Recent developments by German TFP machine manufacturer ZSK which improve the TFP production process now mean carbon composites can be used in many applications.
“TFP completely changed our view of how carbon composites could help to achieve weight and cost targets,” says Elemental’s composites manager, Peter Kent. “We found it created pre-forms very quickly, is cost effective, and very durable. The resulting structural rear bodywork on the Elemental RP1 is tough enough to withstand impacts such as extensive stone chips and has a complex 3D shape with compound curves. This is at odds with the traditional qualities of carbon fibre components.”
Shape Group has developed its TFP facility using technology from ZSK, which has developed a number of innovations to allow scaleable mass production. Based upon techniques used in the embroidery industry, TFP involves the laying down of carbon fibre threads or rovings onto a substrate to make a 2 dimensional preform that is ’net shape’. Wastage, handling, and complexity are all reduced over traditional methods, which gradually build up layers of carbon fibre mat by hand as part of a labour-intensive process. TFP has the added advantage of allowing complex 3D shapes to emerge in the mould through clever fibre laying and stitching whilst making the preform.
Shape Group specialises in carbon composite tooling, and has a division dedicated to design and manufacture of TFP components. Peter McCool, managing director, says the motivation to consider TFP came from his time as a chief designer in Formula One.
“Traditional methods can be very limiting, not just in terms of design and cost, but also the properties of the material, which is brittle and not able to withstand knocks or abrasion. I felt certain there must be a better way.” McCool found that ZSK’s TFP solution was a perfect fit: “A scaleable, flexible and cost-effective technique which opens up many new opportunities for carbon composites. ZSK has worked hard to make the process efficient and effective with high reproducibility and built-in quality control.”
Driving efficiency over tradition
The traditional method of carbon composite manufacture involves a complex cutting and hand-laying process which can see more than a third of the material wasted before it is even used. Since carbon is at its strongest in the direction of the fibres, accurate orientation is critical to providing a strong component.
“Hand laying is labour and energy intensive and open to error, and the result is often sub-optimal when considering the components’ strength,” explains McCool. “This leads to over-engineered designs with extra layers. However, TFP allows us to align the fibres precisely to optimise strength, to bear the loads present on the component and accelerate development and manufacturing times.”
Peter Kent agrees. “We have been able to design a bodywork component with Shape in carbon composite using TFP which can act as a structural component, carrying bodywork and the rear luggage bins, and considerable aerodynamic forces.”
TFP comprises a thermoplastic resin, which helps overcome the brittle nature traditionally associated with carbon fibre. It also offers significant benefits when it comes to end of life recycling, as the carbon can be melted out of the heated component at about 300°C and recovered, rather than going to land fill.
As Peter Kent demonstrates, the technique is able to create a much tougher material than thermoset alternatives: “We took a component from a development car for examination, and there wasn’t a mark on it,” he concludes. “At Elemental we’ve been very impressed – there are so many parts that could be made in carbon fibre using TFP. It really is very exciting.”
Companies: ZSK Stickmaschinen
Industries: Automotive and Road Transportation
Technologies: Fiber Placement