Study On Simulation Of Long Fiber Reinforced Thermoplastic Direct Injection Molding Technology

Long fiber reinforced thermoplastic composites are widely used in automotive,aerospace,mechanical and electrical,construction and other industries due to their high toughness,high impact resistance,easy recycling and low material storage requirements.Long fiber/thermoplastic direct injection molding technology refers to the molding method that the long fiber and thermoplastic are directly injected into the product through special equipment,Long fiber/thermoplastic direct injection molding technology,which makes the process of injection molding products simpler,shorter and more energy-saving,can meet the needs of manufacturers to customize the product formula.Long fiber/thermoplastic direct injection molding technology can be divided into In-line Compounding Extrusion and Injection Molding Technology and Direct Fiber Feeding Injection Molding Technology.The technology of In-line Compounding Extrusion and Injection Molding Technology is relatively mature.Germany and Japan first started the research of Direct Fiber Feeding Injection Molding.Through the design of a special injection molding machine,the fiber was added into the barrel of the injection molding machine through the fiber adding port of the injection molding machine,and the fiber and molten resin were injected into the mold through the mixing forward motion of the screw of the injection molding machine.Compared with on-line mixed injection molding,Direct Fiber Feeding Injection Molding greatly reduces the cost of equipment and energy consumption.However,there is no relevant research in China.In this paper,the technology of Direct Fiber Feeding Injection Molding is studied.The main research contents are as follows:(1)The plasticizing system plays an important role in the melt plasticization of thermoplastics and the mixing of thermoplastics and fibers.By analyzing the relationship between the output of two-stage screw and the amount of fiber feeding,the formulas of maximum back pressure and optimum pump ratio are established,and the maximum amount of fiber feeding when the screw parameters are determined,and the special screw for direct injection molding of long fiber/thermoplastics is designed.The influence of the structure of the fiber feeding port on the overflow is analyzed,and the structure of the fiber feeding port is determined.(2)Based on the POLYFLOW numerical simulation of pressure,shear rate,shear stress,mixing index and cumulative residence time in the mixed flow field of long fiber/thermoplastic plasticizing system,the influence of rotational speed on each index in the mixed flow field was analyzed,and the influence of screw element and rotational speed on fiber mixing and length was studied(3)Mold flow was used to simulate the filling process of tensile samples,and the fiber orientation and fracture mechanism were analyzed.The single variable of mold temperature,melt temperature and filling time was used to simulate the fiber orientation and fracture,and the influence of single factor process parameters on the fiber orientation and length was obtained(4)Based on the response surface method,which takes the mold temperature,melt temperature and filling time as variables and the shortest fiber length as response,the second-order polynomial model fitting and variance analysis are carried out to obtain the optimal combination of process parameters to improve the fiber length.Through the comparison of simulation results under the optimal process parameters and model prediction results,it is proved that the feasibility of the response surface method in the optimization of injection molding process parameters.