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Emerald Group Publishing Limited
Copyright © 2008, Emerald Group Publishing Limited
High-speed, five-axis machining of A380 parts
Article Type: Aerospace world From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 80, Issue 4
At the Bournemouth factory of Magellan Aerospace (UK) Ltd, an EcoSpeed F HT twin-pallet, five-axis, horizontal machining centre from DS Technology (UK) is producing false rear spar trailing edges for the Airbus A380 in faster cutting cycles than was possible on the machines previously used. Moreover, the parts are completed in just two clampings, one per pallet, rather than three or four separate operations on two different machines.
Substantial though this benefit is, the biggest advantage is the elimination of fettling after machining. This has cut further time out of the manufacturing process and has dramatically improved workflow through the factory. Consequently, production lead-time for the trailing edges has been reduced by two weeks.
There is also less work-in-progress. The parts were previously transported after machining to another area of the factory for dye penetrant inspection and then back to the machine shop where they queued for fettling, which cannot be carried out before the inspection for technical reasons. This tortuous journey, and the attendant risk of damage to the components, is no longer necessary.
DST’s kinematically-driven, two-axis Sprint Z3 spindle head is the key to reducing the number of machining set-ups and removing the need for bench polishing of areas on the component where there used to be a slight mismatch in adjacent cutter paths. The head tilts through ±40° in the vertical rotary A-axis as well as in the horizontal rotary B-axis, the latter aided by equal and opposite rotation of the table carrying the fixtured part, which improves access further. The result is that short cutters, predominantly from Mitsubishi Carbide, are able to reach even the most awkward areas on the component without having to reclamp it.
With the conventional five-axis horizontal machining centre previously used at Bournemouth for this work, longer cutters were needed to access deep slots. There was a risk of damaging the component with the unwieldy tools, which caused mismatches in certain areas due to their lower inherent rigidity. Moreover, some slots and other features such as small pockets requiring five-axis milling could not be machined at all without repositioning the part. Both of these problems have been solved by the dexterity and accuracy of the Sprint Z3 head.
The highly dynamic EcoSpeed F HT, which is capable of 8,000 cm3/min chip removal from billets of high tensile aluminium alloy, was delivered to Magellan Aerospace in Bournemouth at the end of October 2007, three months after order, and started full production at the beginning of 2008.
When interviewed during mid-February, Engineering Manager Keith Summers commented, “We are currently reprogramming 26 sets of the handed A380 ribs in Catia to transfer production to the EcoSpeed F HT. So far we have completed five sets and not one of the components has required polishing after machining.”
He went on to describe the background to the £800,000 machine purchase, which was dictated by A380 production being ramped up from 1.5 aircraft per month in 2008 to four per month by 2010. Extra production capacity was needed at Bournemouth to cope with the increasing volumes, but more importantly a different type of machine was considered necessary, as the existing machining centres were too large to produce the relatively small trailing edge components economically.
The X:1,250 × Y: 1,350 × Z: 670 mm envelope of the EcoSpeed F HT with its 50 m/min cutting feed rate, 1 g acc/dec, and 80 kW/30,000 rpm spindle, with full power available from 16,000 rpm, were deemed to be the ideal combination. DS Technology (UK) delivered the machine as a turnkey with a program already written for one part number and a guaranteed cycle time, which was easily achieved.
To meet the specified time, however, DS Technology (UK) had to keep overall table load, including the 1 × 1 m pallet, to one tonne or less. To achieve that with a maximum aluminium billet weight of 289 kg, a special cube fixture with a hollow internal structure stiffened by spars had to be designed to reduce weight yet maintain rigidity.
Included also in the turnkey project were a Blum laser checking system that stops the machine automatically if it detects that a tool has been set incorrectly; and Balluff chips in the Seco toolholders to store information on tool offsets and remaining life, and also on coolant pressure, as it is critical when spray mist is used. An HSK63 taper is employed with an 80 mm flange to provide added rigidity, in view of the need for vibration-free machining to achieve good surface finish and eliminate fettling.
The resulting accuracy and repeatability obtained with this set-up has allowed Magellan Aerospace to develop the manufacturing process further. It has already proved the feasibility of bolting two ribs back to back, probing off the spar feet and machining the assembly. In one application, a hole is bored through both ribs to 25 μm total tolerance for accepting a bush, avoiding the need to use a jig borer and thereby deskilling the job. In another application, brackets are fitted first and subsequently drilled.
On the relationship between Magellan Aerospace and DS Technology (UK), Keith Summers concluded, “The EcoSpeed is our group’s first machine from this supplier in the UK. We went to the Mönchengladbach factory of the parent company, Dörries Scharmann Technologie, to see the machine in build and noted during tests an accuracy of better than 10 microns over one metre of travel in all linear axes.”
“The project was managed meticulously by the UK subsidiary and a German manager over a six-week period. The quality of the engineers was excellent and we developed a good relationship with the supplier at all levels.”
“Minor problems were solved without fuss. For example, when we found that the roof of the machine was slightly too high for our gantry crane to clear, Dörries Scharmann Technologie went off to make a modified version and we did not hear about the matter again.”
“We have had first class service since the machine was installed. The term ‘customer-supplier partnership’ is somewhat overused these days, but this exercise could certainly be put into that category.”
Details available from: DS Technology (UK) Ltd, Tel: +44 (0)121 359 3637, Fax: +44 (0) 121 359 1868.