Foam injection eliminates need for defect-hiding textured surfaces

A new process for molding airbag covers promises a 30% reduction in the amount of material used, less distortion in finished parts, and easier designing for engineers. At K 2013, Research institute Fraunhofer Institute for Chemical Technology ICT (Pfinztal, Germany; Stand 7/B05) will showcase thermoplastic foam injection (FIM) as a means to produce structural parts like airbag covers without the striations that can form during standard foam injection. Typically those surface marks are hidden thanks to the textured appearance. Fraunhofer Institute for Chemical Technology ICT (Pfinztal, Germany), now believe they can eliminate these striations, making the FIM the process suitable for highly visible components without the need for a textured surface.

A FIM machine operates as a standard injection press would, with one key difference: it introduces a propellant into the melt, and when this mixture is sprayed into the mold, the air pressure drops dramatically. Fraunhofer compares it to carbonated liquid in a bottle which is shaken, then opened. The reaction converts the polymer into a foam. The finished part is therefore not isopycnic, meaning equally dense inside and out, but instead has a structure more like a sandwich, with the softer foam on the interior, while the outer surface is solid and hard....

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