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The Domino Effect of Precision Die Changes

By: Brad Kuvin

Sunday, July 01, 2012
 

You’ve done a good job of staging dies in roll-off die racks near the presses in which the dies will run. You’ve installed bolster arm extensions to ease forklift access and ensure safety, and invested in die carts. What’s left to eliminate wasted time from die changeovers?

Answers can be found deep within the 650,000-sq.-ft. Rheem Water Heating plant in Montgomery, AL, where a quick-die-change (QDC) program has made life easier for die setters working on three of the plant’s biggest mechanical presses. Until recently, setters working at those three presses took pry bars in hand to jockey and align dies weighing as much as 20,000 lb. Checking for accurate die alignment by inching the ram down and manually prying the die into position was a time-consuming and tedious process.

Late in 2009 the firm embarked on a leaner approach to die changes for its heaviest hitters—three presses and some 25 dies used to form water-heater tank heads and bottoms from hot-rolled steel to 0.312 in. thick.

“We wanted to give our die setters a solution that, as they inserted a die using a die cart,” says manufacturing process engineer Jeremy Krauss, “would automatically align the die set to the press bolster, have enough capacity to easily lift the die, and then hydraulically clamp the die from the side.”

Reduced WIP—Let the Dominos Fall

Capital improvements to improve QDC included new roller-type hydraulic lifters and upper hollow piston clamps, shown here parked and extended.
Tank heads and bottoms run on three of the firm’s 23 mechanical presses—two 550-ton presses and a 400-ton press. Operations are hand-fed, single-hit and run at eight to 10 strokes/min. Dies typically stay in the press for 2- to 6-hr. runs, to feed the plant’s six assembly lines, as well as to build inventory. Of course, reducing work in process (WIP) is an ongoing goal, as it is for most OEM pressrooms. Krauss cites reduced WIP as one of the many domino effects of the plant’s quick-die-change (QDC) initiatives.

“Our Kanban levels are at about 1.5 shifts,” Krauss notes, “down significantly, and we’ve reduced changeover time by as much as 28 percent for our most challenging dies. Also, improving the effectiveness of our die changes has led to a 10-percent boost in productivity from those three presses.”

The capital improvements made early in 2010 to improve QDC revolved around allowing the operator to roll in their die sets on roller-type hydraulic lifters. Dies roll in under fixed, mounted ledge clamps installed on the press bed. Once the die lifters lower, the bed clamps pressurize with the flip of a switch. Then the upper hollow piston clamps advance into position by the pneumatic travelling clamps. Proximity sensors monitor the extend and retract positions of the air cylinders. Once in position, the clamps are pressurized. Upper clamps are protected by a slide-mounted connection block that creates dual diagonal clamp circuits.

All of the QDC apparatus was provided by Hilma, including an air-hydraulic power unit and pressure switches on each clamp circuit. These switches provide feedback that ensures the press runs only when full operating pressure is available. The die-lifter circuit includes a relief valve that dumps pressure back to the oil reservoir if the rollblocks are overloaded.

While outfitting the press rams with the new clamps, Rheem fabricated a 3-in. ram plate, cut pathways into the plate and fabricated covers for it, “so we‘re able to run all of the sensor and air cables out to minimize the footprint,” Krauss says, “a more effective solution than using swing clamps on the outside.”
“As the two 550-ton presses already had quick-change clamps on their rams, most of the recent work for this project was done on the 400-ton press,” recalls Krauss. “We fabricated a 3-in. ram plate, cut wire/utility pathways into the plate and fabricated covers for it, so we’re able to run all of the sensor and air cables out to minimize the footprint. The alternative would have been to use swing clamps on the outside, to keep the utilities out of the way. However, using hollow piston travelling advance clamps proved to be a less-expensive and more-effective solution.”

The Hilma QDC package includes a ready-made control panel that ties in the valve manifold, pressure switches, actuation switches and the run circuit. “If we lose any of the pressure switches,” Krauss says, “it kills power to the flywheel, preventing the press from stroking.”

Rollblocks Better Protected

Krauss also notes additional benefits of the new QDC system components:

“Hilma’s new RHS-style rollblock features independent rollers. Using the pressure relief in the manifold supplied each roller acts independently to prevent overload. With previous rollblock styles, the entire rollblock would move up and down, frequently becoming damaged. The new model stays in the T-slot and below the bolster level, where it’s protected.  Only the roller rises when needed.”

Rollers can be configured, according to Hilma, for either linear or transverse die movement. It rates rolling resistance of 1 to 3 percent of die weight.

“Also,” Krauss continues, “the entire package of slide and bolster safeties is a definite plus when it comes to installation. Included in the valve package are pressure switches for each clamping circuit, one switch for the bolster-clamping circuit and one switch for the slide-clamping circuit. The slide-clamping circuit goes through a slide-mounted connection block that creates dual diagonal clamp circuits. If one clamp/ circuit fails, there are still two clamps under pressure to hold the upper section of the die on the press. If this would happen, there would be a loss of pressure on the pressure switch at the manifold and the press would stop.” MF

 

See also: Hilma Div. of Carr Lane Roemheld

Related Enterprise Zones: Tool & Die


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