Application and modelling of hybrid stereolithography injection mould tooling

The use of stereolithography (SL) to make injection moulding tools has been shown previously to be an efficient way of producing rapid tools for simple geometries, aiming at small lot sizes with an acceptable degree of accuracy. This paper highlights the unexplored potential of using SL inserts in hybrid tools using practical experiments and FEA mould filling models. The practical experiments reveal problems incurred by uneven flow as a result of differential thermal conductivity between dissimilar mould materials in a hybrid tool. The FEA flow models confirm that this uneven flow would be anticipated when using finite element analysis (FEA) software. A further FEA stress analysis predicts that catastrophic mould failure will be expected under some conditions and these reflect the results found in the practical experiments. The use of a homogeneous SL tool eliminates the issues caused by uneven mould filling but results in thermal distortion of the female mould. Ultimately, a SL tool backfilled with low melt point alloy provides a solution that eliminates the problems of uneven filling and thermal distortion.