Abstract
A burn mark is a sort of serious surface defect on injection-molded parts. In some cases, it can be difficult to reduce the burn marks by traditional methods. In this study, external gas-assisted injection molding (EGAIM) was introduced to reduce the burn marks, as EGAIM has been reported to reduce the holding pressure. The parts with different severities of burn marks were produced by EGAIM and conventional injection molding (CIM) with the same molding parameters but different gas parameters. The burn marks were quantified by an image processing method and the quantitative method was introduced to discuss the influence of the gas parameters on burn marks. The results show that the burn marks can be eliminated by EGAIM without changing the structure of the part or the mold, and the severity of the burn marks changed from 4.98% with CIM to 0% with EGAIM. Additionally, the gas delay time is the most important gas parameter affecting the burn marks.
Highlights
Manuel Mercado-Colmenero, Injection molding is one of the most important mass production methods of plastic parts [1–3]
The parts were molded by conventional injection molding (CIM) and external gas-assisted injection molding (EGAIM), and different severities of burn marks appeared on the molded parts
The severities of burn marks were quantified by the image processing method
Summary
Manuel Mercado-Colmenero, Injection molding is one of the most important mass production methods of plastic parts [1–3]. Some defects commonly appear in injection-molded parts, such as flashes [4], warpage [5], weld lines [6], burn marks [7], sink marks [8], etc. A burn mark is a kind of surface defect that shows a dark or black character in certain places on the part surface. This defect affects the appearance and mechanical properties of the molded parts greatly. Mesgaran et al [10] modified the mold structure to eliminate burn marks. The burn marks decreased with the modified mold. It is not always possible to modify the gate location or mold structure of injection molds
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