Visual Investigation Of The In-mold Shrinkage Of Injection-molded Plastic Parts

Injection molding is a primary technology as it has been widely used in yielding complex and high accuracy plastic parts. However, shrinkage is the most influencing factor in dimensional precision of production. In order to find the relationship between the shape of the cavity and the plastic part shrinkage, based on particular learning former research on this study, a new experimental method and a data processing was applied to comprehend the shrinkage which occurred in cavity.Firstly, a new visual mold that would be used in observing the shrinkage from two face-to-face directions was designed and manufactured independently on the base of other visual equipments. Half structure was applied and two quartz plane glasses was mounted on half parts to insure the shrinkage can be seen from two opposite directions.Secondly, six groups of short-shots samples were obtained by controlling the shot quantity. A digital single lens reflection camera was employed to take the shrinkage picture of the short-shots sample after it had been kept in cavity for 24 hours.Then, a date processing was used to distinguish the boundary of the mold cavity and the plastic sample in the picture. The data of shrinkage and its direction were got through locating the marginal turning points of the mold cavity and the plastic sample by using line fitting and intersectant point computing.Finally, the conclusions are summarized through comprehensive analyzing the processed data. The shrinkage directions will gradually change away from the gate and intersect in an area between the sample centroid and the gate while their distance increasing. The longitudinal shrinkage is larger than the transverse under a condition that no prevention comes from the cavity. The angle of two neighboring borders of the plastic sample, while relative to the cavity, changes according to "180°inclination Principle" .