The Research On Microporous Injection Simulation And Optimization Of Microporous Injection Molding Assisted By Supercritical CO₂

Nowadays,the shortage of fossil materials in the world leads to the increasing cost of plastic materials and the increasing demand for plastic products.Microcellular foamed plastics have many advantages,such as light weight,material saving,high impact resistance,high fracture resistance,high specific strength,sound insulation and heat resistance,etc.However,the technology of domestic microcellular foaming injection molding is still immature and needs to be further improved.In view of the limitation of equipment development and experimental research,this paper studies the foaming mechanism and distribution of microcellular foaming injection molding by means of simulation technology,and analyzes the influence of molding process parameters on the quality of microcellular foaming injection molding products,it provides theoretical basis and reference for its application in practice.In this paper,a supercritical CO2 pre-foaming device is designed to realize a novel scheme combining gas-filled TPU particles with microcellular injection molding technology.Firstly,the key parameters and the structure of the device are designed and studied,and then the safety reliability of the pressure vessel is analyzed and optimized,and the minimum value under the condition of satisfying the target parameters is obtained,in order to save materials and economic and reasonable purposes.The injection molding model of microcellular foaming was established by using Moldflow simulation software,and the filling and packing processes were simulated.The results show that with the increase of the pressure,the increasing rate of the melt injection weight increases rapidly at first and then slowly,and the pressure decreases with the increase of the holding time.The process parameters of microcellular injection molding(Mim)have an important effect on the cell structure,and the effect of process parameters on the cell radius is analyzed by software simulation.The results show that the mold temperature has a certain effect on the distribution of the bubbles,and the radius of the bubbles increases in a small range with the increase of the location away from the gate.The radius of the bubbles increases with the increase of the melt temperature and increases rapidly near the center of the bubbles.With the increase of the content of CO2 in the supercritical fluid,the cell radius decreased at first and then increased,and the decrease process was relatively smooth.The influence of filling volume on the cell radius is also obvious.The cell radius increases with the increasing of filling volume,and the cell radius increases with the distance from the center.In the course of simulation analysis,the potential defects in microcellular foaming were predicted,and two obvious weld lines and many cavitation were found.The optimum process parameters were obtained by orthogonal experimental design.In the experiment,the weld line,cavitation and residual stress were taken as the experimental indexes,and the mold temperature,melt temperature and injection time were taken as the factors,the influence of three factors on the defects of micro-hole injection molded products was analyzed,and the optimum processing parameters were obtained.The results show that the weld quality is improved and the cavitation and residual stress are significantly reduced.