MONITORING OF INJECTION MOLDING OF THERMOPLASTICS: ADOPTING PRESSURE TRANSDUCERS TO ESTIMATE THE SOLIDIFICATION HISTORY AND THE SHRINKAGE OF MOLDED PARTS

摘要

In this work, a series of injection moulding tests were conducted using a general purpose PolyStyrene, PS, and changing the holding pressure, injection temperature and cavity dimensions. The pressures at the interface with the mould at several positions along the flow-path were measured by means of pressure-temperature transducers. The samples were measured after moulding to determine dimensional accuracy, which was taken to be the target quality parameter. The pressure profiles obtained were then analysed using a recently developed procedure that is able to estimate the local solidification history from pressure measurements. The local average solidification pressure, namely the average along the thickness direction of the pressures at which each layer solidifies, could thus be estimated. This parameter is known to correlate well with shrinkage and thus a master-curve can be created that can be adopted to monitor the quality of the moulded part on line.