Abstract
In plastic goods which have rib/boss structures, partial deformation due to thermal shrinkage, called a "sink-mark" is formed. In this study, to make clear the characteristics of the sink-mark growth, and experimental and analytical approach is made. By using a T-shaped experimental mold cavity, the depths of the sink-marks are compared with both shape parameters and processing parameters. As a result, the pressure on the packing stage and the rib thickness are the most effective to cause the sink-mark growth. Also, and analytical method for evaluating the sinkmark in rib structures is proposed. In the analysis model, when the shape of the cross section does not change in the longitudinal direction, 2-dimensional transient thermal analysis by FDM is used. At the same time, by assuming the fiber elements, and by treating the model as a thermoelastic-plastic strain problem, the growth of the sink-mark in the die is theoretically evaluated. In consideration of the P-V-T characteristics of the resin, the analytical results are well-fitted to the experimental data.
