The Shrinkage Comparison of Plastic Injection Molding inserts, Made of Low Melting Point Metal Casting Alloy and Epoxy Resin Material

This paper compares the shrinkage of the components manufactured by injection molding, using inserts made of epoxy resin and metal alloys with low melting point (LMPA). For this purpose, in first stage, two cube molds (inserts) manufactured by epoxy resin and a low melting point alloy (150MCP). At the using an injection machine, two types of polymers, (polyethylene and polystyrene) were injected into the inserts. Then exact dimensions of the injected components, plus shrinkage caused by inserts materials, (epoxy resin and metal alloys with low melting point) were measured. Also, the effect of injection parameters on shrinkage of the components, investigated, these parameters include injection pressure, holding time and temperature of the polymer melt. The results indicate a reduction in shrinkage in components of polyethylene, which is made in LMPA insert. Reduction in length and width and height are 62/0, 46/0 and 75/0 respectively. Polystyrene components made by both inserts, have about the same percentage of the shrinkage. Increasing the injection pressure and holding time, significantly reduced the shrinkage of components in both inserts.