Machining and CMM cell checks carbon fibre panels

CMM in a machining cell ensures that drilled and machined carbon fibre panels for the aft fuselage and tail of the F-35 Joint Strike Fighter fit perfectly, avoiding rework and aircraft downtime.

A cell that machines carbon fibre panels for the aft fuselage and tail assembly of the F-35 Joint Strike Fighter (JSF) became fully operational earlier this year at BAE SystemsS Samlesbury, near Preston, UK.

The facility was installed as part of a multi million pound investment for designing, engineering and building major assemblies for the supersonic multi-role stealth aircraft.

The cell comprises a Dorries Scharmann Technologie (DST) five-axis, high-speed machining centre to mill and drill the moulded panels and a co-ordinate measuring machine (CMM) supplied by LK to inspect them.

The first of 22 aft fuselages in the SDD (System Development and Demonstration) phase of the JSF programme was delivered in May 2005 from Samlesbury to Lockheed Martin Aeronautics Co in Fort Worth, Texas, USA, on schedule for the plane's inaugural flight in 2006.

The innovative precision machining techniques ensure that the F-35 meets its stealth requirements.

Very high accuracy is also required so that panel replacements fit perfectly, avoiding rework and aircraft downtime in service.

LK's measuring equipment underpins these vital interchangeability requirements.

The machining and inspection cell is housed in a 45 x 18 x 9m high room, the temperature of which is controlled to 22.8 +/-1 deg C.

LK's G90CR rail-type CMM has a quoted volumetric accuracy over one metre of 7.5 microns (an accuracy normally quoted for smaller machines), although 6.1 microns or better was achieved in testing on the machine when installed at Samlesbury, according to Martin Knott from the Facilities Engineering department.

A measuring envelope of 5000 x 3500 x 2500mm was specified for the LK machine so that the largest 3 x 2.5m component for the F-35 can be inspected while clamped on a vacuum fixture which in turn is mounted on a machine pallet.

This is exactly how parts are fixtured for the machining centre, eliminating any unnecessary variation in the process.

Machining operations involve milling the periphery of the carbon fibre panels, machining the landings where the panels fit to the aluminium/titanium structure, and drilling fixing holes, the number varying from a couple of dozen up to several hundred, depending on panel size.

Around 150 different composite components will be machined in the facility at Samlesbury for the three F-35 variants - conventional, short take-off and vertical landing, and the carrier version - each aircraft containing some 75 carbon fibre elements including both structure and panels.

During SDD, 100% feature checking will be carried out on components using the CMM in cycles ranging from 30 minutes to four hours.

Commented Knott, "Before setting up the new cell, we evaluated all available metrology systems including laser scanning and portable arms, but found that inspection of discrete points using a touch trigger probe on a bridge-type CMM was the best solution for this application".

" "We selected the LK G90CR as it was a standard machine that met the required accuracy and speed at the right price, with metrology and project management support.

It is backed by a full service contract from the firm's principal factory and headquarters at East Midlands Airport.

"The manufacturer has been the dominant provider of CMMs to this site for the past 20 years and we have developed a good working partnership." For example, in this case LK provided an interface allowing connectivity to third party software that BAE uses company-wide on its server network to import data from Catia CAD systems into its metrology environments, drive CMMs and analyse inspection results.

Manual programming of inspection routines is, however, performed within LK CAMIO software.

Lockheed Martin is developing the F-35 in collaboration with principal partners Northrop Grumman and BAE Systems.

After SDD, BAE Samlesbury is aiming to play a major part in the JSF project and will be looking to obtain the full production contract to produce 22 aft fuselages per month when production reaches its peak in 2015.

With these volumes in mind, the company has future-proofed the machining and inspection cell so that manual craneage of parts on and off the machines can be replaced by a multi-level, automated storage and retrieval system for machine pallets.

Aircraft have exploited carbon fibre for many years.

The next-generation, world-leading expertise that BAE Samlesbury is developing for the JSF project will therefore position the company to help achieve its goal to become the world's leading aerospace and defence contractor for years to come.

LK's experience in the forefront of supplying the requisite inspection systems makes it a world leader in this field too.

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