Inspection/Measurement Helps GM Stay Ahead of the Competition
Delcam and Romer technologies help General Motors design and develop more customer friendly cars.
When a problem arises, the design check team quickly provides precise dimensional data to the engineers and designers responsible for virtual design validation. The team also performs many other dimensional measurement and analysis tasks, including:
- Fielding a steady stream of design-check measurements from the body, chassis, and power train engineers.
- Examining vehicles from competitors that may have gained an edge in some area. Conducting "What-If" Studies
The primary tools for Sturgis's team are a pair of portable CMM (coordinate measuring machine) systems, inspection, arms, with 8- and 12-foot-diameter working envelopes. Developed by ROMER CimCore (Farmington Hills, MI), these arms provide nearly limitless flexibility in measurements. The arms 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 ROMER 3000i systems are equipped with Power-INSPECT (DELCAM Inc., Windsor, ON). PowerINSPECT formats the data gather-ing, creates the coordinate reference systems, identifies key features, and provides the integration with the GM math model.
The actual data are gathered as points with touch-probes and laser-scanners. For measuring large objects, such as the frame or underbody of an entire car, the design check team also has a ROMER 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 challenges is measuring the underbody alignment of an entire car. It involves a calibration check on the body framing weld-assembly system with which the car had just been built. These inspections are called the "integration build activity."
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. This is where the math meets the molecules.
"We align the vehicle with the GridLOK system to create a full body global alignment, the same as would be done with a fixed-axis CMM," Sturgis 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 Power-INSPECT, 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. The software preserves the body coordinates and the arm's reference to the vehicle. That means GM 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 ROMER 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, and are part of GM's Class A surface inspections for fits and finishes.
Inspection scans are often color mapped 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 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.
Another frequent team task is competitive analysis. In a recent project, the team touch-probed and partially digitized the front passenger compartment of a European-made luxury car. They 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 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 point to where problems lie. And in this context, the location of the design check team's facility is significant: In the basement of GMs 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."
For more information contact John Sturgis, General Motors design check liaison engineer (Warren MI), at (586) 575-4937, or Jack Thorton, Mindfeed Marcomm (New York, NY) at (888) 607-8088.
