Electrical discharge machining
Electrical discharge machining, also refer as EDM, is a non-convention form of machining. It uses electrical sparks and erodes the material from designated are to shape the workpiece.
It is normally employed for shaping conductive and hard materials. However, on special consideration, EDM can work with non-conductive materials, such as composite and ceramics. It can create complicated shapes and contours, which are not possible with CNC milling & turning. This article will discuss the workings of EDM, its types, advantages, and applications in detail.
What is Electrical Discharge Machining (EDM)?
Like the laser cutting technique, EDM is a non-contact subtractive manufacturing approach. It utilizes thermal energy (concentrated sparks) to cut, engrave, and shape the material generated by electrical discharging. It is based on a scientific discovery made in the 18th century, the erosion effects of electrical discharge. Then, in the 1960s, the EDM process underwent additional development. Since then, it has undergone a tremendous change (B.M. Schumacher, 2013).
The EDM process manipulates the erosion on a designated workpiece’s area with electrical discharging to create required cuts and shapes. Spark causes the local melting or vapourization of material and removes it from the workpiece. The limit of EDM is far beyond other traditional manufacturing processes in terms of small-cuts capability.
How Does Electrical Discharge Machining (EDM) Work?
The working principle of an EDM process involves creating a series of electrical discharges (sparks) between two electrodes, one is the shaping tool, and another is the workpiece itself. The sparks come from the contact of two electrodes eroding material from the workpiece and creating an intended form or shape.
Working in EDM (Ved Prakash, 2018)
Step 1: Arrangement of dielectric medium with electrode and workpiece.
The workpiece and electrode are placed in a dielectric fluid, usually kerosene or deionized water. Generally, the electrode (or shaping tool) is connected to a negative terminal and the workpiece to a positive power source terminal. As previously mentioned, it is a non-contact manufacturing approach; the gap between the shaping tool and workpiece with the dielectric medium is maintained.
Step2: Introduction of current
A high-voltage power supply generates the current between the workpiece and the electrode. As the electrical current passes through the dielectric medium, it ionizes the fluid and creates a plasma channel. The collision between electrons from the electrode (shaping tool) and dielectric medium molecules is responsible for the ionization of fluid.
Step3: Plasma channel and erosion
The ionization generates a plasma channel that creates a series of sparks or electrical discharges. These sparks erode material from the workpiece and create the desired shape or form, while dielectric liquid flushes away the eroded material. This process is repeated, and erosion occurs continuously until the desired shape or form is achieved.
The correct positioning of the workpiece and shaping tool is essential for a precise result. Therefore, positioning with computer numerical control (CNC) equipment is very accurate because it allows for precise control over the shape and location of the machined features.
Types of Electrical Discharge Machining
Sinker, wire, and drilling EDM
EDM is cutting-edge manufacturing technology. There are several ways to cut and shape conductive materials using the EDM principle. Based on electrode shape and specific process, EDM can be categorized into four types;
- Wire EDM
- Die or sinker EDM
- Hole Drilling EDM
- Rotatory EDM
1. Wire EDM
As the name suggested, wire EDM uses a hair-thin, wire-shaped electrode to cut and shape the workpiece. Cooper, brass, or tungsten wire are popular wire materials. The standard diameter of the wire is 0.25mm. Although, it can range from 0.020 to 0.15 mm, depending on part features, such as corner radii, slot widths, and thin-wall (Devin Wendorf, 2009).
When the current passes to the wire, it creates a spark and erodes the targeted area through the ionization of the dielectric fluid. It can create micro-level shapes, such as needles and stents. Additionally, wire EDM is also useful in creating molds and dies. The capability of manufacturing tiny shapes with great detail and accuracy makes wire EDM a unique process in manufacturing.
Prolean’s Wire EDM workshop
2. Plunge or Sinker EDM
The Sinker EDM refers to the machining process that involves an electrode with a negative shape of desired geometry. While applying the electrode onto the workpiece generates the negative version of the original geometry. Therefore, sinker EDM is also called die EDM.
It is especially used in creating complex cavities and addresses the sharp internal corner issue with CNC machining. Sinker or Die EDM is widely used in manufacturing die casting or injection molding devices, which is not accurate with CNC machining operation. It has the ability to micro-machine mold cavities with extremely fine details without applying no machining or impact stress on the mold.
Besides die and mold making, Sinker EDM is applicable in producing intricate and delicate parts, such as those used in the aerospace, medical, and electronics industries. Since sinker EDM can create a very smooth surface finish on the workpiece, it is frequently employed as a finishing technique along with other manufacturing approaches, such as CNC milling.
3. Hole Drilling EDM
The Hole drilling EDM is a specialized EDM process that creates very small holes with high accuracy. The wire EDM technique utilizes an electrically charged wire as an electrode that creates the holes using a series of electrical discharges to the workpiece. Furthermore, the hole is typically drilled from both ends to ensure accuracy.
It can drill holes as small as 0.0650 mm in diameter and depths up to 1m. However, it depends on various factors, such as workpiece material, electrode material, current magnitude, and many more (Kuppan, 2008).
4. Rotatory EDM
Movement in rotatory EDM (About Rotatory EDM)
In the rotatory EDM process, an electrode is mounted on a rotary axis, which allows it to move in a circular path around the workpiece. The top wire portion of the wire EDM machine can move in the U and V directions. Due to this multi-axis machining process, various shapes can be machined (About Rotatory EDM).
What are the Advantages of Electrical Discharge Machining (EDM)?
EDM has several advantages in precise machining. It allows the creation of micro-level shapes with high accuracy and repeatability. The following are the key advantages of the EDM process;
- EDM creates parts with extremely tight tolerances and excellent surface finishes.
- It can produce parts with complex shapes and features.
- Hard materials like tungsten carbide, Inconel, cobalt chrome, and Stellite can be machined with EDM, which is difficult with traditional approaches.
- There is no risk of failure due to stress since it is a non-contact manufacturing approach.
- It can create very small-scale features, such as internal corners, tiny holes, engraving, and many more.
- It is cost-effective compared to traditional methods that require the use of diverse & expensive tooling.
Applications of Electrical Discharge Machining (EDM)
EDM’s precise micro-level machining capability makes it a suitable manufacturing technology for various industries. It applies in a simple tool-making process to advanced aerospace parts, whether for prototyping or full-scale production.
Parts created with EDM.
Automotive
The significant application of EDM in automotive is the manufacturing of fuel injectors. It requires extremely-precise holes and shapes, and EDM allows manufacturers to achieve the necessary levels of accuracy and finish. Other applications in automotive are internal threads, helical gear, engine components, and transmission parts.
Aerospace
EDM plays a significant role in the production of aircraft turbine blades because it enables the required levels of precision and polish. Additionally, it is commonly utilized to produce aerospace-grade fasteners like screws, bolts, and nuts that must adhere to strict dimensions and surface finish specifications. The Panels, wing components, nozzles, engine components, and structural parts are examples of further uses.
Medical
Micro-level precise machining is mandatory in medical products, and EDM addresses this issue for various medical equipment and implants.
- Surgical instruments, such as scalpels and forceps
- MRI machines and CT scanners
- Manufacturing or repair of molds for medical devices, such as catheters and stents.
- Dental implants and prosthetics
- Surgical needles
- Medical-grade tubes
Molding and Die Casting
Various injection molding and die-casting parts use EDM to create precise parts. Common applications include stamping dies, extrusion dies, precise cavities for molds, and repairing.
When to Use Electrical Discharge Machining (EDM)?
First, it is a go-to option when you have micro-level features in your parts, such as a hole with a diameter of 1 mm. It can create tiny features with extremely tight tolerances and an excellent surface finish. Following are the four scenarios where it is wise to choose the EDM process.
- When materials are extremely hard and difficult to process with traditional manufacturing, such as tungsten carbide.
- When you have complex shapes and need extremely tight tolerance.
- For thin or delicate parts that can be damaged or affected by cutting force.
- When you need to create complex internal features, such as holes and channels.
Conclusion
EDM process involves creating a series of electrical discharges between two electrodes that creates sparks and erode material from the workpiece to convert into desired shape or form. It can create various parts and features, making it a versatile manufacturing process.
Since most applications require micro-level machining, it is important to consider several factors for precise results. At Prolean, we have experts who have more than a decade of experience in EDM. If you are looking for any EDM service for your current or upcoming project, upload your design and request a quote.
FAQ’s
What is Electrical Discharge Machining (EDM)?
EDM is a non-conventional form of machining that uses electrical sparks to erode material from a designated position to cut and shape the workpiece.
What are the types of Electrical Discharge Machining?
EDM can be categorized into four types: Wire EDM, Die or sinker EDM, Hole Drilling EDM, and Rotatory EDM. Each of the EDM processes has its unique ability and applications.
What are the advantages of EDM?
EDM can create complicated shapes and contours that are impossible with traditional manufacturing processes like CNC milling and turning. Additionally, it can make small, precise features and work with hard materials without limitations.
What are the applications of EDM?
EDM is used in various industrial and manufacturing applications, particularly in the aerospace, automotive, die casting & mold, and medical device industries. It is a reliable option for the creation of small and complicated features.
Bibliography
- (n.d.). About Rotatory EDM. Relaiable EDM, from https://reliableedm.com/.
- M.Schumacher, R. J. (2013). Historical Phases of EDM Development Driven by the Dual Influence of “Market Pull” and “Science Push.” ELSEVIER.
- Devin Wendorf, M. M. (2009). Things to consider when wire. EDM notes, from https://www.xactedm.com/.
- Kuppan, P. (2008). Influence of EDM process parameters in deep hole drilling of Inconel 718. The International Journal of Advanced Manufacturing Technology.
- Ved Prakash, P. K. (2018). Surface alloying of miniature components by micro-electrical discharge process. ResearchGate.
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