Study On High Pressure Water Penetration Mechanism Of Short-Glass-Fiber Reinforced Polymer Cross Section Elbow

Water assisted injection molding(WAIM)technology is one of the most widely used fluid assisted injection molding technologies.Compared with traditional injection molding and gas assisted injection molding,it has unique advantages and wide application prospects.At present,more and more scholars combine short fiber reinforced polymers with WAIM technology to produce excellent parts that retain the quality of pure polymers and the excellent mechanical properties of composites;The current research basically focuses on the research of constant cross-section pipe fittings,and there is little research on variable cross-section pipe fittings,but there are many variable cross-section products in real life,such as automobile pedal,door handle,etc.,and these products are very suitable for water assisted injection molding.In order to make the water assisted injection molding technology successfully applied in the production of such products,It is very important to clarify the influence mechanism of relevant parameters on variable cross-section elbow short fiber reinforced polymer water assisted injection molding parts.Therefore,through the combination of experiment and numerical simulation,this paper studies the water assisted injection molding technology of variable cross-section elbow,analyzes the influence mechanism of relevant parameters on short glass fiber reinforced polymer water assisted injection molding of variable cross-section elbow,and defines the influence of mold structure and process parameters on high-pressure water penetration behavior,in order to provide theoretical guidance for practical production in the future.The main research work and conclusions of this paper are as follows:1、Combined with the actual molding situation of water assisted injection molding,the numerical simulation is carried out,and the reasonable model is selected.Firstly,in order to make the calculation converge,reasonable assumptions are made for the forming process,and the basic governing equations of the flow process are constructed;Based on the analysis of the viscosity model commonly used in short fiber reinforced polymer water assisted injection molding,a suitable viscosity model is selected according to the material characteristics of short glass fiber reinforced polypropylene;Reasonably select the free interface tracking technology in numerical simulation.2、The influence of water injection delay time on short glass fiber reinforced polypropylene elbow in overflow water assisted injection molding technology is experimentally studied.It is found that with the penetration of high-pressure water,the section of the pipe at the front and back of the corner will be more inclined to the inner diameter of the corner;With the increase of water injection delay time,the overall penetration rate of pipe fittings decreases,and the reduction speed tends to be the same.Then it is simulated by moldex 3D numerical simulation software.The results show that the numerical simulation is consistent with the experimental results,which confirms the availability of the selected model in the numerical simulation.3、The effects of section ratio and bending angle on variable section elbow in overflow water assisted injection molding short fiber reinforced polypropylene were studied by numerical simulation.The results show that the penetration rate of pipe fittings along the penetration direction of high-pressure water increases first and then decreases,and the penetration rate of the last section of pipe fittings decreases in a cliff style;With the penetration of high-pressure water,the residual wall thickness is uneven at the corner and the rear section of the corner(the residual wall thickness near the inner side of the corner is thinner,and the wall thickness outside the corner is thicker);At the same time,with the increase of section ratio,the overall penetration rate of the workpiece fluctuates little.It can be seen that the section ratio has little effect on the overall performance of pipe fittings.With the decrease of bending angle,the hollow area of the pipe fitting at the corner increases gradually,but the residual wall thickness of the pipe fitting near the outside of the bending changes little,and only the residual wall thickness near the inside decreases gradually.When the bending angle is reduced from 150°to 120°,the penetration rate of pipe fittings increases obviously.When the bending angle is in the range of 120°to 90°,the influence of bending angle on the penetration rate of pipe fittings is not obvious.4、Taking the 90°curved circular pipe fitting with variable cross-section similar to the automobile pedal as the object,using the numerical simulation method of overflow water assisted injection molding,the effects of melt temperature,water injection delay time and water injection pressure on the penetration rate of pipe fitting,as well as the influence degree and optimal combination of various factors are studied through single factor experiment and orthogonal experiment L16(4~3).The results show that the penetration rate of variable cross-section elbow increases gradually with the increase of melt temperature and water injection pressure in overflow water assisted injection molding;With the increase of water injection delay time,the penetration rate of pipe fittings decreases gradually,and with the increase of time,the influence of bending section on pipe fittings is more obvious,and the penetration rate decreases at the beginning of corner;At the same time,there is a sudden drop in the penetration rate at the end of the pipe due to the sudden decrease in the diameter at the connection between the pipe and the overflow chamber.Through orthogonal test,it is found that in the numerical simulation of overflow water assisted injection molding,the influence of melt temperature on the penetration rate of pipe fittings is the highest,the delay time of water injection is the second,and the influence of water injection pressure is the least;The best combination of pipe fitting performance is melt temperature 270℃,water injection delay time 0s and water injection pressure 10MPa.