Post shrinkage comparison of plastic injection products by using solid mold, laminated steel tooling mold, and soft tooling mold

Abstract

Plastic product development requires dimensional accuracy in the product. One method to improve the accuracy of dimension is by making a mold that has a uniform cooling channel following the contour of the cavity, so that the direction of product shrinkage on cooling cycle can be uneven. The existing solid-type mold has several limitations on the cooling channel system. Meanwhile, products with complicated shapes mostly require cooling channel that follows the shape of the cavity (conformal). Type of conformal cooling channels can be made by the method of manufacturing each layer laminate plate arranged with adhesive into a single unit (laminated steel tooling) and the method of using a resin molding mixed with metal powder in which there is a pipe that follows the shape of the cavity (soft tooling). The present study compares the shrinkage of plastic products made from three types of mold, namely: a solid mold with straight cooling channel, laminated steel tooling with conformal cooling channel, and soft tooling with conformal cooling channel. Analysis of shrinkage measurement products includes high direction and inside diameter and outside diameter of elongated cylindrical products. Three types of mold were made, namely mold with a straight cooling channel, laminated steel tooling mold with conformal channel, and soft tooling mold with conformal channel. Three specimens were made from each mold. Plastic material for injection was Polypropylene. The volume of cooling channels between the straight-type channel and conformal was set equal. Data were collected after the injected products were stored for 24 hours. The results show that the percentage of both shrinkage lamination conformal cooling system and soft tooling is smaller when compared to that of a straight cooling system. Moreover, the shrinkage difference of diameter dimension on the X axis and Y axis is insignificant. It proves that the lamination conformal cooling systems and soft tooling are more optimal in controlling the shrinkage dimensions of the product.