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
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.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.