Sinker EDM Basic Terminology – Part I
RAM EDM, otherwise known as “Sinker EDM” or “Plunge EDM” has been around for over fifty years. Though widely used, there are some who are unfamiliar with certain EDM terminology.
Since Sinker EDM uses electrical energy to remove material, it stands to reason that the make-up of the material will have a direct impact on the rate of removal. This being the case there are three critical things to keep in mind.
• Since machining with Sinker EDM or Plunge EDM occurs by using electrical energy the electrical conductivity plays a key role in how fast the Spark Gap can ionize allowing a spark to occur.
• Materials that are less electrically conductive will machine slower, such as carbides and PCD.
• Pulse energy (heat) is conducted away from the surface of the part with flushing and temperature controlled dielectric fluid. Some of this heat will dissipate into the work piece. Certain materials, like beryllium copper alloys used in molds, are designed to dissipate heat quickly. This will slow down the metal removal rate of the EDM process.
When we see a flash of lightning we are witnessing EDM on a grand scale. The lightning bolt is electrical energy flowing between an electrode (cloud) and a (grounded) workpiece in a natural kind of EDM phenomena. This discharge is the same as what occurs in an EDM machine.
• An EDM Pulse is highly controllable and there are parameters to determine the size and intensity of the spark.
• On-Time is the length of time the spark is turned on. This determines the depth the spark can travel into the workpiece. On-Time will have a direct impact on final part size and surface finish.
• Off-Time is the period of time between the end of one spark and the ignition of the next. Off-Time allows for efficient chip removal and cooling in the spark gap.
• The combination of the EDM Pulse On and the Pulse Off is one cycle. It has been said that the EDM process can develop as many as 250,000 cycles per second, but only one spark at a time.
• Amperage is the electrical power of the spark. The higher the amperage, the more aggressive the spark, and the deeper the spark can go into the metal. Like On-Time, Amperage will have a direct impact on final part size and surface finish.
The combination of ON TIME and AMPERAGE are the two parameters that will determine spark length, or overburn. Changing the ON TIME and/or AMPERAGE during a burn will change the size and finish of the final result. All other machine parameters will affect MMR and/or electrode wear, but not spark length. To better understand your machine’s parameters, consult your owner’s manual or machine builder.
In our next post we’ll address flushing.