Prediction and characterization of compression mould flow for unsaturated polyester resin sheet moulding compound

During the past twenty years there has been considerable interest in developing the technology for manufacturing engineering articles from sheet moulding compound (SMC) by compression moulding. Some of the problems with this technology are associated with the flow of SMC during moulding. This research work proposes methods for characterising the rheological behaviour of SMC and predicting the shape of charges for moulding articles free of weld-lines without substantially altering the initial fibre orientation of the matrix. The theoretical development'of the charge shape prediction procedure for moulding symmetrical and unsymmetrical plates includes a mathematical model of the compression flow process. which is used to determine flow front development, and mould cavity pressure and velocity distributions. The mathematical model assumes a Newtonian flow behaviour. An instrumented mould was designed. manufactured and used to test the mathematical model of the compression flow process. The analysis of the experimental work includes: moulding conditions (such as mould cavity pressure, platen displacement and ram-force); fibre orientation measurements (using X-ray techniques); quantification of fibre glass distribution by chemical methods; and material mechanical properties (e.g. tensile strength). There was good agreement between the theoretical and experimental results for moulded symmetrical and unsymmetrical plates. A theoretical and experimental analysis of the rheological behaviour of 5MC was carried out as a second stage of the research work to test the validity of the Newtonian flow assumption. The work analyses squeeze flow of SMC discs with the aim of obtaining a better understanding of the basic rheological behaviour of SMC during compression moulding. The theoretical analysis treats the SMC as a viscoelastic material having an equation of state with equal viscous. elastic and yield strain components. The time variation of compression force when squeezing the SMC discs between two parallel plates (one fixed and one mobile) has been derived from the equation of state. The values of the elastic, viscous and yield components were determined by using a least-squares method of curve fitting to the experimental results. The last part of the research work includes the application of the charge shape prediction procedure to mould an engineering article under industrial compression-moulding conditions. ·The results of this practical application of the theory are discussed.