quality
The Planar provides a
dimensional check
rather than a visual
comparison, so first-article
inspection reports can be
generated to ensure that
the part produced matches
the design intent
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quality at
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www.visioneng.com
Modern manufacturing methods bring major benefits in checking the
accuracy of sheet metal parts for aircraft.
New inspection routes
for ’plane maker
THE UK’s leading independent aerospace contractor,
Cambridge-based Marshall Aerospace has done away with
the time-consuming and inaccurate process of inspecting
flat components visually using foil lofts. It uses the latest
InspecVision Planar machine to be installed in the UK, to
check the profile and hole positions in sheet aluminium
components to within ±25μm. Other 2D parts made from
titanium, steel and plastic are similarly inspected.
The need for a more accurate way to check the 0.7 to
3.0mm thick components after they have been routed and
drilled is driven by increasing use of predeterminate
assemblies, requiring components whose machined
features are so precise that they fit together perfectly,
without having to use jigs on the factory floor and ream
out pilot holes. This avoids the expense and lead-time of
producing jigs, and means faster assembly and less risk of
damage, especially when working in a confined space.
Says Kevin Patterson, manufacturing support manager
at Marshall: ‘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 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.’
Since copy routing of a component using a template
produced from the loft profile gave way to CNC routing
in the late 90s, Patterson had sought a way to modernise
the inspection process as well. The existing CMMs at
Cambridge had the precision, but it would have been
difficult to fixture the sheet component off the surface of
the granite to allow a touch probe to access the profile
and holes. In any case, the inspection cycle would have
been slow. Complex go/no-go gauges were considered,
but such a procedure would have been expensive and
inflexible, especially with the large number of one-offs.
A vision system seemed to be the best way forward, but a
scanning solution on a CMM would have been too costly,
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82 MWP november 2007
and standard optical profile projectors on the market
could not accommodate the large component sizes
produced by Marshall Aerospace.
At MACH he saw the solution. The Planar would
accommodate most sheet metal parts produced by
Marshall, as not only is the light table large, but the
control software can snap together two sets of results
from an oversize component that has been repositioned
and measured again. It was relatively inexpensive, quick to
use and its simple, robust construction with no moving
parts, allows it to be used on the shop floor. (Ordinary
glass and fluorescent lights are used in its construction, so
it costs only a few hundred Euros to restore functionality
even if a component is dropped right through the table.)
As the Planar 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, 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’ enthuses 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 is its ability to reverse-engineer
replacement legacy parts when no CAD data is available,
the original foil lofts are no longer available, and perhaps
only undimensioned drawings exist.
www.pressandshear.com
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