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Hydraulic Presses

Streamlining work steps

By Lynn Stanley

A caster manufacturer consolidates production processes with hydraulic press technology

July/August 2012 - Getting to the root of a problem versus simply addressing the symptoms is a key step for any effective continuous quality improvement program. When Tente Casters Inc. needed to increase volume production for its low-carbon steel 40-series hospital-grade caster, the ISO 9002-certified manufacturer examined its continuous flow process, a multiple-step procedure involving two press stations and one operator.

At the first press station, the operator assembled a precision bearing into a fork cup housing before attaching a stem into the bearing. Depending on part configuration, the operator also might be required to attach functional elements to the end of the stem such as a brake pad. The second press was set up to roll over the top portion of the cup housing, securing the components inside.

“We were experiencing a bottleneck with the first press operation,” says Mike Hollabaugh, development engineer for Tente. “The travel distance between the two presses exposed the operator to substantial physical exertion. We nicknamed this press operation area the ‘Jenny Craig workout.’”

The Hebron, Ky.-based manufacturing facility began evaluating options to improve press productivity. Tente Casters is a subsidiary of Tente International GmbH based in Cologne, Germany. The global company engineers and produces institutional, medical, industrial and heavy-duty casters for a range of applications.

Saving resources

“Our primary goal was to consolidate both operations into one press to save time, labor and power usage, all while enhancing quality,” says Hollabaugh. “We needed a press with enough tonnage to complete sub-assembly of the 40-series caster in just one operation but we also wanted to maintain a small footprint with the new machine.”

Tente was looking for a press to accommodate different sizes and types of steel fork assemblies and to meet quality requirements for dimension (long and short casters) and cosmetic appearance. Tente’s caster products include swivel, steer, total lock and lock and directional combinations.

“We considered several press manufacturers, including Greenerd Press & Machine Co.,” says Hollabaugh. Previous experience with Greenerd and the press manufacturer’s efforts to review and understand Tente’s work processes were deciding factors for the fabricator.

Tente already was using a custom-built 75-ton Greenerd hydraulic press to form blanks into the 40-series caster fork bodies, an operation that takes place prior to the multi-step process the fabricator wanted to consolidate. “We were achieving a good-sized draw, so we felt that hydraulic press technology versus mechanical was the best solution for us,” says Hollabaugh.

Greenerd, Nashua, N.H., is a supplier of hydraulic press equipment with product capability up to 40,000 tons and bed sizes exceeding 240 in. Greenerd engineers custom design applications in press styles ranging from gap frame and straightside to die spotting and forging presses.

Custom press

Hydraulic presses can be equipped with two separate rams to perform multiple functions in the same machine. A mechanical press lacks that capability. In addition, a conventional mechanical press delivers full tonnage with each stroke, preventing the operator from reducing tonnage based on part requirements. Because tool speed during forming can’t be controlled or slowed on a traditional mechanical press, an application like Tente’s rollover operation would have to be performed at high speed, creating a potentially abusive environment for tooling.

With a hydraulic press, full power can be delivered at any point in the stroke—not just during bottom stroke work. The ram force, direction, speed, release of force and duration of pressure dwell also can be adjusted to fit a particular job. Lighter dies, like those used by Tente, can be operated with the pressure turned down. On a hydraulic press, the ram can be adjusted to approach the work rapidly then modified to a slower speed before making contact with the part, a feature that can prolong tool life.

“For Tente, a hydraulic press offered the option to optimize production by performing the rollover operation at a slower speed, giving material time to move and allowing the operator to use a lighter tool,” says Thomas Lavoie, applications engineering manager for Greenerd. “Because the press can deliver full power when it’s needed, you don’t have to buy a 200-ton press to get 100 tons throughout the stroke. Setup on a mechanical press can run from minutes to hours because the machine’s work height must be changed from tool to tool.

“The depth also must be set properly to avoid damaging the tool. The hydraulic press does not need to consider different heights, so the machine can’t lock up on bottom due to incorrect ram depth settings. Setup times are faster on the hydraulic press since the operator doesn’t have to adjust the stroke nut on the slide to accommodate different dies,” says Lavoie.

In evaluating Tente’s requirements for a single press that could install a precision ball-bearing component into a caster fork, Greenerd faced a couple of challenges. The press manufacturer had to prevent roll-overs of the subassembly to avoid blemishes on a powder-coated or zinc-plated finish. The press also had to be capable of precise bearing placement.

“We integrated a rotary index unit, which allowed the operator to load parts at a load station,” says Lavoie. “The assembly then travels through the press for processing. A secondary bushing insertion ram was added to the outside of the press frame to allow for two operations during each press cycle.”

Greenerd worked with a tooling house to integrate assembly fixtures to locate and position the caster and bushing at the load station. The tapered end of an insertion tool picks up a pilot hole in the bushing and lowers tooling prior to the component’s insertion. “This ensured that the punch and die were perfectly lined up prior to insertion of the bushing,” says Lavoie. “The rotary index unit also has a positional repeatability measured in arc seconds to allow for consistent location of the lower fixture position.”

Improved production

Tente installed the Greenerd HPB-16 16-ton hydraulic press in September 2011. Equipped with two rams, the first operation inserts the ball-bearing component into the fork cup housing. In the second operation, cup housing rollover secures the component in the fork body. Both operations happen simultaneously on an eight-station indexing turntable. The larger 75-ton Greenerd press produces preformed forks and then feeds them to the new machine.

“The operator simply places both the fork body and ball bearing component on a nest holder and within four seconds, removes a completed sub-assembly,” says Hollabaugh. “The press times were four seconds for each machine in the old setup.”

The Greenerd press currently produces 25,000 components a month with a cycle time of less than four seconds to complete both caster-producing operations. That means cycle time has been reduced by four seconds per caster.

To be competitive in the current manufacturing environment, faster production times and streamlined operations are critical.

“We’ve had an excellent return on investment with the Greenerd press,” says Hollabaugh. “In addition to increasing our initial production, the press has allowed us to go to three shifts, six days a week, often running for a full 24 hours at a time.”

For Tente, the cost-effective press solution supports production of the fabricator’s 40-series hospital and institutional casters while meeting delivery schedules and tight quality specifications. “The new press has kept our productivity rolling and our medical customers happy,” says Hollabaugh. “It also has freed up our operator to handle more tasks without the physical workout.” FFJ

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Sources

  • Greenerd Press & Machine Co. Inc.
    Nashua, N.H.
    phone: 603/889-4101
    fax: 603/889-7601
  • Tente Casters
    Hebron, Ky.
    phone: 859/586-5558
    fax: 859/586-5859


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