Two new cars built in General Motors Corp.’s assembly operations in Lansing, Michigan, currently rank Number 1 and Number 3 in a crucial quality audit. This puts Lansing, the biggest assembly plant in North America, at the pinnacle of the automaker’s ceaseless efforts to build better cars.

The ranking is especially impressive because the cars -- Pontiac Grand Am and Oldsmobile Alero -- are ranked so high in the Global Delivery Survey (GDS) in their first year of production, “right out of the chute,” said Plant Manager Jim Zubkus. The GDS benchmark is the rigorous final evaluation every GM car gets from independent teams of quality assurance people. (The GDS audit is sometimes called the “railhead” audit because it’s conducted at the end of the railroad portion of every new car’s journey from factory to dealer.)

“It has never happened before for any car to rank Number One in its first production year,” Zubkus said. Alero reached Number Three spot after just six weeks of production, an unprecedented quality achievement. The Grand Am and Alero were evaluated against more than five dozen car and truck models turned out by GM’s 32 North American plants.

“There are a huge number of factors behind this success beginning with the individual efforts of thousands of hourly and salaried people,” Zubkus added. He also credits “a lot of new methods, processes and technologies” and one of these is a standout, namely the portable coordinate measuring machines (CMMs) from ROMER CimCore.

“We attribute a portion of the GDS audit success to the extremely good body fits on the Grand Am and the Alero,” Zubkus said. “The portable CMM allows us to qualify the tooling in the body weld-assembly systems better then ever before. The ROMER CimCore portable CMMs have been a big part of this.”

“With the ROMER’s we can, for the first time, catch problems in tooling location, positioning, and orientation that we never would have uncovered before..." 

The portable CMM frees Lansing’s dimensional integrity team, the engineers and skilled tradespeople responsible for the fit of the body sheet metal, from the tedious guesswork of indirect measurement. The teams are no longer shackled to the traditional stationary CMM - huge and accurate but slow and expensive. Previously weld-tool locations and orientations were, for all practical purposes, extrapolated from measurements of parts that come off the tools. [In quality assurance, it is axiomatic that if the tools are correct, the parts will be. Unfortunately, the reverse is not necessarily true.]

“For the first time, the ROMER CimCore lets us measure the [weld assembly] tools directly now rather than indirectly,” Zubkus continued. “Before, we verified the tools by carrying sample panels or subassemblies to the CMM room and measuring the product. Now we measure the tools right where they sit in the production system.

“It doesn’t matter if the CMM room is just three feet away from the line,” he continued. “By the time you get the measurements back it may be two days. And even if it’s only two hours, dozens of cars have been built which may have a dimensional discrepancy. All of them have to be chased down, inspected and fixed.”

Final weld assembly tools, which GM calls Robogates, contain many individual spot welders -- some fixed, some on slides, and some mounted on robot arms. The Robogate fixtures the car’s complete body side panels in place and welds them to the complete underbody. In about a minute this system makes hundreds spot welds. Doors, hoods and deck lids go on later.

“What the ROMER’s let us do is take Mohammed to the mountain,” Zubkus summarized. In other words, portable CMMs take dimensional measurement for verification and fine tuning of weld-assembly tools one step closer to online processing -- in both computer and manufacturing terms.

The Dimensional Integrity teams at GM Lansing use the ROMERs primarily for location, position, and orientation of the tooling to defined nominal dimensions. But they do a lot more than measuring. “They are also used to determine root causes of dimensional build problems by measuring the welded subassembly and the tooling and developing dimensional correlations between them,” Sturgis said.

As with any sequential process, the further along in manufacturing and engineering that problems are uncovered, the harder they are to isolate and identify -- and the more costly and time consuming the fixes. In some cases costs of fixes rise geometrically between successive steps.

“With the ROMER’s we can, for the first time, catch problems in tooling location, positioning, and orientation that we never would have uncovered before,” he added. These problems arise from the way the tools were shipped to Lansing, how they were initially fastened down, and simple human error, he explained. “With the ROMER we find and fix these things right away,” Sturgis said. “The ROMER is absolutely leading to some very important changes in the way we do things here.”

“The only change I would make in this whole experience is that I wish I had had this business case sooner,” he concluded. “We would have been able to get started sooner. The portable CMM is a great innovation in this industry.”