Secondary gas penetrations in ribs during full‐shot gas‐assisted injection molding

Although gas‐assisted injection molding (GAIM) eliminates sink marks and prevents warpage, many problems are encountered during gas‐assisted filling owing to gas–melt flow interactions. Large voids created by gas penetration during gas‐assisted filling result in degraded rigidity. To avoid gas‐assisted filling, the shot weight is increased to 100%. Gas is injected after the cavity is completely filled. The so‐called “full‐shot gas‐assisted injection molding” process is investigated in this paper. The effects of the processing conditions and rib geometry on the behavior of gas penetration are systematically investigated. High melt temperature and a short gas injection delay time are found to increase the length of gas penetration during full‐shot GAIM. Wide ribs and ribs with fillets cause the gas penetration length to decrease. Although the mechanisms of gas penetration for short‐shot and full‐shot GAIMs are not identical, the resulting penetration patterns of the gas void shape are similar.© 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 225–237, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10051