EDM or Electrical Discharge Machining is one of the break through technology developed in metal machining. The EDM machines can be used to machine complex profiles where conventional machines fail. It can also be used to finish the milled surface where sharp corners are required.
EDM machine removes material from work piece by eroding material by an electrode. The machine removes material in the path of electrical discharges that form an arc between an electrode and the work piece. The work piece is immersed in a dielectric fluid. The electrode of required profile or the wire is brought very close to the work piece to produce the arching, thus eroding the material from work piece.
One of the biggest advantage of EDM machining is that, it can machine hardened work pieces extremely accurate. EDM machining can produce highly accurate and complicated profiles on work pieces. Today EDM is widely used in tooling field, especially in mold making. During the recent years EDM machining has become really affordable for tooling manufacturers.
One of the major disadvantage of EDM machining is that, it works only on work pieces which conducts electricity.
Types of EDM Machines
There are mainly two types of EDM machines. The RAM EDM machine and the Wire EDM machine. The RAM EDM machine or the spark erosion machine is mainly used for machining blind profiles, machining threads etc. The wire EDM on the other hand is mainly used for machining through profiles accurately. In most of the cases wire EDM is more accurate than the RAM EDM machining.
RAM EDM Machine- Die Sinker
The die sinker or the ram type edm machines are used for machining blind holes, complicated profiles, slots and for thread machining. Unlike wire edm machines, a die sinker edm machine doesn’t need a pre-hole for machining. The work piece which is mounted on the bed is immersed inside the edm dielectric fluid. The electrode which is made out of copper, graphite or similar high conducting materials is mounted on the ram of the edm machine. During the EDM machining process the electrode is guided along the desired path very close to the work piece but it does not touch the piece. The arching creates continuous sparks and a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization. Continuous flow of dielectric fluid is provided near the eroding area to wash away the the eroded material particles.
Wire EDM Machine
Wire EDM machine can produce extremely accurate profiles which are through. Wirecut or wire EDM machining is widely used in stamping industry to cut die profiles, stripper and punch holder profiles. Cutting punches which are designed with same profile throughout the length also can be produced by edm machining. Wire EDM works in the same principle of a die sinker edm. Instead of a profiled electrode, a thin brass wire is used in wire edm machines.
Before cutting off the profile by wire edm, a pre-hole needs to be created by drilling or by spark erosion. The work piece is then loaded on the wire edm machine bed and simmered in the dielectric fluid. The wire is passed through the pre-drilled hole and the bed starts moving according to the profile which needs to be cut out. The edm wire, which is constantly fed from a spool, is held between upper and lower guides of the edm machine. The path movement of the wire is normally CNC controlled which enables the wire edm machines to produce precise holes and die profiles. In most of the modern wire edm machines the guides can be tilted to cut a draft (taper) on work piece along with the profile. This is extremely useful while cutting die profiles which need a draft for slug relief.