Optimize Design Of Runner System In Micro Molding Based On Numerical Simulation

Micro-injection molding, an important processing method for molding micro-parts, has been received more and more attention, which is coming a hot area of research in 21 century. As micro-parts are very small and light, with high precision, the corresponding molds are usually designed to be with multi-cavity structure for high production. Therefore, it is significant to fill all cavities in a balance way in order to gain all micro-parts with uniform quality and performance.This paper analyzed the filling process in runner system by numerical simulation and optimized its runner system based on simulation result. And the first beginning is changing the shape of runner, focusing on runner system used in micro-injection molding system to analyze and optimize by means of numerical simulation, hoping to obtain some results which have significance influence on filling balanced in microinjection molding. The content and result as follows:(1) Analyzing the imbalanced filling happened in microinjection molding with multi-cavities. We have found that the shear heat is the most important factor, reset the shear rate field and temperature field when the polymer melt flows from pre-runner to later runner can improve unbalanced filling. The theoretical result of polymer melt flow in curved tube illustrated that the shear rate pattern and temperature pattern have changed. Correspondingly, we have the idea of designing a curved runner by changing the shape of the first-class runner in micro-injection runner system.(2) Firstly, We use CAE software to simulate the melted polymer filling process in curved runner. The result shows that they’re basically agree with theoretical values. When the melt flows in curved tube, its numerical data distribution in the cross-section is not symmetric. As the injection rate improves, the maximum of flow rate and shear rate show partially to inner wall, and the maximum of temperature show partially to outer wall. The migration degree of the contour of shear rate has same trend with temperature difference. Therefore, the shear rate and temperature distribution are changed, which can guide the following works. (3) Design the runner system with curved runner based on the above results. Establish the straight runner system for comparing with the filling result. By comparing the polymer melt filling effect in these two runner systems, we found that the novel runner system is not very good to improve the imbalanced filling. From the reason of imbalanced flow and optimize the novel curve runner system.Compared the filling result of optimized runner system with the former result again, we found the optimized runner system is good to improve imbalanced filling. The pressure distribution in each cavity is identical.(4) Analyzing the process of polymer melt flow in optimized runner system by setting gating system as a research objective, the result demonstrate that:the thickness of low temperature layer distribute in mid plane of optimized runner system is more uniform than the straight runner system at the same injection rate. Melt flows through curved runner to sub-runner composed of two shares, one is from the inner of previous runner and the other is melt near wall of previous runner. Because of intense shear occurred in curved runner, weaken the temperature difference about sub-channels caused by melt stream, so the curved runner improve the filling balance; the distribution range of melt temperature on secondary sub-runner of curved runner is smaller 20% than the corresponding straight runners, with the injection rate increasing, the range becomes smaller.Analysis of filling result polymer melt in multi-cavities under these two runner systems, at the ending of filling process, the pressure-distribution of the fourth cavities is imbalance in the straight runner system. In which the pressure of the two cavities near sprue is higher than the other cavities. But the four cavities in the optimized curved runner system have more balance pressure-distribution.We analyzed imbalanced filling in these two runner systems with three different materials, and found the optimized runner system have general significance to improve the imbalanced flow of these materials.