Machine replaces manual aircraft panel inspection

A machine that checks the profile and hole positions in sheet aluminium components to within +/-25 microns has replaced the slow and inaccurate inspection of flat components visually in foil lofts.

An independent UK aerospace contractor, Marshall Aerospace, has eliminated the time-consuming and inaccurate process of inspecting flat aircraft components visually using foil lofts.

Instead, the Cambridge-based company is using an InspecVision Planar machine supplied through the Northern Irish machine manufacturer's UK agent, Press and Shear.

The InspecVision Planar machine checks the profile and hole positions in sheet aluminium components to within +/-25 microns.

The machine also checks other 2D parts made from titanium, steel and plastics.

More aircraft manufacturers are using predeterminate assemblies, so a more accurate method was needed to check the 22 to 10 gauge (0.7-3.0mm thick) components following routing and drilling.

These components are required to provide a perfect fit-up during assembly, without having to use jigs or ream out pilot holes.

Advantages include the following.

* Expense and lead-time of producing jigs are avoided.

* Faster assembly and less risk of damage, especially if the operator is working in a confined space.

Said Kevin Patterson, Manufacturing Support manager at Marshall Aerospace, "To support the manufacture of predeterminate assemblies, we need to be able to inspect to positional tolerances of five thousandths of an inch".

"This is not possible for an operator to do by the conventional method of checking a sheet metal component by eye against a foil loft, which is essentially a semi-transparent sheet of film with the profile of the component traced onto it".

Ever since copy routing of a component using a template produced from the loft profile had given way to CNC routing in the late 1990s, Patterson had been looking for a way to modernise the inspection process.

The existing co-ordinate measuring machines (CMM) at Cambridge had the precision to do the work.

The poblem lay in the difficulty of fixturing the sheet component off the surface of the CMMs' granite tables to allow a touch probe to access the profile and holes.

Even if it had been done, the inspection cycle would have been slow.

Marshalls also considered using complex 'go/no-go' gauges, but such a procedure would have been expensive and inflexible - many components are required on a 'one-off' basis.

The company also considered using a vision system, but scanning on a CMM would have been too costly.

Nor could the standard optical profile projectors available accommodate the large component sizes.

At the UK's last MACH 2006 show in Birmingham, Patterson saw the Planar machine.

It could accommodate most of Marshalls' sheet metal parts.

The Planar machine's light table is large and the control software is able to 'snap together' two sets of results from an oversize component that has been repositioned and measured again.

The machine was also relatively inexpensive, quick to use and is of simple, robust construction with no moving parts and could be used on the shop floor by the router operators.

InspecVision said that, as ordinary glass and fluorescent lights are used in the machine construction, it costs only a few hundred Euros to get the system up and running again even if a component is dropped right through the table.

As the Planar machine provides a dimensional check rather than a visual comparison, first-article inspection reports can be generated to ensure that the part produced matches the design intent, which is especially useful if there has been a change in the production process.

Customers can be supplied with copies of the report for their own quality audit purposes.

"It takes just a fraction of a second for the overhead digital camera to take a picture of the part and a few minutes for the Planar software to compare the measured data against the Catia CAD model from which the CNC routing cycle was derived," enthused Patterson.

"We have virtually eliminated the need for drawings, resulting in savings throughout the production process".

The first job on the measuring machine was the cover that forms the vertical, leak-proof corners of a fuel tank.

It was used to test the effectiveness of the system before the Planar equipment was purchased.

Other parts have quickly followed, such as cockpit console components, wing rib brackets and leading-edge panels, and more are being put on all the time.

An additional benefit of the Planar machine are as follows.

* It can 'reverse-engineer' replacement legacy parts when no CAD data is available.

* The machine is able to digitise a drawing in seconds by converting it automatically into a DXF file, enabling the part to be remanufactured on a CNC router.

* The system even includes optical character recognition and neural networks to extract any text and dimensions if they appear on the drawing.

To create an accurate DXF manually can take hours, or even days.

If a drawing is not available, the legacy component itself can be flattened and measured.

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