The drive for precision in foundries has reached a high point among the six automatic molding machines of Waupaca Foundry Co.’s Plant 1 in Waupaca, Wisconsin. From this small industrial town west of Green Bay and north of Madison, come some of the most dimensionally precise gray iron sand castings produced anywhere.

Waupaca Foundry’s Plant 1 produces brake rotors and brake drums, transmission housings, hydraulic pump housings, flywheels, intake and exhaust manifolds, cylinder heads, crankshafts, pulleys, brackets, and covers for electric motors. These castings go into cars, SUVs and a wide range of trucks and buses plus construction machinery and farm equipment.

Precision with respect to inspection measurements is held to 0.002 or 0.003 inch, a span smaller than the grains of sand fed into its molding machines. To get the job done, Plant 1’s Layout Department uses a portable CMM and PowerINSPECT dimensional inspection software from ROMER, Farmington Hills, Michigan.

There are four primary reasons why Waupaca’s inspection teams work to these levels of precision:

• Customers have automated the machining of castings they get from Waupaca. In those operations, there are no human machine-tool operators to adjust tool offsets or tweak N/C programs. Without those, very little part-to-part variability can be accommodated in machining.

• Many parts are used by customers as-cast, that is, as received from the foundry and with little to no machining.

• Tight tolerances reduce time castings spend in the grinding operations. This reduction speeds deliveries and saves labor.

• All dimensional inspections of molds are measured from known reference points on the molding machines. This ensures that every mold’s ram and swing halves fit together exactly. It also ensures that every mold is properly positioned and aligned on the conveyor that carries it to the pouring area. Alignment for pouring controls what traditionally was a significant cause of source of variability among castings in a job lot.

It is not enough, in other words, to ensure that the molds are dimensionally correct in and of themselves, i.e., measured only in reference to the individual mold’s coordinates. Instead, the precision demanded by Waupaca’s customers requires that molds be checked against the tooling that produces them.

If the molds were measured just by themselves, some of these tolerance errors might cancel each other out. The dimensional errors would still exist, but they may be harder to find. More importantly, the errors would be much harder to trace back to root causes in the molding and core setting machines such as ram or swing arm maladjustments or bushing wear.

This can only be done by verifying that the pattern is correctly pressed into the sand as each mold is produced and that the core-setting machines are running correctly. Once dimensional relationships are established among patterns, cores and key components of the automatic molding machines, molds can be checked by reference to known points on the molding machines. This adds to the need for precision because in linear measurements such as these, tolerances stack up.

If molds and cores are removed from the production line and carried to a conventional CMM, there is no verifiable way to address problems that occur within the molding machines or core-setters themselves. Symptoms can be identified, but that’s all. Once a mold or core’s dimensional relationships are severed from the molding or core-setting machinery that produced it, there is no straightforward way to translate some of the dimensional discrepancies into actions to be taken by the tooling maintenance people.

Taken together, these factors are why Waupaca Plant 1 engineers, tooling experts and machinery maintenance people now do most of their dimensional measurement with a portable coordinate measuring machine (CMM) in one of the hottest, noisiest and most confined areas of the foundry. That’s between the automatic molding machines and the ladles that pour molten metal into the molds.

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 "...the arm and the software were easy to understand and very easy to learn to use effectively. The way the Romer and PowerINSPECT are set up eliminated any potential headaches for us." 

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Waupaca Plant 1 is a high-production and thus fast-paced operation. EACH of its six automated molding machines makes about 300 molds per hour, i.e., five or six molds per minute. That works out to a new mold every 10 or 12 seconds per machine. Anywhere from one to six parts are produced per mold. Job lots are always more than 100 pieces.

“Customer demands pushed us to use the portable CMM and PowerINSPECT,” reported Steve Buck, Plant 1 layout engineer and the primary user of the Romer-PowerINSPECT system. “Customers insist that we maintain tight control over the way the patterns are pressed into the sand in the molding machines. “When we are looking for root causes, we go all the way back to the pattern that makes the impression the mold’s sand and start measuring from there.

“We also have to make sure that the cores are set correctly, that no core shifts occur, and that there is no shifting between ram and swing halves of the mol,” he added.

“It is only the portability of the Romer arm that allows us to do this, to check molds against the molding machine itself,” he continued. “That could never be done with conventional fixed CMM because the inspections always have to be referenced back to the molders. We have to work to common zero points on the machines,” he explained, “and not just to the mold.”

Major uses of the measurements and trends are for Waupaca most demanding customers. “PowerINSPECT allows us to generate complete, step by step reports to the customers for verification of inspections on production, sample and first-time castings,” Buck added. “Once the point data has been electronically downloaded into a template, all the statistical process control and trending functions are available to us.” Templates are made with Excel spreadsheets from Microsoft Corp.

Waupaca has also begun using DELCAM’s automated report generator to create initial sample inspection reports (ISIRs) for Caterpillar Inc., a major customer. “We designed the PowerINSPECT report to look just like the forms that Cat requires,” Buck said. “This saves us a huge amount of time; before, we had to enter the data manually. This also eliminates a potential source of error since the inspection report data is downloaded right into each ISIR.”

“Our in-house troubleshooting measurements are very helpful for preventive maintenance,” Buck noted. “This includes identifying things like wear in bearings and bushings before they begin to cause ‘slop’ in the equipment and finding inaccuracies in pattern setting and out-of-tolerance molds.”

Among the system’s many tasks are assisting the Maintenance Department with setting up the molders, ensuring that molds are square, that they do not shift, and that they remain aligned when they come out of the molding chamber. Waupaca often measures a mold’s parallelism and perpendicularity as it comes out of the machine, right before the molten iron is poured in. “Sometimes we even have to measure inside the machines for the pattern positioning and orientation relative to the machine’s ram and swing arm,” Buck said.

The Romer arm-- a 9-foot Model 3000i -- is in constant use. “To get the best measurements in and around the molding machines, we clamp the arm as close as possible to the machine’s swing arm and its actuating cylinders -- sometimes right to the bed plate of the machine,” he noted. “We can get even closer by using the Leapfrog system,” also from ROMER.

The inspection machines they were using, old manual Bendix Portage machines, are used much less now. “The portability makes it possible to check virtually anything, both in the layout shop and out in the plant,” Buck continued. In other words, measurement and dimensional verification has moved almost completely to the production floor. Instead of the slow and somewhat artificial conditions the CMM room, measurement at Waupaca Plant 1 is now flexible, intuitive, and highly responsive.

Waupaca is also pleased with the portable CMM’s durability. “The arm is often used within 10 or 15 feet of the bull ladle full of molten iron which is over 2,600 degrees F.,” he noted. “When measurements are carried out during production, we sometimes get even closer to the pouring ladle.

“We keep measuring even with the hot iron going by. It’s a good thing that Romer made the arm out of a carbon-fiber composite. We know it will be dimensionally stable no matter how close we get to those ladles,” Buck pointed out “The system is impervious to foundry dust, too, and is unaffected by the slight vibration from the molding machines.”

Other measurement approaches were considered. The big reason Romer - DELCAM won was the ability to work outside the controlled environment of the layout room. “Basically, we saw the need to get with the times,” Buck said. “We needed to be able to check the automatic molders while they are making molds, to be able to take the Layout Department to the areas that need things checked during production.”

The ROMER arm and PowerINSPECT are also used in the pattern shop for checking cores, core boxes and patterns. This is much faster than the previous practice of bringing them into the layout department where the conventional CMM is. One reason for the speed is that core boxes and patterns are heavy, awkward and sandy/dusty. Engineering changes are measured both with and without CAD.

The ROMER PowerINSPECT system was “an easy choice” for other reasons, too. Buck cited:
• The ability to change probes on the fly without having to recalibrate the arm to them.
• Better measuring tolerances.
• The arm’s light weight and counter-balanced design. “In this day and age of ergonomic considerations, it’s very easy to operate, even during lengthy and complex series of measurements.”

Asked if Waupaca’s expectations have been met, Buck replied with a resounding “YES!!!

Customer demands for the best possible as-cast surfaces drove Waupaca to demo (and probably buy) a highly sensitive PowerPROBE, also from ROMER. Compared to conventional probe tips, the PowerPROBE requires almost no pressure to register a point. The pressure needed to register a point with conventional probes can leave a detectable dimple in the surface of the mold. In the as-cast part, the dimple produces a detectable bump -- tiny but still unacceptable. Probes currently used include a 15-millimeter (mm) ball, an 80 mm ball with a 6-inch extension, and a 20 mm ball with a 4-inch extension.

Ease of use is a big issue for Waupaca. “None of us using the system now had any prior experience with CAD layout,” Buck said. “At first we found that laying out jobs without a knowledge of CAD was very intimidating. Yet the arm and the software were easy to understand and very easy to learn use effectively. The way the Romer and PowerINSPECT are set up eliminated any potential headaches for us.”

Keeping layout process simple is important for another reason, too. Blueprints and plots from CAD files are no longer routinely supplied with the jobs to foundries. Now the foundry is expected to work from downloaded CAD data derived directly from the customer’s math model. Issues of data traceability aside, consistently holding 0.002- or 0.003-inch tolerances working from plots and blueprints has never been easy.

Buck has worked 18 years in foundries, starting in maintenance and reaching the layout room only after long stints in production and grinding. “All the people doing the layouts and inspections here have worked their way up through foundry operations,” Buck noted.

The physical side of ease of use is equally important. Measurements made directly from the molding machines often require working in cramped spaces. To ease the burden, Waupaca purchased a Brunson stand for the ROMER arm. “The stand provides a lot of additional stability for the arm. The stand has a shelf for the laptop, too, which is very convenient in tight spots,” Buck noted.

The “acid test” of dimensional measurement is repeatability and the ROMER - PowerINSPECT system passed with flying colors. Buck explains:

“One day we were asked to measure a bolster plate for one of the automatic molding machines. The operator of the machine was a real ‘show-me’ kind of guy. Bolsters are used when we have to run small patterns in larger machines. Bolster measurements are complicated. First we have to level and align. Then we measure through two bushings, measure a preset dimension to a round bushing, and then measure a series of planes on two different surfaces.

“Two days later, we were asked to come back to measure a large number of additional bolsters. The operator slipped the bolster we had already measured into the new lot. As he hoped, we didn’t notice it, so we measured it again -- but the second time in different ways. Both sets of recorded dimensions came within 0.001 inch repeatability. This is amazing -- especially considering the arm had been trucked in and out twice and set up, torn down and packed away twice.”