HARRIS, R.A....et al., 2003. Part shrinkage anomilies from stereolithography injection mould tooling . International Journal of Machine Tools and Manufacture, 43(9), pp. 879-887.
The use of stereolithography (SL) tooling allows plastic parts to be produced by
injection moulding in a very short time due to the speed of mould production. One of the
supposed advantages of the process is that it provides a low volume of parts that are the
same as parts that would be produced by the conventional hard tooling in a fraction of the
time and cost.
However, this work demonstrates different rates of polymer shrinkage are
developed by parts produced by SL and conventional tooling methods. These revelations
may counter the greatest advantages of the SL injection moulding tooling process as the
parts do not replicate those that would be produced by conventional hard tooling.
This work identifies the different shrinkage that occurs in mouldings produced by
an SL mould as compared to those produced from an aluminium mould. The experiments
utilise two very different types of polymers and two mould geometries, which are
processed in the same manner so that the heat transfer characteristics of the moulds are
isolated as the only experimental variable.
The work demonstrates how the two mould materials exhibit very different rates
of expansion due to the temperature profiles experienced during moulding. This
expansion must be compensated for to establish the total amount of shrinkage incurred by
moulded parts. The compensation is derived by a mathematical approach and by
modelling using finite element analysis. Both techniques depend upon knowledge of the
thermal conditions during moulding. Knowledge of these thermal conditions are obtained
by real-time data acquisition and simulated by FEA modeling. The application of the
findings provide knowledge of the complete shrinkage values relating to the mould
material and polymer used which would enable the production of geometrically accurate