All about Electrical Discharge Machining

As per Technavio, the global electrical discharge machine market is anticipated to grow at a steady rate and will post a CAGR of 8% during 2017-2021. This growth for the global electrical discharge machine market is driven by the increasing production rate of light vehicles.

Although the origin of Electrical Discharge Machining (EDM) goes back to 1770, this technology has rapidly earned its place alongside milling and grinding equipment as a proactive, mainstream technology. The reason behind its rise is the ability of the EDM process to machine complex shapes in very hard metals. Hence, the most common uses of EDM are in machining dies, tools, and molds made of hardened steel, tungsten carbide, high-speed steel, and other workpiece materials that are difficult to machine by “traditional” methods.

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Joseph Priestly, an English scientist, discovered the erosive effect of electrical discharges in 1770. Then in 1943, Soviet scientists B. Lazarenko and N. Lazarenko had the idea of exploiting the destructive effect of an electrical discharge and developing a controlled process for machining materials that are conductors of electricity. This idea led to the birth of the EDM process, also known as the Lazarenko Circuit. The Lazarenko brothers perfected the electrical discharge process, which consists of a succession of discharges made to take place between two conductors separated from each other by a film of non-conducting liquid called a dielectric. 

How It Works

During the EDM process, a series of non-stationary, timed electrical pulses remove material from a workpiece. The electrode and the workpiece are held by the machine tool that also contains the dielectric. A power supply controls the timing and intensity of the electrical charges and the movement of the electrode in relation to the workpiece.

At the spot where the electric field is the strongest, a discharge is initiated. Under the effect of this field, electrons and positive free ions are accelerated to high velocities and rapidly form an ionized channel that conducts electricity. At this stage, current can flow, and a spark forms between the electrode and workpiece, causing a great number of collisions between the particles. During this process, a bubble of gas develops, and its pressure rises steadily until a plasma zone is formed. The plasma zone then quickly reaches very high temperatures, in the region of 8,000 to 12,000° Centigrade, due to the effect of the ever-increasing number of collisions. These high temperatures cause instantaneous localized melting of the material at the surface of the two conductors. When the current is cut off, the sudden reduction in temperature causes the bubble to implode, projecting the melted material away from the workpiece to leave a tiny crater. The eroded material then resolidifies in the dielectric in the form of small spheres and is removed by the dielectric.

This whole process occurs without the electrode ever touching the workpiece, making EDM a no-contact machining process. With EDM, organizations can achieve tighter tolerances and better finishes in a wide range of materials that are otherwise difficult or impossible to machine with traditional processes.

Benefits

  • Tolerances of +/- 0.005 mm can be achieved.
  • Material hardness does not affect the process, solving a number of problems related to the machining of materials such as Tungsten Carbide, Stellite, Hastelloy,  Nitralloy, Waspaloy, Nimonic, and Inconel. All of these materials can be successfully machined by EDM.
  • Cutting complex shapes and thin-walled configurations is possible without distortion.
  • EDM is a no-contact, no-force process, making it well suited for delicate or fragile parts that cannot take would break or be broken by conventional cutting tools.
  • The EDM process does not leave burrs.  
  • With the reduction in electrode wear and increased sophistication of EDM controls in rams, new EDM processes use simple-shaped electrodes to 3D mill complex shapes.
  • EDM can also be used for polishing small, intricate surfaces. 

This machining course covers the practices most commonly used to remove excess and unwanted material from a part.  Want to know more?

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