Design Chain – Advantage foam in the automotive world
By Lou Reade
Posted 20 November 2012
The use of foam in car exterior and interior trim parts can lead to significant weight reduction.
Mecaplast, a Monaco-based supplier of plastic automotive components, says it can cut the weight of interior and exterior trim parts by at least 30%, using a new injection moulding process.
It has just begun working on a project called Plume, sponsored by the French government, which uses moving cores - 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 between 5 and 7kg," says Elsa Germain, research and innovation engineer at Mecaplast.
In the process, material is injected into a mould with moving walls (which begin in the forward position). Once all the material has been injected, and the skins of the part have solidified, the walls retract. This reduces pressure in the cavity, causing a chemical blowing agent - which had been dissolved in the melt - to come out of solution in those areas that are still molten.
This creates a cellular structure, which fills the newly created space. The foaming process alone can deliver a weight reduction of at least 30%, compared to a conventional solid moulding.
This can be increased by the compound formulation. These compounds incorporate new types of reinforcing filler that improve surface quality and reduce part weight (by up to 7%) without loss of mechanical properties.
Compounds with various fillers will be trialled during the project. The new compounds, based on PP impact copolymer, are being developed exclusively for Mecaplast. They 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.
Cemef will study the effects of melt rheology on the process, as well as carrying out analysis of the microstructures created by the chemical foaming. The role of IMP is to study the mechanical behaviour of parts made under various conditions. The project, which started in September, will run for two years with a total budget of €2.4m (£1.9m).
Take a seat
Seating is another area where OEMs and Tier Ones are trying hard to reduce weight. Two recent projects show how plastics are being used in this area.
Rhodia, for instance, is helping Faurecia to reduce the weight of seat components, as part of the Lightweight Hybrid Composite Structures (Lycos) project.
The two companies are designing and developing metal-replacing seat cushion structural components using Rhodia's Evolite - a thermoplastic composite, based on Technyl polyamide that contains continuous fibres of glass, carbon or other materials.
Evolite is available in recyclable matrix, pre-impregnated fabric, unidirectional tapes and consolidated plates.
"Co-innovation projects compress R&D schedules and are a significant step towards the introduction of advanced polyamide thermoplastic composite materials as an alternative to steel for automotive structural parts and applications," says Thierry Renault, manager of partnerships & expertise network at Faurecia Automotive Seating.
At the same time, the Opel Astra OPC - a sports coupé that saw its debut earlier this year at the Geneva Motor Show - features a seat pan made from continuous fibre-reinforced thermoplastic laminate (known as 'organo sheet').
The laminate comprises two special grades of BASF's Ultramid polyamide specialties: a non-reinforced grade, which serves as an impregnating material for the glass-fibre fabric, and an impact-modified, short fibre-reinforced Ultramid that is used to overmould the preform, creating the necessary strengthening ribs and edges.
The high strength of the laminate allows wall thickness to be reduced, cutting the weight of the seat pan by 45%.
"This is the world's first auto seat pan in a mass-produced vehicle that uses this technology," says BASF.
This is just one aspect of BASF's efforts to identify lightweight automotive components. Last year, it established a cross-divisional collaboration, which it calls the lightweight composite team. The team is investigating the suitability of three plastics - epoxy resin, polyurethane and polyamide - for making continuous fibre reinforced parts using mass production processes like resin transfer moulding (RTM).
It has already built a demonstrator component, in the shape of a multi-segmented convertible roof module in which a PUR foam core is sandwiched between carbon-fibre reinforced cover layers.
The core is a closed cell structural PUR foam called Elastolit D. It acts as a spacer between the skins of the laminate, ensuring high component stiffness - and also provides the roof module with good insulating properties.
The roof segment made using this technology weighs just 2.6kg. BASF says this is 40% lighter than a comparable aluminium part, and 60% lighter than one made of steel.
Although plastics are used more extensively than ever before in the automotive industry - accounting for around 20% of the average car by weight - the weight of cars has been increasing by around 15kg per year over the last few decades.
"This now needs to reverse, in order to deliver CO2 reduction targets," says Patrique Cazuk, EMEA marketing manager for automotive at DuPont Performance Polymers. "The main driver for weight saving is undoubtedly CO2 reduction."
Cazuk: Cutting CO2 emissions is behind weight-saving
And the targets are very tough, especially in Europe: current CO2 emission levels of 165g per km driven must be reduced to 130g/km by 2015 - and down to 95g/km by 2020.
On average, every 100kg of weight reduction brings a 10g reduction in CO2 emissions. Simple maths shows the magnitude of the task in hand.
"Lightweighting is one of the primary factors that can help to achieve this reduction," he says, though says it will achieved alongside other factors such as greater engine efficiency and reduced rolling resistance of tyres.
Plastics have already consigned many metal parts to history: air intake manifolds are just one example. But the changing nature of modern cars - whose engines often run at higher temperatures - means that materials must be more robust than before.
An example here is engines that use exhaust gas recirculation, or EGR, which helps to reduce emissions of NOx gases. These gases are produced at very high temperatures,
"An air duct that was once a simple part must now withstand a much harsher environment," he says. "It's this kind of thing that drove us to develop our Zytel Plus range."
Zytel Plus is a family of PA66 resins that have higher heat stability and temperature resistance. The materials were developed in direct response to the needs of OEMs.
Replacing a large metal part with plastics is the surest way to start reducing car weight, and make progress towards the new emission targets. But plastics will continue to 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.
"At the end of the day, every gramme counts," says Cazuk. "Any saving, at gramme level, is worth it."
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