Abstract: By use of visualization equipments, photos of in-mold shrinkage were taken while the injection-molded plastic parts were in the mold for 24 h. By image processing of the photos, including edge extraction, beeline fit, and intersection calculation, positions of sign spots for the mold cavity and the part were determined. By a radial line from a sign spot on the cavity to the corresponding sign spot on the part, the shrinking direction of the sign spot on the part was obtained. From the experimental data concerning shrinkage directions, it was found that the points of part shrink were directed towards a region between the part’s centroid and the gate, and thus were determined by the positions of both centroid and gate.

Key words: injection molded plastic part, visualization, image processing, shrinking direction