Fighter aircraft displays produced 60 per cent faster
Fighter aircraft displays produced 60 per cent fasterKeywords: NCMT, Machining
The lead time for machining a head-up display (HUD) chassis for the European Fighter Aircraft (EFA) has reportedly been reduced from 53 days to 20 by Thales Optics (formerly Pilkington Optronics), as a direct result of installing an Okuma MA50 half-metre-cube, horizontal machining centre from NCMT (see Plate 4). It was supplied with various options including a full fourth axis, Renishaw probing, glass linear scales and a media-free swarf management system requiring no paper filters (see Plate 5).
Plate 4 The Okuma MA50 horizontal machining centre in use at the St Asaph factory of Thales Optics
Plate 5Close-up of the MA50 working area, showing two part-machined EFA HUD lens cells
Faster machining of key elements which go to make up the HUD results in dramatic productivity improvements. Typical is said to be the decrease in the number of operations needed to machine the chassis. Previously, 16 machining cycles were performed in four clampings on three pre-existing horizontal machining centres equipped with 400mm square pallets. Total set-up time was 111 hours and run time was 33 hours. The same is now reported to be completed in six operations on the Okuma MA50, total set-up time being 22.5 hours with machining reduced to just 13 hours (see Plate 6).
Plate 6Thales Optics produces the EFA HUD chassis (background) in six operations on the Okuma MA50 instead of 16 as previously; and there are similar savings in lens cell manufacture (foreground)
Said Gareth Ryan, machine shop manager at Thales Optics' St Asaph site in North Wales, "Based on these figures we calculate a three and a half year payback for the machine. We looked at having the chassis made outside, but such is the complexity of the component that subcontractors we approached could not get near our in-house production cost – they were quoting prices around 50 per cent higher."
"Impressive as the savings are, we're looking to cut process times by a further 30 per cent. Our plan is to use ramping cutters from Walter and change our programming methods to increase cutting feed rates fivefold; and to employ the full power of the 23.5kW 110,000rpm Okuma spindle to remove up to 90CM3of aluminium per minute. With EFA production expected to exceed 670 units over the next ten years, savings will be considerable."
The chassis starts life as an L99 (aerospace specification) aluminium investment casting and undergoes skimming and dowel hole drilling in the first operation, followed by two roughing and three finishing operations. However,this is only one of many components which make up an EFA HUD. The other parts requiring prismatic metalcutting on the Okuma MA50 are nine internal lens cells requiring a total of 219 hours' machining. All are produced from solid, many features being thin wall; and tolerances are tight – down to ±15 microns flatness and hole pitch. The use of BIG Daishowa toolholders, also supplied by NCMT, are said to contribute to the achievement of such high levels of accuracy.
Similar savings are reportedly being achieved using the Okuma MA50 for the production at St Asaph of the new US F22 fighter HUD. Additionally, the machine is helping to produce display components for other fighter planes (F16, C17,Raphael) as well as commercial aircraft (Boeing, McDonnell Douglas). Two shifts,five days a week is sufficient to cope with the current workload, so there is plenty of spare capacity.
Thales Optics chose Okuma for this application owing to the three micron repeatability of the MA50 and because NCMT service and applications engineering were known to be of a high standard because two Okuma mill-turn centres have been used on site for seven years.
Retrofitting of full five-axis capability to the MA50 will be the next step for Thales Optics. The X, Y, Z, B axes will be supplemented by a C axis in the form of a Nikken rotary table which will allow, for example, machining of helical cam gears for a thermal weapon sight. Integration of the fifth axis into the Okuma OSP 100 control will be seamless as the facility already exists. Locking the Z and C axes and interpolating the others will obviate the use of inherently inaccurate angle heads currently used on the other horizontal machining centres.
Further details are available from NCMT Limited. Tel: +44 (0) 20 8398 4277;Fax: +44 (0) 20 8398 3631; E-mail: richardtrimbee@ncmt.co.uk
