Research On Center Defects Of Cross Wedge Rolling Shafts Based On Modified GTN Model

Cross wedge rolling technology is a new process for producing shaft parts,which is widely used in the transportation industry because of its higher efficiency and higher material utilization and so on.However,the defects in the center of the rolled parts limit the promotion of this process.Cross wedge rolling is generally used as transmission components to bear heavy and alternating working load,and internal defects are not allowed.Therefore,the research of the center defects is of great significance for the further promotion of the process.Most of the metals used in actual production are multi-phase materials.The micro-holes and micro-cracks that originally exist in the material have an important influence on the evolution of the damage of the rolled parts.The modified GTN model can be used to analyze the metal fracture behavior by linking the damage evolution with the tensile and shear processes of the material.Applying the modified GTN model to the research of the center defects is of great significance to reduce defects and optimize die parameters.Firstly,the numerical algorithm and subroutine flow-process diagram of modified GTN model are given.By establishing the uniaxial tensile finite element simulation of cylindrical rods and shear plates,the verification model can be used for the stress state dominated by the tensile load or the shear load.And then,the stress-strain curve and shear fracture strain of 25 Cr Mo4 steel were obtained through high-temperature tensile test of bar and shear plate.The fracture mechanism of metal under different stress states was obtained by observing the fracture of the specimen after breaking.Orthogonal test was designed,the damage parameters of the modified GTN model of 25crmo4 steel were obtained by combining the finite element reverse solution with the microscopic image analysis.Finally,the feature modeling method of cross wedge rolling die is completed in Creo software.Through the simulation analysis of cross wedge rolling,it is concluded that the main causes of the center defects are the excessive axial tensile stress and the alternating shear stress.The simulation model of cross wedge rolling with coupling damage is established based on the characteristics of stress and deformation of the workpiece center and the modified damage model,and the evolution law of each damage component in the rolling process is obtained.Based on this analysis,the influence of different forming parameters on the damage of the center of the rolled piece is provided,which provides a reference for the rational design of the die in the actual production and reduction of the defects in the center of the rolled piece.