Void shape in gas-channel ribs in gas-assisted injection-molded plates

Large, thin, plate-shaped parts are usually strengthened with structural ribs. Ribs also serve as gas channels with gas-assisted technology. Gas penetration in the gas channels results in improved moldability and also eliminates sink marks and prevents warpage. However, gas leaves the rib core void, which degrades rigidity. This study examines the shape of the gas void and its relation to rib geometry and processing conditions. The effects of rib geometry, including aspect ratio and fillet geometry, along with processing conditions such as delay time, melt temperature, gas pressure and characteristics of the GAIM molded parts on void shapes are investigated. Numerical simulation of temperature distribution in the rib area is used to aid interpretations of gas void shapes. © 1999 John Wiley & Sons, Inc.