Electrical Discharge Machining (Sinker EDM): Principles, Characteristics, Applications, and Technical Details
In CNC machining, many parts often exhibit features that cannot be achieved using conventional processes. However, these features can be realized through an alternative machining process: Sinker EDM. This non-traditional machining process excels in machining scenarios requiring extremely high precision. Unlike traditional mechanical cutting, which generates stress and alters material properties, these methods utilize other forms of energy to shape and remove material. This article will introduce the principles of this process, the various materials it can process, its advantages and disadvantages, and its applications in various industries.
What is Sinker EDM?
Electrical discharge machining (EDM) is an unconventional method that uses thermal energy to remove material from a workpiece. No mechanical force is required during the cutting process. Therefore, the machining process utilizes thermal energy, not mechanical force. It primarily creates extremely precise blind cavities through electric sparks in conductive materials; a custom-designed electrode is immersed in a dielectric fluid, close to the workpiece but not in contact with it; when high voltage is applied, a series of electric sparks are generated in the narrow gap between the electrode and the workpiece. The localized high temperatures generated by these sparks cause material corrosion.
Experts use different names for EDM processes, such as die EDM, wire cutting, spark machining, spark etching, and wire burning. This technology is mainly used to manufacture precision parts; it is chosen because these applications cannot withstand the stress generated by conventional cutting forces, making EDM particularly suitable.
working principle of Sinker EDM (electrical discharge machining)
The process begins by immersing the workpiece in a dielectric fluid bath equipped with a circulation and filtration system. A servo mechanism supports a custom-designed tool, shaped like a CNC machine tool, which is the positive image of the cavity. One pole of the pulse power supply is connected to the tool electrode, and the other to the workpiece electrode, both immersed in a liquid medium with a certain degree of insulation. The tool electrode is controlled by an automatic feed regulator to ensure that a very small discharge gap (0.01–0.05 mm) is maintained between the tool and the workpiece during normal machining. When a pulse voltage is applied between the two poles, it breaks down the liquid medium at the closest point between the poles under the given conditions, forming a discharge channel. Due to the small cross-sectional area of the channel and the extremely short discharge time, the energy is highly concentrated (10–107 W/mm). The instantaneous high temperature generated in the discharge area is sufficient to melt or even evaporate the material, resulting in a small pit. After the first pulse discharge ends, a second pulse breaks down the liquid medium at the closest point between the poles after a very short interval. This cycle repeats at a high frequency, with the tool electrode continuously feeding towards the workpiece, and its shape is eventually replicated on the workpiece to form the desired machined surface. At the same time, a small portion of the total energy is also released onto the tool electrode, resulting in tool wear.
Key components of an EDM system
Based on its working principle, we can conclude that a high-efficiency electrical discharge machining system basically includes the following core components:
| power supply | Provide the necessary electrical energy to erode the material on the workpiece. |
| electrode | This typically involves conductive materials such as copper or graphite, used to form complex shapes within the workpiece. |
| Dielectric fluid | It is used as a coolant for the system and helps to push the material being eroded away from the processing area. |
| Control Unit | Managing the movement of machine parts and the precise release of electrical discharges. |
| Working slot | This component houses the workpiece and dielectric fluid, ensuring that the system accurately processes raw materials into the required output. |
| Flushing system | Provides a constant dielectric fluid flow to the EDM system, cools other components, and supports proper removal of erosion particles. |
| Servo Control System | Maintaining and adjusting the gap between the electrode and the workpiece allows for the management of the spark generation process. |
| Workpiece clamps and fixtures | It helps to hold the workpiece in place throughout the entire processing, ensuring its stability and thus achieving high-efficiency precision of the electrode. |
Features of Sinker EDM
Electrical discharge machining (EDM), as a precision machining technology, plays a vital role in modern industrial production due to its unique machining principles and wide range of applications. With continuous technological advancements, EDM technology is constantly developing and improving. The following are the characteristics of this manufacturing technology.
High-precision machining
Electrical discharge machining (EDM) can achieve micron-level machining precision. This is because the discharge process is localized and instantaneous, removing a very small amount of material with each discharge, allowing for precise control of the machining dimensions. This process is unaffected by material hardness and can easily handle some high-hardness materials that are difficult to machine using traditional methods, such as cemented carbide and titanium alloys.
Complex shape processing
Electrical discharge machining (EDM) can produce parts with various complex shapes, such as deep holes, narrow slots, and irregular curved surfaces. This is because the tool electrode can be customized according to the shape of the part, and the movement trajectory of the electrode is controlled by a CNC system to achieve the machining of complex shapes.
Machining without cutting force
Electrical discharge machining (EDM) is a non-contact machining method that does not involve cutting forces. This is highly advantageous for machining thin-walled or easily deformable parts, as it avoids deformation caused by cutting forces and ensures machining accuracy.
What are overcut, tool wear, and material removal rate in Sinker EDM?
Based on the working principle and characteristics of electrical discharge machining, we can gain a deeper understanding of the technical details of this process, including overcutting, tool wear, and material removal rate.
Overcutting in electrical discharge machining
In electrical discharge machining (EDM), overcutting refers to the extent to which the workpiece cavity extends beyond the electrode dimensions. This is because the discharge and material erosion processes also occur on the tool side. However, the degree of overcutting is extremely small (only one-hundredth of a millimeter) and is fully considered during tool design.
Tool wear
Tool wear is an inherent component of electrical discharge machining (EDM). The high temperatures of melting the workpiece also wear the electrode, but to a lesser extent. Electrode wear is measured as the ratio of workpiece material removed to tool material removed.
Material removal rate
The material removal rate (RMR) in electrical discharge machining (EDM) is controlled by two parameters: discharge current and frequency. Higher discharge current and frequency increase the cutting rate. To obtain the optimal surface finish, a higher frequency and a lower discharge current should be used. Mathematically, RMR is a function of current and the melting point of the material. The calculation formula is: RMR (mm³/s) = K × I / Tm (where k is a proportionality constant, 664 in SI units, I is the supply current, and Tm is the melting point of the workpiece).
Does Sinker EDM alter the surface structure of a workpiece?
Electrical discharge machining (EDM) alters not only the workpiece surface but also its subsurface. The resulting workpiece surface structure consists of three layers. The EDM impact layer is formed by the impact of ejected molten metal and a small amount of electrode particles. This layer is easily removed.
The next layer is the hard layer (oxide layer). Electrical discharge machining (EDM) fundamentally alters the metallurgical structure and properties of this hard layer. Under the influence of the oil medium, the molten metal cools rapidly, and any molten metal that is not ejected solidifies in the cavity, forming the hard layer. This hard and brittle oxide layer is prone to microcracks. If this layer is too thick, or cannot be thinned or removed by polishing, the workpiece may fail prematurely under certain operating conditions.
The final layer is the heat-treated/annealed layer. It is only heated, not melted. The thickness of the hardened layer and the heat-treated layer is determined by the heat dissipation capacity of the workpiece material and the processing energy. In any case, altered metal layers will affect the original properties of the workpiece surface.
Ideal electrode material for Sinker EDM (electrical discharge machining)
In electrical discharge machining (EDM), you need to select materials for two components: the electrode and the workpiece. Electrodes are typically made of materials with high strength, high temperature resistance, and wear resistance. Commonly used materials include the following.
| graphite | Due to its high strength, high temperature resistance, and wear resistance, it is the preferred electrode. It also provides a cleaning effect at low speeds and is economical and efficient. |
| brass | Copper and zinc alloys are used for electrical discharge wires and small tubular electrodes. They are easier to process than copper or tungsten, but have poorer wear resistance. |
| Copper and copper alloys | It is more wear-resistant and has better electrical conductivity than brass. It is more difficult to process and more expensive than graphite. It is commonly used in the processing of tungsten carbide or for precision machining. |
| molybdenum | It possesses high tensile strength and excellent electrical conductivity. It is ideal for manufacturing electrical discharge wires, especially suitable for small slot machining and applications requiring small corner radii. |
| Tellurium copper | Suitable for electrical discharge machining (EDM) requiring fine surface treatment. Its machinability is similar to that of brass and superior to that of pure copper. |
Advantages and limitations of Sinker EDM
| advantage | shortcoming |
| It can cut all conductive metals into the desired shape. | Fragile workpieces at room temperature may face surface cracking. |
| Polishing is not required after the process is completed. | The main limitation is that sharp corners can be reproduced. |
| No burrs will be formed during processing. | It cannot process non-conductive metals. |
| It can effectively create small holes | Unable to perform contouring processing of complex outlines. |
| with other machining processes, the processing time is longer. | electrode tools are required. |
| No mechanical stress is generated during the processing. | Electrodes and cutting tools wear out very quickly. |
| It can precisely process complex shapes. | The metal removal rate is very low. |
| No deformation occurs when machining slender, fragile workpieces. | |
| It helps to form a corrosion-resistant and hard surface on precision parts. | |
| It can process extremely hard materials and workpieces. | |
| Tolerances within the range of +/-0.005 can be achieved. |
Which industries most commonly use Sinker EDM?
Sinker EDM is widely used in many industries due to its exceptional precision. The following examples illustrate the importance of achieving precision across different types of applications where no other method can provide the same level of accuracy and quality as finishing.
- Mold making: Widely used in the production of injection molds, die casting, and other molding processes.
- Aerospace: Used for machining complex parts with tight tolerances, such as turbine blades, engine components, and fuel system parts.
- Medical devices: Used to manufacture precision components such as surgical instruments, implants, and medical equipment.
- Semiconductor industry: Used to create microstructures and precise features in semiconductor wafers and other components.
- Tool and mold making: Used to manufacture precision molds, dies, and other tool components.
Sinker EDM Equipment Procurement Recommendations
When purchasing Sinker EDM devices, please be sure to choose a reputable manufacturer with excellent customer support. Below are three brands recommended by Xtproto:
- Mitsubishi: In the electrical discharge machining (EDM) industry, Mitsubishi is a well-known and trusted brand. Mitsubishi EDM machines utilize artificial intelligence technology, boast a high degree of automation, adaptive functions, and a fully enclosed design for enhanced safety. Mitsubishi EDM machines are available in five product series: SV-P series, SG series, EA-S series, EA-V series, and EA series.
- GF Machining Solutions: GF Machining Solutions (formerly Agie Charmilles) is renowned for its high-performance machine tools. Its mold-making division offers four series: the X series for extremely high precision, the P series for increased productivity, the S series for micro-contour machining, and the economical E series.
- Makino: Makino’s EDM machines are renowned for their innovative technology, delivering high precision and surface quality. Like GF Machining, Makino offers a wide range of EDM machines, from small (EDAC series) to large (EDNC series).
Choose Sinker EDM service from Xtproto
You can choose external EDM services without investing in high-cost machinery, especially suitable for specific or one-off projects. Xtproto is a one-stop CNC machining solution provider for your diverse manufacturing needs. We offer advanced EDM services tailored to industries demanding precision cuts. Whether you’re in the prototyping stage, need small-batch testing, or require high-volume production, we can meet the needs of all types of businesses. Send your project to Xtproto’s engineering team now and get an instant quote and free DFM analysis from our experienced engineering support team.
in conclusion
Sinker EDM is a manufacturing technology capable of producing complex and precise part features. It can process materials of varying hardness, especially features that cannot be manufactured using conventional CNC machining. Its advantages lie in its extremely high precision and the fact that it does not create stress on the material during removal. This makes it ideal for custom tooling, mold making, and the manufacture of high-precision parts. If you are looking for Sinker EDM services, whether for rapid prototyping, mass production, or small-batch manufacturing, please contact Xtproto immediately for rapid support from industry experts.