Simulation Tools for Injection Moulding

In this paper the concern is certain simulation tools for the lling phase of injection moulding of plastics. A mathematical model, called the distance model, of the injection moulding process has been developed by Professor Gunnar Aronsson at the University of Linkk oping. From this model one can nd the lling pattern (i.e. ow fronts) of the molten polymer as it enters the mould, by solving a shortest path problem. Based on this model, a code has been developed for computing the ow fronts. To simplify the use of this code a graphical users interface (GUI) has been developed. The purpose of this paper is to demonstrate how this has been solved using Matlab. This interface allows the user to describe the mould geometry by drawing edges and vertices in a Matlab gure window. Also it is possible to perform calculations and visualize simulation results directly from Matlab. This kind of software is potentially useful for solving industrial problems. 1 Background In injection moulding of thermoplastics, molten material is forced into a mould where it is cooled and hardens. The commercial importance of injection moulding comes from the high level of automation and high production rate that is possible. Furthermore , injection moulding allows complex parts to be produced in a single operation. The resulting surface is often good enough and moulded articles require little or usually no extra eeort for nishing. There are some diiculties associated with the injection moulding method. Mould Clamping unit Polymer granules Molten polymer Figure 1.1: A schematic picture of an injection moulding machine the mould must be allowed to escape freely. Otherwise the compression of this air will cause the temperature to rise considerably and destroy the product. When ow fronts of polymer material merge, the molecular structure of the polymer prevents the material from reaching homogeneity at certain lines, called weld lines. The product will be weaker along these lines and may have poor surface nish. Another important problem is warping. It is not discussed here. The result of the injection moulding process depends signiicantly on the conditions under which the part is moulded and it is diicult to predict the quality of the resulting product. Thus simulation software is useful as a tool when designing moulds. 2 The distance model Here we present some background on the model used to describe injection moulding, the distance model.