Page 27 - MetalForming December 2009

mechanical presses from 40 to 250 ton capacity. “We schedule our manufac- turing load one day at a time using a kanban approach,” says Rucker. “The goal is to produce and ship in 48 hr.; we use what we produce, keeping only a few day’s worth of inventory on the shop floor.”
QDC: A Process
The Stemco pressroom embarked on a QDC mission in 2004 by imple- menting die-change process improve- ments such as prestaging of dies in die racks located nearby its presses, and by investing in die carts to efficiently move dies around the plant. “Also during that time,” adds Rucker, “we had been on a press-rebuild schedule of one press per about every five years, and finally deter- mined that the cost to rebuild an aging press was approaching that to purchase a new press.”
In 2005, rather than rebuild another press, Stemco purchased a new machine —a Model SN1-176 (176 ton capacity, 49- by 30-in. bolster) from Seyi Presses, Inc., Walnut, CA. Along with the new press came hydraulic die clamps and die lifters supplied by PFA, Inc., German- town, WI. PFA supplies standard QDC products that can easily be customized to accommodate any clamping height
by adding nose pieces and base plates to the clamps. The die lifters provided were made specifically to fit the press’ T- slots, measure 30 in. long, boast cam- type rollers and, as a pair, can support 10,000 lb.
Clamps and die lifters are controlled by a hydraulic control unit outfitted— per Stemco’s specification—with elec- tronic valves to allow Stemco to tie the hydraulic controller to the press control, a Wintriss SmartPac 2.
The QDC-system control directs four separate zones—two plumbed for the clamps on the press ram, one zone for the clamps on the bolster and a fourth zone for the die lifters. Also, a pressure switch tied to the press will shut the press down in the event of a pressure loss. The control, via an air- over-hydraulic pump, converts shop air pressure to the required 5000 PSI and ensures consistent clamp force. Opera- tor safety is enhanced since the clamps cannot be released while the press oper- ates in the automatic mode.
Die Changes Fast and Easy
“The PFA setup immediately took our die-change times from 15 min. down to 8 min.,” says Rucker. “And, because of the way the clamps are designed, we can set them up and slide
them out of the way easily, moving the dies in and out without worrying about damaging the clamps. Die changes are simple enough now that our press oper- ators often take over at the end of a die change, freeing up our die setters to spend more time moving about the shop and focusing on the next setup.”
Integrating its new QDC-outfitted Seyi press into its overall pressroom production flow went so smoothly that Stemco decided to add two more simi- larly outfitted 176-ton Seyi presses to its stable—one each in 2005 and 2006. Now the three new QDC-equipped presses handle all of the firm’s higher- volume stampings, each press respon- sible for eight to 10 of Stemco’s hardest- working dies, some of which might stay in the press for just a few hundred hits and others that might run as many as 2000 parts per run. Stroke rate averages 30 hits/min.
“Our return-on-investment calcu- lation for the QDC apparatus showed a payback period of just 18 months for each press,” says Rucker. “And, again, it’s been the best thing we could have done to support our people working on the shop floor.
“Our pressroom had been aban- doned for a long time,” Rucker adds, referring back to the beginning of the decade. “At one time we considered out- sourcing our stamping work overseas, but ultimately decided that to ensure we receive the part quality we need and the part-order flexibility required to satisfy our lean initiatives, we had to invest in the stamping technology to get it done here. So far so good.” MF
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PFA supplies standard QDC products that can easily be customized to accommodate any clamping height by adding nose pieces and base plates to the clamps.