A Study of the Injection Molding : 1st Report, Experimental Study of the Partial Thermal Shrinkage in the Rib Structures

Abstract

In plastic goods which have rib/boss structures, partial deformation by thermal shrinkage called "Sink Mark", is formed. In this study, to make clear the characteristics of sink mark growth, an experimental approach was taken. By using a T-shaped experimental mold cavity, the amounts of sink mark were compared with each shape parameter and processing parameter. As a result, the pressure on the packing stage and the rib thickness are the most effective to the sink mark growth. When the pressure of the packing stage is small enough (less than 10 MPa), the profile on the upper plate becomes anti-symmetric because of the pressure distribution of the filling stage.