5-axis machining of composite aircraft components

Large composite components for the Airbus A350 family of wide-body jetliners are being machined in a pair of German-built Zimmermann FZ33 portal machining centres at a specialist subcontractor in England.

Supplied by sole sales and service agent, Geo Kingsbury, each machine has a working envelope of 16 m x 3 m x 1.5 m and an installed weight of 168 tonnes.

The carbon fibre epoxy matrix parts are some of the largest composite components in the world, up to 12 metres long, 25 mm thick and weighing as much as 200 kg. The 5-axis machining cycles, involving edge trimming, face milling and drilling, take up to 16 hours across two operations.

The cycles include a significant amount of on-machine probing, first of the vacuum fixture position and then of the secured component during set-up, followed by post-machining inspection. Dimensional accuracy over a full 12-metre span is within ± 0.2 mm. All parts then go for ultrasonic inspection before being shipped to Airbus, Broughton.

The Zimmermann FZ33s are fitted with a Weiss 45 kW, 25,000 rpm, HSK-A63 spindle mounted in a slimline head that provides 220 degrees of A-axis rotation and the direct-drive rotary C-axis. X/Y/Z travels are actuated via rack and pinion drives, with twin motors in X. Linear scales are employed for accurate positional feedback to the Siemens control. A pair of video cameras has been fitted to allow the operator to conveniently monitor the large working area.

Composite machining results in high cutting loads and rapid tool wear, so carbide and polycrystalline diamond cutters are used. Dry milling and drilling of such materials create a lot of dust, which the FZ33 removes efficiently, both via the extraction and filtration unit at the rear of the machine and through a brush enclosure around the spindle head.