Articles

FEATURE: Knitting the Future – technique enables quick, easy and customisable composite parts

Mike Farish

(Credit: Shutterstock)
(Credit: Shutterstock)

Composite materials are no longer exotic or unusual in applications in which low weight and high performance are the primary requirements.

But the cost of the materials, coupled with complicated and lengthy manufacturing processes in which manual ‘lay-up’ of materials may be followed by extended periods of energy-intensive high-temperature curing, means that they are found only in expensive niche contexts – aerospace, high-end cars and top-of-the-range sports equipment are examples.

But a small UK company with just 23 employees believes it might have come up with a means of making that scenario obsolete, particularly for the manufacture of composite parts using a thermoplastic matrix with a reinforcement such as carbon fibres. 

The company is Shape Machining, which was founded just five years ago and is now based in Witney, Oxfordshire. As founder and managing director Peter McCool explains, the company is confident that it has found a way of enabling the manufacture of such parts that is not just easier and faster than previously, but also enables a higher degree of customisation of their properties.

(Credit: Charlie Best)

Peter McCool (Credit: Charlie Best)

McCool, who originally set up the company as a specialised supplier of machining services after a previous career spent largely in the Formula One racing industry, says that a number of factors are involved, including the type of raw materials and the techniques both for creating the uncured initial ‘preform’ and the curing process itself.

On the first of those counts there is no innovation on the part of Shape – instead it uses readily available materials from a mainstream supplier. But on the second, the company has developed two technologies of its own that provide the key attributes of product customisation and process speed.

The first of those technologies, which it calls ShapeTex, involves the adaptation of a flat-bed embroidery machine to stitch together flexible preforms from bobbins of thread onto a sheet of backing material. This enables the reinforcement fibres to be laid in any required orientation and in variable concentration on a layer-by-layer basis so that the final parts can be highly customised with, for instance, increased strength in areas of higher stress. 

The second technology, which the firm calls FastForm, is a rapid compression forming technique that enables the composite part to be formed and then retrieved several times faster than can be achieved by existing processes.

Carefully shaped

The ShapeTex process has existed at its present level for three years. It came about as the result of an approach from materials supplier Coats, which was looking for a partner to explore the potential of a new material type it had developed for the manufacture of composite parts – a ‘comingled’ mixture of threads of carbon fibre and another material in a roughly 52:48 ratio. 

One input to the embroidery head of the machine will therefore be a bobbin of material of that type while the other will be a bobbin of the identical non-carbon fibre material alone. Both sets of threads will then be stitched by the machine to a backing layer again of whatever non-carbon fibre material is being utilised to create a flexible preform. Commercial director Ryan Muller says that those materials could, for instance, be nylon, ABS, polypropylene or PEAK. 

(Credit: Charlie Best)

(Credit: Charlie Best)

Shape’s contribution to the process has been, says Muller, to adapt a machine that might otherwise be used with materials such as cotton or silk in garment manufacture to the demands of creating lay-ups for what will eventually become composite parts for high-performance engineering applications. This has, he indicates, mainly involved developing programming capabilities to enable the machine to work with the materials involved. Otherwise the machine itself remains unaltered.

The consequence is what Muller says is a comprehensive tailored fibre placement capability, which enables the stitching of very intricate shapes with tight radii that in turn facilitates the creation of complex structures. The alternative, he adds, is an approach known as automated fibre placement which employs a robotically manipulated roller. But that process, he says, requires a larger area in which to operate and cannot create structures of comparable complexity.

Source of strength

Two factors are key to the overall effectiveness of the process when a thermoplastic matrix is being utilised. The first is the comingling of the reinforcement and matrix materials on a single bobbin – the contribution of the material on the other bobbin being to ensure that the directional stability of the carbon fibres is maintained during processing. 

“The comingling of the carbon and the thermoplastic material is what gives the structure its strength,” he says. “The thread on the other bobbin is purely to keep the carbon fibre in a particular orientation, while the purpose of the backing material is to maintain the tension of the thread to lock the whole structure together. If we didn’t have that comingling, then we wouldn’t have enough of the thermoplastic material to wet out the whole structure and the final part would be too dry and hence porous.”

(Credit: Charlie Best)

(Credit: Charlie Best)

The second factor is that the stitching of the preform is a completely automated process in which the machine operator is effectively just a supervisor, although at the moment the tensioning of the backing layer is a manual procedure. Interestingly Muller adds that the process itself cannot be patented but that instead design protection has to be gained for particular products made with it. He indicates that that is being sought now for a “footplate” – effectively the inner sole of a sports shoe. 

Nevertheless he is confident that Shape is the only company anywhere using a machine of this sort for that purpose and that in doing so the combination of “accuracy, speed and repeatability” it can achieve is unprecedented. So, although the machine itself is a standard piece of equipment, what it achieves in the new application that Shape has invented for it is something previously unattainable.

Top secret

But while the ShapeTex machine stands clearly on view on the company’s shopfloor that is not the case for the FastForm process, which the company only formally announced earlier this year. Instead the equipment is kept behind closed doors away from any prying eyes that might gain an insight into its operation. 

What Muller will say, though, is that its rapidity is achieved through its design and its use of an exceptionally rapid cooling technique the details of which are confidential. This means that when the equipment is used to manufacture a part with a thermoplastic matrix the lengthy cooling period that would otherwise be required to allow the part to harden before it can be retrieved is almost entirely obviated. 

(Credit: Charlie Best)

(Credit: Charlie Best)

The process is also marginally faster if a thermoset matrix is involved but since such materials can be retrieved hot in any case the primary benefit the process provides is not of such importance in that instance.

But when a thermoplastic material is involved Peter McCool says that the time from opening the press to put the uncured preform into it to opening the press again to retrieve the now cured composite might typically be “a couple of minutes” compared to a period several times that which might otherwise be the case. 

Energy savings are also considerable with the curing process using less energy in total, he explains, “than might be wasted as noise” by existing techniques. In the case of the footplate that was used as the development test piece he confirms that the part was pressed in a sub-two-minute cycle time at 80bar pressure and appears to be completely void free. In fact, footplate products have already been supplied to customers in the first commercial applications of the technology.

Carmaking targeted

McCool is confident that Shape has developed a process with major potential for enhancing the manufacture of composite materials and that the task for the firm now is to find outlets in further industries, with the automotive manufacturing sector a prime target. “The ability to manufacture carbon parts in minutes, reliably and in a fully automatable process, is a significant breakthrough,” he says. He adds that the process has been used to test a wide range of thermoplastic materials and that in every case processing times were faster than any other composite technology could achieve. 

“For production runs from 50 to 30,000 units per year the FastForm process should be the most cost-effective solution for composite part manufacture,” he states. “But when the process is fully automated production volumes of 100,000 per tool per annum should be possible.”

In turn that enables McCool to be extremely bullish about the prospects for what at the moment is still a small company tucked away in a corner of an industrial estate in a small town. “I am confident that this process will allow us to manufacture high volumes of composite parts for a wide variety of industry sectors,” he says. “We aim to be the UK centre of excellence for thermoplastic composite production.” 


Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.
Share:

Read more related articles

Professional Engineering magazine

Professional Engineering app

  • Industry features and content
  • Engineering and Institution news
  • News and features exclusive to app users

Download the Professional Engineering app

Professional Engineering newsletter

A weekly round-up of the most popular and topical stories featured on our website, so you won't miss anything

Subscribe to the Professional Engineering newsletter

Opt into your industry sector newsletter

Related articles