technology | Foam moulding As part of the project, Mecaplast will trial the
process on two automotive components: a tailgate interior trim and an exterior belt-line moulding. The belt-line moulding will be produced in two versions, one with a grained surface that will require no painting and another that will be paintable. Japanese car maker Mazda has been exploring the
weight saving potential of foamed moulding since the middle of the last decade working with microcellular foam moulding technology developer Trexel. Mazda has a number of patents referencing the use of movable mould surfaces, which it and Trexel call core-back expansion moulding. The core-back expansion moulding process differs
Above: A Wittmann Battenfeld machine equipped for the CellMould system
the creation of a cellular structure that expands to fill the newly-created space. Germain says the formation of the foam depends on a number of factors, including the mould and part design, and the properties and temperature of the polymer. The company says the foaming on its own enables a weight reduction in the part of at least 30% compared to a conventional compact moulding. Mecaplast says the technique, which it has made a
patent application for, is similar to that already used in Japan for production of parts by automotive companies such as Honda and Toyota. However, it claims the Japanese technique has limitations in terms of surface finish because it uses talc-filled PP compounds. The Plume process will use compounds that
Below: Foam structure in a moulding made using the
CellMould “fine structural” system
incorporate new reinforcing fillers that improve surface quality but also help reduce part weight by as much as 7% without loss of mechanical properties. The company has previously published results of trials it has carried out using Milliken’s Hyperform HPP-803i reinforcing agent (see Compounding World, May 2012, page 55) in TPO formulations.
Germain says the Plume project will focus on the
development of a range of compounds using a variety of fillers in impact modified PP copolymers. The resins are being developed specifically for the Mecaplast process, which requires high flow products with melt flow ratings of more than 50 g/10min.
from Trexel’s traditional Mucell moulding process in allowing the creation of a very low density core in the part. In industrial trials carried out with Mazda it has achieved weight reductions in parts such as door panel liners of up to 30% using the technique; using the Mucell conventionally typically results in weight savings of around 10%. According to Trexel, the initial phase of the core-back
process results in the formation of a skin layer with a low level of foaming and relatively good aesthetics. When the mould is opened (or cored-back), the pressure in the mould drops and the gas in the molten core rapidly comes out of solution to create a core with a very low density. Trexel’s Mucell technology is being used by Ford in
its Escape and Kuga instrument panel (IP) carriers, where it has saved about 0.5 kg per part. Volkswagen is also using the technology in its Golf IP carriers. Meanwhile, UK-based Coraltech’s Coralfoam
technology produces lightweight foamed parts using a combination of core-back injection moulding techniques and foam producing additives, claiming potential weight savings of 30% or more along with improved stiffness to weight ratios in parts designed to utilise the technology to the full.
Wittman Battenfeld has been active in the structural
foam and gas assisted moulding sectors for more than 40 years. However, the company also has its own direct nitrogen injection system for production of foamed parts. The system is marketed under the Cellmould
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COMPOUNDING WORLD | August 2012
www.compoundingworld.com
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