Jun 25 2009
GKN Aerospace has radically improved the efficiency and speed of tube bending operations at its wing component operation in Filton UK, 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, 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 2.6mm - 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 millimetres in diameter to over 100 mm. Aircraft applications are its main market, and the materials used - which include titanium, aircraft-grade aluminium and corrosion-resistant steels - are expensive.
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 was almost invariably produced at each batch changeover - sometimes several pieces. 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 the 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 the company's 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.
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 favoured. 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 capitalised 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 on the Unison machines allow GKN to create bending programs that exercise precise control over all aspects of the tooling's speed and force applied during fabrication - including at very low speeds, something that is impossible with hydraulic technology - to achieve optimum material flow and shaping.
The latest machinery installations - the two combined left- and right-hand bending machines - were acquired by GKN to overcome a long-standing problem with some specific component shapes. These include tubular parts with lots of 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 used 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. GKN approached Unison with the problem, and 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 one and a half hours for one of the coiled parts, and from two and half hours to just 30 minutes for a batch of the multi-bend part that used to involve switching machines.
"Aerospace is undoubtedly among the most demanding applications for tube bending out there, and over time the manufacturing tolerances are tending to become much tighter. Yet it's still commonplace to see older-style hydraulically-actuated benders in use - machinery that is much more suited to large-batch production of run-of-the-mill components", says Alan Pickering of Unison Ltd. "All-electric bending automation has helped GKN Aerospace 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."
"We provide commercial tube bending services targeted at precision and high performance applications", says Peter Tiley, Process Unit Manager at GKN Aerospace. "Traditionally, the very high level of operator skills 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 - while simultaneously eliminating almost all scrap on regular batch production. From the time we first invested in new-generation bending automation, we have increased our overall productivity while additionally tightening manufacturing tolerances - and the Unison tube benders have played a key role in this achievement."