Wireless I/O stamps out press machine downtime
At the McCalla, AL, plant of Gestamp Automoción, a tier one automotive supplier based in Spain, everything is oversized. The floor is a vast concrete slab, bare but for two giant 2,000 metric ton transfer presses stretching into the air. To accommodate these beasts, the manufacturing plant ceilings are built so high that the lights above appear dim. In the cavernous space, nothing can be heard above the overwhelming roar of the ram as it slams into sheets of metal, molding the shape of what will soon be structural automotive parts.
Hiss, ka-JUNK, hiss, ka-JUNK, hiss, ka-JUNK….
Mike Mullins, press maintenance team leader, breaks the news to his crew: “Alright everyone, call your wives and tell them you’re going to be late tonight. By the time we get these presses up and running again, we’re all going to have to work late just to meet production requirements. This is going to cost us.” And this wasn’t the first time.
In 56 production centers located in 17 countries, Gestamp Automoción produces metal components for most of the leading automobile manufacturers in the world, including high-end Mercedes-Benz, Porsche, Bentley and BMW, as well as high-volume Ford, GM, Nissan and Suzuki. (Much of the production at the McCalla plant goes to a Mercedes-Benz facility in Tuscaloosa, AL.) The company owns and operates more than 70 transfer presses and 100 progressive presses, but the two transfer presses at McCalla had been become a problem. At least once a quarter, the hardwired network supporting the machines suffered breakage or damage. This frustrated the team on the plant floor, and cost a lot of money.
|The sharp angle of the bolster cable (shown in close-up left) inevitably caused wear that resulted in outages. Radio communication proved a solution, despite the extensive solution, despite the extensive presence of 10-inch-thick steel plate. Source: ProSoft|
Quantifying the loss
The two presses produce up to 1,800 parts per hour, and each occurrence caused the entire operation to shut down for up to two hours. “The RG-6 coaxial cable we were using cost $57 per foot, and we had about 165 feet to replace each time the system went down,” said Mullins. “The cable alone cost between $9,400 and $9,500 to replace, and that’s not including the cost of the system shutdown.”
Mullins said they once estimated the overhead costs of downtime at about $2,500 an hour—and it typically took a couple of hours to replace the cable. In total, it cost Gestamp approximately $14,500 each time it had to replace the cable—plus the value of the 1,500 to 2,400 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,” said Mullins.
Analyzing the application was the beginning of the solution. The application involves two presses that each consists of one ram, two dies, and two bolsters. The bolsters are large, mobile metal plates on which the dies are mounted. A die is used as a mold that defines the shape that the part will take. In this application, each die is roughly the size of a one ton pick-up truck.
During the stamping process, a metal sheet is fed across one bolster and comes to a rest above the dies. The ram rises and drops with a force of 800 to 1,400 metric tons, sandwiching the metal sheet between itself and the die to stamp out the parts. While one of the bolsters stamps a part, the second is loaded.
The network cable that kept breaking wasn’t as much the problem as the demands placed on it. The cable ran in a trough on the bolster, subject to intense vibration. The cable’s path ran along a corner that required it to achieve a sharp angle, which inevitably caused wear that resulted in outages.
|The ram rises and droops with a force of 800 to 1,400 metric tons, causing intense vibration that caused cable wear. Source: ProSoft|
Could wireless work?
Gestamp engineers knew they needed a more reliable network, and the physical constraints were obvious. Could a wireless network solve the problem? Mullins said there was a question about whether a wireless system would be effective in such a harsh environment. Wireless I/O points would need to be affixed in a partially obstructed location beneath the bolsters. “We’ve got a unique application here, involving large moving hunks of steel,” he said. “What we really needed was a radio that could communicate through a ten-inch-thick steel plate.”
The machines are controlled by Rockwell Automation ControlLogix programmable automation controllers (PACs). Since finding a radio that could penetrate steel was not really an option, Mullins asked his local Rockwell Automation distributor for a suggestion. The distributor recommended using six frequency-hopping Ethernet radios (model RLX-FHE) from ProSoft Technology, a Rockwell Automation Encompass partner.
Kevin Zamzow, ProSoft Technology’s strategic product manager for wireless technologies explains how the radios work: “When the direct path (line-of-sight) is obstructed, a signal 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 signals. ProSoft Technology’s frequency hopping spread spectrum (FHSS) radios are able to work with reflected signals because of the narrow band “hops” and changing frequencies. This makes them less affected by multi-path interference when compared to higher speed, wider band technologies such as 802.11.”
Ethernet to the rescue
To replace the hardwired system, four Allen-Bradley Flex I/O ControlNet communication adapters—one for each bolster—were replaced with EtherNet/IP adapters and a ProSoft Technology Ethernet radio. Each PAC was fitted with a second 1756-ENBT Ethernet card and an Ethernet radio.
“EtherNet/IP was designed as a media independent solution,” said Cliff Whitehead, manager of strategic applications for Rockwell Automation. “Gestamp has been able to directly take advantage of this flexibility in its wireless application.” Harry Forbes of ARC Advisory Group elaborates: “One of the key advantages of Ethernet-based automation networks is the wide variety of solutions for wireless Ethernet bridging. These solutions can have enormous value in manufacturing applications.”
Mullins said, “Our initial concerns that the steel would impede the radio performance turned out to be unfounded. When the bolsters interfere with line-of-sight, the radios continuously try to read through the bolsters.”
This specific application shows that though the laws of physics cannot be changed, the obstacles they present can be circumvented when armed with the right technology—in this case, the right industrial wireless solution. After two years of the system being live, Mullins continues to be pleased with its performance and says, “the radios work better than expected. We’ve been very happy with them.”
By using ProSoft Technology’s industrial, frequency-hopping radios, Gestamp has been able to eliminate the downtime plaguing its McCalla facility. This has translated into a savings of up to $174,000 per year, plus the value of parts produced during that time.
|Adrienne Lutovsky is a marketing writer for ProSoft Technology.|