Page 48 - MetalForming April 2011

Metalforming Electronics By George Keremedjiev
Revitalizing a Used Mechanical Power Press, Part 3: What’s in Control?
This third installment in our series on revitalizing used mechanical presses focuses on the press controls. First and foremost, metalformers must ensure that an inherited press control satisfies pertinent OSHA regulations and ANSI standards, and other local, national or regional regulations and standards that may apply. Keep in mind that many used power presses are being brought to the United States only to be shipped overseas, where other regulations also are in place.
Just because a company exports a used press from the United States does not mean that the press receives an auto- matic grandfathering of its existing U.S. controls. There sim- ply are no acceptable short cuts when it comes to the safety aspects of a power press, particularly in a global metal- stamping environment. Metalformers can use the following checklist to get started on their control-upgrade projects.
Home Made, Home Brew and Home Cobbled
Some stampers may have experienced this scenario: You open the power-press control cabinet and not only does it look like a rat’s nest of wires, but there is no wiring schematic, and the person or persons who designed and built the controls have long-ago retired. No one, it seems, remembers anything about the circuitry, its design, history or failure modes. No one in management, engineering, maintenance or the press- room had anything to do with this particular press control.
What to do? Easy—scrap everything. Have the innards removed and start from scratch with a modern press-control system. Do not be swayed by employees who argue that the old controls served the company well for several decades. Operational time is not a measure of appropriateness, safe- ty, legality or regulatory acceptance.
Electro-Mechanical Relay Logic
If the aging press controls are from a commercial profes- sional manufacturer, the metalformer should be able to obtain any missing schematics, either from the control man- ufacturer or a press rebuilder. Hire a professional, licensed
George Keremedjiev has been writing this column for more than 20 years. He regularly consults with metal- forming companies worldwide and provides metal- formers with training on the application and imple- mentation of sensors for die protection. For more information on his seminars and consultancies, con- tact:
Tecknow Education Services, Inc. P.O.Box6448
Bozeman, MT 59771
tel: 406/587-4751 | fax: 406/587-9620 www.mfgadvice.com
gk@mfgadvice.com
electrician or press rebuilder to certify the integrity of relay- based circuitry, along with the relays and wiring, with no home-brew modifications. Also, the relay logic must meet the latest safety and regulatory specifications and standards.
My personal preference, if funding is available: Replace all relay-logic control systems with modern electronic systems that meet safety and regulatory specifications/standards. Thomas Edison invented relay logic more than 100 years ago. Yes, relay logic, when properly implemented, does the job, but so does a horse and buggy. Time to move on.
Programmable Logic Control (PLC)
PLCs were, in part, developed to help electricians in indus- trial settings make the shift away from electromechanical relays and into electronic automation controls. In fact, most PLCs are programmed in a language called Relay Logic. A printout of such a PLC program will resemble a Thomas Edison-style electromechanical relay-logic system. This is no accident, as the PLC-programming approach was designed to make it easier for electricians to transition to electronics.
The PLC was introduced in 1969 for the automotive- manufacturing industry. Very clear standards and regulations apply to the use of PLCs for automatic press controls. These include, but are not limited to, redundancy and external self- checking circuitry and the use of dual microprocessor PLCs. It is paramount, during a thorough check of a used power press, that the PLC-based control system be inspected to identify and correct any short cuts taken when the PLC system was built, and that it meets all current regulations and standards.
Proprietary Electronics
There are several specialized, proprietary, turnkey elec- tronic press controls on the market. A newly acquired used press with such a system also must be professionally checked to ensure that the control circuitry meets current standards and regulations and that the previous press owners did not bypass any of the built-in safety components and/or circuitry. Ask the control manufacturer (if still in business) to inspect the control.
These scenarios in no way represent the full spectrum of what a metalformer might find when investing in a used press. Over the long life of a press, its controls may undergo numerous mod- ifications. These modifications may be poorly documented, if at all. Take all necessary steps to ensure that an inherited press and its control system meet the very latest of any pertinent safe- ty standards and regulations. Do not gamble with safety issues that may arise from using an outdated, outmoded, illegally modified or malfunctioning power-press control system. MF
46 MetalForming/April 2011
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