Machine controllers achieve H7 accuracy on airframe hole drilling

Aircraft Engineering and Aerospace Technology

ISSN: 0002-2667

Article publication date: 1 April 2000




(2000), "Machine controllers achieve H7 accuracy on airframe hole drilling", Aircraft Engineering and Aerospace Technology, Vol. 72 No. 2.



Emerald Group Publishing Limited

Copyright © 2000, MCB UP Limited

Machine controllers achieve H7 accuracy on airframe hole drilling

Machine controllers achieve H7 accuracy on airframe hole drilling

Keywords: Osai, Machining, Drilling

"Unsurpassed accuracy" is claimed for the ICY Machining Development project, established to drill aircraft panels and substructures to interchangeable standards without the use of hard tooling.

ICY describes the customer's requirement to be able to assemble certain components on to any aircraft of the same type and is conventionally achieved through the use of fixed jigs, drill templates and so on.

This has reportedly been achieved at British Aerospace Military Aircraft and Aerostructures, near Preston, through the facility of two huge DST interchangeable structure drilling machines that will take virtually any component without the need for purpose-built jigs or templates. The result is claimed to be positional accuracy measured in microns in a working envelope of 144 m 2 ! This, in part, is said to be the Osai 10/Series advanced CNC used for the 6-axis control of these multi-million pound machines.

A further Osai intelligent work station is fitted to a third DST machine producing carbon-fibre panels in the "Structures" section also at the Samlesbury site.

Osai 10/Series CNC controllers with the Osai WinLink integrated PC workstation are the standard OEM selection on these new machines, which have been jointly developed between DS Technologies and British Aerospace, with Osai being heavily involved in the development of the software. Three machines have been produced to date, with all three being at British Aerospace. BAe AMT Manager, Jon Evans, says:

Hole tolerance requirements are from C11, down to H8 standard, depending on the component, which can mean a positional accuracy of þ 36 microns within the overall working envelope of 8 x 4 x 4.5 metres.

This accuracy is needed because of the fundamental design of the Eurofighter Typhoon, which has very little sub-structure, with the load path being through the panels. A very accurate component profile line (CPL) is needed to maintain the design gap (taken up with liquid metal) between the structure and the panel. This thickness varies depending on the thickness of the component. The holes are drilled in the components to pick up the airframe fixing points and, if panels are to be quickly and precisely interchangeable, there is no room for error.

It is a contractual obligation that all removable panels are completely interchangeable, and this accuracy is achieved in two ways. First, there is the engineering accuracy of the beds and the machine tool itself. Then there's the really clever part, which is in the software. Because the fixture is not accurately defined, it is first probed so that it is fixed in space. Then the software, which incorporates a volumetric correction system, not only corrects everything back to a datum - rotating the part-program in three dimensions - but it also corrects for wear on the machine as a whole. Working with both Osai and DST, we have taken the machine capabilities much further than originally envisaged.

The 10/Series family of numerical controls offers a wide choice of technologically advanced solutions based on standard PC architecture. Capable of managing up to 24 processes and 32 axes simultaneously, the 10-Series communicates with the British Aerospace network via an Ethernet connection, pulling in CAD programs, written in the AMT office, for each component as required.

Each job is processed as a one-off and then requires re-setting - there is no batch work - but this process takes little more than a few minutes to reprogram via the WinLink operator panel. The Windows-based environment makes operation straightforward and logical, with graphics showing job progress.

All components that require ultra-accuracy are machined on the three DST machines. Typically, components include the two halves of the Eurofighter cockpit and parts of the fuselage, including the belly panels and the engine-bay doors.

The 6-axis machine has a pallet-loading station that works on an automatic cycle, taking the workpiece to the machining point. 168 different tools provide the facility to drill, counter-bore, route, counter-sink and light machine with four different spindles giving speeds of up to 23,000rpm. Component materials include carbon fibre, titanium, carbon steel and various alloys. A Rennishaw strain gauge probe checks dimensions and four camera positions give the operator a 360° view of the operation. Jon Evans says:

Our operators really like the Osai CNC, and the capability of the DST machine is fantastic. The facility that we have here is as good as anything in the world and very much better than most.

Details available from Osai UK Ltd. Tel +44 (0) 1908 642687; Fax +44 (0) 1908 642688.

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