Chris,
I'd like to help you out…and its always a pleasure to help someone new coming into the trade!
Your question of “Explain how the various types of materials will affect the feeds and voltage that can be used” is somewhat difficult to explain, as I don’t fully understand the context and intended age of the EDM equipment the question is being asked about, but I will try my best.
General Response:
Different materials types (such as Aluminum, Tool Steels, and Tungsten Carbide) all require different EDM Generator values (On-Time, Off-Time, Amperage, Voltage) to machine with speed, precision, and most importantly process stability. The Electrode Size (Sinker EDM) and material thickness (Wire EDM) also impact the EDM Generator values, as these power levels must be reduced the smaller the machining area becomes. A materials metallurgical alloy make-up and subsequent electrical conductivity can also change the EDM discharge spark gap and machining efficiency.
Modern EDM’s do not operate with a set feedrate like CNC Milling or Turning machines, as EDM’s utilize automatic adaptive power controls to stabilize the EDM process. The adaptive power control monitors the EDM machining spark gap and maintains a precise and proper distance between the electrode and the work piece (these two NEVER touch during machining), and this gap distance is forever changing during EDM machining. The EDM process is inherently unstable, as the machine must disengage and re-engage from the part to establish and maintain a proper spark gap condition, so these is a lot of back-and-forth type motions that occur several thousand times per second within the spark gap. Modern EDM’s still utilize a common set of Generator Settings (On-Time, Off-Time, Amperage, Voltage), but these values become more like “target values” that the machine starts with and then automatically adjusts to optimize speed, precision, and stability.
For example, the EDM power levels and voltages are reduced when machining Tungsten Carbide materials when compared to Tool Steels. The setting changes are due in part to Tungsten Carbide’s higher electrical conductivity and higher melting point temperature of its chemical composition, and the lower power levels prevent damage such as thermal cracking to the Carbide material (Carbide is actually a pretty sensitive material to EDM). It is important to note that the EDM generator value changes are NOT related to the wok piece materials hardness! This means that the EDM process works equally well on a 30RC Steel part vs. a 60RC Steel part…the hardness does not affect the EDM settings values, but from a technical standpoint, hardened steels do technically EDM better because they have less impurities in them as a result of the heat treating process.
Have you learned and understand the basic EDM Generator fundamentals with On-Time, Off-Time, Amperage, Voltage, etc.? I hope the above information is helpful, and please let me know if you have any further questions.
Best of luck to you!
-Brian