Manufacturing processes

What is Electrical Discharge Machining and how does it work?

| Author: Rosemarie Stahl

Electric discharge machining does not use any force to remove material. Instead, an electric discharge occurs between workpiece and tool. In this case, a wire is used to “cut” the material.
Electric discharge machining does not use any force to remove material. Instead, an electric discharge occurs between workpiece and tool. In this case, a wire is used to “cut” the material. (Source: © phuchit.a@gmail.com)

When traditional machining methods reach their limit, electric discharge machining can be the answer. The EDM process allows for high accuracy and is applicable for any conductive material.

Electrical discharge machining, or EDM, is a non-traditional method in which material is removed from a workpiece using thermal energy. Much like processes such as laser cutting, EDM does not need mechanical force in the removal process. This is the reason why it is considered non-traditional contrary to, for example, the processing with cutting tools.

In tool and mould making, EDM is very popular due to its applicability especially for hard materials like titanium or for particularly complex shapes that are hard to achieve with milling.

The EDM process

The Ecyclopædia Britannica gives a short explanation of EDM:

“EDM involves the direction of high-frequency electrical spark discharges from a graphite or soft metal tool, which serves as an electrode, to disintegrate electrically conductive materials such as hardened steel or carbide.”

To put it more simply, electrical discharge machining is a manufacturing process that precisely removes material from conductive materials using an electrode. Similar to pushing a form into soft material, the electrode leaves a negative imprint in the workpiece. The physical process is a little more complicated: In a small gap between workpiece and electrode, a discharge occurs that removes material through melting or vaporizing. For this process, the electrode and the workpiece have to be submerged in a dielectric fluid.

The electrode tool is lowered into the workpiece (left). In the small gap between tool and workpiece, a discharge occurs that removes material (right).
The electrode tool is lowered into the workpiece (left). In the small gap between tool and workpiece, a discharge occurs that removes material (right). (Source: OPS Ingersoll)

The principle behind this process is the ability of controlled electric sparks to erode material. The workpiece and electrode do not touch during this porcess. In between is a gap that is roughly as thick as a human hair. The amount of removed material with a single spark is small, yet the discharge occurs roughly several 100,000 times a second.

While the electrode is moved closer to the workpiece, the electric field in the gap, also known as spark gap, increases until it reaches the breakdown volume. For this process, it is necessary that the fluid in which this discharge occurs is not conductive, or dielectric. The discharge causes strong heating of the material, melting away small amounts of material. This excess material is removed with the steady flow of the dielectric fluid. The liquid is also useful for cooling during the machining. Moreover, it is necessary for controlling the sparks.

Three different types of electrical discharge machining: Wire EDM, sinker EDM and hole drilling EDM

There are three different types of electrical discharge machining. The one described above is called sinker EDM. It is also known as die sinking, cavity type EDM, volume EDM, traditional EDM, or Ram EDM. Using Die sink EDM allows users to produce complex shapes. This method requires electrodes (often made from graphite or copper) that are pre-machined to have the necessary shape. This electrode is then sunk into the workpiece, creating the negative version of its original shape.

An example for parts machined with wire erosion: These pieces have been machined on a Sodick wire EDM machine.
An example for parts machined with wire erosion: These pieces have been machined on a Sodick wire EDM machine. (Source: Stahl/ETMM)

The second type of electrical discharge machining is called wire EDM and is also known as wire erosion, wire burning or spark EDM. In Wire EDM a thin wire is used to cut the work piece. In this case, the wire works as the electrode. During the machining, the wire is constantly coming from an automated feed with a spool. If the cut has to be made in the middle rather than the outside of the workpiece, small hole drilling EDM is used to make a hole in the workpiece through which the wire is threaded afterwards.

The wire is held with diamond guides. Usually the liquid is deionized water. The wire is often made from brass or copper.

The following video gives a short explanation on how wire EDM works:

The last type of electrical discharge machining is called hole drilling EDM. As the name suggests, this process is used for drilling holes. Compared with traditional drilling methods, EDM is able to machine extremely small and deep holes. Additionally, EDM drilled holes don't need any deburring. The electrodes in this process are tubular and the dielectric fluid is fed through the electrode itself.

In general, every conductive material can be machined with electrical discharge machining. Common materials include metals or metal alloys such as hardened steel, titanium, and composites.

Typically, the electrodes for die sinking EDM are made of copper or graphite. The main factors that influence the decision for an electrode material are the electrode's conductivity and its resistance to erosion. Graphite has the advantage that it is easier to machine than copper. However, copper is highly conductive and strong. Brass, an alloy of cupper and zink, is often used for wire EDM or small tubular electrodes.

Contrary to electrodes for die sinking, the wire used for wire EDM does not have to offer good resistance characteristics, as new wire is fed constantly duting the cutting.

Advantages: When applying EDM makes sense

The main advantage of electrical discharge machining is that it can be used on any material as long as it is conductive. It is therefore possible to machine workpieces made from tungsten carbide or titanium that are hard to machine with traditional cutting methods. Another advantage of electrical discharge machining is the lack of mechanical force put into the workpiece. Fragile outlines are easier to produce because there is no high cutting force needed to remove the material.

EDM also allows for shapes and depths that are impossible to reach with a cutting tool. Especially deep processing where the tool length to diameter ration would be very high, is a usual application for EDM. Sharp internal corners, deep ribs and narrow slots are other specialities of electrical discharge machining. Another argument for using EDM is that the surface finish is usually better than with traditional methods. Electrical discharge machining produces surfaces with a fine finish and high precision.

Moreover, EDM allows users to machine hardened workpieces. Whereas other machining techniques need to be executed before the workpiece is hardened with heat treatment, electrical discharge machining can be applied on the hardened material as well. Thus, any potential deformation from heat treatment machining can be avoided.

However, there are numerous examples where electrical discharge machining is not the right solutions. EDM is a high precision machining method. EDM is a rather slow method compared to traditional machining. High-volume tasks are therefore not suited for this method. At the same time, the electro thermal process requires high power consumption.

Similar to traditional chipping methods, the tool life in EDM is not endless. In sinker EDM, the electrode is also vulnerable to erosion. Because of the tool wear, the electrode has to be replaced regularly. In sinker EDM, it is also necessary to produce the correctly shaped electrodes before the workpiece can be machined. This is an additional step compared to machining processes with traditional cutting tools.

There are numerous examples of companies that have managed to implement electrical discharge machining for their benefit. In many cases an update to a newer and more modern EDM machine has done the trick. These are some case studies that tell the stories of some successful companies and their experience with electrical discharge machining:

Investment in EDM machinery and HSC enables impressive growth

Case Study

Investment in EDM machinery and HSC enables impressive growth

02/26/2018 - Gotools is a British company located in Rotherham, a 90-minute drive from Birmingham. In only a little over five years of existence, the company has managed to record a growth of around 50% per year. All that success started with the decision to buy a new EDM machine. read...

From a small hatchback to a supercar with a new EDM machine

Case Study

From a small hatchback to a supercar with a new EDM machine

01/09/2018 - Foremost Specialist Products is a subcontract manufacturer of precision engineered components based in Derby, UK. To take on the “complex and awkward parts that no else wants to tackle”, the company has invested in a Sodick ALC600G CNC wire-erosion machine from Sodi-Tech EDM. Among the jobs being successfully accommodated by the machine are stainless steel tubular stem guides for power generator turbines. read...

Experienced with wire-cut EDM systems for generations

Case Study: Mitsubishi Electric

Experienced with wire-cut EDM systems for generations

04/10/2017 - You don’t often hear of someone claiming to have been surrounded by wire-cut EDM systems as a child. But Andreas Hornung, the managing director of Hornung, fondly remembers the machines of his father’s firm. Today, the company is equipped with several machines from Mitsubishi Electric. read...

The many possibilities of automatising the handling of electrodes

Case Study

The many possibilities of automatising the handling of electrodes

05/30/2017 - Walther Wolf is one of those mould makers that is constantly optimising manufacturing processes. When they wanted to further perfect their automation in machining electrodes, they turned to Zimmer & Kreim to build an automated 23-metre-long machining centre: A Chameleon. read...

EDM and safety?

How safe is EDM? This is actually a question that worries many technicians coming in touch with EDM for the first time. The need for high voltage and reoccurring sparks make it seem like a safety hazard to inexperienced workers. As long as the machine is used according to manufacturer specification, however, there is no great danger involved.

The Metalforming Magazine gives tips on how to ensure process safety. These are some of the measures that need to be taken to run an EDM machine safely:

  • Operators and workers have to be properly trained to work with electrical discharge machining
  • Make sure that fire protection measures are installed and regularly maintained.
  • Keep an eye on the fluid: The level of the dielectric fluid is of utmost importance. The liquid prevents the discharge from crossing to conductive materials other than the workpiece.
  • Proper ventilation can clean the air of gases that might be produced in the fluid due to chemical reactions accompanying the discharge.
  • You have to monitor the dielectric fluid when it is circulating to ensure it retains its non-conductive characteristics.

EDM machines and automation

There are numerous suppliers of EDM machines. Among the most well-known producers are Mitsubishi Electric, OPS Ingersoll, Makino, Excetek, Sodick, GF Machining Solutions and Ona.

The Eagle G5 Precision is the latest addition to OPS Ingersoll's EDM machine range. The die sinking machine is said to offer high precision machining combined with low electrode wear.
The Eagle G5 Precision is the latest addition to OPS Ingersoll's EDM machine range. The die sinking machine is said to offer high precision machining combined with low electrode wear. (Source: OPS Ingersoll)

A current trend is the automation of the EDM process. This does not only include the spark or wire erosion itself but also the machining of the electrodes. Using CNC machine tools to machine electrodes, EDM machines, cleaning and measuring stations and — last but not least — storage areas and robotic units to handle the electrodes, the EDM process can be executed automatically. This ensures that a sparker is always fed quick enough with electrodes. The machining of these electrodes and the erosion process can be programmed to take place over night, thus, making production processes much more time efficient. Additionally, a higher worklode can be processed without additional workforce. Several processes can happen simultaneously, including eroding, measuring, milling, laser engraving and cleaning. Companies that have implemented automation in their production processes have witnessed significant time savings and an increase in turnover.

Companies like Zimmer & Kreim offer automation systems particularly for EDM processes. OPS Ingersoll is another manufacturer that offers a one-stop automation solution designed to fulfill the needs of their clients in the toolmaking industry.

Applications of EDM

Invented in the 1940s, EDM is a very early non-traditional process. Combined with computer numeric controls (CNC), it has become an accurate and reliable machining method that is now standard among more conventional cutting methods. It is particularly popular for small-volume productions such as prototypes. Various processes are possible with electrical discharge machining, including turning, milling, grinding and small hole drilling. Besides die and mould-making, EDM is typically applied in the automotive and aerospace industry, for example, in the production of aircraft engines.

Do you want to know more about EDM? Here are some sources for additional information:

  • Reliable EDM, an North American manufacturer, offers a free handbook with practical information: Complete EDM Handbook.
  • A user of instructables.com, called alchemistdagger, has build his own homemade EDM machine. The complete user manual and instruction can be downloaded online: DIY EDM machine

Comments are being loaded ....

Leave a comment

Discuss anonymously or log in Log In

Avatar
To protect our interests, we store the IP address in addition to the above information. This is solely for the purpose of identifying you as the author of the comment. The legal basis is the protection of legitimate interests in accordance with Art. 6 para. 1 lit. f) DSGVO.
  1. Avatar
    Avatar
    Edited by at
    Edited by at
    1. Avatar
      Avatar
      Edited by at
      Edited by at

Comments are being loaded ....

Report comment

Kommentar Freigeben

Der untenstehende Text wird an den Kommentator gesendet, falls dieser eine Email-hinterlegt hat.

Freigabe entfernen

Der untenstehende Text wird an den Kommentator gesendet, falls dieser eine Email-hinterlegt hat.

copyright

This article is protected by copyright. You want to use it for your own purpose? Infos can be found under www.mycontentfactory.de (ID: 45091883 / EDM)