A Heroic Die-Handling Effort
“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 —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
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
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
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 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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