Fatigue Life Prediction And Experimental Study Of Plastic Gear With Coupled Injection Molding Process Defects

At present,in order to realize lightweight design in automobile industry,plastic gear with plastic instead of steel has been widely concerned and applied in the industry.However,there are some process defects in plastic gear injection molding,such as uneven shrinkage,molecular orientation and melting line,which make the molding quality of plastic gear difficult to control,and these process defects will also affect the life of plastic gear.In this paper,the plastic gear in EPS is taken as the research object to analyze the injection molding process defects and predict the fatigue life of the plastic gear.The main research contents are as follows:1)By using Moldex3 D to analyze the existing forming process of EPS plastic gear,it is found that the volume shrinkage of the ring gear is too large at the wall thickness,and there are inevitable glass fiber orientation and melting line in the middle ring due to the material and multiple gates.Through the structural optimization of the thickness of the ring gear,the volume shrinkage of the ring gear is effectively reduced and the shrinkage defects are improved.2)According to the yield strength of PA66,the stress level of fatigue test is designed reasonably.The S-N curve of PA66 with stress ratio R =0 was measured by fatigue experiment,and the basic S-N curve of PA66 with stress ratio R =-1 was fitted by Goodman mean stress correction theory.It was found that under the double logarithmic coordinate,the low cycle and high cycle stages of PA66 showed obvious two-stage linear relationship,which was in line with the general S-N curve law.3)Based on Digimat,a finite element model of coupling melt line and glass fiber orientation is constructed.The model is used to simulate the torsional stiffness of EPS plastic gear in Abaqus.It is found that the torsional stiffness of plastic gear decreases about 12% after coupling glass fiber orientation,while the effect of melt line on the torsional stiffness of plastic gear is small.4)The static structure of plastic gear is analyzed by using the established process structure coupling model.The results show that after the coupling injection molding process defect,the stress response of plastic gears has increased significantly,and the tooth roots of plastic gears are mainly subjected to tensile stress,which is prone to occur Fracture failure;the tooth tip and tooth surface meshing area is mainly subjected to compressive stress,prone to wear failure.5)Abaqus and FE-safe were used to predict the fatigue life of plastic gear under different torque,and the fatigue life of plastic gear with or without injection molding process defects was compared and analyzed.It was found that injection molding process defects significantly reduced the fatigue life of plastic gear,and the predicted fatigue life was verified by test bench.