Mass pad

The material cushion that forms during the injection moulding process refers to the residual melt that remains in the screw antechamber of the plasticising unit after the injection phase is complete. It forms because the injection moulding machine pushes more plastic material into the mould cavity during the injection process than is required for the final product.

This excess material, the material cushion, plays a decisive role in the further course of the process. During the holding pressure phase, which immediately follows the injection phase, the material cushion is used to compensate for the effect of shrinkage. Shrinkage occurs when the molten plastic material cools in the mould cavity and contracts, which can lead to changes in the dimensions of the final product. The material cushion therefore acts as a reserve to ensure that the finished injection-moulded part has the desired dimensions and properties.