Sinker EDM Basics
A cavity type EDM, volume EDM, or Sinker EDM, will consist of a work piece and an electrode. They will be put in a liquid that is insulating like oil or dielectric fluids. These two will be connected to a supply of power. An electrical potential will be generated between the two. When the electrode approaches the work piece, a breakdown of the dielectric fluid will make a plasma channel and a tiny jumping spark.
The sparks will strike only one at a time. This is because it is very unlikely that another spark could be produced in the many locations of the inter-electrode space due to the fact that it would have to be identical and occur at the same exact time. These sparks will happen in large numbers at different places between the work piece and the electrode.
When the spark gap increases, and the base metal erodes, the machine will lower the electrode automatically. This will help the process to continue without interruption. Per second, hundreds of thousands of sparks occurs. This is because of the setup parameters that are controlling the actual duty cycle. The cycles are known as off time and on time.
Off time cycles means replacing a spark with another. The longer it is on off time, will allow flushing the dielectric fluid through the nozzle to get rid of the debris that is eroded. This also avoids a short circuit.
Using on time cycle, will determine the spark’s duration or length. The longer it is on, will produce a deep cavity for that certain spark and all that follow it in that cycle. On the work piece this will produce a rough finish. The shorter it is on, the smoother the finish will be. These are set to microseconds.