BASF says manufacturing composite components using atomised polyurethane, in a process known as spray transfer moulding (STM), is helping vehicle manufacturers achieve strong, lightweight interior and exterior automotive components in nearly any design or shape.
Spray transfer moulding is a process where atomised polyurethane particles are sprayed onto a non-woven material with a high-pressure nozzle, then moulded into the desired shape, providing a rigid, lightweight design.
“Spray transfer moulding typically uses a fabric supported by a core material such as paper, foam, metal or polymer, which is then overlayed with a fibre reinforcement and sprayed with a two-component polyurethane system,” said Michael Barry, Market Segment Manager at BASF. “Next, it’s put into a press that moulds it to the final shape as the polyurethane cures, and the result is a component that’s very stiff and light, relative to other solutions.”
BASF said these lightweight parts add structural integrity in areas where other materials, such as steel or aluminium, may be too heavy or costly. A polyurethane load floor made with STM, for example, can weigh up to 50 per cent less than one made with heavier polypropylene, without sacrificing performance.
Although spray transfer moulding has been used to create interior automotive components for some time, BASF said the list of applications where it can be used on the vehicle’s exterior is growing quickly. In the interior space, STM is commonly used to create components such as package trays, door panels and sunshades.
“We’re just now starting to scratch the surface for potential exterior applications,” Barry said. “Applications that we’re looking at include reinforcements for body panels and tailgates, tonneau covers and underbody panels – things with relatively simple geometry but where low weights and stiffness are highly desirable properties.”
According to BASF, although the paper core isn’t resistant to water, the surrounding fibre reinforcement and polyurethane provide an extremely tight seal, along with structural integrity, to ensure no failures occur.
“The components we’ve made perform really well with impact testing against stone impacts or other debris from the road,” Barry said. “They also have strong chemical resistance, and the typical exposure to salt, fluids, oils or other debris isn’t really a problem for this type of material.”
BASF said the benefits of this technology also aid aesthetics. In-mould coating, or RIM application, can be seamlessly integrated in the process, enabling manufacturers to achieve excellent Class A exterior surfaces on components made with STM.
The company said every 100-kilogram decrease in vehicle weight results in a 3 to 5 per cent decrease in carbon emissions, depending on total vehicle size and powertrain type.
According to BASF, the ability to incorporate natural renewable fibres is another important benefit of STM components. BASF’s Elastoflex polyurethane is composed of a high percentage of castor oil, a bio-renewable resource derived from the ricinus communis plant, native to tropical areas of Africa and Asia.
“We’ve focused on developing polyurethane chemistries that have, in part, come from bio-renewable resources,” Barry said. “We’ve also done quite a bit of development incorporating natural fibres, like jute.”
BASF said jute fibres are an environmentally friendly natural material produced from jute plants and can deliver strong tensile strength of 104.9 ± 8.8 megapascals when treated.
Some cars on the road today make use of spray transfer moulded components for their exteriors. BASF said the Mercedes-Benz Smart Fortwo’s roof is an example of this technology in action, employing a honeycomb sandwich structure with a Class A film that’s 30 per cent lighter than the standard roof on the previous model.
“BASF has taken a position of leadership, pushing the possibilities that spray transfer moulding can offer for these exterior applications,” Barry said. “We’ve learned a lot and we’re continuing to develop the chemistry and the processes to make it easier and more cost effective to implement STM on a broader scale in other applications, as well.”
The company said it provides expertise and assistance to vehicle parts manufacturers looking to create concepts and test designs for STM components. With BASF’s state-of-the-art lab in Wyandotte, Michigan, customers can design, build and test their ideas, allowing them to test the feasibility of a design with minimal risk and investment.
“We can take an idea from a concept to production, with both the resources and experience to make sure the chemistry works, as well as the manufacturing capability to test it before significant production investments are needed,” Barry said. “Five years from now, I think we’ll have multiple examples of commercially available exterior solutions using spray transfer moulding technology.”