Experimental and Numerical Investigation of Thickness on the Shrinkage and out of Roundness in Cylindrical Parts in Injection Molding Process

Injection molding process is one of the most important methods of forming in the plastics manufacturing industry. Shrinkage and out of roundness are phenomenons that affect the final product quality. In this study, the effect of the thickness of cylindrical parts from polypropylene material on shrinkage and out of roundness has been investigated. For this purpose, injection molding process is simulated and analyzed with MOLDFLOW software. Then a five-cavity injection mold from hallow cylindrical parts with five different thicknesses is made. Using an injection molding machine least five samples of these parts are made. Then dimensions of samples are measured using 3D optical coordinate measuring machine and the amount of shrinkage of each sample is obtained. It can be concluded that with increasing part thickness, shrinkage and out of roundness are increased. It is because of being slower at melting material cools and having more time to make crystals. More crystallize caused to more shrinkage and more out of roundness. At the end, the simulation results are compared with the experimental results and showed a good agreement.