Effect of Cooling in The Injection Molding Process of Acetabular Cup of Hip Joint Prosthesis.

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%. [ABSTRACT FROM AUTHOR]