"“The traditional method works, but it’s slow and not very
accurate. The FaroArm offers accuracy comparable to fixed
CMMs and software that is fully programmable for repetitive
measurement so it greatly increases both the speed and accuracy
of the inspection process. The result is that we are able to get
more parts out the door with the same people while maintaining
higher standards of quality.”
Unitech Composites and Structures, a division of the AGC Aerospace & Defense Composites and Structures
Group, designs and manufactures composite structures in commercial and military aerospace markets. Most
of these parts have critical dimensional and structural requirements so an exacting 100% inspection process
is required. In the past, the company used traditional inspection methods which involved using hand tools for
measurements and manual calculations to determine deviation from true position.
Now, the company uses a FaroArm®, a portable coordinate measuring machine (CMM), to capture points while
Verisurf software uses best fit algorithms to instantaneously compute true position deviation. “We are in a
business where everything we make needs to be carefully measured to ensure it meets our customers’ critical
specifications,” said Alan L. Haase, President & CEO, AGC Aerospace & Defense Composites and Structures
Group. “By using the FaroArm we are getting significantly more parts out the door with the same staffing.”
Traditional Methods Too Slow
“The parts and assemblies we produce are installed in high performance aircraft and there is little room for
error,” Haase said. “Making sure these parts and assemblies meet and exceed customer specifications can
quite literally be the difference in a successful flight or mission for our armed forces.” One of the most critical
challenges is measuring geometry design and tolerancing (GD&T) features including the deviation from true
position of features. The manual methods used in the past were time-consuming and subject to potential
errors. Calipers, height gauges, micrometers and other hand tools were used with an inspection plate to make
measurements and compare feature position to three datums.
The first step, in the case of a hole, for example, was to measure its diameter. Next measurements were taken
of the hole’s closest and further positions to the x and y axes in order to determine its Cartesian coordinates.
The deviation D of the true position from the position called out in the drawing was then calculated using the
equation D = 2√(∆x)2+(∆y)2 where ∆ equals the measured deviation in each axis. This cumbersome procedure
took about 20 minutes even for very simple measurements.
Another problem with the traditional approach
is that it requires someone with both math and
blueprint interpretation skills that are often
difficult to find in today’s workforce. “I am old
school so I still know how to manually calculate
true position based on manual measurements,”
said Tom Van Der Griend, Director of Quality
for United Composites. “But workers with these
skills are becoming harder and harder to find.”
Many of Unitech Composite’s customers have
moved to a model based design (MBD) or digital
product definition (DPD) approach in which the
dimensions, GD&T, annotations and parts lists are
inserted directly into the solid model, eliminating
the need for drawings. The live 3D model with a
prescribed series of annotated and dimensioned
views is provided to United Composites instead
of blueprints. In order to support MBD using
traditional methods, it was necessary to get
multiple layers of the organization involved
to read the model, convert the model to 2D
drawings and then inspect to the 2D conversion.
FARO Arm and Verisurf Software Speeds Process
“It became obvious that we needed to find an inspection method based on MBD and DPD,” Van Der Griend said.
“We looked at laser scanners and CMMs. Laser scanners are powerful tools but they require a considerable
amount of manual effort to perform a true position inspection. On the other hand, the FaroArm and Verisurf
software provide a truly seamless solution that can be programmed to dramatically reduce the time involved
in inspection while also reducing the potential for error.”
In the case mentioned above of determining the true position of a hole, the operator clamps the part in place
using simple tools because the part does not need to be accurately positioned. The operator captures data
points by using the device’s probe. The FaroArm determines and records the location of the probe in 2D space
and reports the results through software.
The rotational angle of each joint and the length of each segment in the arm is determined using optical
encoders that count rotations incrementally via detection of accurately spaced lines on a glass grating disc.
Software converts the counts into angle changes and determines the position of the probe. The device’s laptop
computer simultaneously illustrates the 3D measurements on-screen and records all of the data.
The operator begins by taking several points along the datums to accurately establish the position of the part. The process is repeated for the hole. The software then dimensions the position of the hole. When all of the
points are taken, the user pulls away from the part. The entire process takes less than five minutes.