Experimental Research For Shrinkage Laws Of Injection Molding Products

With improvement of property of plastics and development of injection molding technology, injection molding products are used more and more widely, and with higher requirement of dimension accuracy and surface quality. But shrinkage of injection molding products can influence the dimension accuracy and surface quality, even cause structural distortion or in-side defects. Selection of shrinkage rate and process parameter becomes a difficulty in precision plastic parts production. So it is necessary to study the shrinkage laws of injection molding products.On the basis of roundly analyzing study state of shrinkage of injection molding products, shrinkage laws of injection molding products is fully studied via experiment in this paper, At first, the influence of process parameter on shrinkage rate and shrinkage anisotropy (difference between transverse shrinkage rate and longitudinal shrinkage rate) of injection molding products is studied through orthogonal experiment. It's found that holding pressure, holding time and melt temperature are significant effect factors on the shrinkage rate of injection molding products, while holding pressure and injection rat influence shrinkage anisotropy greatly. On the basis of the former orthogonal experiment, shrinkage trend of some injection molding parts with typical shape (square, convex, concave, sector-shaped) are studied experimentally. Result indicated that plastic parts shrink along its geometry centre. Then a single factor experiment is used to research the regularity of influence of thickness on shrinkage rate. It is indicated that thickness is an important factor of shrinkage rate, the shrinkage rate increase with thickness non-linearly, while shrinkage anisotropy reduce with thickness.At last, a static visualization method for filling of injection molding is used to observe the steady expanding flow of the melt plastic in mold cavity. According to the analysis of the three stages of expanding flow, filling in injection molding is understood more impressively...