Numerical Simulation Of Hot Extrusion Process And The Thermal Insulation Performance Of Mould Surface Coating For Forming 304 Stainless Steel Impeller

Stainless steel impeller is a typical thin-walled part with complex curved surfaces, and widely used in the industrial pumps, ventilation pipe and other equipments. Poor performance of the impeller was obtained by the traditional manufacturing processes such as casting or welding after sectional molding, can easily bring about its unstable quality and short service life. Thus the hot extrusion forming process of 304 stainless steel impeller was studied in this paper by FEM numerical simulation. For the mould has to suffer huge thermal load in the hot extrusion process, in order to prolong its service life, it is necessary to modify the surface of mould with thermal barrier coatings.In this paper, hot extrusion forming process of 304 stainless steel impeller was simulated on the finite element software DEFORM-3D. The structure of the mould cavity was designed and improved, and the influences of different extrusion speeds on the temperature, the equivalent stress of the 304 stainless steel billets and the load of extrusion mould were analyzed based on the simulation results. Then the appropriate extrusion speed was determined. Finally, by comparing the material properties of thermal barrier coatings, the double-ceramic-layer LZ/8YSZ TBCs was confirmed to modify the surface of the mould, and the thermal insulation properties of the DCL LZ/8YSZ TBCs were analyzed on DEFORM-3D. Finally, correct the measurement hysteresis of thermocouple. The main conclusions are as follows:1) When the mould structure with upper and lower extrusion shafts was adopted, the cylindrical billets with equal diameter to the extrusion shaft flowed more difficultly along the radial direction than along the axial direction in the immobile extrusion mould cavity, and the impeller was more difficult to be formed. The radial flow performance of the billets was greatly enhanced, when the upper and lower integral mould structure was utilized, but the draft angle and the transition radius on the impeller hub inner surface of the extrusion mould cavity should be increased for the difficulty of forming.2) With the increase of the extrusion speed, the total heat loss by heat conduction decreased, the temperature difference in the extruded part reduced gradually, the temperature distribution of the extruded part was more uniform, and the equivalent stress also gradually decreased. But the reduction degree of the temperature difference and the equivalent stress went down with increase of the extrusion speed.3) With the increase of the extrusion speed, the load of the extrusion mould first decreased and then increased, and reached the minimum when the extrusion speed was 15mm/s. Therefore, when the billet preheat temperature was 1200℃, the reasonable extrusion speed was 15mm/s.4) When the thickness of LZ layer was 200 um and 8YSZ layer thickness was 100 um, the near surface temperature of the extrusion mould where the contact time of the mould and the billet was the longest, reduced by 75℃, and the lowest temperature of the billet increased by 58℃. It showed that the DCL LZ/8YSZ thermal barrier coating had a good thermal insulation effect in the hot extrusion process.5) A prediction correction method based on the combination forecasting model was proposed for the TMDT2-41 thermocouple to correct the measurement hysteresis of the thermocouple, the experimental results showed that the response time of the thermocouple was reduced by 32%, the correction effect was good.