Lightweighting – the future of mobility
Special nonwovens have been at the heart of the BMW i Series initiative which is aiming to completely change the face of the automotive industry – with lightweight, carbon fibre-based cars achieving new records in fuel consumption and performance.
The lightweight nonwoven materials in question are being made from carbon fibres at a plant in Wackersdorf, Germany, as one step in a chain which sees them eventually converted into carbon fibre reinforced plastic (CFRP) components.
BMW observes that in contrast to woven fabrics, nonwoven bonding methods do not kink the fibres and detract from their special properties. The alignment of the fibres in the fabric is crucial to achieving optimal quality in a CFRP component.
CFRP has a wealth of benefits as a material for a car body. It is extremely corrosion-resistant and does not rust, giving it a far longer lifespan than metal. Complex corrosion protection measures are unnecessary and CFRP retains its integrity under all climatic conditions.
In its dry, resin-free state, CFRP can be worked almost like a regular textile, and as such allows a high degree of flexibility in how it is shaped. The composite only gains its rigid, final form after the resin injected into the lattice has hardened.
The high tear resistance along the length of the fibres also allows CFRP components to be given a high-strength design by following their direction of loading. To this end, the fibres are arranged within the component according to their load characteristics. By overlaying the fibre alignment, components can also be strengthened against load in several different directions. As a result, the components can be given a significantly more efficient and effective design than is possible with any other material.
The ability of CFRP to absorb energy is also unique.
Back in April 2010 BMW announced a joint venture with SGL to build a state-of-the-art carbon fibre manufacturing plant in Moses Lake, Washington, USA. Representing an initial investment of US$100 million, this was completed on time in May 2011 and the first of two lines became operational in the third quarter of 2011. It has subsequently expanded to become one of the biggest carbon fibre plants globally – and certainly the fastest growing.
Fibres manufactured at Moses Lake are being used for BMW’s new i3 electric vehicle which was launched in 2013 and is assembled in Leipzig, Germany.
“The selection of CFRP on this scale for a volume-produced vehicle is unprecedented, because it has previously been thought of as too expensive and still not sufficiently flexible to work with and produce,” says Hanno Pfitzer, who works in process development for BMW at Landshut in Germany, where the nonwoven fabrics are being turned into CFRP parts and components. “The extensive use of CFRP makes modules extremely light and gives the car both a longer range and improved performance. In addition, it has clear benefits in terms of the car’s handling – the stiffness of the material makes the driving experience more direct, with even rapid steering movements executed with flawless precision. At the same time, CFRP enables a higher level of ride comfort, because the stiff body dampens energy inputs extremely effectively. As a result, unwanted vibrations are eliminated.”
The BMW Group’s CFRP strategy also extends beyond the life cycle of the product and it has developed a concept for recycling segregated production waste into commercial-quality raw material. This system allows a substantial proportion of carbon fibre waste to be returned to the production process. Thanks to a special refining procedure, the resulting material can even be used as a substitute for primary fabric.
“Using CFRP is more than simply a straight substitution, like using aluminium in place of steel,” Mr Pfitzer said. “With its special properties, this material also opens the door to completely new approaches and design concepts. Provided that this material is properly understood, it can be strategically deployed to achieve vast improvements in a wide range of lightweight products.”
In a March 2016 update, BMW’s vehicle project concept manager Stephan Huber explained how the company is going further in closing the loop in this programme across the value chain – from carbon precursor to finished car component, but just as significantly, in terms of second life usage.
BMW has now developed a range of secondary uses for its production waste carbon fibre, in the forms of granulates to replace glass fibres where possible, and nonwoven fabrics for flat surfaces. Its combination of secondary carbon fibres sourced from i Series programme production is already to be found in the new centre console for the Mini Clubman, but this is seen as only the start. Other components envisaged include intake silencers, engine covers, clutch pedals, load floors and package trays.
“We are now moving towards making carbon fibre a common material in the automotive industry,” Huber concluded, “but further developments are needed to boost optimum utilisation.”
Visitors to INDEX™17 will be able to gain first-hand knowledge of the many nonwoven products currently benefiting the automotive industry.
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