may result in elastic recovery of workpiece after ejecting.Therefore,in order to improve the accuracy of the workpiece,it is very essential to study the elastic deformation of the forming die and the elastic recovery phenomenon of the workpiece.Firstly,the forming loads are studied.The upper bound method is used to establish the kinematically admissible velocity field on a single tooth,and the formula for calculating the forming load was obtained and validated its reliability through finite element simulation in Deform-3D and experiment.And then the forming force was used as a known boundary condition when analyze the stress distribution on the contact surface between the workpiece and die using modified slab method.The stress calculation formulas in the addendum and transition region of the die were obtained.At the same time,the stress analysis of the die is simulated by finite element method,which gives the stress distribution law on the side wall of the die.The reliability of the stress calculation formulas is verified by comparing the theoretical value with the simulation result.Based on the theoretical calculation formula,two methods for determining the elastic deformation values of the involute toothed area and the root circle area of the die are proposed.Meanwhile,the elastic recovery values of the involute toothed area and the addendum circle area of the forged piece are obtained by means of linear fitting.After the die elastic deformation values and the component spring-back values are superimposed,they are used as the amount of shape modification to compensate the mold inversely.The simulation of the forming process was repeated and the changes in the tooth profile of the workpiece before and after the optimization of the mold were compared.The study found that the error between the theoretical value of forming force and the simulation result was within 5%;The error between the theoretical and simulated values in different parts of the tooth basically meet the engineering requirements.The error of radial stress at the addendum circle is between 5.9% and 13.7%,and that of circumferential stress in the transition zone is between 7.25% and 16.3%.In addition,the simulation results show that the stress stress on the die is different at different parts.The radial elastic recovery of the workpiece increased with the increasing of the tooth radius.After the modification of the die by the displacement translation method,the radial and circumferential errors of the workpiece are smaller and the tooth profile is more closer to the standard,so the forming accuracy of the helical gears is improved.