Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
Complex machining of wing parts
Keywords NCMT, BAe Systems, Machining, Wings
Following the consolidation of manufacturing processes on the Samlesbury site, near Blackburn, of BAe Systems (formerly British Aerospace Military Aircraft & Aerostructures), a series of dedicated manufacturing cells have been established to focus on complex, multi-axis aircraft components. One cell is dedicated to completing the majority of operations required to produce the foreplane spigot, one "as drawn" and one "opposite hand", for the Eurofighter Typhoon (Plate 2). Requiring cutting of steel hardened to 47 HRC, the spigots are the attachment points for the left and right hand canard wings and also adjust their positions.
Plate 2 Close-up of foreplane spigot machining in progress at NCMT's Coventry centre
The chosen supplier was NCMT, which was awarded a turnkey contract to configure a customised version of an Okuma MacTurn 50 mill-turning centre, design and construct the foundations, provide equipment necessary for setting the cutting tools, and supply full engineering back-up including the provision of all NC part programs.
The cell is due to be installed at the British Aerospace Samlesbury site near Blackburn by mid-2000. Compared with previous production methods, the new technique will, it is believed, have profound advantages for BAe Systems.
These may be summarised as follows:
Number of process operations reduced from 28 to eight (one of which now involves five machining operations on the MacTurn), a 71 per cent reduction.
Number of component fixtures reduced from 22 to four, an 82 per cent reduction.
Number of inter-operation transports reduced from 22 to seven, a 68 per cent reduction.
Number of machine types reduced from six to three, a 50 per cent reduction.
Machine cycle time reduced from 84 hours to 19 hours, a 77 per cent reduction with a proportional reduction in associated labour requirements.
Production lead time reduced from 12 to two weeks, an 83 per cent reduction.
The reductions in consumable costs are very high. However, the precise scale of the benefits is difficult to quantify accurately at this stage, until full production is undertaken later this year.
Additional advantages include better component quality, reduced manual finishing operations, less scrap and rework costs, and reduced work-in-progress.
The new process
Along with the MacTurn 50, additional equipment being supplied under the turnkey contract includes a Forkardt quick-change spindle nose and setting station for component/fixture assembly, a Messma Kelch tool presetter connected directly to the lathe control, a manual handling system from Dalmec for loading both the machine and the setting facility, and program generation equipment to enable scan milling of complex surfaces.
Included also are a workholding package to interface with the quick change system on the lathe, BIG Daishowa Seiki BT50 "BIG PLUS" spindle tooling (also from NCMT) for rotating and static toolholders and Sandvik tooling for both rotating and turning stations. Detailed applications engineering and full project management are being supplied by NCMT.
The machining sequence for both left and right hand spigots comprises 11 operations, of which ops 50, 60, 190, 210 and 220 (operation numbers in increments of ten are not sequential) involve turning, milling, drilling, boring and threading on the MacTurn 50. Of particular interest is thought to be the way in which, as the part progresses through its manufacturing cycle, datum faces and bores are machined to locate and clamp the component during subsequent operations.
The steel forgings are supplied to the cell with the barrel turned to a defined tolerance and are presented on stillages in the correct orientation for loading into the fixture. The op 50 collet-type fixture is clamped on to the headstock of a separate off-machine setting facility. The component is clamped into the fixture so that the blade slot centreline runs parallel to that of the machine tool.
The component/fixture assembly is loaded to the machine spindle nose with the help of lifting equipment. The fixture is radially located then hydraulically clamped to the spindle nose by means of a foot switch, an air sensing system then ensuring correct fixture location. The cycle consists of machining the initial component datums and rough milling the blade faces. Each loading for subsequent operations is similarly executed.
Op 60 involves locating the component with the blade end of the component towards the machine headstock in a slave fixture using datums machined during op 50 and then clamping the part via tapped holes also machined during the previous operation. The machining cycle consists of rough and fine turning, advancing a hydraulic steady rest for component location, retracting the tailstock to allow access to the internal features of the component, U-drilling a 60mm diameter hole to a depth of 216mm, various rough boring operations on the chamber, and profile milling of the surfaces.
Op 190 is preceded by rough slot machining on dedicated equipment and heat treatment in a fixture to prevent undue distortion. In the MacTurn 50, the part is clamped as for op 50 and the cycle starts by advancing the hydraulic tailstock fitted with a special damping device to eliminate blade vibration due to the fact that the slot has now been machined. Metal cutting is restricted to proof machining of the tooling lug faces, opening up existing dowel holes and reaming location holes.
Op 200 is finish machining of the slot, again on dedicated machinery.
During op 210, new location holes are drilled and reamed, component clamping holes are drilled and counterbored, and drilling and fine boring is performed between the blades into the barrel section.
The last stage on the MacTurn 50 is op 220 for which the component is fixtured with the blade end of the component towards the machine headstock. A complex sequence of finish machining operations is performed including turning, drilling, threading, boring, and scan milling.
An angle head is used for part of the cycle to drill and fine bore one of the holes. Subsequent ops 230 and 240 are for finish grinding the journals and for frazing respectively.
The MacTurn 50 itself is a little different from the standard version. It has a 72-tool magazine instead of the normal 32 tools, a 37(30)kW spindle motor and larger spindle bearings to support the heavy fixturing.
An automatic work gauging and offset system is based on Renishaw probing. Tool life management software is included to enable the use of sister tooling. BIG plus spindles have also been specified on both stationary and rotating spindles to give additional rigidity during machining.
Other facilities are air blow for the tailstock centre, absolute scales for the X, Y and Z axes for improved accuracy and repeatability, and high pressure coolant for deep hole drilling and boring. Swarf and coolant management includes a 50-micron medialess filtration system. Owing to the size of the machining programs, a DNC interface is provided to drip feed the programs to the Okuma CNC system.
Geometric accuracy tests on the machine have been carried out by Okuma in Japan. When the machine arrived in the UK, it was installed at NCMT's technical centre where it currently is still located while the component engineering elements of the turnkey package are undertaken in conjunction with the customer and partner suppliers.
Initial part programs have been prepared; and set-up and prove-out are in progress for both left and right hand foreplane spigot components for each of the five ops on the MacTurn 50. Machine run-off of 30 components to SPC criteria has successfully been carried out at NCMT's Coventry premises.
The new process claims considerable advantages to BAe Systems in terms of reduced cost per part and faster lead time, consistent with the company's JIT requirements. Full machining trials have been completed on aluminium castings and the process works well.
Machining of hardened steel is now in progress and early indications are that expectations will be met.
Details available from: NCMT Limited. Tel: +44 (0) 2083 984277; Fax: +44 (0) 2083 983631.