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. Structural properties of the foamed part like surface finish, overall density, and skin layer-thickness as well as mechanical properties are examined.

Keywords

polypropylene structural foam foam injection molding mold design high density reduction.

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