Sapel Blog
What Is EDM (Spark Erosion Machining)?
Electrical discharge machining (EDM), also known as spark erosion, is a subtractive, non-traditional manufacturing method (used, for example, in plastic injection mold making) that melts and vaporizes the workpiece with repeated electrical sparks in a dielectric fluid. The tool and the workpiece never touch, so delicate parts can be produced to micron-level accuracy without any mechanical stress or distortion. This technology is the best alternative to conventional methods for machining extremely hard metals and creating very complex geometries.
The History and Evolution of EDM
The First EDM Machine
In 1943, two scientists in the Soviet Union, B. R. Lazarenko and N. I. Lazarenko, were tasked with finding ways to prevent erosion and sparking on tungsten electrical contacts. Although they did not succeed in their original task, they made a valuable discovery: if the electrodes were immersed in a dielectric (insulating) fluid, the erosion caused by sparks could be controlled far more precisely. This breakthrough led the Lazarenkos to invent the first practical electrical discharge machine (EDM) for working hard materials such as tungsten.
Development in the United States
At the same time, and completely independently, an American team developed a spark machine to remove broken drills and taps from aluminum castings. Their first attempts, using weak electric etching tools, were not very successful. But by combining more powerful spark units, automatic spark repetition and a fluid replacement system driven by an electromagnetic interrupter, they went on to build practical machines that could produce 60 sparks per second. Later machines based on their design used vacuum-tube circuits that could produce thousands of sparks per second and dramatically increased cutting speed.
The Arrival of Wire EDM
A new variant of the technology, wire EDM, emerged in the 1960s for making tools and dies from hardened steel. In this method the tool electrode became a thin wire that moved continuously between two spools, so that its active section was always changing and the wire would not snap from erosion.
The Spark Erosion Process, Step by Step
- Positioning without contact: The tool electrode and the workpiece are positioned very close to each other, without touching, immersed in a dielectric fluid.
- Building the electric field: When the power supply applies a voltage, the electric field across the micron-sized gap between the electrodes rises sharply.
- Electrical breakdown and plasma formation: This strong field breaks down the insulation of the dielectric fluid, and a conductive plasma channel forms at the point of discharge.
- Melting and vaporization: The plasma generates intense heat that instantly melts and vaporizes a tiny area of the workpiece surface.
- Flushing away the particles: When the current is switched off, the plasma collapses and the dielectric fluid washes the molten particles out of the gap so the insulation is restored.
The Vital Role of the Dielectric Fluid (Oil or Deionized Water)
Until the breakdown voltage is reached, the dielectric acts as an insulator. The fluid also carries heat away to cool the tool and the workpiece, and continuously flushes away debris to prevent short circuits.
Key Machine Settings
Spark on-time sets how long each spark lasts; longer on-times create deeper craters and a rougher surface finish. Spark off-time is the interval between sparks, which gives the dielectric flow enough time to clear the eroded particles from the cutting zone.
Advantages and Disadvantages of EDM
Compared with conventional chip-cutting methods, EDM has distinctive characteristics, clear advantages and, of course, certain technical limitations:
Advantages of EDM
- Machining extremely hard metals regardless of hardness: One of the biggest advantages of this method is its unmatched ability to machine very hard metals such as titanium, hardened steel, superalloys and carbides.
- No mechanical force on the workpiece: In EDM there is no direct physical contact between the tool (electrode) and the workpiece. This contactless nature eliminates mechanical stress, deformation and distortion of the workpiece, making it possible to produce extremely delicate parts, tubes, mold cavities, very thin walls and sensitive structures without damage.
- Exceptionally high accuracy and an excellent surface finish: The technology can achieve very tight tolerances of around 2.5 micrometers (±0.0001 in), and even micron-level geometric accuracy with wire EDM. Electrical discharge produces a very high-quality surface, which greatly reduces the need for secondary finishing (such as grinding or polishing).
- Complex geometries and deep slots: EDM lets manufacturers create very narrow slots, extremely small holes, tapered angles and deep 3D cavities that are impossible to produce with conventional rotating cutting tools. Producing perfectly sharp internal corners with very small radii is another key advantage of this method.
Disadvantages of EDM
- Low material removal rate: Because the sparks remove material by gradual melting and vaporization, EDM removes material much more slowly than conventional methods (such as milling or turning).
- Limited to electrically conductive materials: EDM fundamentally depends on the workpiece being electrically conductive. Although methods have been proposed for machining some insulating ceramics under special conditions and setups, non-conductive materials generally cannot be machined this way.
- Constant electrode wear (tool wear): As the discharge removes material from the workpiece, it also erodes the electrode itself, leaving small craters on the tool. This constant electrode wear makes it difficult to reproduce perfectly sharp corners on the workpiece and calls for frequent tool changes or wear-compensation strategies.
- Recast layer formation : The intense heat of the plasma channel melts and vaporizes some of the material. Part of this molten metal re-solidifies on the surface before the dielectric can flush it away, forming what is called a recast layer, which can introduce tensile residual stresses into the part.
- High energy use and equipment costs: EDM machines have very high specific energy consumption. In addition, buying and setting up these complex machines, training operators and supplying suitable electrodes and dielectric fluid involve high upfront and running costs.
