Study On The Simulation Of Metal Ring Cold Rolling Process

As the requirement demand of product quality become higher and higher, and the product development cycle is constantly shortened, the experience based and pure analytical method can not meet the demands of application and study of cold ring rolling process. Therefore,the study on numerical simulation method is an urgent task. Because cold ring rolling process is a complicated and integrated process with the nonlinearity of material, geometry and boundary,its process simulation is very difficult. The study on the numerical simulation method of the process and developing a special software system have become an urgent need of the development of new products, new equipments and die structure optimization.This study is supported by the National Natural Science Foundation Key Project, metal cold ring rolling forming mechanism and process equipment research (No. 50335060). The forming simulation algorithm and key technologies are studied. A ring cold rolling process simulation system has beed developed.The elasto-plastic dynamic explicit finite element analysis method for ring rolling process simulation is studied. Based on the kinetic differential equation of cold ring rolling process, geometrical equation, Mises isotropic hardened subsequent yield function, and stress and displacement boundary condition, the dynamic explicit finite element equation and its central difference solver algorithm are established. The element minimum nominal length is calculated. To ensure the analysis stability, the critical time-step and the scale ratio of the time-step is provided.Since the contact area is small in the cold rolling process, a single point contact is easily to appear, and the hourglass is difficult to control. To control the hourglass, a new control method is proposed. User defined control factor is not required any more in this method. Hourglass resistance force is calculated in accordance with the strain of the element. Failed simulation resulted from the lack of experience or complexity of the system is avoided. The hourglass energy is decreased by the automatically determined hourglass force so that the energy balance of the system and accuracy of the calculations are improved.According to the cold ring rolling contact characteristics, a two-step method including global search and local search is adopted. The contact judgment time is reduced to the level less than 10% of the total computing time. The punishment method is used to calculate the contact force.In order to improve simulation accuracy, remesh technology of the element are studied in the study on ring rolling process simulation. The field variables are transferred to the new elements from the old ones after remesh to ensure the accordance of the field variables in the remesh.A dynamic explicit parallel algorithm is proposed. The structure of the dynamic explicit algorithm is studied. With the paralleled solver based on shared memory, computation acceleration ratio can reach more than 1.9. The solver has high accuracy after paralleled. The simulation results difference between the parallel and sequential solver is only 0.1%.Based on the theoretical research, a special simulation system has been developed for cold ring rolling process for the first time. The system can simulate metal flow in the ring rolling process. The simulation system is consists of pre-processing module, solver module and post-processing module. In the pre-processing module, the geometric model of ring rolling system can be created and discretized. The ring rolling model can also be imported from CAD/CAE data format. The forming parameters, remesh parameters, hourglass control method can be defined in the module. In the post-processing module, the results data is read in, and the variation of the field parameters, such as stress, strain and displacement, is displayed in the ways of cloud, contour or video.The cold ring rolling process is simulated with the newly developed simulation system. Compared with the experimental results, the simulation results are proven to be accurate. The simulation results of the new ring rolling process simulation system is compared with the simulation results of the famous software ABAQUS to verify the reliability of the simulation system.