Surface Visual Quality of Gas-Assisted Injection Molded ABS Parts with Various Gas Channel Designs

Gas-assisted injection molding (GAIM) provides many more advantages than conventional injection molding (CIM), but its applications are limited to the surface visual quality problem. ABS plate parts designed with gas channels having five different types of cross-section but with the same section area were gas-assisted injection molded. Furthermore, various plate thickness parts designed with semicircular gas channel of different radii were also molded. Surface visual quality of GAIM parts was investigated by gloss and chromatics measurements. Effects of processing parameters and geometrical factors, introduced by part thickness, shape, and associated dimensions of gas channels on glossy difference and chromatic aberration of GAIM parts were studied. Influence of mold with etching treatment on surface visual quality was also examined. Basically, it was found that glossy difference is very sensitive to the degree of crystallinity whereas gas channel residual skin melt thickness plays a dominant factor for chromatic aberration. The surface visual quality shows a strong dependence on processing conditions. In general, gas channel design of semicircular cross section (shape A) provides better surface effect than the other designs in visual quality. Meanwhile, to obtain best surface visual quality, the ratio of equivalent radius to plate thickness should be ranged from 2.2 to 2.4. Alternatively, the surface visual quality can be improved by etching treatment on mold core-side. The results of this research may provide part design guideline for choosing the most effective gas channel design to achieve the best surface visual quality.