Electrical Discharge Machining (EDM) is a technique for material removal or production. This technique was first applied in 1770. Its creator is Joseph Priestly. However, it should be noted that due to the modernization of technology and devices, it is currently combined with Computer Numerical Control (CNC).
Modern EDM machines are integrated with automated CNC operations and are used for:
- metal cutting,
- removal of material and more.
EDM is popular in CNC machining operations and other manufacturing activities. How does this process work? What are the advantages of EDM? We write about this below!
What is EDM electrical discharge machining?
Despite its popularity, many people still do not understand this technology. Electrical Discharge Machining (EDM) is a process of removing material by subjecting it again to a controlled electrical discharge. It works like a thermoelectric phenomenon. Thermal energy is generated on the workpiece by an electrical discharge between the electrode/wire and the workpiece. Such behavior results in the removal of a layer of material. Generally speaking, EDM machines are divided into three types:
- EDM sinking
- Wire EDM,
- Hole drilling EDM.
However, in modern production, the EDM line is integrated with CNC. Therefore, automated EDM machines find wide application in the industry.
Die sinking EDM
EDM (also known as ram, sinker, conventional, volume or cavity) is the best EDM process for manufacturing parts with complex cavities. It is also an ideal method for solving the problem of sharp internal corners in CNC machining. The method uses a graphite or copper electrode, dielectric fluid, and an electric spark induced between the electrode and the workpiece.
How does the process work?
In the first stage, electrodes are created in a shape opposite to the desired cavity. This will create a cube. Then, when the mold is immersed in a dielectric fluid, such as oil, voltage is induced between the mold and the conductive workpiece being machined. The die is slowly lowered towards the workpiece until an "electrical breakdown" occurs and a spark passes through the "spark gap". This evaporates and melts the material on the workpiece, while the dielectric fluid removes the ejected particles. During this process, small amounts of electrodes often corrode as well. As a series of high-frequency sparks repeatedly removes small amounts of material from the workpiece, the desired shape will begin to appear and be precisely cut. Every part of the process between the server, power supply, and positioning of the electrodes is completely controlled by precision machining.
Wire EDM
Wire EDM, also known as wire corrosion, is a process widely used in the production of die for embossing. It cuts using the same mechanism as notching. However, the die has been replaced with very thin tensioned wires used as electrodes. This procedure is the equivalent of a cheese slicer, cutting a three-dimensional part in two dimensions. The wires are usually very thin, with a diameter of about 0.05 mm to 0.35 mm. New wire is automatically coiled throughout the process, avoiding the use of burning wire, thus ensuring precise cutting. Indeed, this process provides incredibly precise cutting, but if you want to cut sharp internal corners, remember that wire cutting alone will not give a true square corner. The wire and spark will create a small radius of about 0.13 mm to 0.15 mm, but it can be smaller or larger depending on the wire diameter. If this is not enough for your project, you can use a small bone-shaped corner to create perfectly square internal corners. Sometimes it is necessary to start cutting from the middle of the part, not from one of the edges. For example, complex shapes are machined in the middle of the die for embossing. In such a case, an EDM drill can make a small hole for the wire, through which the wire should enter the EDM wire.
EDM Drilling
As the name suggests, EDM drilling is used for making holes. However, compared to traditional drilling methods, this technique allows for precise machining of very small and deep holes without burring. It also uses the same basic principles as EDM machines. However, the cutting is done using a pulsating cylindrical electrode, and the cutting area is overlaid when the dielectric fluid penetrates deeply into the machined object. This method is crucial for the development of high-temperature turbine blades, as it allows for the creation of very complex cooling channels inside the turbine blades.
What are the advantages of EDM?
Below we present the benefits of using electrical discharge machining:
- 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 internal corners. The machining process does not produce burrs, which is an additional benefit.
- Processing without deformation - unlike conventional machining methods, the tool never comes into direct contact with the object being processed during this process. If no force is applied to the part, no deformation will occur. This allows for the manipulation of very thin elements without breaking them. Moreover, since there are no deformations, very narrow tolerances of +/- 0.012 mm can be achieved.
- High quality of machining - traditional material removal processes, such as CNC milling, leave machining marks on the processed object, which need to be removed after finishing. EDM has zero directionality of surface finish, providing a uniformly smooth surface without additional machining. Remember that high-speed EDM leaves a slight sandblasted texture.
- Precision - limited in terms of production efficiency for large orders, the EDM machine is perfect for producing small parts and prototypes due to its high precision. For example, this technology is often used in the automotive industry, which requires the production of complex engine components with high precision.
- It 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, can be processed.
Disadvantages of EDM
Like any method, this one also has disadvantages and advantages. The disadvantages of using EDM technology include:
- Low material removal rate - material removal is slow compared to traditional machining methods. Since the production process is very energy-intensive, an increase in production time affects the total cost. Therefore, EDM is not an effective method for larger projects and is often overlooked.
- Type of material - to process a material using EDM, it must be conductive. It should also be noted that although the process is technically trouble-free, machining is still a thermal change process, which can alter the metallurgy of the workpiece.
- Electrode cost - in the case of EDM, custom electrodes are required, not functional ones. Electrode processing may seem costly for small-scale production, but for large-scale production, this additional cost can be absorbed by many components.
- Carbon footprint - due to the amount of electrical energy required to perform EDM, it is not an environmentally friendly machining method. Currently, many companies around the world want to take steps to reduce their carbon footprint, preferring other processing methods that require less electrical energy, and therefore are less harmful to the environment.
What kind of surface finish can be achieved with EDM?
As with all machining processes, there is a balance between cutting speed and surface finish quality. The initial cut is usually faster and rougher, and subsequent ones are performed at a slower speed to achieve a clean surface finish. The tool can continue to cut at a lower speed to achieve an excellent surface finish, but this extends the machining time, and thus the costs.
Is the EDM method accurate?
EDM can work with very narrow tolerances +/- 0.012 mm. Therefore, the aviation and medical industry take advantage of this process. Generally speaking, all conductive materials can be galvanized. Some materials, such as high-nickel aviation-grade alloys, may pose certain challenges in machining. However, the solution is usually to change the electrode material or processing speed. The main factors influencing the choice of electrode material are its electrical conductivity and corrosion resistance. It 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 jobs are not the best concept for this method.
Summary
This is a concept that is precise, leaves no traces, is free-flowing, and does not affect the hardness of the material. However, it has some disadvantages that may exclude this process from potential use. These are slowness and costs and limitations in materials to be processed. Nevertheless, we believe that this process is noteworthy for smaller businesses that do not produce bulk quantities of parts.