March 9, 2010
A stamper streamlines part handling, replacing the grunt work with a part manipulator, and designing a flexible manufacturing cell. In the end, the company's efforts improved worker ergonomics and part quality.
It's not often you hear "squid head" and "metal stamping" in the same breath. But that's exactly what you'd hear when talking to shop managers at NIC Global in Gallatin, Tenn., north of Nashville.
Employees at the 90,000-square-foot contract fabrication shop recently put together a workcell consisting of a 500-ton mechanical press, a part preparation and lube station, and a hardware insertion system. Carrying parts between operations is the so-called squid head, which has small suction cups grouped at the end of a manipulating arm (see Figure 1). If a certain suction cup comes in contact with a hole in the part, then the suction to that specific cup automatically shuts off, while the holding pressure is maintained by the remaining cups on the squid head.
Compared with some traditional automotive or appliance stamping operations, NIC Global's setup would be considered low-volume—mostly hand transfers here. Still, as a low-volume provider, the company sells itself as being fast and flexible, and the cellular layout helps make this possible.
The new cell was born from lessons learned. Managers analyzed the scrap and ergonomics issues associated with a previous program. The new job involved cosmetically sensitive material, and revamping the material handling for the job was essential. The company devised a cellular arrangement that not only improved ergonomics, but efficiency and quality as well. "This is the first time we've done something like this for the heavy stamping area," said Troy Wood, NIC Global's plant manager.
Previously, metal blanks were brought to the press area. There operators manually sprayed them before lifting them deep into the press. After each cycle, operators would remove the part, clean it, and then insert the hardware.
For the new job, managers knew they needed to devise a way to apply lubricant consistently and quickly. In the end, they developed a specialized lubrication table consisting of a sponge with pins sticking up, representing the pins in the actual dies of the press. With the part placed against the pins on the table, lubrication from the sponge below coats the part exactly where needed every time.
Next came another efficiency idea: Why not stamp two parts at a time? The press had adequate tonnage and a wide enough bed to handle it. So engineers designed the lubrication table to handle two blanks at a time; this meant that two parts could be transported simultaneously from the lube station to the press bed. With the manipulating arm doing the grunt work, it just made sense.
"We were able to decrease our cycle time by syncing up the manipulating arm with the hardware [insertion process] and material prep and forming functions," said Rodney Reynolds, continuous improvement project engineer at NIC.
The process starts at the blanking press, a shared resource separate from the cell. Raw material, coated with a protective PVC film, enters the single-stage blanking operation. After the press blanks the part perimeter and punches various holes, workers move a pallet of blanks to the new cell. There they peel off the protective film and place two blanks side by side onto the lubrication table (see Figure 2).
A specialized fixture on the manipulator (see Figure 3) is adjusted so that operators can place these blanks precisely where they need to go, butting against the pins on the lube table. After this the operator, using the manipulating arm, lifts the blanks and places them into the press bed, which has two die sets side by side. Once aligned, the arm releases the blanks.
At this point the press forms a 1-in.-deep, 90-degree flange into the blanks. After the press cycles, the same operator uses the manipulator to move the formed part to the cleaning area and the hardware insertion station. Hardware operators then apply another protective PVC film to protect parts during shipment.
The manipulating arm is able to reach deep to move parts into and out of the press. The manipulator itself uses what the supplier, TDA Buddy Inc., calls "neutral balance" technology. Gripping the part, the squid head senses a solid connection. "The machine has mechanisms that sense when it has a hold of the part, and once it does, it switches to a loaded neutral balance," said Drew Elliott, president of TDA Buddy, based in Kalamazoo, Mich. "The two parts together weigh 30 pounds, but as far as what the worker feels operating the manipulating arm, the parts are weightless.
"When the unit senses it has the part, it sends more air to its lifting cylinder," Elliott continued. That pressurized lifting cylinder serves as a counteracting force to neutralize, or balance, the part load. The heavier the part, the more pressurized the lifting cylinder becomes to float the load.
This setup needed to be flexible, since NIC Global runs different production jobs across the stamping equipment. The cell is designed to break down and be reconfigured. The press has quick-release hydraulic clamps, so dies can be quickly changed out every few weeks.
Every component surrounding the press—including the insertion press, the manipulating arm, and the lube station—is modular. Thanks to its squid head, the manipulator can be reconfigured quickly to lift other parts and moved to another area of the plant if needed. The hardware insertion press can be moved as well, and other secondary operations could take its place or complement it—a resistance welder, for instance. That flexibility, sources said, will grow ever more important as NIC Global expands its presence in the low- and medium-volume stamping arena.
STAMPING Journal® is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping. Print subscriptions are free to qualified stamping professionals in North America.