Determination of Robust Conditions for Injection Moulding of Recycled Polypropylene

The aim of the robust design method is to determine the process conditions that minimize the influence of external noise factors, such as varying environmental conditions and material characteristics. In particular, in the injection moulding of recycled polymers, the properties of the raw material are subjected to significant variations due to changes in the mixtures, frequent batches changes and difficulty in controlling the characteristics of incoming materials. In this paper numerical simulations were used to test the influence of the rheological properties of recycled polypropylene blends on the warpage of a plastic component. The planning of the simulations was designed in according to the Mixture Design technique, and the polymer blends were characterized by rotational and capillary rheometers, to get the experimental rheological curve for both low and high shear rates. Experimental results were fitted to the Cross-WLF model, and then implemented into Moldflow Plastics Insight© to predict part warpage. Monte Carlo simulations were used to determine the probability distribution of two responses in terms of part warpage and to determine robust conditions to maintain warpage within designed tolerances.