Managers of the huge Caterpillar Inc. factory in Aurora, Ill., have found that the operational flexibility offered by rapid new-product introductions, outsourcing and Just-in-Time (JIT) inventory demands a matching level of flexibility in dimensional measurement.

In the hands of Don Barkman, supervisor for “G” operations and his team of seven quality specialists, flexibility in dimensional measurement takes several forms on the factory floor:

• Simple portability. This is the capability of taking measurements anywhere in the 4,000,000-square-foot plant at just about any time—often beginning within minutes. Portable coordinate measuring machines (CMMs) are the key to Barkman’s department’s ability to resolve quality concerns on the spot in an assembly line, for example, or with a welding fixture.

• Ability to handle a wide variety of measuring situations. This is the key to the unparalleled ability of portable CMMs in ferreting out root causes in trouble-shooting situations that can occur anywhere in this sprawling fabrication and assembly facility.

• A complete spectrum of measurement techniques. At Caterpillar in Aurora, this includes four conventional, fixed-in-place CMMs, a portable laser tracker, a GridLOK® dimensional measuring system that also uses a portable CMM, and 100% inspection of machined parts with on-the-machine gauging or the use of long-proven setups, fixturing, tooling and programming.

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The portable CMMs are “easily three times more accurate than the old linear-encoder based measuring systems. And they are at least 75% faster in measuring, too, not counting setup time.”

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“There is little overlap among the systems and no gaps between them, providing the plant with a complete and essentially seamless set of dimensional measuring capabilities,” Barkman said.

The Aurora plant has six portable CMMs, all of them touch-probe systems with 12-foot arms. These are 3000i™ systems from ROMER CimCore, Farmington Hills, Michigan. Five are on the factory floor and one is the tool room. The ability to measure almost anything, in almost any orientation, comes from the ROMER arm’s infinite rotation in three principal axes. The rigid but lightweight arms can go almost anywhere, including more than once to a nearby subcontractor’s plant.

All six arms came equipped with PowerINSPECT™ software developed by Delcam Inc., Windsor, Ontario, Canada. The flexibility of the measurement methods offered by the Delcam software, and its ease of use, are important factors in the 3000i systems’ fast set-ups and unambiguous outputs.

The plant also has a portable laser tracker system equipped with its own uninterruptible power supply and mounted on a motorized cart. “It has excellent precision and can measure increments spanning up to 200 feet,” Barkman pointed out, “but it is costlier and less flexible than the portable CMMs.” Like all lasers, whether portable or fixed in place, it is limited to line-of-sight checking—no reaching underneath, around, over, behind or inside.

Dimensional measurements are also met with a ROMER GridLOK system adjacent to the plant’s CMM room. Pointing to a wheel-loader “tower” mounted on the GridLOK’s 16- by-20-foot steel base floor plate, Barkman observed: “This is a life saver for us because of the large parts we have to check.” Fabricated and welded steel towers link the fronts and rears of the articulated wheeled loaders (the majority of the machines built at Aurora).

The GridLOK system was created on top of a steel floor mounted measuring plate leftover when a 25-year-old Portage measuring system was retired in 2002. A state-of-the-art system in the 1980s the Portage system had one big drawback: It could only measure orthogonally. That meant anything being measured “had to line up precisely and squarely with the machine,” Barkman explained.

“Some of our subassemblies weigh thousands of pounds,” he noted. “With the old systems, you could spend hours banging on them with a maul to get them lined up before they could be checked. With the portable CMMs, whether GridLOK is being used or not, the machines line up with the parts.”

Installation of the GridLOK required only the countersinking of pre-existing locator holes in the Portage floor plate. The holes act as fixtures, allowing the portable CMM’s arm to be repositioned as needed without losing registration. This lets Aurora benefit from the set-up speed and measurement flexibility of any portable CMM while offering convenient 360-degree access to the workpiece. Working from any of the 54 locator points in the GridLOK base plate, the arm can measure virtually anything within a 12-foot radius. GridLOK measuring accuracy is typically 0.006 to 0.007 inch, Barkman said.

The portable CMMs are “easily three times more accurate than the old linear-encoder based measuring systems,” he noted. “And they are at least 75% faster in measuring, too, not counting setup time.”