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Correcting the
Fit Between Disparate Materials in Rotor Housings
The Company
A leading worldwide provider
of outdoor maintenance and beautification products for home, recreation,
and commercial landscapes, well known both with homeowners and
professional groundskeepers.
The Challenge
The company
was in the final phase of developing a new single-stage
snowthrower when it ran into an interference problem between two large
rotor housing components. One of the parts was made of an injection
molded polymer, the other was stamped steel.
The senior
principal designer on the project explained, “The design required major
portions of adjacent surfaces on the two parts
to align in order to assemble and function properly.” The first
parts off tooling were difficult to assemble because of interferences
between the two parts. “To add to the complexity in solving the
interference problem, the surfaces in question had large curved contours
that were difficult to inspect.” Since both parts were already tooled,
the company needed accurate inspection data that could be compared to
existing Pro-E 3D models in order to determine where the interferences
were occurring, and how to modify the tooling to get the parts to fit.
“We decided the
best way to create the inspection data was to laser scan the parts, so
we called Larry Carlberg at GKS,” said the designer. GKS is a division
of Laser Design, Inc., based in Minneapolis, MN.
The Solution
 Since
it was a repeat customer, the company was confident in Carlberg’s
ability to quickly create excellent scan data to solve the fit problem
between the snowthrower parts.
With over 25 years
in the business, GKS metrologists have experience with all kinds of
custom projects. Carlberg explained the approach he would take and how
to address the issues of the large curved contours. Because the laser
scanning system projects a line of laser light onto surfaces while
cameras continuously triangulate the changing distance and profile of
the laser line as it sweeps along, the problem of missing data on a
curved surface is eliminated. The system measures fine details and
captures complex freeform geometry so that the object can be exactly
modeled. Laser scanners quickly measure articles, picking up tens of
thousands of points per second, and generating huge numbers of data
points without the need
for templates or fixtures.
“Working together
with Larry and the scanning technician, we discussed which surfaces to
scan, how the parts should be set up, and the tolerances we were
expecting from the scan results,” the designer continued.
Both of the parts
were set up on a FARO scanning system with a Laser Design SLP-330 laser
probe. Carlberg elaborated on his method: “This setup provided a fast
method to capture all the surfaces required with minimal time.”
Carlberg performed three quick preliminary scans to determine the
correct shape and placement of the two parts in relation to each other
when they were assembled. This trial-and-error “mock assembly process”
aligned the housing to a manufacturing datum, ensuring that the
snowthrower auger axis datum was in an acceptable position with respect
to the rest of the housing. “When an assembly doesn’t fit together
correctly it is difficult to determine where the interference is with
the real physical parts because if you force them together you distort
the shapes. With the virtual scan data, we can overlay one part’s data
with the other’s until they are aligned correctly in the model. The
agility and quickness of using the portable arm system allowed us to do
several test scans to verify acceptable alignment in just a few hours,
even using a trial-and-error method of datum alignment.”
After the correct
alignment was achieved, GKS scanned the rest of the housings, paying
close attention to key areas, such as the critical mounting locations
used to fasten the two parts together. Carlberg summarized, “Once we
completed the scan of the steel rotor housing and the injection molded
liner, the solution was quite simple. We aligned the parts by centering
the holes used to fasten them together. This technique simulates the
physical assembly that occurs during manufacturing.” Carlberg then
created surfaces from the data, focusing especially on the critical
locations. “When the two point clouds representing each of the two parts
were aligned by the holes’ centers, interference between these parts was
immediately evident. We exported color coded comparison reports to the
company’s engineering team showing this interference.”
The Results
GKS completed the
scanning and sent the processed scan files to the designer in just a few
days. The scan data indicated that both parts had significant areas
contributing to the interference problem. The engineers were then able
to download the scan data files directly into Pro-E, and compare the
results to the 3D models.
 The
designer clarified, “At this point we were able to see where the
interferences were occurring, and determine the best method to solve the
problem. Fortunately, we were able to make a relatively simple change to
deepen the offset in the stamped steel part, which overcame the
interferences caused by both parts.”
“The process was
very successful for us,” concluded the designer. The mating assembly
holes in the initial parts were almost one-half diameter off, but by
using the scan data, the engineers were able to correct the problem
quickly and accurately before the pre-production pilot build, and more
importantly, before the production process was online.
The original
service plan called for GKS to perform another set of scans on the parts
after the tooling had been modified based on the first set of scan data,
but the results from the performed process were so successful that the
engineers did not feel a secondary scan was necessary to verify the
tooling corrections.
They were right.
According to the designer, “We just completed the pre-production pilot
build for this product, and are happy to report that the fit between
both parts was excellent.”
About GKS
GKS Inspection
Services has been a leading provider of dimensional inspection, 3D laser
scanning and terrestrial scanning services for over
25 years. The company’s Plymouth, MI lab (Detroit metro area) is
accredited by the A2LA for Mechanical Testing and Calibration and
features numerous CMMs, vision systems, 3D laser scanners,
surface analyzers and other inspection equipment. GKS also has U.S.
offices in Minneapolis and Seattle and international locations in India,
Korea, China, Taiwan and the
Netherlands. The company’s metrologists and engineers are experienced
in the automotive, defense, electronics and many other manufacturing
industries.
More Information
For additional
information about how GKS Inspection Services can improve your
manufactured product, save you money and decrease your development time,
contact GKS Inspection Services at 952-252-3433 or by email
at:
measure@gks.com
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