Materials
3-99
 Technical Feature  


Robots chop and change composites

Mark Fletcher reviews a process that simplifies composite part creation, defeating the cost and time limitations normally imposed by complex geometries

A consortium in the US has developed a fabrication process that promises to deliver faster turnarounds, and substantial cost savings, in the creation of complex composite parts for the automotive industry.

Instead of relying on pre-prepared mat shapes, or manual placement, the programmable powder preform process (P4) uses a fibre dispensing method which ‘sprays’ the fibres onto a screen, creating the desired 3D mat geometry prior to mould placement.

The US Council for Automotive Research (USCAR), a partnership between Chrysler, Ford and GM, is developing it for use in the automotive industry, particularly with regard to the Partnership for a New Generation of Vehicles (PNGV). The development partner is the inventor of the technology, Owens-Corning. Military projects are also under development, using carbon fibre composites for aerospace applications.

Because of the flexibility and benefits offered by composites, the application base of P4 could be huge. Those who have been restricted by budget or time constraints could use the technique to great effect.

Composites are playing an increasingly important role in engineering. Light weight and high strength are two factors that have sold this concept to numerous engineers. Another is flexibility in part shape. But there is often a cost and time penalty when it comes to fabricating geometries associated with car body components. In the past it has been possible to create bespoke mats to fit specific shapes but these are often made up of numerous pieces which are fitted together like a jigsaw – often a time intensive manual process.

P4 will remove the need for many of the manual constraints placed on this type of part creation. It uses two perforated screens which exhibit the same shape as the tool used to mould the final part. Using a computer-controlled robot, equipped with a chopper, a veil is formed by spraying glass fibre filaments onto the lower screen. Air is sucked through the screen to hold the glass in place.

Once the veil is formed, chopped or continuous glass fibres are sprayed over the veil, along with a dry powder binder. The fibres being added can either be distributed randomly or oriented to ensure specific properties. An economic advantage of the process is that it uses rovings as opposed to mats, cutting the process steps inherent with existing and manual methods.

After the veil and fibres are sprayed on to the lower screens, the upper screen is applied in the compaction station to compress the preform. At the same time, hot air is forced through the screen to melt the binder. After a short cooling, the preform is ready for demoulding. The entire cycle, including unloading lasts approximately four minutes, a massive improvement on the average time of a manual lay up process. The system is expected to run non-stop for up to eight hours without maintenance.

Because the system is automated, there is less wastage. Fibre distribution is more precise and there is less of a problem with overspray, leading to less post-forming trimming. Constant part thickness is another result of precise control.

USCAR’s Advanced Composites Consortium (ACC) P4 development work is part of a larger program aimed at lowering the cost and increasing the manufacturing rate of composites made by the liquid moulding process. The ACC and its suppliers are demonstrating this improved technology by making composite pickup truck boxes.

The ACC's manufacturing cell is the first full-scale, automated demonstration of the process. The P4 machine located at the NCC is the culmination of three years and $4 million by the ACC, Textron Automotive, Aplicator System AB, and the US Department of Energy. It has been suggested that the process could save up to 50 per cent of the costs of certain applications when metal parts are replaced by composites.

The possibility of a more affordable, highly automated composite manufacturing process caught the attention of the US Air Force last year. The Air Force Research Laboratory's Materials and Manufacturing Directorate awarded a $7.24 million contract to the National Composite’s Centre to adapt and develop the P4 process for aerospace applications.

 

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