Simulation And Experimental Study On Injection Molding Of 316L Stainless Steel Powder

Metal injection molding technology is a near net technology, which has an unique advantage in the preparation of complex shape, uniformity structure and high performance metal parts. But injection molding parts often appear defects such as uneven density distribution, surface flow mark, cracks and connecting line, whick not only affect artistic but the use value. Therefore, it is very important to study the reasons for the formation of injection molding defects, combing with injection molding experiment and simulation studies.This article choosed the aerosol and water atomized powder 316L stainless steel powder which have the same size, and mixed them with the same binder at the proportion of 25,50 and 75. Tested and analysised the performance of injection feed by using the tester of melt flow rate, the thermo-gravimetric analyzer and the capillary rheometer, and then injected, debinded and sintered. Moreover, analyzed emphatically the effect of injection parameters on the properties of injection green and the effect of sintering temperature on the properties of sintered parts. Finally, simulated the injection filling process by using Moldex 3D software, and discussed the effect of injection parameters on two phase separation. Studies have shown that:In the preparation of feed, feedstock made by spherical powder leads to good liquidity and conformal performance, therefore we can doped into the spherical powder with the irregular shape powder which does not exceed the percent of 50. Thermogravimetric and rheological properties of the injection feedstock were analyzed, the results showed that 190℃ is the most suitable for injection molding. According to the principle of capillary rheometer test, designed the archimedean screw test method, and this test method was verified by an experiment and simulation software reliability.The defects appear in the injection process cannot eliminate in the subsequent process, injection defects are mainly related to the filling process of two phase separation. In order to further study on filling process of two phase separation phenomenon, we used Moldex 3D simulation software for simulating injection filling process, and analysised the the effect of mold temperature, injection temperature, injection speed, injection pressure and mold filling mode on two phase separation. Studies have shown that:mold temperature too high or too low would seriously affect two phase separation, injection pressure has little effect on the two-phase separation. The injection temperature and injection speed affected the two-phase separation by changing the viscosity of the feedstock, which filling the cavity in a fountain flow way, powder and binder are separated because of the different flow rates, resulting in uneven distribution of green density injection, high binder content near the gate and in descending order in the cyclic waveform way, and the binder content is higher in the mold wall with the action of shear heating.After the injection molding process, degreased by using the same degreasing process, and sinted at 1320℃,1340℃,1360℃,1380℃ for two hours,studies showed that when the sintering temperature is lower than 1360℃, the properties of the sintered parts such as shrinkage, density, hardness and mechanical increased significantly when the temperature raised. When the sintering temperature continued to rise, the sintered density, shrinkage, hardness and mechanical properties droped.