AIRCRAFT COMPONENT MAKER ELEVATES TUBE BENDING TO NEW LEVEL

GKN Aerospace (Filton, UK) is a first tier supplier to the global aviation industry, working on major fixed- and rotary-wing aerospace platforms in military and civil aviation markets. The tube bending operation for wing components based in Filton is a core part of the company's broader activity. It is capable of producing virtually any complex shape using any standard tubing material, including the hardest and most difficult to form exotic alloys.

The workshop has a track record dating back some 40 years and a long-serving team of highly skilled technicians. In addition to its investment in a broad range of all-electric tube benders, the operation has developed an extensive array of support functions required for parts and assembly production, including cells for welding, assembling tube fitting ends, and performing the high-integrity testing required for aerospace applications.

Capital investments for the latter function range from coordinate measuring machinery used to inspect regular tubular part production, to real-time X-ray and dye penetrant testing to verify the integrity of assemblies destined for military aircraft or critical systems in civil aircraft.

GKN has radically improved the efficiency and speed of tube bending operations at its wing component operation in Filton, despite using some of the most demanding tubing materials and fabricating extremely complex part shapes.

Successive installations of all-electric tube bending machinery from Unison Ltd., culminating in the recent installation of novel combined left- and right-hand bending machines, underpin a fabrication process that now manufactures ultra-precise parts in very small batches ? typically without generating any scrap.

Among the extreme challenges the tube bending team face every day are tubular parts with as many as 19 bends, highly complex shapes with multi-radius coils, and bending titanium tubing with wall thicknesses up to 2.6 mm to cope with the high pressure systems on its customer Airbus' latest double-deck A380 aircraft.

GKN Aerospace's tube bending facility fabricates around three to four thousand parts per week, using tubing ranging from a few millimeters in diameter to over 100 mm. Aircraft applications are its main market, and the materials used ? which include titanium, aircraft-grade aluminum and corrosion-resistant steels ? are expensive.

?We provide commercial tube bending services targeted at precision and high performance applications,? says Peter Tiley, the process unit manager at GKN Aerospace. ?The very high level of operator skills traditionally required for this kind of fabrication leaves little scope to improve throughput. But with the catalyst of all-electric tube bending automation, we have managed to multiply productivity without compromising quality. And all of this while simultaneously eliminating almost all scrap on regular batch production.?

The starting point for the company's interest in all-electric tube benders was the need to cope more efficiently with small batch sizes which are typically less than 20 parts. Until some seven years ago, the workshop used hydraulically-actuated bending machines, and the skilled attention required to reconfigure a machine for a new batch meant that scrap ? sometimes several pieces ? was almost invariably produced at each batch changeover. For materials such as titanium this was extremely expensive, and GKN initiated a search for machines offering higher levels of accuracy and repeatability.

Over 15 tube bending machinery manufacturers competed for this business, with Unison winning the contract with a 65 mm diameter version of its all-electric tube bender. The precision and repeatability of set-up provided by it servomotor-controlled architecture proved the key factor.

Scrap on regular production runs was virtually eliminated and productivity increased, to the extent that the machine paid for itself in three months. GKN quickly acquired two more machines to handle smaller sized tubular parts, then a 115 mm diameter bender to handle the largest parts it bends, and most recently two custom-made combined left- and right-handed machines to improve productivity on the most complex tubing shapes it has to fabricate.

?From the time we first invested in new-generation bending automation, we have increased our overall productivity while additionally tightening manufacturing tolerances,? notes Tiley. ?The new tube benders have played a key role in this achievement.?

GKN has exploited the capability of the all-electric machines to continually improve the workshop's tube bending processes and productivity. Bends are typically made to 1 mm 3D envelope accuracy ? sometimes as tight as 0.3 mm for the workshop's military aircraft output ? and the machines? ability to meet this specification reliably has allowed the workshop to eliminate a lot of the jig-based inspection processes previously favored.

This process improvement helped achieve cost reductions on the component parts. Instead of inspection jigs, a coordinate measuring machine is now usually employed for post-bending inspection. Unison also wrote an interface utility to this to speed the development of new bending programs by automatically compensating for tolerance variations in the first prototype component.

The precision and repeatability of bending also allowed GKN to eliminate any need for sawing operations following bending to meet the target length, yielding yet more savings. The workshop further capitalized on this attribute by purchasing many of its steel tubes pre-sawn to the exact lengths required.

The intrinsic quality of the bend is another area where all-electric operation has supported significant improvements. The ductility characteristics of titanium in particular mean that slowing the bending process down improves forming. This can be a particular issue with some of the material that GKN has to process, such as thin-wall titanium tubing. The servomotor-controlled bending axes allow GKN to create bending programs that exercise precise control over all aspects of the tooling's speed and force applied during fabrication ? including those at very low speeds, something that is impossible with hydraulic technology ? to achieve optimum material flow and shaping.

?Aerospace is undoubtedly among the most demanding applications for tube bending. Over time, the manufacturing tolerances have tended to become much tighter. Yet it's still commonplace to see older-style hydraulically-actuated benders in use, the type of machinery that is much more suited to large-batch production of run-of-the-mill components,? notes Alan Pickering of Unison. ?All-electric bending automation has helped GKN to evolve a component production process that is at the vanguard of what is technically possible, in terms of precision, shape creation, and cost effectiveness.?

The latest machinery installations of the two combined left- and right-hand bending machines were acquired to overcome a long-standing problem with some specific component shapes. These include tubular parts that have many closely-spaced bends and tubes with coil structures that provide the mechanical flexibility to accommodate flexing movement during the operation of wing flaps.

One part has so many bends that GKN previously had to make it on two machines to avoid collisions. The operator skill required was very high. Other coiled parts posed further problems in that the need for variable radii necessitated an individual hand-crafted approach.

A solution was devised in the form of combined left- and right-hand bending machines, the first all-electric version of this unusual automation. Workpieces can now be transferred automatically from left to right hand tool heads as many times as required to bend the required shape in a single stage. As a result, batch fabrication times have come down dramatically: from three days to 1.5 hours for one of the coiled parts, and from 2.5 hours to just 30 minutes for a batch of the multi-bend part that previously involved switching machines.

?There's a bright future for component manufacturers who are able to help aircraft manufacturers combat today's complex challenges of much tighter tolerances and very high cost materials,? adds Tiley. ?Sophisticated automation will clearly be a critical element for success in this emerging market environment. This technology stands behind our continued investments to enhance both our technical fabrication capability and business flexibility.?

Editor?s note: Unison tube bending machines are available in the U.S. from Horn Machine Tools.

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GKN Aerospace (Filton), PO Box 500, Golf Course Lane, Filton, United Kingdom BS34 9AU, +44 (0)117 317 5000, Fax: +44 (0)117 317 5001, www.gknaerospace.com.

Unison Ltd., Olympian Trading Estate, Cayton Low Road, Eastfield, Scarborough, North Yorkshire, United Kingdom YO11 3BT, www.unisonltd.com.

Horn Machine Tools, 40473 Brickyard Drive, Madera, CA 93638, 559-431-4131, Fax: 559-431-4431, www.hornmachinetools.com.