Sensors Outside the Die
There is much more to die protection than just placing sensors in the tooling. Other opportunities exist to avert a possible die crash by monitoring motions and energy in the general press area surrounding the running die. Think about the various fluids and air streams counted on to make the stamping process possible. We tend not to think of these as part of the die-protection program, but nothing could be further from the truth. Here is a list of some items to think about that relate directly to the proper functioning of the die.
Shakers and conveyor belts—These scrap- and part-removing press attachments are crucial to the proper functioning of the die. It is not rare for these devices to stop functioning and the scrap (or the parts) to build up into the die, causing a severe detonation of a die section (or more). Be vigilant in monitoring the shakers and conveyors. The motion of each must be sensed. If the shakers stop shaking or the conveyor stops moving, the die-protection system can stop the press and alert the operator to the nature of the problem.
Gas pressure—The delivery of pressurized air to the press area should be monitored with a pressure sensor. Likewise for pressurized nitrogen that may be used for cylinders in the die. These sensors should tie into the die-protection controls to stop the press and alert the operator.
Fluid pressure—Like air, we depend upon pressurized fluids to deliver energy or lubricity to various devices. Hydraulics are prevalent in some dies for the proper functioning of high-force cylinders. Likewise for the hydraulics used when clamping the die to the press. Oils are sprayed into the die with pressure. Monitor these pressurized fluids with the appropriate sensors and connect them to the die-protection control.
End of strip—This causes nightmares in many shops: The operator does not notice that the coil is about to run out of material and the end of the strip enters the die, causing some interesting modifications to the tooling, not to mention partial parts that may even make their way to the customer. A sensor, located away from the dies that monitors for the approaching end of the strip, should be connected to the die-protection controls.
Strip thickness—Some critical jobs have no window for error with regard to strip thickness. This can be especially so with the latest crop of high-strength steels. Here, monitor the strip thickness with analog sensing placed outside of the die. This can be done with a stand-alone fixture that mounts to the press. The strip first feeds through this fixture and then into the die. The fixture also ties into the die-protection system.
The above-cited examples are just a few meant to tickle your imagination into accepting the concept that die protection is not limited to the die itself. The current crop of die-protection controls with dozens of sensor inputs makes additional sensing a snap. For those with limited inputs on die-sensing systems, use a PLC to expand the number of channels to accommodate these additional sensors.
Do not limit your definition of die protection only to the die itself. Sense the total die-stamping ecosystem—the complex interrelationships between the tooling, press, energy and strip. MF
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