A fire-truck manufacturer uses a portable CMM feeding data through engineering software to cut production time, keep money in-house, and document quality control.

Edited by Richard Harris, consulting editor

A Pierce Mfg. custom fire-truck cab enclosure is ready for shipment to the final assembly plant in Appleton, Wis.

Lang verifies the location of one of the moveable stops on the primary weld-assembly fixture for cabs.

Manufacturing engineer Ryan Lang checks part of the primary weld-assembly fixture for a fire-truck cab using a Romer CimCore System 3000i with PowerInspect.

Don Nennig, manufacturing engineer, uses Catia (large monitor) and Delcam's PowerInspect software (laptop screen) to check part of a weld-assembly fixture.

Andy Smazinski, receiving inspector, uses a Romer CMM to check roundness and dimensions on a fan shroud.

Many fabricating companies think outsourcing will open the productivity valve. But outsourced inspections can put a crimp in the productivity pipe. That was the case at Pierce Mfg., Appleton, Wis., builder of custom fire trucks.

"Before we purchased inspection machines, we were at the mercy of a contract coordinate measuring machine (CMM) service to help us," says Don Nennig, a manufacturing engineer who programs the portable CMM arms at Pierce. "These inspections cost roughly $300 apiece and, if they were backlogged, several days of delay. It was a big expense."

Fire-truck cabs fabrication at Pierce revolves around seven large welding fixtures used for wheel wells, doors, step-box assembles, engine-tunnel assemblies, roofs, sides, and rear walls. Pierce makes six different cabs, built on five distinctly different weld-assembly fixtures. Stops accommodate the multiple sizes of otherwise standard fabricated-aluminum components. In the final-assembly fixture, operators fit sheetmetal components against the stops for each cab then manually arc-welded the joints.

Pierce builds high-end fire apparatus, with most units costing $200,000 or more. Both the production rate and the backlog are strong, "So we are always trying to find ways to increase our production and maintain our high quality," Nennig comments.

The firm fabricates nearly all the components for its cabs and chassis and all assembly fixtures in its 150,000-ft ² vertically integrated plant. Pierce, with about 1,600 employ-ees, builds over 1,300 custom fire trucks a year.

But Pierce has more than 60 competitors, half a dozen of which present serious competition. To maintain its market leadership, Pierce stresses productivity improvements. Three of its many CMM-related efforts are:

• Engineering the aluminum fittings that hold the halves of the oversized windshields in place.
• Engineering the forward-most side roof-support pillars of the cabs for better structural integrity. Measurements originating from these A pillars determine dimensions and tolerances for other cab components.
• Checking and troubleshooting assembly fixtures. Pierce designs and builds nearly all its fixtures in-house. The dimensional measurements are critical to productivity.

In addition, it is replacing labor-intensive sheetmetal work with redesigns and material substitutions. For example, the firm is redesigning fabricated-steel mounting brackets as iron castings (each fire truck has dozens of different brackets, many in left-and right-hand versions).

In addition, it has switched fan shrouds — one per truck but awkward to inspect — from steel fabrications to reaction-injected molded (RIM) plastic.

"We do first-article inspections with the CMM as new parts come in from suppliers," states Nenning. "It helps us make fast and accurate inspections — the key to production efficiency. We apply data from these inspections to continuous product improvements to our castings and composite-part innovations. Because of the CMM, we can accurately scrutinize every part and compare the results over time."

In the past two years, Pierce bought two 3000i portable CMMs from Romer CimCore, Farmington Hills, Mich. Both came with PowerInspect inspection software developed by Delcam Plc, Windsor, Ont. Romer provides sales support, application assistance, training, and ongoing telephone support for the system.

Prior to getting the first Romer CMM in 2000, in-house inspectors worked with "hand" measuring devices such as tapes, height gages, calipers, and micrometers or subcontracted to companies with CMMs. After the second 3000i purchase to accommodate the CMM workload at Pierce, the firm moved the first machine to its parent company, Oshkosh Truck Corp. in nearby Oshkosh, Wis.

"The most obvious impact of the CMM is the quick set up of welding fixtures with verifiable proof of the accuracy of the stops," Nennig explains. "Plus we can work with our design engineers to develop and build fixtures before production starts a big boost in faster production start up."

Getting good dimensions quickly
The firm's engineers use the CMM to obtain a surface model of the windshield. Each roughly 44 32-in. glass piece curves in three axes. They insert this surface model into the solid model to design the cab windshield openings. Hand-stamped aluminum "trim" parts hold the glass in place.

Dimensionally precise parts had been a production bottleneck, so Nennig digitized the windshield glass panels with the point-cloud and guidedplanes functions within the PowerInspect software. Point-cloud-based reverse engineering generates an CAD/math model of a component built or modified by hand. The user measures surface points. These are exported as raw points or as a series of curves to a CAD system to produce a CAD or math model.

"Every time I crossed the predetermined 'guided plane' with the probe of the CMM, it gave me a series of points in an exact row, all lying on that plane. That took a mere two hours," Nennig says.

"The first one, when we were still new to computerized-measuring techniques and without guided planes, took two days," he adds. "Without the CMM, it would have been virtually impossible to create a sophisticated set of fittings for each of the windshield panels."

The A pillars of the cab create a similar CMM challenge. Structurally, the A pillar is critical. "It is the origination point for all the cab dimensions," Nennig says.

"It was taking us three to four hours to form each of these pillars — tap, adjust and check, saw, hammer, weld, and grind," adds Ryan Lang, manufacturing engineer for Cab Fabrication. Pierce engineers wanted to eliminate an hour of that for each pillar. And because the A pillar itself is curved in two axes — in part to hold the outside edge of the windshield glass — its tooling is among the most complex. The other cab pillars — B, C, and D — are vertical and the glass held is flat.

"We take extra care to support the tooling for the A pillars. We ensure that all three planes of motion are locked down," Nennig explains. "We meticulously set and reset, check, and double check the stops before the A-pillar welding fixture leaves the toolroom for production."

"With a correct geometric model from the CMM software, we can produce a new A pillar and the die to form it in one step," Nennig says. "We also give extra measurement attention to the cab pivot and lock-down stops, wheel wells and step heights, and engine tunnel widths and heights, because other dimensions depend on these."

According to Andy Smazinski, "As the incoming inspector, a first-article casting inspection consumes a good portion of my day. It takes me an hour or two to program in the geometry and set up the planes and tolerances. After working with the CMM for a short time, I could program fairly complicated part inspection files."

He sets up the portable machine with magnetic clamps in 15 to 20 min. "Most inspections have 30 to 40 dimensions to verify with a minimum of 10 to 15," he points out.

Better dimensional control, better production
"The beauty of using the CMM is that if just one stop in a fixture is moved," says Lang, "we can identify it quickly and see exactly how much and in what direction it moved. Since each fixture has dozens of stops, previously finding one that was out-of-position might have taken us a week. This means huge time savings when troubleshooting on the shop floor."

Nennig confirms Lang's point by explaining the complexity of Pierce's fixtures. "The main final-assembly fixture is 12-ft long and weighs a ton. Depending on the cab model, size, and type being built, it has 120 to 150 individual stops. At best, we can 'set' 30 stops a day, and 25 is the norm. Because of the cab variants, some stops have two or three settings to accommodate different component sizes for the six cab models."

For example, the "base" or cab floor frame measures 60 102132 in. On to this frame, employees bolt approximately 40 stops with about a hundred "stopping surfaces." Each is dimensionally located and spatially oriented in three dimensions. "These stops range in size from 3 32 to 4 615 in. with some larger in a particular direction," Nennig states. "Not only do we build and check these fixtures, but we recalibrate them on a rotating basis. We reverify the cab weldment setups every year. So the CMM helps us keep production moving."

Nennig adds that the company typically creates its own part-specific files directly in PowerInspect rather than using downloaded CAD and IGES files. "The CAD tools in the software make this easy," he says. "I usually have the CMM laptop computer on my desk beside my CAD system monitor. I type data from the CAD screen directly into the program I am writing."

On the other hand, "mainly for part inspections," he says, "we use solid models from our Catia software and import it directly into PowerInspect. This is useful for rapid part checking. This lets us upload accurate tooling files to the CAD system. When we verify the location of a stop or verify that it has not moved, we use PowerInspect's spheres of alignment tools."

Inspectors use the 3 Spheres Alignment tool to inspect engineering fixtures by reference to tooling spheres in three known, specified locations. They enter the nominal positions for the three spheres and measure them. The software matches these positions to the nominal positions. This allows all measurements to be taken in the same datum as in the CAD/math model or engineering drawing.

Buying criteria
"When we bought the first Romer machine, we considered the competition, too," Nennig says. "We liked the PowerInspect software better than the other packages, because it is a more powerful organizational tool for handling geometry and groups of measurements. We gather measurements in large groups, all at once, when we troubleshoot or do first-article inspections," he explains. "Then we break the groups apart to retrieve the specific data and look for root causes and process-improvement opportunities. We could not do that with any other system."

He suggests the arm was a better product as well. "Plus the 3000i was more attractively priced," he says. "And we liked the level of service we got from Dean Solberg, the Romer distributor, Exact Metrology, Algonquin, Ill."

The Pierce engineers run the PowerInspect software on Dell Computer Corp. Latitude PP01L models. These have 1.6 GHz Intel Corp. Pentium III CPUs with 128 Mbyte of RAM and 20-Gbyte disk drives. The operating system is Microsoft Corp. Windows XP Professional. Pierce is upgrading PowerInspect to Version 3.00 from Vers. 2.200 (Service Pack 3).

No more road trips for inspections
The biggest gains in inspection at Pierce stem from a fundamental change: The CMM inspection systems now travel to the parts and fixtures rather than the parts traveling to contract CMM shops. No longer do those "road trips" determine when work will start on new parts.

The CMMs increase the effectiveness of the quality-control team. "The 3000i allows us to control the quality and, to some extent, the speed of the build process," Nennig points out. "We can be certain that the fixtures are correct and that they were built that way."

The infinite rotation of the arm saves the company time and averts frustration too. "Our cab welding fixtures are big and many of the points are taken from the inside of them," remarks Nennig. "Without infinite rotation, we would be backtracking a large percentage of the time. When an inspector has to back out of a welding fixture to unwind the joints of an arm, he can lose registration. In that case, he starts over again."

The accuracy of the arm meets many needs. "We check machined parts to five or seven-thousandths of an inch," Nennig continues, "as well as for setting up larger welding fixtures where tolerances are a little more forgiving."

"The machine is rarely wrong," states Lang. "Once in a while, a number will appear to be way off. After investigation, we find that it was our fault. The system makes the whole dimensional-measuring process foolproof."

The CMM minimizes human factors responsible for measuring errors. "If a dimension is off, it's obvious. You can see the operator error, correct it, and keep on measuring," Lang continues.

"The 3000i also gives us better control over the content of the work instructions that go to production," Nennig explains. "There is more data in the work instructions, it is presented better, and it is more current. Since Pierce is ISO 9001:2000 certified, this is important. We provide foolproof dimensional data to engineering and purchasing. That's a great reassurance for them as they make decisions."

Since joining quality control in December 2003, says Smazinski, "I have seen a constant improvement in what's being measured, how accurately that's being done, and in the processes to make sure it's done correctly."

For more information: Pierce Manufacturing, Appleton, WI, piercemfg.com; Delcam Inc., Windsor, Ont., 519/ 974-8088, delcam.com; Romer CimCore, Farmington Hills, MI, 800/ 218-7125 X104, romer.com; or Exact Metrology Inc., Algonquin, IL 60102, (847) 854-1575.