The Study Of Isothermal Extrusion Based On Numerical Simulation

In the conventional hot extrusion of metallic materials, the temperature of the workpiece varies during the whole extrusion process, leading to the non-uniformity of the product dimensions, shape, microstructure, properties and so on. However, the isothermal extrusion is an efficient method which can reduce this kind of non-uniformity. Presently, the closed-loop control isothermal extrusion technology has already became the most advanced technology method for control of the extrusion exit temperature. But it is difficult to popularize and apply in the actual extrusion industry due to the inaccuracy of the temperature measuring equipment and the low efficient of the control system. Therefore, this article proposed the method which was a FEM simulation model based on the increasing type numerical PID algorithm. In this model, the real time extrusion ram speed was adjusted according to the simulated exit temperature at the real time in order to obtain the simulation isothermal extrusion. The ram speed curve which obtained from the simulation isothermal extrusion could be applied to realize the real isothermal extrusion. At the same time the ALE arithmetic FEM method in DEFORM-3D software package was used to simulate the steady state extrusion of large sized cross section extrusion, to save computation resources.Firstly, the conventional iso-speed extrusion process of the AZ31 magnesium alloy by the constant speed was investigated by means of FEM simulation. Results showed that the simulation process was approach to the real process. According to comparison between the simulation and experiment results, the simulation was reliable and could be used for guiding real extrusion process design. Afterwards according the FEM simulation based on the increasing type numeral PID algorithm simulated the isothermal extrusion processes of the AZ31 magnesium alloy of +-section and the square tube were. The simulation results were compared with the iso-speed extrusion process which had the average ram speed. Results showed that using the PI algorithm control, the simulation of extrusion processes about different profile could achieve the isothermal extrusion and the simulated workpiece temperature was controlled in a small range of±2℃. At the same time, the obtained ram speed curve for isothermal extrusion could afford a very useful guideline for the extrusion industry; the temperature control was more necessary for the extrusion process of the big reduction ratio just as this square tube extrusion, which could obviously improve the bad effect to product because of the high temperature rise. Simulation results also showed that the temperature distribution in the workpiece and die in the isothermal extrusion were more uniform than in the iso-speed extrusion process, and it was more availability to implement the homogeneity of the produce quality along the length and the section direction, and it was beneficial to prolong the life of die. Finally the steady state extrusion processes of large-sized of the rectangular pipe and the circular pipe were simulated using the ALE arithmetic of DEFORM-3D, to save computation resources and enhance calculated efficiency. The simulation results showed that the distributions of the temperature and the velocity reflect the actual situation in real extrusion process. The simulation results were useful for guiding die design.