Optimized Structural Design And Basic Manufactural Study Of Ceramic Extrusion Die

From the ceramic with highly brittle and poor tension ability, in order to improve useful life of ceramic die and prevent early longitudinal and transverse crack, with target function that the ceramic do not have tensile stress and outer hoop just yield, theoretical calculation of ceramic-steel combined die was further derived. Ceramic die was simulated with finite element analysis software, and also ceramic die was prepared by the hot pressing technique.Based on the elastic mechanics theory of thick wall cylinder, the tangential stress and interference value of combined die was derived. The results show that previous method which ignores the difference of elastic modulus between ceramic and steel material enhance pre-tightening force of combined die and compressive stress of internal wall of ceramic die when driving tangential stress of ceramic die without considering contact pre-tightening force of combined die. For example with three layers combined die, a method of combining the finite element numerical simulation and the orthogonal experiment was studied. Finally the optimal data of the orthogonal experiment was calculated by the theoretical formula, and also numerical simulation results and the theoretical solution were compared. The results show that theoretical formula better express stress of ceramic-steel combined die.By selecting nano-micro ceramic material ZrO₂/TiB₂/Al₂O₃, based on static structure analysis of finite element analysis software ANSYS, the radius and magnitude of interference vlalue of ceramic die and outer rim of combined die was optimized. The friction analysis was studied by using finite element analysis software ANSYS/LS_DYNA. The results show that with the increase of friction coefficient lateral pressure and tensile stress of ceramic were continually increased. Transient thermal analysis was studied on combined die and the results show that with the extrusion temperature increases, maximum tensile stress of ceramic slowly increases and it is better to decrease extrusion temperature for useful life of ceramic die. Besides, hot extrusion process was studied, and the results show that there is high temperature gradient among the working area of ceramic die, which have high thermal expansion, but non-working area have low thermal expansion, so the non-working area will exist high tensile stress. For target function that the ceramic does not have tensile stress, rod extrusion ceramic die was studied by the finite element analysis. In order to further eliminate axial tensile stress, the cavity of ceramic die was axial segmented which reduce the half of stress compared with reducing clearance of working chamber and discharging chamber. Finally, the angle of working chamber and discharging chamber and magnitude of interference of rod hot extrusion die was optimized.The results show that residual stress produced by the mismatch of elastic modulus and thermal expansion coefficient between ceramic die and die core of graphite in the preparation of ceramic die cause the longitudinal crack of ceramic die finally, but when selecting ceramic material Si3N4 which has relatively smaller elastic modulus and thermal expansion coefficient can avoid early longitudinal crack. Based on optimized structure of chapter three, the magnitude of interference vlalue of ceramic die of micro ceramic material Si3N4 and outer rim of combined die was optimized.