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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.
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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.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.
"...the arm and the software were easy to understand and very easy to
learn to use effectively. The way the arm and PowerINSPECT are set up
eliminated any potential headaches for us."
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 portable CMM 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 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 arm-- a 9-foot 3000i Series -- 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 technique.”
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 CimCore 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 CimCore
& 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 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 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. 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 arm 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 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 arm - 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.”
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