Page 10 - MetalForming June 2009

TechUpdate
Wireless I/O Stamps Out Press Downtime at Gestamp
At the Gestamp plant in McCalla, AL, a pair of 2000-met- ric-ton transfer presses produces automotive stampings at pro- duction rates as high as 1800 parts/hr. Recently, the plant strug- gled with the big presses, as at least once a quarter the hardwired network controlling the presses suffered cable degradation and caused a downtime event. Each occurrence caused the entire operation to shut down for as long as 2 hr.
Gestamp, a Tier One Spanish-based automotive supplier, oper- ates 56 production centers in 17 countries; the McCalla plant pri- marily feeds the Mercedes-Benz assembly plant in Tuscaloosa, AL.
“The RG-6 coaxial cable we were using for the hardwired net- work cost $57/ft. to replace,” says Mike Mullins, press main- tenance team leader, “and we had to replace about 165 ft. each time the system went down. The cable alone cost $9400 to $9500 per outage, plus the costs related to system shutdown. We once estimated overhead costs of downtime at $2500/hr., and it typically took a couple of hours to replace the cable.”
In total, the plant would spend approximately $14,500 each time it had to replace the cable, plus the value of the 1500 to 2400 parts that could not be produced during the outage.
“It wasn’t uncommon for this cycle to repeat every two to
three months per press,” says Mullins.
The cable wasn’t as much the problem as were the demands
placed on it. The cable ran along a corner at such a sharp angle that it inevitably wore. So, Gestamp searched for a more reliable wire- less network, but questioned whether a wireless system would be effective given that wireless points would need to be affixed in a partially obstructed location beneath the press bolsters.
“What we really needed was a radio that could communi- cate through a 10-in.-thick plate of steel,” comments Mullins. For a solution, Mullins installed, in 2007, six frequency-hop- ping Ethernet radios from ProSoft Technology, Bakersfield, CA, to work with Gestamp’s existing ControlLogix programmable
automation controllers.
Kevin Zamzow, ProSoft Technology’s strategic product
manager for wireless technologies, explains how the solution works: “When the direct path (line-of-sight) is obstructed, a sig- nal will reflect off of other objects, taking an alternate path to the receiving radio. Because there are multiple reflections, the signals arrive at the receiving radio at different times, so the radio needs to be able to distinguish between the different sig- nals. The frequency-hopping radios can work with reflected sig- nals because of the narrow band “hops” and changing fre- quencies, making them less impacted by multipath interference compared to higher speed, wider band technologies.”
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