Study On The Mechanism Of Folding Defects In Rotary Extrusion Forming Of Inner Ring Cylinder

Inner shell of magnesium alloy as a typical light structure is widely used in aerospace,aviation field.The traditional processing methods have many disadvantages,such as high reject rate,poor performance and high cost,which can not meet the requirements of lightweight and high performance.Based on the structural characteristics of the inner shell and the deformation characteristics of the magnesium alloy,a rotary extrusion method was proposed to realize the integral plastic forming of the component.Rotary extrusion can reduce the load and improve the formality and refine grain,weaken the anisotropy and streamline rib complete etc..However,the particularity of the loading mode leads to easy folding defect.In this paper,finite element numerical simulation and simulation experiments were used to study the formation mechanism of folding defects during the process of rotating extrusion of magnesium alloy inner ring bars.The influence of mold structure parameters and forming process parameters on the formation of defects was revealed.According to the structural characteristics of the inner ring cylinder,the rotary extrusion process was developed and the theoretical analysis was carried out to obtain the stress,strain and metal flow in each area.It was founded that the deformation zone is not only under the three dimensional compressive stress state but also by the shearing force.It can not only give full play to the plasticity of the magnesium alloy but also produce the plastic deformation of the micro-area,so that the performance can be greatly improved;Which provides a theoretical basis for the study of folding defects.In order to further understand the generation of the folding defects,the numerical simulation was carried out to study the rotary extrusion process of the inner ring cylinder.The value of the axial load extremum,the radial load extremum and the forming torque extremumis 57.1kN,57.6kN and 2867.1kNmm,respectively.The equivalent stress and strain distribution characteristics are obtained.The equivalent strain of the wall and the inner ring is large,and the grain was refinement,which effectively improved the overall performance of the component.Based on the research,the reason for the formation of the folding defect was the the unreasonable design of the mold structure and the process parameters,which increased the resistance of the radial deformation.The velocity of the metal of the convex was lower than that of the metal of edge leading to the folding defect.The metal stacks were formed on the side of the punch working belt,and the folding defects were generated with the unformed metal.The influence of the mold structure and the process parameters on the folding defects was determined,and the folding limit diagram was drawn to provide the simulation basis for the actual production and experiment to avoid the folding defects.According to the characteristics of metal flow and the reason of folding defects during the process of rotary extrusion,the simulation experiment was designed to verify the accuracy of simulation.The simulation results showed that the reliability of the numerical simulation results is verified by the thermal simulation experiment of the Gleeble-3500 hot compression simulation machine.