Programming and cycle times improved

Programming and cycle times improved

Keywords: LK, BAe Systems, Measurement, CAD

LK Ltd informs us that one of its co-ordinate measuring machines (CMMs) with an extra long table measuring seven metres in the X axis has since the mid-1990s carried out 100 per cent inspection of aluminium wing spars for all Airbus variants in the Major Components Centre at BAe Systems Airbus UK, Broughton, UK(Plate 1). Following a recent CMM upgrade with LK's CAMIO software, CAD models are now imported directly from a CADDS 5 computer-aided design system on site;this is said to have more than halved the time taken to program the measuring machine.

  Plate 1 An Airbus A320 mid rear spar being checked on the LK G80 CMM at BAe Systems Airbus UK, Broughton. Inspection is carried out in two set-ups due to the length of the component

In the past, a drawing of the spar used to be supplied together with a set of about 250 X, Y, Z co-ordinates for the outside winding angle, a critical compound surface which needs to be held to a tolerance of +0.010"/–0.006". Including other key features such as hole positions, rib post locations and wall thicknesses, a total of some 500 inspection points had to be laboriously keyed in by hand, which took on average four-and-a-half weeks.

The new process involves downloading the solid model from the CAD system and saving it as a SAT file in CAMIO, where it can be worked on directly to create the inspection program (Plate 2). For the latest A340-600 Airbus, a 168MB CAD file of a 10 metres x 1.6 metres inner front spar was reportedly converted on a PC in the Windows NT environment in ten minutes.

  Plate 2 On-screen view of the 168MB solid model of the new Airbus A340-600 inner front spar,imported into CAMIO and saved as a SAT file

It then took two weeks to generate the inspection program, which is said to represent a time saving of over 50 per cent compared with the manual method. However, this was the first component which Mike Smith, product acceptance controller at BAe Systems Airbus UK, had programmed in this way. Time savings are expected to be considerably greater as the process becomes more familiar.

Another significant benefit, according to Mike Smith, is that programs from CAMIO are output in the latest industry standard DMIS code, rather than in CMES as before. The new measuring cycles are more efficient and have comprehensive crash detection with on-screen verification which allows the CMM to run at higher speeds during production inspection. The combined effect is to cut measuring cycles by a third. As 240 spars are inspected each month, the increase in machine availability is considerable.

The CAMIO/DMIS system is also thought to be more efficient for data management. Reporting is fully computerised and automatic, enabling, for example, the straightforward creation of audit and statistical process control documentation.

A spin-off advantage claimed of the new programming method is that in theory it can be performed off-line. In practice, the CMM is tied up for just 5 per cent of the time to prove out and edit programs. With the old manual method,about half the programming was performed on the machine, taking it out of service for more than two weeks every time a new spar design came along.

"We have had an exceptional level of support from LK, particularly in respect of operator training and early programming assistance", concludes Mike Smith. "We took our first CAD model on CD to LK's Donington factory on one particular day and were still working on it at 7.30 p.m., such was the level of commitment offered by the company".

LK also report that a fundamental change is taking place in the way BAe Systems recalibrates the jigs and fixtures (tools) used in Airbus wing production at the company's Broughton site in North Wales. The old process currently being phased out involves checking the tools by placing them on an appropriate tooling master reference, essentially an elaborate hard gauge. The new process hinges on creating virtual models of the masters by reverse engineering them on an LK co-ordinate measuring machine (CMM).

Digital models are thus created, against which the accuracy of production tools can be periodically verified or, in BAe Systems parlance, "recertified",during subsequent inspection on the same CMM.

In this way, inspecting each of the 693 recertifiable tools at Broughton will, it is believed, be five times faster than the current system of putting a jig or fixture on to a physical master, so substantial savings will result every time a virtual master is used. It is planned over the next three years to reverse-engineer all 130 masters.

Further savings are expected to result as there will no longer be a need for occasional recertification of the master references against a model of the actual wing, or "static site", housed at BAe Systems Airbus UK's other site in Filton, near Bristol.

Says Trevor Wiggins from the Tool Engineering Department at Broughton, "The beauty of reverse engineering using LK's CAMIO software supplied with the CMM is that it is quick enough to be able to create a virtual master in an average of three to four hours. We can complete this one-off exercise and check a jig or fixture on the CMM within the time it previously took us just to recertify the tool.

"As first-off checking using the new process takes no longer than tool recertification did before, the entire three-year digitisation process will be'for free' in terms of metrology departmental time."

Another advantage claimed of co-ordinate inspection over using physical masters is that, instead of giving go/no-go results, the CMM produces absolute measurements. This enables statistical process control (SPC) techniques to be employed to compare successive measurements on a tool, plot trends and take management decisions such as whether to redesign parts of the tool, or perhaps extend the recertification period, which currently is anything from six months to three years.

The relevant LK SPC software was supplied as part of the CAMIO package along with a geometric interface for part programming and surface analysis for 3D best-fitting of measured data to the digital model. A graphical reporting package has been included to speed the creation of management data and to assist in traceability from the wing back to the tool in accordance with JAR, CAA and other aircraft standards.

Hitherto, a subcontract metrology firm has inspected some larger Airbus tools which were time-consuming to check using physical masters. An example cited is the recertification of the main assembly jig for profile boards on the A330/340 wing, which takes two days on a CMM for the port side and the same for starboard, but which would take a prohibitive ten days to inspect by the conventional route. All subcontract work will now be brought in-house following the installation of the long-bed LK G-90C with its nominal 4.5 x 1.5 x 1.5 metres measuring envelope, resulting in further financial savings.

As assembly of a wing progresses, the size of sub-assemblies becomes so large that the use of static metrology equipment is no longer feasible. (The latest A340-600 wing, for example, is over 30 metres long!) Another benefit of digitising the smaller masters is said to be that the mobile laser checking rig which takes over is able to use the same virtual models against which to check the corresponding elements within a larger jig or fixture.

In February 1999 when Trevor Wiggins and his team were researching the market and deciding which CMM to buy, they evaluated six or seven suppliers. Reasons given for opting for LK were the competitive price for a long-bed machine, which other companies tend to class as a special and charge more for, and commonality of software with other LK CMMs on site. They also liked the use of modern materials in the machine construction, notably ceramic for the bridge and quill.

Details available from: LK Limited. Tel: +44 (0)1332 811349; Fax: +44 (0)1332 850149; E-mail: sales@lkuk.co.uk; Web site: www.lk-cmm.com