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A Heroic Die-Handling Effort

By: Brad Kuvin

Saturday, January 01, 2011
 
You won’t find too many presses as large as Press 25 at the Hopkinsville, KY, Tier One automotive plant of Metalsa. It’s one big press—a 3000-ton Clearing with 300- by 72-in. bed, blank-loaded
Automation abounds at Press 25
Automation abounds at Press 25 (3000-ton Clearing, 300- by 72-in. bed) at the Metalsa Structural Products (formerly Dana) facility in Hopkinsville, KY. Robots (right) move blanks and parts on and off the press, and a two-position die cart shuttles 80,000- to 100,000-lb. dies on and off the press bolster.
to stamp frame rails for pickup trucks and motor homes. The press hit the production floor of the 420,000-sq.-ft. plant in 2000, commissioned for manual transfer work. For ergonomic reasons—the large frame rails proved a challenge for workers to man-handle—in 2004 plant management added four robots to the press line to move parts in and out of the dies. But while the robots solved one issue, they created others.

“When we were manually transferring stampings in and out of the dies at Press 25, precise die location was not a critical requirement,” says Barry West, a project engineer at the Metalsa Structural Products facility. The plant supplies structures for light and heavy trucks, buses and passenger cars. Die locating via a groove machined into the bottom of each tool and a ball-shaped locator in the press bed produced die-location repeatability to within ½ in. or so, accurate enough to accommodate manual parts transfer. However, when robots entered service, the half inch of die-position variability required operators to reprogram the robots with every die change—a regular occurrence.

“We’ve run anywhere from eight to 12 different tools on that press over the years, and we change the dies out at least once per shift,” says West. “Reprogramming the robots added at least 30 min. to each die-change cycle.”

Overall, die changes would take an average of 200 min., West recalls, thanks not only to robot reprogramming but also in part to yet another issue presented when the plant added the robots to Press 25: it had to add a blank feeder to the front of the press. “Every time we went to change dies,” West adds, “we had to use a crane to move the blank feeder out of the way—there’s no room (in the 100- by 200-ft. press bay) behind the press to accommodate die changes.”

There’s Got to be a Better Way

When operators finally had had enough of completing 3-plus-hr. die changes using what West refers to as a flat-bed die hauler to move dies in and out of Press 25, West and the Hopkinsville team went looking for a more efficient and accurate solution. Goals included improving die-locating accuracy; enabling die changes without having to endure the time-consuming

Die-change system
The die-change system includes a retractable drawbridge to span the 22-ft. gap between the die cart and press. Telescopic rigid-chain actuators combine with a gear motor to create a push-pull
system that powers controlled
die movement.
task of moving the blank feeder out of the way and then back into position with each die change; and the ability to handle the newest dies sent to the press—huge two-piece 300-in. 100,000-lb. tools for stamping motor-home frame rails.

What the team settled on is a two-position die cart positioned at the rear of the press and outside of the operating bounds of the existing automated part-palletizing carts, which accept the robot-unloaded stampings. The system (engineered and manufactured by Serapid Inc., Sterling Heights, MI) moves the dies 22 ft. between the press and die cart via a retractable bridge extension. Serapid engineered the drawbridge concept to bridge the gap between cart and press when it was discovered that the press bay lacked sufficient room behind the press to accommodate telescopic bolster extensions.

Serapid’s RollBeam telescopic rigid-chain actuators combine with a gear motor to form a push-pull system to power die movement from the die cart to the press. One die-cart position stages the next die to run while the second die cart accepts the previous die as it leaves the press.

70-Percent Faster,50-Times More Precise

Die-change time now averages 60 min. from last part to first part, including disconnecting and reconnecting lubrication lines and changing out shaker-tray scrap conveyors. And, there’s no longer any need to fuss with the blank feeder or reprogram the robots. From the cell control station, a press operator triggers the completely automated die-change cycle: part-palletizing carts (on an embedded floor rail) and the robots move out of the way as the drawbridge indexes down into place between the die cart and the press; the old die rolls out and new die rolls in; the drawbridge raises and the line is ready for action.

What about locating accuracy? The slow, controlled movement of rolling the die onto the bolster, rather than bumping it into position as it used to, allows the machined V-groove to more precisely mate to the locator in the bolster. To take full advantage of the precise, controlled push-pull action, West had the die shop machine sharper-angled V grooves in the dies.

“In Serapid’s initial quote,” West says, “they specified die-position repeatability of ±1⁄8 in. In reality, we’re seeing significantly more precise location than that, more like ±0.010 in.” MF

 

See also: Serapid, Inc.

Related Enterprise Zones: Tool & Die


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