Study on surface quality and cell morphology of foamed components fabricated using gas counter‐pressure with core‐back and high‐pressure foam injection molding with core‐back process

The core‐back process has substantially increased the range of applicability of foam injection molding (FIM) by increasing the pressure drop rate and expansion ratio. However, cell nucleation and growth occur concurrently with the flow of the melt/gas mixture during the filling stage, resulting in poor surface quality and a non‐uniform cell structure. This study investigated foam injection molding with gas counter pressure (GCP) and core‐back to produce foamed components, with comparison to high‐pressure FIM with core‐back process. Through this method, the nucleation during filling is suppressed. The surface roughness was improved to 0.987 μm, a 59% reduction compared to high‐pressure injection molding foam with core‐back. In addition, the cell uniformity was improved, measured at two locations near and far from the gate, the cell density reaching 1.7 × 105 and 2.1 × 105 cells/cm3, and cell size measuring 120.88 and 129.57 μm, respectively. GCP also prevented the formation of the bubbles larger than 500 μm at the location far from the gate. Even at the lowest recommended mold temperature, the combination of GCP and core‐back enables the production of high‐quality foamed components with reduced cooling time.Highlights Preventing the simultaneous occurrence of cell nucleation, growth and melt flow. Foamed material with high surface quality produced by FIM. Improving the cell uniformity throughout the foamed component. Feasibility of GCP technology in conjunction with core‐back process.