GKN Aerospace has seen automation bring major improvements to composites production. Five years ago, the company began to introduce automation into its composites’ manufacturing processes, initially replacing traditional hand lay-up. The potential economic viability was soon realized and deposition rates rapidly increased.
The advent of production of the Airbus A400M wing spar in late 2006 at the company’s Advanced Composites Facility on the Isle of Wight in the U.K. brought with it the opportunity to further enhance its automation capability with the introduction of automated tape lay-up (ATL). “The machine used is an MTorres gantry-mounted tape head capable of laying either 150- or 300-mm wide tapes at up to 40 lb/h,” said John Cornforth, GKN Aerospace’s Head of Technology. “The manufacturing process comprises preparing a flat laminated stack on the ATL and hot drape forming it into its final ‘C’-section spar shape before autoclave curing on a male tool. The design process uses Catia V5 to capture the geometric definition and FibreSIM to accurately determine the developed shape of the plies from the true spar shape.”
The ATL is able to produce a flat laminated stack much more rapidly than hand lay-up can achieve. “Longitudinal ply orientations can also be put down very quickly,” said Cornforth. “Transverse ply orientations take considerably longer. After each 300-mm wide strip, the machine has to stop, cut, and turn the head before starting the next one.”
Although an ATL provides a very efficient means of producing spar-type components, there are limitations to the geometric features that it can handle at tape widths of 150 mm and above. The more highly shaped the component, the narrower the tape has to be to successfully lay on to that surface without encountering fiber buckling. Also, the longer the tape consolidation roller, the shallower the ramps must be for successful deposition.
It is such limitations associated with ATL that are driving the demand for automated fiber placement (AFP) once a certain level of geometric complexity has been reached. “AFP machines have a number of narrower separate tapes making up the overall width, each of which can be started and stopped independently,” said Cornforth. “Whilst the rate of material deposition may be lower on the more complex regions of a shaped component, it is higher on the less complex areas.”
GKN is now working on the next iteration of composite wing spar design, which has a more complex outer profile at the interface with the skins and ever more demanding ramps rates at reinforcements for weight optimization. The other key parameter in deciding whether “lay flat and form” is appropriate for any given component concerns the characteristics of the material being used.
“As with any manufacturing process, both ATL and AFP have their advantages and disadvantages,” said Cornforth. “ATL is highly efficient for long straight components without excessive shape; AFP is essential for components with more curvature at the cost of a reduced rate of deposition today. However, AFP is able to recover some of this penalty because deposition is generally done directly onto a tool that is the final component shape, thereby taking out the process of hot drape form.”
A further advantage of AFP is that it can lay directly onto honeycomb cores to produce structural sandwich panels—providing the ramp rates are designed accordingly.
“Significant benefits can be gained for certain components if they lend themselves to back-to-back manufacture, e.g. two fan cowl doors on a single mandrel,” said Cornforth. “The recent explosion in the use of composite materials within airframe structure is also being reflected within the low pressure sections of aero engines.”
GKN is carrying out research and development involving several other engine component applications including hybrid fan blades and fan containment cases and acoustic liners. In the future, the manufacture of such components would undoubtedly employ automation, believes Cornforth. The equipment used might comprise bespoke AFP heads and material delivery systems mounted on either conventional robotic arms or on bespoke NC machines. “And they may combine AFP, ATL, pick-and-place technologies with linked, tool-mounted mandrel systems to create a highly efficient work cell,” he said.
The capabilities of machines of this type open up the likelihood of future products from GKN using extensive automation throughout its worldwide facilities on products such as spars, wing fixed trailing edges, winglets, fan cowl doors, inlets, and nacelles cowlings.
“There are many challenges ahead, but the development and application of automated technologies for rapid deposition of fiber reinforced composite materials has facilitated much innovation within the aerospace industry,” said Cornforth. “Automation will re-shape the factory and workforce in the years ahead and presents new ways of producing parts economically."