Automotive Design
the best way to work towards the new emission targets. But plastics can make an incremental difference as well, helping designers to shave off small amounts of weight here and there - which may end up being just as important. “Any saving, at gramme level, is worth it,” says Cazuc.
Reduction factor
While metal-replacement is the usual route to reduce weight, some techniques are looking to reduce the weight of existing plastic components. Mecaplast, the Monaco-based supplier of plastic automotive components, claims it can cut the weight of interior and exterior trim parts by about one-third using a new injection moulding process. It is working on a project called Plume, sponsored by the
French government, which uses specially designed ‘adjustable’ moulds - and a blowing agent - to reduce the density of moulded polypropylene (PP) components. “Parts made by this process could lead to a total vehicle
weight reduction of 5 to 7kg,” says Elsa Germain, research and innovation engineer at Mecaplast. Material is injected into a mould that has moving walls.
Once the skins of the part have solidified, the walls retract slightly. This reduces pressure in the cavity, causing a chemical
blowing agent - which had been dissolved in the melt - to come out of solution in areas that are still molten. This creates a cellular structure, which fills the newly
created space. The foaming process on its own can create a weight reduction of at least 30 per cent, compared to conventional injection moulding. But this can be improved upon by adjusting the compound
formulation. The compounds incorporate new types of reinforcing filler that improve surface quality and reduce part weight (by up to 7 per cent, while maintaining mechanical properties. Compounds with different fillers will be trialled during the project. The compounds, based on PP impact copolymer, have good flow properties and a melt flow index above 50g/10min. Mecaplast will run trials of the process on two components: a tailgate interior trim, and exterior beltline mouldings. The beltline mouldings will be produced in two versions - one with a grained surface (that requires no painting) and another that will be paintable. The project involves a number of French companies,
including compound producer Sumika Polymer Compounds (part of Sumitomo Chemical Group), mould-maker Cero, polymer science research laboratory IMP, and Cemef. The project, which started in September 2012, will run for two years with a total budget of €2.4 million.
Fibre increase But it’s carbon fibre reinforced plastics (CFRPs) that could have the greatest effect on the automotive industry - and their use is expected to accelerate in future. Consultancy Frost & Sullivan estimates an annual growth rate of more than 30 per cent, taking the market to nearly $100m by 2017 - from its current position of just below $15m. This is despite several factors that will hamper the take-up of the technology. “We identified four factors that could restrain the market,”
Fig. 2. Mecaplast’s new injection moulding process could cut part weight by more than 30 per cent.
Mainstream aim A
two-year UK research project, ACOMPLICE (Affordable Composites for Lightweight Car
Structures), is looking to develop composite materials that could one day be used in mainstream cars.
“The targets we’ve set are vehicles like BMWs or high-end Toyotas,” said Elaine Arnold, collaborative R&T project manager at Umeco and the project’s co-ordinator. Composites are usually restricted to high-end cars, as they too expensive to be used in mass market models. Arnold says that SMC short fibre materials have
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been fitted in some cars – for applications like parcel shelves – but “nothing really structural”.
The manufacturing partner in the project
is Aston Martin – due mainly to it being a UK-owned car manufacturer, rather than as a producer of mass market vehicles. Another partner is Delta Manufacturing, which will handle design for manufacture of components. The partners have identified two semi-structural components that will be redesigned in composites to save weight. Arnold says it is too early to reveal details
about them. Automation plays a key role in reducing the cost of composite component manufacture, as does materials development. Umeco is working on fast- curing resins, which would allow cycle times to be reduced. Work on the project will focus on the company’s pre-impregnated DForm material – which, says Arnold, maintains unidirectional fibre orientation while being highly formable. “It’s not yet optimised for automated manufacturing, but that’s what we’d like to do in the project,” she says. ●
says Sandeepan Mondal, senior research analyst at the company. “These are: high cost; long cycle times; a lack of engineering expertise with these materials; and recyclability issues.” The ‘low modulus’ grades of carbon fibre used by the
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