Wednesday, February 22, 2017

Why Bother With EDM Copper

Why bother with EDM copper, when graphite is so much easier to machine and, in many cases, performs better? The fact that you find copper electrodes in nearly every EDM department shows that it is important in injection mold making.

The use of EDM copper electrodes goes back to the first days of electrical discharge machining, before graphite even entered the picture. Those early Swiss and Asian machines were designed around copper and performed quite well.

EDM Copper
EMD Inc. Copper Electrode

Deciding which material fits your application is important, and time spent analyzing this can save you many headaches, not to mention time and money.

What are the advantages of EDM copper?

  • Copper is more efficiently cut on WEDM machines, which makes it cut much faster than graphite in WEDM. Highly detailed electrodes, which were formerly manufactured on surface grinders, required many hours of highly skilled labor. The use of copper and WEDM to produce these electrodes has dramatically changed EDM machining.
  • It is less likely to cause pits in the steel workpiece. The tendency of any electrode to “DC arc” is the curse of EDM. When the flushing is poor, machining conditions are ripe for a short circuit to occur in the EDM process, causing the tell-tale pits in the workpiece. It is much more forgiving and less likely to DC arc.
  • Copper is usually used to produce a finer finish in the steel. These  electrodes are sometimes polished to reproduce the fine finish on the mold surface. Newer EDM machines have polishing settings that can produce mirror finishes, and usually copper is used.
  • It is the best for small cavities, especially where polishing is difficult. Because of it’s resistance to pitting and the finer finishes attainable, copper is often used in these applications. Adding tungsten to copper increases it’s excellent wear characteristics, but also is very difficult to machine.
  • Copper can be machined by coining. In this process, the electrode is stamped with an image, just like a coin, and then used as an EDM electrode. This can be an excellent application for designs such as logos.
  • It is clean to machine and leaves no annoying dust. Also, tellurium copper leaves much less of a burr than pure copper.

What kind of EDM copper should be used?

Tellurium copper (Telco) performs the same as pure copper as an electrode material. It has a huge advantage, however, because of it’s high machinability rating: 90% (free cutting brass = 100%). Pure copper has a rating of 20%.

Telco EDM copper is highly recommended for use on machines which have been designed to work best with copper. Its high machinability rating and fast WEDM speeds make it ideal for highly detailed, difficult to flush electrodes.

EDM Copper
EMD Inc. Injection Mold Cavity

Not so long ago EDM copper was used almost exclusively by European and Asian mold makers. Gradually this has changed, for several reasons.

When the first generation of machines were developed in these areas, the power supplies were R-C, or Resistor Condenser. Metallic electrodes such copper and brass were the only materials that efficiently performed in these machines.

Then, as newer generations of machines were developed, the use of EDM copper was well established. Plus, EDM grade graphite was simply unavailable, which left uses with one option.

The use of copper has declined as technology has progressed because the newer EDM machines are designed to use graphite as well as copper. Also, the dust problem has been overcome now that high speed machining centers are equipped with vacuum environments to remove the annoying graphite dust.

Industrial supplies, especially EDM supplies are not the place to cut corners and buy cheap imitation products. This will only lead to frustration and disappointment.

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