Shrinkage predictions of injection moulded parts in semi-crystalline polymers: experimental verification

The aim of this work is to explore the concordance between the shrinkage of injection moulded parts and its simulation from a commercial CAE system (C-Mold from AC Technology). An isotactic polypropylene was injected in a normalized mould following a standard test method for measuring part shrinkage. The influence of geometrical factors (like part thickness, length, longitudinal and normal flow orientation) has been studied. Also, the effect of process conditions (injection temperature holding pressure and time of application of holding pressure) has been taken into account. The need for using appropriated PVT curves is deducted from this work. In order to achieve accurate results, these curves should be built with similar cooling rates to the injected parts, especially in semi-crystalline polymers. The use of PVT curves obtained under equilibrium induce overestimation of the shrinkage. This work is included in the project of the development of an intelligent software for mould design, “Multimold”