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The company has
fabricated the leading-edge slats from aluminum alloy for every Airbus
aircraft made since the A310. The company produces most parts in-house on
numerically controlled milling machines or by stretching in combination
with chemical milling. They also produce structural bonding and composite
parts for the A320 and A340 series planes. The company assembles the
Airbus leading edges with the most advanced technologies, such as
automatic riveting and flexible assembly lines like those used in the
automotive industry. As a risk sharing partner on the Embraer ERJ 135/145,
they are responsible for the detailed design of the center fuselage
section and also the wing fixed leading edges, including the anti-icing
system. In the Embraer program, the company fabricates a tremendous number
of elementary references, mainly sheet metal parts by stretching, fluid
cell stamping and chemical milling. The company also uses graphite fiber
composites in the nacelle fairings and supports that contribute to local
stiffening of the cabin floor. They assemble two fuselage sections for the
ERJ 135/145, demonstrating their ability to succeed in a very
cost-competitive environment.
Previous
inspection method
The
company produces sheet metal components for both Airbus and Embraer using
two different technologies, one involving forming on a stamping press and
the other folding with a press brake. Tolerances for these parts are
typically 0.2 mm on the contours and hole positions. A thorough inspection
of these parts is required on a regular basis, such as the first parts
produced at the beginning of every shift or after a design change. In the
past, this type of inspection was performed by inscribing the part
geometry onto a mylar sheet, laying the mylar sheet on a light table and
placing the part on top of it. Then highly experienced inspectors examined
the parts and were able to easily identify out of tolerance errors. This
process took about 15 minutes. One problem is that this method was
difficultly applicable with more complicated 3D shapes. Another problem is
that producing the mylar patterns is an expensive task that had to be
performed partially by an outside supplier. Another problem is that this
method provides little documentation or traceability besides the
confidence that the company holds in the ability of its inspectors.
The customer’s objective was to digitalize the inspection within
a full numeric manufacturing process.
The
QC Manager looked for ways to improve the existing inspection process. She
considered the idea of moving the inspection to a CMM. Programming the CMM
to move its probe automatically to the points needed to inspect the part
would have allowed for inspection of most 3D parts and would have provided
electronic documentation of each part. However, it would have been a long
and involved process to program the CMM for each of the many different
parts produced by the company and the programs would have to be modified
for every design change. In addition, she expected the trend towards more
complex 3D designs to continue and was concerned that the company would
soon begin to produce contours that were too complicated to be inspected
in a reasonable amount of time using the CMM’s point-by-point approach.
“When I heard about the relatively recent innovation of laser scanning I
immediately decided that it deserved further investigation as a possible
solution to this problem,” she said.
Adapting
a laser probe on a CMM
Rather
than absorbing the expense of purchasing a complete laser scanning
machine, the company purchased a relatively inexpensive laser probe from
Laser Design, Minneapolis, Minnesota and installed it on a Mitutoyo CMM
machine. The laser probe is mounted to the CMM in place of the traditional
contact probe. Integrating the laser probe with the CMM is relatively
simple because a laser probe, unlike typical touch probes, does not need
to be in an exact location to measure because of its large field of view.
It just needs to know exactly where it was when the data was collected so
that the scan data can be accurately positioned in space. With a depth of
field ranging from one to several inches, all that matters is that the
laser probe passes through the area of interest on the part.
Additional
information improves process
The
laser probe comes with a computer that collects the laser scan data and
converts it to a 3D point cloud. Instead of collecting points one by one,
the laser scanner picks up tens of thousands of points every second. This
means that reverse engineering of the most complicated parts can often
accomplished incomparably faster than with touch probe digitization of the
part. Laser scanning can reverse engineer parts that are so complex that
they would be practically impossible one point at a time. The Geomagic
Studio software provided with the scanner greatly simplifies the process
of moving from point cloud to computer aided design (CAD) model, making it
possible in minimal time to generate a CAD Model of the scanned part that
faithfully duplicates the original part. Geomagic Qualify software is used
to compare original design geometry to the actual physical part,
generating an overall graduated color error plot that shows in a glance
where and by how much surfaces deviate from the original design.
“It takes about 15
minutes to set up the CMM and scan the part and another 15 minutes to
analyze the data and generate a plot that shows the complete geometry of
the part in comparison to our specifications (for our smallest and easiest
parts),” the QC Manager said. “This is only a little bit more time
than was required in the past but we generate far more digitalized
information now. We now obtain a
complete 3D model of the part that is annotated so that it shows any
discrepancies from the customer’s specifications. The part of the model
that is within tolerances is colored green. The areas of the part that are
out of tolerance are colored on a scale that depends on how far from the
tolerance band they are. This provides solid electronic documentation that
we can show to our customer to demonstrate that we have met their
specifications. In case there is a problem, these charts provide detailed
diagnostic information to our manufacturing people that helps them resolve
it. |
