The Utilization of Flow Control During Multi-Cavity Injection Molding Processes

Abstract

Process control is an important factor for improving the performance and consistency of thermoplastic parts manufactured by injection molding processes. A critical process parameter for manufacturing of high quality plastic parts is cavity pressure. This paper presents a continuation of a numerical based study of the utilization of flow control specifically for cold runner applications in multi-cavity injection molding processes. A cold runner system supplying polymer melt to a multi-cavity mold incorporating several types of mechanical valves in the runner systems was modeled and manufactured. Each valve independently controls the flow and pressure to its portion of the mold. The goal of the numerical simulation phase of the present investigation was to numerically simulate and thus validate a physical capability to modify the filling of individual cavities during injection molding of products utilizing multi-cavity tooling. A decision was made to attempt to do so by physically controlling the flow rate of polymer into each cavity. The tooling set was made adaptive through the incorporation of custom designed control valves into the runner channels leading to each product cavity. Simulations of both the overall adaptive tooling concept and the specific control valve designs were performed with LCP and PPS as a molding material. It was concluded that the flow control concept developed was numerically validated [1–3], and it was shown that the valve system proposed here is applicable to control melt flow through cavities at industrial manufacturing facilities. The adaptive tooling developed and simulated during the current investigation yielded significant variations in both processing parameters and resultant product quality in response to in-tooling control valve adjustments. It was found that by changing valve angle settings, the flow rate to each cavity could be controlled individually without degrading desired material properties. In an attempt to further promote the flow control concept, an experimental mold was developed and forms the basis for this paper. Preliminary experimental results verifying previous work and the future directions for the continuing project are also discussed.