quality
Specialised hardware and software help Alcoa Howmet’s UK foundry
layout department cut turbine blade inspection times by up to 70%.
Inspection investment
MAJOR improvements to the inspection process at
Alcoa Howmet’s foundry have been enabled by the
introduction of a GOM ATOS II optical measurement
system and Geomagic Qualify computer-aided
inspection software. ‘What used to take us a week or
more we can now complete in one day’ says Steven
Edwards, layout and tool room manager. He’s referring
to the proof inspection of newly-cast turbine blades and
other airfoil components, a process which has been
transformed with the introduction of digital shape
sampling and processing (DSSP) and computer-aided
inspection software from Geomagic.
Alcoa Howmet’s products include castings of superalloy,
titanium and aluminium alloys - components
such as turbine blades and vanes - for companies such as
Siemens, Alstom, Rolls-Royce and ABB. The lost-wax,
or investment casting process, is favoured for these
products. Castings can be manufactured with complex
features, such as 3D contours, thin walls and undercuts,
while control of the process variables enables closer
tolerances. It is also an economical process for both
prototype and production run quantities.
Nevertheless distortions of the cast parts can occur, so
inspection is critical in ensuring parts that meet all
geometric tolerance and quality standards. Thet
inspection process, both for first-article and for
changed parts inspection, relies mainly on new digital
shape sampling and processing (DSSP) technology.
DSSP encompasses the convergence of multiple
technologies, and describes the ability to use scanning
hardware and processing software to digitally capture
physical objects and automatically create accurate 3D
digital models with associated structural properties for
design, engineering, inspection and custom
manufacturing.
At Alcoa Howmet the DSSP technology used
comprises a GOM ATOS II optical measurement
system, which captures part geometry as a dense ‘point
cloud’ or polygon mesh that precisely describes an
object’s surface and primitives, and Geomagic Qualify
computer-aided inspection software.
‘The use of Geomagic
Qualify has not only
speeded up the actual
inspection process but also
the production of the
reports,’ states Matt
Willacy, Alcoa Howmet
layout engineer. ‘They
contain both graphical
representations of the
inspected part, such as
colour-shaded deviation
plots, etc, as well as actual
numerical values, so they
are much easier to
understand than the
reports we used to
produce.’
76 MWP november 2007
The inspection process relies on two inputs: the 3D
scan data of the part to be inspected and the original 3D
CAD model of the part. Both are read into Geomagic
Qualify, using industry-standard data transfer methods,
or directly in the case of the data from Alcoa Howmet's
Unigraphics CAD system. Datums and features upon
which the inspection is going to be based are then
created on the CAD model. The scan data is then
aligned with the nominal CAD model using both the
manual and the automatic alignment facilities
provided by Geomagic Qualify.
Once the scan data and the CAD model are aligned
correctly the inspection process starts. This includes
overall three-dimensional analysis of any deviation
between the physical part and the nominal CAD model,
with the results being presented as a colour-shaded plot
of the part, showing deviation values. Areas of the part
that fall outside assigned geometric tolerances are also
displayed for easy identification, along with geometric
dimensioning and tolerance (GD&T) call-outs, whisker
plots of cross-sections and wall thickness analysis
results.
Alcoa Howmet also takes advantage of the specialised
inspection capabilities offered with Geomagic Blade, an
optional extension to Geomagic Qualify. Geomagic
Blade focuses on the turbine machinery industry,
providing specific functionality to enable the analysis
of rotors, stators, impellers and specific internal blade
features.
‘With the Blade extension we can readily undertake
multiple airfoil analysis by analysing and reporting on
dimensions related to turbine segments, such as
minimum opening, or throat, and minimum distance
blade to blade, as well as other turbine-specific
inspection requirements such as twist analysis and cross
section and chord length measurements,’ says Matt
Willacy, Alcoa Howmet layout engineer and Geomagic
Qualify user. ‘What’s more, the software is easier to use
and faster than our earlier system and Geomagic is
always willing to listen to our needs and to come up
with new capabilities.’ www.geomagic.com
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