Did you ever have one of those days when anything when anything that could go wrong did? Well, one of our die room EDM operators recently had such a day. He was EDMing a forging die that was flood welded. Welds are always tougher to EDM, but this one was causing more than the normal amount of trouble. It was arc city! It should be pointed out that we have 10 large EDM sinkers with our own CNC controls on them. Arcing is not a normal problem for us since our controls automatically adjust on-times, off-times, pulses, and all the regular tricks to burn through most arcs. That is, unless we're EDMing what we call a dirty weld - one that likes to cause arcing.
One of our engineers working on NDA (see previous newsletter for information on NDA research and development) was waiting for this particular machine to finish its current job so he could install the NDA circuitry. We are in the Beta test stage of NDA development and will place the new circuitry in several of our own and customers' EDMs, to measure the results.
The EDM stopped with a granddaddy of an arc, one about the size of a peanut. We immediately installed the NDA circuitry, and asked the operator not to grind out the arc spike or bench the electrode. He really gave a funny look , because we all know, unless you remove the arc, it will only start arcing again right away. But our goal was to test the circuitry in the worst possible conditions, and what could be worse then a dirty weld with an arc already present.. The operator, not believing or trusting what the engineer was telling him, left the tank full of dielectric oil to prevent the engineer from sneaking in and grinding off the arc; then, watched with a smug look from another machine.
Even the engineer was surprised at the aggressiveness of the cut when the operator resumed burning with NDA installed. The operator couldn't believe what he was seeing. The EDM burned through the arc, and burned much more aggressively to depth without another problem or arc. He was surprised that he didn't have to clean the sludge off the die face (it was a female parting line that normally traps roughing sludge that often causes arcing or slows the cut). With NDA, it burned right through the sludge without any problems or slow down.
He had another surprise when he changed electrodes for finishing. He discovered that without him knowing it, the roughing electrode was too thin. This caused one of the mounting clamps and part of the fixture plate to burn about a 1/2 inch into the die face. Even with steel-on-steel and no flushing the machine didn't slow down or interrupt the cut. The operator had a bad day, and the die face needed some welding, but NDA proved its worth.
The next job scheduled for the NDA equipped EDM was a normal job, in that it had no weld and was a relatively clean steel (Finkl FX-2). Taking advantage of the aggressive anti-arcing nature of NDA, the operator was able to use a much more aggressive duty cycle (around 10%) for finishing. This naturally reduced the time needed to finish. Call or e-mail us if you have any questions or want to see a demonstration.
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