Controlling Morphology of Injection Molded Structural Foams by Mold Design and Processing Parameters

Abstract

By the invention of foam processing techniques using physical blowing agents, the area of foam injection molding has caught the attention of product developers in industry as well as of researchers. Compared to conventional injection molding, the foaming approach delivers a great potential in the manufacturing as well as in the part itself, offering a monetary benefit, being vantages for example automotive and consumer goods producer (Hyde, L.J., Kishbaugh, L.A. and Katterman, J.A. (2002) [1]. How Microcellular Foam Molding Changes the Cost Structure of Injection Molded Automotive Components: A Review of the Process and Automotive Applications, SAE Technical Paper Series). The pros are facing several cons in the part quality,notably an impaired surface finish, an over-pronounced loss in mechanical strength and toughness or some uncertainties in subsequent processing steps like varnishing and plastic welding. Actual researchers are approaching those challenges in different ways (Dassow, J. (2003) [2]. Foamed Parts with Excellent Surface Quality, Kunststoffe-Plast Europe, 93(9): 65). On the one hand, the choice of the appropriate polymeric materials has a big impact on the morphologies and the properties of the obtained foam injection molded parts. The mold as well as the processing parameters have a big effect on the obtainable foam morphologies and thus the final part properties.This study presents some possibilities to control the morphology of structural foams at high-density reductions (>50%) by an intelligent mold and process design. Parameters affecting the morphology of the foamed part like the foaming temperature, the cavity pressure, and the expansion ratio are varied.

Thermoplastic Foams: Processing, Manufacturing, and Characterization

“…As a result, a frontal low in the core of the polymer melt is generated as shown in Figure 7. This results in a compact skin layer and a foamed core [18][19][20].…”

“…It is generally deined as 0.04-0.30 g/cm 3 . Cell distances have shown that they have a deinite inluence on the mechanical properties of thermoplastic foams [16,19]. The morphology of the foam injected part can be divided into ive zones.…”

“…As shown in Figure 8, the zones from one mold wall to the other mold in the cavity are skin layer-outer foam core-inner foam core-outer foam core-skin layer. Inner core has the cells with the largest diameter due to the slow cooling rate of the material in the core region, and cells have time to expand [16,[18][19][20].…”

“…Sporrer and Altstadt [19] obtained PP foams by physical foaming, MuCell technique. The efect of process conditions on cell morphology was observed.…”

A new insight into foaming mechanisms in injection molding via a novel visualization mold

“…The location of the viewing windows in the fixed plate, on the opposite side of the mold cavity, makes it possible to perform various experiments by simply changing the mold insert, some of which includes, but is not limited to, gasassisted FIM studies, shear/extension induced FIM, and the study of flow in various channels. Also, the mold can be utilized to investigate other FIM technologies such as gas-counter pressure (GCP) [12,13] and mold opening (core back) [9,10,14,15]. The designed mold can be utilized to further investigate the mechanisms of bubble nucleation/growth, interaction between bubbles and fillers [16,17], the effect of formed crystals on foaming [18], weld-line studies [19], defects [20], and model verifications [21].…”