Crossing the finishing line for large carbon fibre components

Headquartered in Fontwell, West Sussex and operating from four sites near the south coast of England, GTR Composites is probably best known for supplying Formula One teams with high quality carbon fibre components and assemblies.

However, it is much more than just a motorsport expert, with an ever-increasing reputation for special projects and all things automotive. The highly specialised subcontractor has produced lightweight chassis and other large parts from composite materials for a long time, but at the beginning of 2021 it started final-machining them to tolerances measured in tens of microns.

Introduction of this new service followed the purchase of a German-built Zimmermann FZU400 5-axis machining centre, installed at GTR's Bognor Regis facility at the end of 2020 by UK sales and service agent Kingsbury. Having a 4,000 x 3,000 x 1,250mm working envelope, the portal machine was selected from a shortlist of three due to its ability to hold very high accuracy.

For example, a positional tolerance of 50µm is achieved on features across a full chassis, while holes and counterbores are held to within 10 or 20µm. As the components being produced are of high value, GTR adopts a policy of having an operator permanently in attendance, even when the FZU400 is running overnight.

Simon Kingdon-Butcher, joint owner, with John Biddlecombe, of GTR explains: "The investment has allowed us to expand our business not only in the motorsport sector but also on special projects and into more production chassis work for road-going supercars. We are presently producing 14 chassis for the research and development phase of such a vehicle.

"The Zimmermann machine stood out in terms of its rigidity, which translates into the tight tolerances we are able to hold when cutting carbon fibre. We’re able to impress our customers by hitting really tight limits that our competitors cannot achieve. This investment has quite literally moved us ahead of the rest.

"High spindle power – 34kW continuous/41kW peak – enables us to rough aluminium moulds, while spindle speeds up to 24,000rpm means their surfaces can be finish-machined to very high quality using minimum quantity lubrication.

"MQL also enables us to mill and drill carbon fibre components containing titanium or aluminium inserts in the presence of a specific type of coolant approved by our customers."

He added that their other large capacity 5-axis machining centres are focused on pattern making and while carbon fibre can be cut on them, the parts would typically be of less demanding accuracy than the Zimmerman FZU400 is capable of delivering, despite its much larger working envelope. However, the machine is also used for large pattern work and he regards the versatility of the new capacity as an ideal fit for GTR.

The company is no stranger to making big components in large quantities, having produced 250 chassis in recent years for the MoD's Foxhound patrol vehicle. Transition to final machining of larger structures and assemblies in carbon fibre, which entails cutting cycles of up to 60 hours, is therefore proving seamless for the subcontractor.

The addition of production volumes for supercars is seeing work for the motorsport sector, although remaining at a constant level, fall gradually from 90% of turnover to probably around two-thirds as the company expands.

The HSK-A63 spindle head of the thermo-symmetrically designed Zimmermann FZU400, which is fitted with extraction to manage the carbon fibre dust, has ±300° C-axis rotation and an A-axis swivel of +125/-95°, the resolution being 0.0001°. Tools are exchanged automatically from a 61-station magazine. Acceleration at up to 3m/s² to 60 m/minute feed rate in the linear axes ensures high productivity and short non-cutting times.

Discussing the subcontractor's relationship with the machine supplier Kingsbury, Mr Kingdon-Butcher concludes: "We've had some horror stories with unreliable machine tool companies in the past but we made the right choice this time.

"Kingsbury's local engineering support, service and parts availability could not be better. Back-up has been impressive since they installed a pair of smaller 5-axis machining centres of a different make a couple of years ago and it is proving to be so again.

"They understood the high knowledge level of the GTR machinists they were instructing after the Zimmermann was commissioned and tailored their training to suit their needs. It was a good all-round experience."

A video of Simon Kingdon-Butcher speaking about the installation of the Zimmermann FZU400 at GTR Composites can be viewed at: https://kingsburyuk.com/video/gtr/

Kingsbury
www.kingsburyuk.com