PREDICTION OF PROCESS-INDUCED WARPAGE IN INJECTION-MOLDED THERMOPLASTICS

The main cause of warpage in injection moldings is the imbalance of th e thermal residual stresses that are caused by a non-uniform temperatu re distribution through the thickness of the moldings resulting from v ariation in cross sections, part geometries, and temperature differenc e between the mold surfaces. As the hot plastic melt is injected into the relatively cooler mold, a temperature gradient develops between th e core of the molding and its surfaces, determining the magnitude of t he residual stresses and warpage deflection. The relationship between the temperature difference of the two halves of the mold and warpage f or a flat plate was measured and predicted by use of a finite element software package. The development of warpage in a 3D component (L-shap ed bracket) was also measured, and the results were compared with comp uter predictions.