Shallow depressions, called sink marks, may form on the surface of plastic parts produced by injection molding. These depressions are caused by partial differences in the amount of shrinkage of plastic parts during the solidification process. The appearance of such depressions in the exterior of the product degrade its aesthetic quality. In this study, we propose a shape modeling technique of possible sink marks. The input data of the method is a polyhedral model of a part. This model is transformed to another polyhedral model of the same shape and whose surface polygons have a sufficiently small size. For each vertex of the part, the amount of shrinkage is determined using the result of the thickness analysis at the vertex of the model. The position of the vertex is then modified according to the shrinkage value to obtain a solid model with shallow depressions on its surface. By properly visualizing the model using the computer graphics technique, it becomes possible for the designer to evaluate the influence of sink marks on the part appearance.

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