Modelling and Optimization of Part Ejection in Magnesium High Pressure Die Casting

摘要

One important process step in Magnesium HPDC (High Pressure Die Casting) is the ejection of part from the mold. Due to solidification and cooling down the part shrinks onto the mold. To overcome the strong forces that hold the part on the mold, ejection pins are used that push the part outside. Often the number of ejection pins is exaggerated since it is currently difficult to estimate if a reduced number could already be sufficient to eject the part without actually trying it. Reducing the number of ejection pins would decrease production costs and also give more flexibility to the mold maker to set cooling channels since these are occupying the same design space as the ejection pins.This article presents a novel modelling approach to virtually test the part ejection. The approach is a simulation chain built of two steps. In the first step a multi-physic modelling of the casting process, taking into account flow, thermal and mechanical aspects, is performed. Target of this simulation is to predict the stresses in the part that fix the part to the mold. This stress distribution is used as the initial state for the second part which represents the modelling of the ejection process taking into account all friction effects. Outcome of the modelling provides information if the stresses in the part during ejection will remain in the elastic range or if there are regions where plastic deformation occurs, which would indicate that the process parameters are not set well. Using this methodology will enable the virtual testing of different distribution and settings of ejections pins.The article is structured in the following way. First the principle approach to solve the problem by modelling will be described. The details include material properties, boundary conditions and other information that are used by the modelling. This framework will then be applied on a conceptual case to show that the model is behaving in a consistent way. The obtained results of this case will be explained in detailed. In the last section the modelling will be applied on an industrial case.