Automotive OEMs are more and more interested in structural foam for both interior and exterior applications. European Plastics News reviews what four OEMs said about the process at VDI's 2012 event.
BMW, Ford, Porsche and VW all presented papers at the VDI plastics in automotive engineering conference in Mannheim, Germany, in March, about how foam moulding can save weight and cost.
Ford started using structural foam in 2003 to avoid warping and sink marks, as well as the weight and cost benefits, said Ford research engineer Dr Carsten Starke.
Ford has produced a climate control panel made with 17% glass fibre reinforced ABS by using Trexel's MuCell microcellular physical foam process. More recently, the company applied MuCell to Ecoboost engine covers on various cars and the instrument panel on the 2012/2013 model year Ford Kuga CUV.
Starke said Ford is looking at online pressure, viscosity and temperature measurement to more reliably predict processing conditions and part properties.
Wheel surround body panels, made in a structural foam with a Class A painted surface, were described by Fred Wšlfle, Porsche materials specialist, and Ralf MŸller, product development manager at moulder Scherer+Trier.
The 20% talc-filled PP material exhibited flow front bubbles, surface streaking and creases with high physical foam pressure (100-250bar). The company selected low pressure (less than 30bar) chemical foaming with Hydrocerol blowing agent masterbatch to mould a complex ribbed part without sink marks.
Closer temperature control reduced variations in weight and eliminated occasional "hammered" surface effects which were due to an inhomogeneous foam structure.
Surface appearance was still matt, requiring four-layer painting instead of conventional three-layer painting. Wšlfle said the single part solution is much less expensive than two-part designs in hand-painted low series cars.
He added that three-layer painting may be possible using gas counter pressure, variotherm tool temperature control, thermal insulation coating of tools and/or two-component sandwich moulding. This would favour large series production, he concluded.
Dr Ignacio Bersch, based in the component development department at Volkswagen's Wolfsburg plant, described a material concept for large-scale production of finished colour horizontal body panels. This process involves in-mould coated structural foam moulding, and is intended to compete with resin transfer moulding, sheet moulding compounds and steel/aluminium.
Bersch presented "same bending strength" comparisons to benchmark 0.75mm steel, for which the cost was represented as 100%. To achieve the same bending strength would require: 1.1mm aluminium (at 192% cost); 4.2mm compact mineral filled EPDM and modified PP (at 109%); and 2.7mm mineral filled PC-ABS (at 196%). Foaming reduced the latter to 140%, and its weight fell by 40% from 3.5kg/m3 to 2.5kg/m3. Comparative kg/m3 figures are 5.9 for steel, 3.0 for aluminium and 4.6 for compact mineral filled EPDM/PP.
Bersch said the in-mould PUR coating reflowed to self-heal scratches after one hour at 60°C or one week at room temperature.
VW's new Golf 7's IP will involve MuCell foam when launched at the end of 2012. R&D chief Dr Ulrich Hackenberg showed 20% IP stiffness improvement with structural foam over compact thermoplastic. It also provides a 20% weight saving and 15% cost reduction.
"Structural foam looks like a coming trend," said Hackenburg.
Borealis said BMW is using its Nepol GB215HP material in its SGI (SpritzgussIntegralschaum) chemical integral foaming injection process. The material is 60% long glass fibre reinforced PP masterbatch, and this is dosed 33% with unfilled virgin and recycled PP for instrument carrier panels.
In a paper on a cockpit concept of the future, based on the BMW 1 and 3 series cars, Thomas Reisch, interiors project manager at BMW, said masterbatch saves 20% material cost over ready LGF PP granulate, and recyclate saves another 8%.
Reisch said further lightweighting should come from using injection-compression structural foam moulding to reduce component wall thickness from 2.0mm to 1.8mm.
