Electrical discharge machining (EDM) is a technique for removing material or manufacturing. The method was first used in 1770. Its creator is Joseph Priestly. However, it should be noted that it is now combined with computer numerical control (CNC) due to the modernization of technology and equipment. Modern EDM machines are integrated with automated CNC operations and are used for:
- Metal cutting,
- material removal, and more.
EDM is popular in CNC machining operations and other manufacturing operations. How does the process work? What are the advantages of EDM? We write about it below!
What is EDM machining?
Despite its popularity, many people do not yet understand this technology. Electrical discharge machining (EDM) is the process of removing material by subjecting it again to a controlled electrical discharge. It works like a thermoelectric phenomenon. Heat energy is generated on the workpiece by an electrical discharge between the electrode/wire and the workpiece. This behavior removes a layer of material. In general, EDM machines are divided into three types:
- Plunge EDMs
- Wire EDMs,
- EDM for holes.
However, in modern manufacturing, the EDM line is integrated with CNC. Therefore, automated EDM machines are widely used in industry.
Die sinking EDM
EDM (also known as ram, weight, traditional, volumetric, or cavity) is the best EDM process for producing parts with complex cavities. It is also an ideal method for solving the problem of sharp inside corners in CNC machining. The technique uses a graphite or copper electrode, dielectric fluid, and an electric spark between the electrode and the workpiece.
How does the process work?
In the first step, electrodes are created that are shaped opposite to the desired cavity. This will create a cube. Then, when the mold is immersed in a dielectric fluid, such as oil, a voltage is induced between the mold and the conductive workpiece. The mold is slowly lowered toward the workpiece until an „electrical breakthrough” occurs, and a spark passes through the „spark gap.” This vaporizes and melts the material on the workpiece while the dielectric fluid removes the ejected particles. During this process, small amounts of electrodes often erode as well. As a series of high-frequency sparks repeatedly remove small amounts of material from the workpiece, the desired shape will begin to emerge and be precisely cut. Every part of the process between the server, power supply, and electrode positioning is entirely controlled by precision machining.
Wire EDM, also known as wire corrosion. It is a process widely used in extrusion die manufacturing. It cuts using the exact mechanism as indentation. However, the die is replaced by skinny live wires used as electrodes. The procedure is the equivalent of a cheese slicer, cutting through a three-dimensional part in two dimensions. The wires are usually fragile, measuring about 0.05 mm to 0.35 mm in diameter. The new wire is automatically coiled throughout the process, avoiding burning wire, thus ensuring an accurate cut. Admittedly, this process provides an exact cut, but if you want to cut sharp inside corners, remember that cutting the wire alone will not produce an actual square corner. The wire and sparkle will form a small radius of about 0.13mm to 0.15mm, but it can be smaller or larger depending on the diameter of the wire. If this is not enough for your project, you can use a small bone-shaped corner to create perfectly square inside corners. Sometimes it is necessary to start cutting from the center of the part rather than from one of the edges. For example, complex shapes are machined in the center of an extrusion die. In this case, the EDM drill can make a small wire hole through which the wire should enter the EDM wire.
As the name suggests, EDM drilling is used to make holes. However, compared to traditional drilling methods, this technique allows precise machining of tiny and deep holes without deburring. It also uses the same basic principles as EDM machines. However, cutting is done with a pulsating cylindrical electrode, and the cutting area is applied when the dielectric fluid penetrates deep into the workpiece. This method is crucial to developing high-temperature turbine blades, as it creates highly complex cooling channels inside the turbine blades.
What are the advantages of EDM?
The following are the advantages that come with using EDM:
- Greater design freedom – one of the main advantages of EDM is the ability to cut shapes and depths that cannot be achieved with traditional machining methods. These include undercuts and perfectly square inside corners. The machining process does not produce burrs, which is an added benefit.
- Deformation-free processing – unlike conventional machining methods, the tool never directly contacts the workpiece during the process. If no force is applied to the part, no deformation will occur. This makes it possible to manipulate very delicate parts without breaking them. In addition, since there is no deformation, very tight tolerances of +/- 0.012 mm can be achieved.
- High-quality machining – Traditional material removal processes, such as CNC milling, leave machining marks on the workpiece that must be removed after finishing. EDM has zero directional surface finish, resulting in a uniformly smooth surface without additional machining. Keep in mind that high-speed EDM leaves a slight sandblasted texture.
- Precision – limited in production capacity for large orders, EDM is ideal for small parts and prototypes due to its high accuracy. For example, the technology is often used in the automotive industry, requiring high precision manufacturing complex engine components.
- This does not affect the hardness of the material – the main feature of EDM is that it can process any material as long as it is conductive. This means that hard materials such as tungsten carbide, for example, can be machined.
Disadvantages of EDM
Like any method, this one has advantages and disadvantages. Disadvantages of using EDM technology include:
- Low material removal rate – material removal is slow compared to traditional machining methods. Since the manufacturing process is very energy-intensive, the increase in production time affects the total cost. As a result, EDM is not an effective method for larger projects and is often overlooked.
- Type of material – It must be conductive to process material with EDM. It should also be taken into account that although the process is technically seamless, the processing is still a thermal change process that can alter the metallurgy of the workpiece.
- Electrode cost – custom electrodes, rather than functional electrodes, are required for EDM. Electrode machining may seem costly for low-volume production, but for high-volume production, this additional cost can be absorbed by many components.
- Carbon footprint: This is not an environmentally friendly machining method due to the amount of electricity required to perform EDM. Today, many companies around the world want to take steps to reduce their carbon footprint; other processing methods that require less electricity and are therefore less harmful to the environment are preferred.
What surface finishes can be achieved with EDM?
As in all machining processes, there is a balance between cutting speed and surface finish quality. The initial cut is usually faster and rougher, and subsequent cuts are made at slower speeds to achieve a clean surface finish. The tool can be cut further at a lower rate to achieve an excellent surface finish, increasing machining time and thus cost.
Is the EDM method accurate?
EDM can work to very tight tolerances of +/- 0.012 mm. This is why the aerospace and medical industries use the process. In general, all conductive materials can be electroplated. Some materials, such as high-nickel aerospace-grade alloys, can pose some challenges in processing. However, the solution usually changes the electrode material or processing speed. The main factors influencing the choice of electrode material are its electrical conductivity and corrosion resistance. EDM is an excellent method to use in conjunction with traditional machining techniques, such as CNC machining of parts with specific geometric requirements. However, the machining process is relatively slow, so high-volume work is not the best concept for this method.
EDM is a concept that is precise, non-marking, free, and does not affect the hardness of the material. Nevertheless, it has some drawbacks that may exclude the process from potential use. These include slowness, as well as cost and limitations in machining materials. Nonetheless, we believe it is a worthy process for smaller companies that do not produce bulk quantities of parts.