Large composite components for the Airbus A350 family of wide-body airliners are being machined in a pair of German-built Zimmermann FZ33 portal machining centres at a specialist subcontractor based in England. Supplied by sole sales and service agent, Geo Kingsbury, each machine has a working envelope of 16m x 3m x 1.5m and an installed weight of 168 tonnes.
The machines are part of a new generation of modular, highly dynamic, portal machining centres with a counterbalanced, overhead gantry and fixed bed. As the moving mass is constant, comprising the structurally stiff gantry, cross slide, Z-axis ram and milling head, the machine's dynamic behaviour is unvarying, resulting in optimum surface finish and accuracy.
The carbon fibre epoxy matrix parts are some of the largest composite components in the world, up to 12m long, 25mm thick and weighing as much as 200kg. 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 12m span is within ±0.2mm. All parts then go for ultrasonic inspection before being shipped to Airbus, Broughton.
The Zimmermann FZ33s are fitted with a Weiss 45kW, 25,000rpm, HSK-A63 spindle mounted in a slimline head that provides 220° of A-axis rotation and the 360° rotary C-axis. The 1,200Nm A-axis is driven by two electronically preloaded, backlash-free torque motors while the C-axis has a direct drive torque motor. A 24kW/18,000rpm head with single A-axis drive is available for machining lighter materials.
X/Y/Z travels are actuated via rack and pinion drives, with twin motors in X. Acceleration up to 5m/s2 to linear feed rates of 60m/min in the linear axes and rotation of 360° per second in the rotary A and C axes lead to fast cycle times and high productivity. 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.
The combination of stability and stiffness, constant moving masses and dynamic drives allows high precision machining, making the machine particularly well suited to finish milling of moulds and dies. Accurate 3- and 4-axis machining is assisted by a holding torque of 3,000Nm in the rotary axes. Even higher machining accuracy is possible using temperature stabilisation options.
A smaller machine model, the Zimmermann FZ33 Compact, is also available with linear travels of 2.5m x 3m x 1.25m in X/Y/Z respectively. It has the option of a heavier duty, 60kW (100% duty cycle)/22,000rpm spindle and can be installed on a shopfloor without the need for a special foundation.
