The influence of flow and thermal properties on injection pressure and cooling time prediction

• An experimental and numerical case study for injection moulding is presented.
• The effect of material properties for mould filling/cooling stages was studied.
• True viscosity and no-flow temperature set to Tg yielded accurate pressure estimation.
• Thermal conductivity had negligible effect on pressure prediction.
• Molten state heat capacity and thermal conductivity gave best estimate for cooling time.

Thermoplastic materials properties play an important role in mould filling and cooling analysis of injection moulding. Among the many, the melt's viscosity, heat capacity and thermal conductivity may be the critical ones. An experimental and computational case study to determine the injection moulding window of a rectangular ABS plate is presented. When apparent viscosity of the material was adopted for cavity filling simulations, it was found that the computed injection pressure was overestimated in contrast to experimental data. Shear stress and rate corrections applied to apparent viscosity as well as the no-flow temperature (NFT) set to Tg (glass-transition temperature) helped to achieve more accurate pressure estimation. The heat capacity and thermal conductivity were both measured separately in solid and molten states and it was found that the best estimation for pressure and cooling time was achieved when molten state heat capacity was adopted for computation. The effect of thermal conductivity was negligible on pressure prediction, although the most accurate prediction for cooling time was attained when both molten state heat capacity and thermal conductivity were utilised.Therefore, the quality of material data input was found to be a critical factor in achieving reliable flow properties. Accurate data available for mould and process design purposes may help to generate less production waste and save costs, making a step towards sustainable manufacturing.