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Ag Stamper Takes Control of Part Flatness

By: Brad Kuvin

Tuesday, September 01, 2009
 
Ag business is still strong, and is dominating the product mix at contract manufacturer GMP Metal Products, St. Louis, MO, a supplier of stampings, fabricated-metal parts
Gm operates 70 stamping presses to produce a variety of Ag parts.
GMP operates 70 stamping presses to produce a variety of Ag parts, from precise and close-tolerance transmission parts to large deep-drawn parts formed on this 1500-ton transfer press.
and assemblies. The 220,000-sq.-ft. facility houses 70 stamping presses, to 1500-ton capacity, as well as equipment for laser-beam blanking and cutting, sheet and plate fabrication, robotic welding, and finishing. In addition to the Ag industry, GMP also supplies the construction and defense industries, and operates a second manufacturing facility in Tennessee.

For 20 years, GMP has specialized in the stamping of transmission separator plates and brake and clutch plates for the Ag industry, and continues to invest in new metalforming technology and fine-tune its processes to improve quality, productivity, and—of course—reduce costs for its customers.

“We’ve gone through a crash course to become more organized, install 5S practices, upgrade our building and equipment, and institute Six Sigma training,” says GMP engineering manager Bob Mallmann, “including executive-level training and blackbelt training for a few people. And, with the addition of new press controls on a few of our presses, a focus on quick-die-change practices and other improvements, we’ve been able to exceed customer expectations for quality and delivery, while meeting cost-reduction targets.”

Straight Edges, Flat Surfaces

GMP processes some 700 part numbers just for its Ag business, many of the part numbers comprising transmission separator plates of varying different sizes and designs. Its use of EDI to communicate is critical to successful production planning, says Mallmann, to keep up with order changes.

“We receive changes every day,” he says, “and a major download weekly. We use that information for order entry and feed the orders through our ERP system (TCM, from WorkWise, Inc., Milwaukee, WI) to initiate raw-material planning and production scheduling.”

Transmission separator plates are of a modified Type 1035 steel (Rc 20-28 hardness), 0.068-in. thick and typically 10- to 20-in. dia., although the firm does stamp a much smaller plate—5-in. dia. —that it ships to an assembly plant in China.

“The customer can’t purchase steel in China to the level of quality we can here,” says Mallmann. “So, our customer assembling the transmissions in China purchases stamped parts from us here in St. Louis.”

GMP specialies in stamping transmission separator plates.
GMP specializes in stamping transmission separator plates (shown here), of a modified Type 1035 steel (Rc 20-28 hardness), 0.068-in. thick and typically 10- to 20-in. dia. Part flatness is critical, specified to a tolerance of 0.004 in. per 6 in., with surface finish specified to 32 RMS minimum. To meet these requirements, GMP runs parts through a series of secondary processes.

GMP produces the separator plates from coil, fed through a straightener and into a compound die installed on either a 500-ton Minster mechanical press or a recently overhauled Bliss press, designed for very tight bed deflection. Plates are flat stampings that might look simple, but can prove quite challenging. Part flatness is critical, specified to a tolerance of 0.004 in. per 6 in., with surface finish specified to 32 RMS minimum. To meet these requirements, GMP runs parts through a series of secondary processes.

“In most cases, we use compound dies for this product line to gain optimum control over flatness,” says Mallmann, “since the die cuts all of the surfaces in one stroke. But we still have to run the stampings through secondary processes. The tangs on the outside edge of the separator plates are specified with critical edge conditions, requiring a secondary shaving operation to straighten the edges. Then we feed the parts through a rotary deburring operation and into a series of levelers (straighteners from Bruderer) to attain the required flatness in two directions.”

The compound die employs an upper punch that cuts the plate OD and also acts as the die to knock out the center hole of the blank. A punch below the stamping works the ID. GMP stocks 40 different dies for the plates in various styles and sizes, and changes dies an average of two times per shift; the press runs at 20 to 25 strokes/min.

QDC, Through Training

Within the last two years, the firm has focused on implementing quick-die-change processes, including standardizing on die sets, employing self-locating plates, and staging dies closer to the presses. Die changes that once averaged 4 hr. now occur in 30 min. or less.

“The key to making such a significant improvement was implementing the die-set training course produced by the Precision Metalforming Association (PMA),” shares Mallmann. “We trained all of our press operators using that course a couple of years ago, and it proved to be a real eye-opener. We are an old company that historically used a lot of old and accepted methods, and the PMA system did a great job of getting everyone to think of s to improve the processes, and to do it together, uniformly throughout the plant.”

Also yielding a significant improvement in productivity has been the plant’s recent addition of a new die-protection system (with a Link Systems’ OmniLink II control) on its 500-ton Minster press. Installed early in 2008, the system features a vacuum sensor that detects a stamped part being gripped by the top tool.

GMP converted a fabricated door assembly for a skid steer into a set of stamped components
GMP converted a fabricated door assembly for a skid steer into a set of stamped components that now are robotically welded in this production cell. One robot in the cell acts as a material handler, holding and manipulating the parts—including the heavy, 173-lb. drawn shell, of 6-mm-thick cold-rolled steel—while a second robot, mounted overhead, performs the welding operation, adding 16 parts to the door.
“With a lot of the compound dies, the challenge is getting the part out, and we use suction to hold the part up until just the right moment when it can be dropped out of the die and onto a mechanical slide conveyor,” says Mallman. “If we lose suction at the wrong time, the part can remain in the die set and cause a crash. Adding the vacuum sensor to the press so that it can connect to each die set, and tying it to the OmniLink II controller, allows us to protect every die that runs on that press with one sensor. When the die picks up the part, the sensor looks for a vacuum generated, and communicates to the controller to indicate whether or not the part is present.

“The vacuum sensor has solved most of the problems we had experienced with most of our dies,” Mallman continues, noting that the firm had to retrofit some of its dies with an additional part-ejection sensor. Results: Die crashes have been reduced by 80 percent, the firm spends significantly less time repairing die sets and grinding tools, and downtime due to damaged dies has been reduced by more than half.

Stamping Big Parts Better than Fabricating

Helping customers meet cost-down goals from year to year has GMP working more often than ever on collaborative engineering projects with its customers. Some of the results of these programs, described by Mallmann, include modifying stamping tools to reduce blank size, and combining operations in its dies to eliminate secondary operations. The firm also has invested recently in two laser-cutting machines to allow it to perform laser blanking for relatively low-volume parts—2000 to 5000 per year—rather than suffer the expense of building a blanking die.

Mallmann describes one significant collaborative project in which GMP converted a fabricated door assembly for a skid steer into a set of stamped components that now are robotically welded on the GMP production floor. “One robot in the assembly and welding cell acts as a material handler, holding and manipulating the parts—including the heavy, 173-lb. drawn shell, of 6-mm-thick cold-rolled steel—while a second robot performs the welding operation,” he says.

Redesigning the assembly with stampings—a drawn shell for the door skin, produced on the firm’s 1500-ton tandem presses, and several stamped brackets—rather than fabricating the parts provides dramatically improved dimensional repeatability. “The dimensional stability achieved by deep drawing the door skin allows us to employ robotic arc welding for assembly,” says Mallmann. “We began working on this project with our customer fours years ago, and it’s now been production since 2008. The appearance of the door is improved, and we deliver the door as one piece to the assembly line rather than two separate fabricated pieces, simplifying the assembly process for our customer.” MF

 

See also: Nidec Minster Corporation, Bruderer Machinery, Inc., Link Systems

Related Enterprise Zones: Other Processes, Presses, Quality Control, Sensing/Electronics, Software


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