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Hip Joint is located between the hip and the base of the upper femur. Diseases such as osteoarthritis and rheumatoid arthritis can cause total replacement of hip joints with prosthesis. Hip joint prosthesis’s components consist of acetabular cup, femoral head, and femoral stem. One of acetabular cup material is a polymer. Therefore, injection molding is one of the processes that can be used to produce it. The problem that often arises is a product defect due to shrinkage. Regarding to shrinkage, the research will investigate the effect of water cooling on the shrinkage of the product’s size in the injection molding process of making acetabular cup. The work begins with the manufacture of molds, then two injections of liquid polypropylene are carried out into the mold. The first injection is for mold without cooling and the second with cooling. The resulting shrinkage is then compared. The shrinkage measurement of the outer part of the product is taken from three directions, namely the product’s height, the product’s outer diameter in the direction of y axis, and the outer diameter of the product in the direction of z axis. For the interior of the product with a half-ball shape, shrinkage measurements are carried out by measuring the average radius. Test result shows that shrinkage in injection molding testing with cooling is lower than injection molding testing without cooling. The average shrinkage of the product’s height on the test with cooling is 1.224%, while the test without cooling is 1.591%. The average shrinkage of the outer diameter in the direction of y axis on the test with cooling is 1.857%, while the test without cooling is 2.32%. The average shrinkage of the outer diameter in z axis on the test with cooling is 1.83%, while the test without cooling is 2.369%. Measurement the average shrinkage of the product’s radius is also obtained the similar trend. The test with cooling obtains the average shrinkage of the product’s radius of 0.825%, while the test without cooling is 1.267%.

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.