|
GM Warren Vehicle Engineering Center Stays Out Front With Fits And Finishes |
|
|
|
|
When General Motors Corp. (GM) engineers want to make sure a vehicle is
fitting together properly, or find out why if it’s not, they often turn
to a group of five men in Warren, Michigan, who are equipped with the
latest in portable coordinate measurement machine (PCMM) and laser
scanning technology.
Decades of buyer surveys have shown GM, and the rest of the auto
industry, that the way the sheet-metal skins of cars fit together—the
“fits and finishes” and overall appearance—is a huge factor in the
decision to buy any given car. “As we push to achieve better fits and
finishes, we need to constantly validate our tolerance and variation
stack-ups,” said Jesse Ortega, director of vehicle architecture and
design check. |
The team in Warren—GM’s Design Check and Vehicle Assessment team—plays
a critical role in making sure the fits and finishes are exactly as
designed. As part of the corporate engineering team in the sprawling
Warren Vehicle Engineering Center (WVEC), their main tasks are “vehicle
integration” and “design integration.” The team constantly checks fits
and finishes, helping strengthen and refine virtual builds based on the
GM Math Model.
When there is a problem, the design-check team quickly provides precise
dimensional data to engineers and designers assigned to virtual design
validation. The Design Check team has many other dimensional
measurement and analysis tasks, including:
• What-if studies.
• Fielding a steady stream of design-check measurements from the body,
chassis and powertrain engineers who are the core of WVEC.
• Examining vehicles from competitors that may have gained an edge in some area.
“Those color maps also show how whether any section of the surface is
out of tolerance and, if so, how far out. That kind of data is very
handy for stamping-die rework”
John C. Sturgis, Design Check team liaison engineer and
team leader, explains that “for us, this is all about the physical
integration of as-designed parts, how they fit together, rather than
focusing on the dimensional measurements of individual parts.” Those
kinds of inspections are always done at the production line—and are
always referenced back to the math model. Sturgis is a former product
design engineer himself.
In the WVEC, the primary tools for Sturgis’s team are a pair of
portable CMM dimensional measurement systems—inspection “arms” with 8-
and 12-foot-diameter working envelopes. Built by CimCore, Farmington
Hills, Michigan, these arms provide nearly limitless flexibility in
measurements. They replace manual methods such as rulers, tape measures
and height gages. They also do away with the need to trek back and
forth to a stationary CMM, a machine that is usually in an isolated
location.
Both of the WVEC’s 3000i Series™ portable CMM systems are equipped with
the aptly named PowerINSPECT from DELCAM Inc., Windsor, Ontario,
Canada. PowerINSPECT formats the data gathering, creates the coordinate
reference systems, identifies key features, and provides the
integration with the GM math model. CimCore provides pre-sales and
post-sales support, application assistance, training and on-going
telephone support for the complete CMM system.
The actual data is gathered as points with touch-probes or
laser-scanners. For measuring large objects, such as the frame or
underbody of an entire car rather than, for example, a door with its
hinges mounted in its frame, the Design Check team also has a GridLOK™
system. GridLOK simplifies orienting the CMM to the car body while
eliminating the need for “leapfrogging” with its unavoidable cumulative
positioning error.
One of the Design Check team’s biggest measuring challenges is the
underbody alignment of an entire car. This is a calibration check on
the body framing weld-assembly system with which the car had just been
built. “This was for a global alignment of the frame, corner to
corner,” Sturgis said. “These inspections are what we call the
‘integration build activity.’” The team does not do inspections per se.
Team member Paul Bucilli noted that the practical accuracy of the
portable CMMs as the WVEC team uses them is ±0.2 mm or ±0.008 inch.
Adds Design Check team member Phil Karas, “this is where the math meets
the molecules.”
Sturgis and his team leave nothing to chance. “We align to the vehicle
with the GridLOK system to create a full body global alignment, the
same as would be done with a fixed-axis CMM,” he said. “We use the
body-build datums on the vehicle and if we need more we can glue on
additional datum targets.
“Once we get all this set up with GridLOK and its data plotted into the
car-body coordinate system with PowerINSPECT,” Sturgis said, “we take
the car out into the shop where we can lift it up and get underneath to
measure exhaust system locations, placements of bumpers and bumper
fascia, and other parts of the underbody.”
“The latest version of PowerINSPECT combined with laser scanning [also
known as laser probing] is very good for this kind of work,” added Jon
Sajewski, also on the Design Check team. “The software preserves the
body coordinates and the arm’s reference to the vehicle. That means we
can use the same vehicle reference and coordinate systems even though
these measuring jobs require two separate layouts.”
Another Design Check challenge is sheet metal fit-ups between doors,
door frames and body pillars plus hinge alignments. Here the portable
arm, working with the math model data downloaded with PowerINSPECT, is
used to check a rectangular array of lines a few inches apart on all
the exterior parts for accuracy. These kinds of measurements are often
referred to as a “gap and flush” check but they are all part of GM’s
“Class A” surface inspections for fits and finishes.
These scans are often color mapped, too, to show deviations from
nominal as the surface is described in the math model or in a
supplier’s CAD system. “Those color maps also show how whether any
section of the surface is out of tolerance and, if so, how far out.
That kind of data is very handy for stamping-die rework,” Sturgis added.
A frequent Design Check Team task is competitive analysis. In a recent
project, Sajewski and another member of Sturgis’s team, Greg McDonald,
touch-probed and partially digitized the front passenger compartment of
a European-made luxury car.
McDonald explained: “We used the laser scanner to handle volumetric
data generated from scanning hundreds of points all over the front of
the passenger compartment” including the dashboard, steering wheel and
the reach to the controls.
What GM gets from these efforts at the WVEC is assurance that vehicle
bodies are fitting together as designed and, for those rare times when
they don’t, reliable and easily understood dimensional data that points
to where the problems lie. And in this context, the location of the
Design Check team’s facility is significant: In the basement of GM’s
largest corporate engineering facility.
“Almost everything the Design Check and Vehicle Assessment team does is
tied to appearance,” said Jeffrey Holland, GM Design Center
communications manager. “This is about what the appearance of our cars
communicates, how the cars communicate it, and how they look when they
communicate it. This is all very important to us. GM has a legacy of
great designs and great designers. We are working to keep that legacy
strong.” |
|
|
|
CIMCORE
a brand of ROMER Inc.
a Hexagon Metrology Company
51170 Grand River Ave.
Wixom, MI 48393
Toll Free Phone: 800.218.7125
Phone: 248.449.9519
Fax: 248.449.9445
sales@cimcore.com
|