Travelling light

Materials World magazine
,
3 Jul 2015

Keith Watkinson and Simon Frost report from the Global Automotive Lightweight Materials conference, in London. 

Lightweighting is a key concern across the board in manufacture. A lighter automobile, aircraft or sea vessel consumes less fuel and creates fewer emissions on its journey from A to B. Its weight, of course, is also determined by its contents, so it’s an increasingly dominant factor in the design of everything from packaging to building materials. The automotive industry is making new holes in its belt every year, and representatives of the sector met in London this April to discuss their latest weight loss strategies. 

There were three recurring themes that surfaced throughout the conference, particularly in the discussions following the presentations of the papers. The major theme was the use of non-traditional lower density, high stiffness materials to achieve lighter structures. But this developed into discussion of component design, assembly and assuring quality when using new materials. The third theme, which could probably warrant a conference in itself, was the topic of damage assessment and repair following impact and this was particularly relevant to carbon fibre-reinforced composites.

Bruno Barthelemy, Ford’s Chief Engineer for Body Structures, illustrated how the company was proving an aluminium alloy strong enough for the latest incarnation of its F-150 flatbed pickup truck. A weight saving of 45% was achieved on the body-in-white – the bare frame – by replacing the majority of steel components with aluminium, and, where steel was essential, favouring the post-forming heat-treatable variety, offering higher strength with lower mass. Panels were joined together through structural adhesive, self-piercing rivets, hydroforming, mechanical spot joining and resistance spot welding. 

The use of adhesives for joining panels was mentioned by many speakers, by some as a method of achieving increased structural stiffness and by some as a problem at the end of life of a vehicle. Professor Allan Hutchinson of Oxford Brookes University showed the growth in use of adhesives so that today some cars now have adhesive bond lines adding up to more than 140 metres. He introduced an adhesive that incorporates a microspherical filler that expands when heated. Typically the filler is 10–30µm in diameter, has been surface activated and is added at 10% by weight to the adhesive. At the end of life, when exposed to a temperature in the range from 110 to 140°C for 2–3 minutes depending on the filler type, the microspheres expand and break the bond line allowing the parts to be separated. 

It was the wheels that Michael Dorney of Lacks Enterprises, USA, discussed making weight savings in, using aluminium through a novel design methodology it calls Metalltec. This involves considering a wheel as two parts – the structural part and the design surface. The structural part could be made in aluminium and its design optimised to achieve the required performance characteristics for the wheel. The car designer then has freedom to style the design surface to compliment the overall concept. It is bonded to the wheel using a lightweight foam adhesive. This design concept also allows more cost-effective model year updates. Dorney quoted examples of weight savings between 4–16kg per car by adopting this methodology.

Testing

Jan Olav Endrerud, CEO of DolphiTech, Norway, introduced a non-destructive inspection instrument that generates 2D and 3D images of an area of composite part to identify defects. To help the user interpret the images there is an extensive online library of defect images. Mark Lessard of ThermoFisher Scientific, USA, demonstrated a handheld non-destructive testing instrument that uses X-ray fluorescence to identify the chemical composition of an alloy anywhere between magnesium and rhenium on the periodic table within seconds, listing the alloy’s elemental makeup and quantities of each element on screen. The gun-shaped device, Lessard said, is already used extensively in the scrap metal and oil and gas industries, but automotive hasn’t yet taken note. 

Professor Robert A Smith, current President of the British Institute of Non-Destructive Testing, continued the topic with an overview of the work done to detect zero-volume dis-bonds (also known as kissing dis-bonds) in multilayer composites. He described five different techniques that have been assessed with none of them proving to be capable. Further work looking at the non-linear response of such defects is continuing.

Timo Huber of the Fraunhofer Institute for Chemical Technology, Germany, gave a thorough account of their work to increase the production rate and quality of composite parts through automation. He estimates that 50% of a composite's final cost when manufactured by Resin Transfer Moulding (RTM) is in the preform cutting and forming. Huber demonstrated the benefit of using clamps during preform moulding to minimise wrinkling during manufacture of a boot lid with two integral lamp holders. They favour high pressure compression RTM as it requires lower pressure and achieves much better resin impregnation into the fibres than standard high pressure injection RTM. In the former technique the mould is partially closed, the two-component resin injected over the fibre preform and then the tool fully closed to force the resin into the fibres.

Recovery

Adrian Tautscher of Jaguar Land Rover told the audience about the development of the Range Rover Sport LWV whose aluminium chassis and body is 42% lighter than its predecessor, but is 111% stiffer and has superior NVH characteristics. This development has been accompanied by changes throughout the supply chain and in working practices to implement a closed-loop recovery system. In mixed metal press shops the skeletal scrap (which can be up to 50%) of the two aluminium alloys used – 5000 and 6000 series – are kept separate and returned to the supplier to be recycled back into ingots. The project has led to the development of RC5754, a new iron tolerant grade of aluminium. It is planned for use on future models and to gradually replace NC5754 on current models. 

In the follow-on project, REALCAR2, the focus is on retaining the value of scrap aluminium material. In the UK in 2009, 42kT of aluminium drinks cans were landfilled while industry used 189kT of aluminium in transport applications. The project aims to reduce this waste by incorporating post-consumer aluminium into the alloy recovered from its pressing operations. 

In another project, carried out with the KTN/IOM3 Materials and Design Exchange (MaDE) team, car seats from a 1988 and a 2010 Range Rover were compared. It was immediately apparent how the design had developed over the 22 years. There was a significant increase in the number of components in the 2010 seat and the parts were more complicated with a number of pieces of electronics. To capture the energy in these components, rather than simply granulate and remelt them, a competition for design students was devised. The competitors were invited to re-purpose the parts. The winning design was a desk lamp built from door mirror and door lock parts. The automotive industry is set not only on reducing its weight, but its waste as well.