The use of computer-aided simulation calculations at an early stage in mould design provides well-founded information on the injection behaviour expected during the elastomer injection moulding process. The effect of the predicted junction seams and pressure distribution, resulting from the chosen gating system can be used at an early development stage to assess subsequent functioning of the part. Varying the gate length and the gate design during the simulation stage means that the mould design can be optimized at no great expense.