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EDM -- Spark Erosion
Words used to describe a process that requires sparks to remove metal. Most EDM users goal is to produce as many sparks as possible, thereby, removing as much metal as possible per microsecond.. Sparks are good. Right? Maybe not. The correct statement should read - most sparks are good - some can be harmful.
The problem is that EDMing requires a dielectric oil to carry the spark from the electrode to the work piece, and the oil is flammable. The EDM spark not only removes metal, it breaks down the hydrocarbons in the oil to produce flammable hydrogen gases. These gases float to the surface (the white bubbles you see while EDMing) and mix harmlessly into the atmosphere. The gases can be ignited if they come into contact with a spark. This usually happens on the surface of the oil and is called a flare up. If the gas production continues, they add fuel to the fire and keep it going. Shutting off the power supply (the source that produces sparks that cause the gases) normally stops the flare up.
If the flare up is allowed to continue, it will raise the temperature of the oil to its flash point. At that point, the fire can only be put out with a fire extinguisher. This type fire is dangerous and can cause damage to equipment.
To prevent this type of flare ups, Hausermann invented their unique FD sensor system. The FD sensor is a light sensor that has the ability to distinguish between light and flame. When the FD sensor detects a flare up, it immediately shuts off the source of the flare up - the power supply. The machine remains off until the cause of the flare up is corrected.
We also recommend that the FD sensor shut off the mist collectors over the EDM. Very often a flare up can cause the oil mist in the collector to ignite. The mist has a lower flash point and normally will continue to burn even after the flare up is extinguished. By turning off the collectors along with the power supply, the chances of the flame being sucked into the collector are reduced.
To insure the reliability of the FD sensor, a PLC is included in the unit for self diagnostics. If the sensor bulb is burned out or the sensor fails in some manner, the power supply is shut off until the sensor is repaired or removed from service.
The FD sensor system comes with 2 sensors mounted on a bracket for installation on each side over the EDM dielectric tank. The kit also comes with a self-diagnostic PLC to insure reliability and a pendent interface.
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