Physically based dynamic model for control of cavity pressure in injection moulding of amorphous plastics

Cavily pressure plays an important role in determining the quality of injection moulded articles. However, the non-linear and time varying behaviour of the process causes difficulties in implementing an efficient control system, since these generally employ linear lime invariant design strategics. Conversely, advanced control methods such as self tuning control do not provide physical information about the process. A physically based model has been developed. This model is used tu control cavity pressure during the tilling and packing phases. F.xperimental results indicate that this control yields accurate results for the injection moulding of polystyrene. Different control algorithms with different tuning criteria were implemented on a microcomputer to control the cavity pressure. The results indicate that this method is superior to the classical empirical control approach.