Getting hydraulic press problems under control
Control system upgrade solves reliability problems, expands press capabilities
Arco Industries Inc. bought a 15-year-old, 500-ton Tranemo hydraulic punching press with an antiquated control system. For about one-quarter the cost of a new press, Arco was able to rejuvenate an obsolete press by providing it with contemporary levels of control and productivity.
Although there are many good reasons for investing in used equipment, the downside is that a used machine seldom has the exact configuration you need. And sometimes a specification decision made years earlier by someone at a different company can return to haunt the new owners, which is precisely what happed to Acro Industries Inc. of Rochester, N.Y.
Six years ago Acro bought a 500-ton Tranemo hydraulic punching press from Eastman Kodak, another Rochester-based company that was streamlining operations by eliminating noncore manufacturing operations. "We picked up some of Kodak's business, and decided to purchase the equipment they were using to fulfill the orders," Acro Operations Manager Bob Coyne said.
The press was about 15 years old and in very good condition. And because it had been set up for the heavy-gauge railroad and agriculture equipment parts it would be producing, the press performed well for years after its acquisition.
Increased Downtime, Scrap Rates
Unfortunately for the stamper, the company that provided the press control system components went out of business. With no direct source for upgrades, spare parts, and other support, the control system became more obsolete and unreliable. "A circuit board on the programmable logic controller would go down, and we'd have to try to repair it ourselves," Coyne said. "When that no longer worked, we had to rely on AP&T [a result of a merger of Tranemo and other manufacturers] to find replacement parts for us."
Finding replacement parts was becoming a near-impossible task. Acro's supplier had to scrounge through old machines with the same system every time another component was needed. All these efforts failed to keep the problem under control. The system's performance and reliability continued to suffer. Downtime steadily increased, and by spring 2005 press downtime was hovering around 40 percent. But that wasn't the only problem. The press's erratic control system was causing significant quality issues with hole position and form height.
"We had very little confidence in the machine," Coyne admitted. As a result, frequent in-process quality control checks were needed that slowed production down even more. Acro even resorted to modifying press tools to compensate for the press's poor precision. Despite all this, scrap rates on some jobs reached 14 percent—one out of every seven parts was bad. Safety also had become a concern. The press's light curtain had failed, which forced operators to keep both hands on buttons during the entire press cycle.
The press had become a liability, and there were very strong fears that its unreliability could cause missed deadlines, forfeited contracts, and lost clients. "We could see that the problem was only going to get worse and more expensive to address," Coyne said. Except for the control system, the press was still in excellent hydraulic and mechanical shape. With the right control system replacement, the press had the potential to deliver many more years of cost-effective production.
A graphic interface further simplifies programming and controls by allowing operators to monitor position and force during the cycle.
Before choosing a press control system supplier, Acro established four criteria to select the right partner: price, supplier capability, lead-time, and experience with this type of rebuild. Several potential suppliers were evaluated, but when the search was completed, the team chose AP&T. "We wanted to make certain that the new system was going to be supported five or 10 years down the road," Coyne said. "AP&T responded by engineering a system that relied completely on components from well-established suppliers like Allen-Bradley and Siemens."
The new system required that the press be completely stripped of all the existing electrical components before the new controls could be installed. The installation process, including training and testing, took approximately three weeks.
In the 20 years since the original control system was installed, massive advances in control and computer technology have been made. In addition to the essential level of reliability and repeatability, the new control system can provide productivity- and quality-enhancing capabilities. For instance, the old system had no recipe storage capabilities. Every time a job changed, the operator had to use paper cards to program the press. Parameters like stroke speed, cushion, knockout cylinder, dwell, and pressure had to be keyed in every time—for over 50 separate tools.
A graphic interface further simplifies programming and controls by allowing operators to monitor position and force during the cycle (see Figure 1). This freely programmable system means operators are not limited to fixed sequences. All hydraulic cylinder movement can be programmed, and new software and hardware can control external components such as coil handling equipment and robots.
For about one-quarter the cost of a new press, Acro was able to rejuvenate an obsolete press by providing it with contemporary levels of control and productivity. Coyne also learned that his supplier rebuilds and upgrades all kinds of presses, not just AP&T brands.
Back to Work
Training was another critical issue with the press rebuild. "Because we bought this press used, we didn't receive good training," Coyne said. "The best we could do was hire the former press operator from Kodak to instruct our people. So even with its limited capabilities, there were still press features we didn't fully understand or use."
After the new controls were installed, the pressure was on Acro's supplier to familiarize operators and production engineers with the press's new control parameters. It took the operators and production engineers a while to get used to all the control options and choices they now had. "We still weren't sure we were doing everything right," Coyne said. So he asked AP&T to provide more training. A single onea-day training session was sufficient to clear up any lingering issues. Since that session, "There hasn't been a single problem," Coyne said.
The key metric involved in the rebuild decision—downtime—has shown the most improvement. Before the rebuild, downtime reached a high of 45 percent. Coyne now estimates downtime has been reduced to less than 1 percent. Greater reliability accounts for much of this improvement, but fully automated tool changeovers also play a big role in increasing press availability.
Improvements in process uniformity and product quality have been equally impressive. Scrap rates have plunged from 14 percent to roughly 2 percent. Coyne predicted that scrap rates will continue to decrease as operators become more skilled at working with the new controls.
Many of the quality control steps that once were necessary are now redundant and may soon be eliminated. With a fully operational light curtain and other safety upgrades, press operators now are better protected and more productive.
With far greater reliability, precision, and versatility, this control system upgrade has added years of productive—and profitable—life to the press. And what was recently a liability is now once again a valuable asset.
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.