Filling Analysis Of Micro Injection Molding With Curl Runners Based On Numerical Simulation

With the development of science and technology, micro-injection molding of plastic parts has been used in industrial production extensively. As most of parts made by micro-injection molding are very small, the corresponding molds are usually designed to be with multi-cavity structure. This paper is based on the novel curved runner systems that have been put into use. A coordinate transformation method is used to establish the theory model of polymer melt flowing in the curved tube under ring coordinate system of the curved tube flow theory model on the basis based on necessary assumptions; Analysis is made on the filling process through sub-channels of curved runners with CAE software, the theory model has been verified with the simulation result; Then the CAE software has been used to analyze the filling differences among several runners with various radius. The conclusions are as follows:1. Calculated via the curved tube flowing theory model, it is found that:when polymer melt flows in a curved tube, its velocity, shear rate, viscosity and temperature distribution in the pipe cross-section is not symmetric:the extremes of velocity and viscosity evidently appears to be near the inner wall. While shear rate and temperature reach extremes in the outer wall.2. Analysis on polymer melt flowing through the curved tube with various injection rates has been made via Moldflow software. The results show that, the distributions of the flow rate, shear rate and viscosity in the cross section of the tube meet the numerical solution of the curved tube flowing theory model. With the low injection rate, there is no dramatically difference in temperature near the inner and outer wall of the tube. With the injection rate increasing, the temperature near the outer wall gets higher than the inner one. As the flow length increases, the outer shear rate exceeds the inner first and then drops. This shows that the Temperature difference is caused by the shear heat. The changes of melt temperature near the outer and the inner wall lags behind the changes of shear rate. With the flow length increasing, the outer shear rate is no longer higher than the inner one; while the outer temperature is still higher than the inner one.3. The filling simulation with various process parameters has been made via CAE software to compare melt behavior flowing through the runners featuring different radius. The results show that, the injection pressure for melt flowing through the curved runners is higher than that through the linear runners, and it becomes higher as the radius of the runner increases; With the same flow rate, injection pressure differences between the two kinds of runners vary as material changes, and it reaches its minimum when PP is considered, which is a kind of shearing sensitive materials. It is indicated that, the shear sensitive materials with better flowing properties are more suitable for curved runners to get balanced filling. With the same flow rate, melt temperature in the right and left parts of the secondary sub-runner is different, which means the differences within the linear runners are bigger than those of the curved ones. The temperature distribution on the cross section of the secondary sub-runner is not symmetric. What is more, such unsymmetrical deviation is relevant to runners'radius, but scarcely to the flow rate.