MATHEMATICAL-MODELING OF THE IN-MOLD COATING PROCESS

Fiber glass reinforced polyester parts compression molded from sheet molding compound (SMC) are prone to such surface inconsistencies as porosity and sinks. Even though it appears that some of these defects could be eliminated by techniques such as vacuum molding, the resulting surface, with current technology, is not yet consistently up to automotive standards for exterior body panels. In‐mold coating (IMC) of SMC, is designed to fill porosity, reduce sinks, and furnish a primer‐like coating, thus upgrading the part surface to automotive standards. As a consequence, IMC is generally an integral part of the molding cycle when producing compression molded SMC exterior automotive body panels. Most commonly, in‐mold coating is injected after opening the press slightly so as to separate the mold cavity and the exterior surface of the part to make room for the coating. A second approach is to let the hydraulic pressure of the injected IMC open the mold. Here, we present a mathematical model of the process and show application in predicting injection pressures, fill times, and filling patterns. A comparison with experimental results is also presented. Cycle times required for IMC injection methods is also discussed. Copyright © 1990 Society of Plastics Engineers