Electrical Discharge Machining: Principle and Manufacturing Applications

EDM or electric discharge machining is a machining technique that makes parts without the need for direct contact with the workpiece. It erodes the surface of conductive materials through the use of electricity. EDM can maintain good surface finishes even on complex and sensitive items since no EDM tool makes physical contact with the workpiece.

The method is divided into subtypes for drilling, wire, and die. EDM facilitates the manufacture of different parts and components, including die molds and medical equipment like pacemakers, as well as hip and knee implants.

In this article, we’ll discuss electrical discharge machining, how it works, the types of materials used for the process, and when to use it for manufacturing. Do read on.

What’s Electrical Discharge Machining (EDM)?

So, what is EDM machining? It is an alternative machining technique used for making parts that would be difficult to make using traditional machining practices. It is important to note that it only works on conductive metals. The process involves the use of electricity to erode the surface of a workpiece. There is usually no contact between the tool used during the cutting process and the workpiece, thus guaranteeing that parts produced using this process have the best surface finish.

While the process might seem modern, it is not, EDM was first discovered in 1770 by a British physicist called Joseph Priestley. He discovered that electrical discharges can have a corrosive effect. Nonetheless in the 1940s a pair of soviet scientists B.R Lazarenko and N. I Lazarenko recognized as the inventors of EDM were able to modify Priestley’s discovery by controlling the corrosive effects of the electrical discharges on metal. They did so by introducing conductors and a dielectric liquid.

In the 1960s wire EDM was developed and the first wire EDM machine was launched in the Soviet Union in 1967. Since then, the EDM process has become more robust and advanced.

The major purpose of the EDM process is that it facilitates the creation of parts with delicate or thin walls. Parts that risk damage when machined using traditional methods. It is a contactless technique that guarantees high precision and a seamless surface finish.

How EDM Machining Works

Another popular question is; How does EDM work? Well, to kick start the process, a soft electrode made of graphite creates a spark between the electrode and the target area. The spark created usually has a temperature ranging between 14,500 and 21,500 ºF and when it occurs, it vaporizes or cuts part of the workpiece. After the cut/ vaporization, a dielectric fluid, which is another component of the system, carries the vaporized part away from the already machined region of the workpiece. This occurs repeatedly until the part is completely machined.

EDM engineering can machine most materials that conduct electricity flawlessly, aside from premium nickel often used in aircraft manufacture. However, with the aid of specific electrodes, the EDM technique can be great for machining parts using this material.

Key Components of EDM Machines

There are several key components of EDM machines, each playing a specific role in ensuring the production of parts that are precise and accurate.

Power Supply

Power Supply powers the entire system. It supplies the spark necessary to erode the workpiece. This component also helps regulate the voltage, current, and frequency of electricity supplied to the system. The regulation is based on the properties of the job at hand. In EDM, the power supply has to be optimal, as it runs the whole process.

Electrode

The electrodes integrated into this system boast exceptional conductivity. When positioned near the workpiece, they are designed to initiate a spark effectively. In an EDM system, common materials for electrodes include graphite, copper, tungsten, brass, and various metal alloys. The specific choice of electrode material typically depends on the EDM application, whether for wire, die, or tube processes. Notably, during the EDM operation, the electrode maintains a gap from the workpiece, ensuring there is no direct contact.

Dielectric System

The dielectric system serves as the fluid component in an EDM setup, consisting of non-conductive lubricating oil or deionized water. This fluid plays a critical role, not only by cooling the system but also by removing eroded materials from the machining zones. Without an effective dielectric system, these particles could migrate toward the electrode, potentially bonding with it and damaging the tool. Therefore, it is crucial to maintain a constant circulation of the dielectric fluid. Additionally, this system is essential for preventing untimely sparks during the machining process.

Servo Control System

The primary role of the servo control system in an EDM setup is to manage the gap between the electrode and the workpiece, enhancing the efficiency of spark generation. Beyond just spatial adjustments, this system is pivotal in regulating the actual spark production during the EDM manufacturing process.

Control Panel

This component is one of the most important parts of an EDM system. It manages the movement of parts, as well as the timing of electrical discharge. The control panel also makes sure EDM cuts are more accurate and precise.

Three Types of EDM

There are three major types of EDM. These different methods cater to a wide range of conductive materials, and they include:

Die-sinking EDM

Sometimes referred to as “ram” or “cavity” EDM, die-sinking EDM operates by utilizing discharge from an essentially 2D electrode. An intricate three-dimensional end to this two-dimensional electrode can be elevated a short distance on the Z-axis to remove debris and repeatedly descend to arc erode into the work. The electrode in question has a complicated end form devoid of undercuts and can take on any cross-sectional shape. To erode the correct cavity form into hard materials, the sinker type requires precision EDM machining of copper and/or graphite electrodes.

Furthermore, using sinker EDM machining reduces the need for post-processing to enhance surface quality or harden it. It is perfect for fabricating dies and molds because of its ability to create deep ribs and sharp inside corners.

Wire EDM

Known as wire-cut EDM, this process erodes material by sparking between the wire and the workpiece, using a wire as the “cutter.” Wire EDM uses a very thin wire usually around 0.05mm to 0.35mm in diameter for its operation. This type of EDM finds application in the production of automotive and aerospace parts, blanking punches, and extrusion dies, as well as medical and dental devices.

In the EDM cutting process, the wire electrode passes through and discharges along the entire length of a cut. Though its complexity has increased, the technology was originally designed to conduct 2D cuts in hard materials—in other words, cuts that could only be made along a part’s X and Y axes, with the material’s thickness measured along the Z-axis.

It was feasible to make cuts at a regulated angle to the Z-axis by offsetting the wire rollers from one another. Subsequently, the wire EDM method also allowed for the addition of a rotational axis, leading to the creation of extremely powerful 5-axial wire EDM centers.

It is important to note that wire EDM cannot be used for machining blind cavities, only through cavities. Using this type of EDM wire guide attached to the top and bottom of the machine is important as it helps ensure the accuracy of the machine’s movement.

Also, the guides are mobile and can move up and down depending on the height of the workpiece. Another point to note is that any workpiece the wire EDM cuts must have a through-hole, which acts as the starting point as the wire used during the process has to go through this hole before cutting commences. The act of passing the wire through the hole in the workpiece is known as threading. Wire EDM is best for producing automotive and aerospace parts as well as blank punches and extrusion dies.

Hole-drilling EDM

Hole drilling is a vital tool in many industries, including the aerospace, medical, technological, and scientific industries. This is because it presents the only method for cutting long, straight, tiny boreholes. A hole that perfectly reflects the tool’s profile is eroded using a straight electrode. One merit of hole-drilling EDM is that it keeps exact dimensional correctness the whole way through the hole. This technique is ideal for making start holes in wire EDM cutting, removing broken taps and drills in machinery, and creating cooling channels in turbine blades.

This technique can produce straight holes of any depth and with a diameter of 0.0015″ or more, even with small diameters and high aspect ratios. An EDM drill machine makes it possible to drill both blind and through-holes, with smooth walls, in materials that would otherwise be impossible to deal with. Holes made using hole drilling EDM have a smooth enough surface finish right out of the machine to be used as bearing surfaces without further post-processing.

Which EDM Type is Suitable for Parts with Complex Cavities?

Sinker discharge machining is the most effective EDM method for producing parts with complex or intricate cavities. This is because it is more appropriate for drilling, deburring, finishing, 3D contouring, and other machining processes. Sinker EDM is particularly ideal for making parts that cannot be produced using conventional machining techniques, as its ability to cut through a material is not affected by the material’s hardness. Its cutting ability makes sinker EDM the go-to method for working on parts with complex internal features like cavities and pockets.

Conductive Materials for the EDM Process

Almost any conductive material can be machined using electric discharge machining without too many difficulties. Materials that are not conductive, such as composites, glass, ceramics, plastics, and wood, cannot be worked with by EDM. The substance of the workpiece must carry electricity since it is a component of the spark’s circuit. Materials suitable for EDM machining include:

Brass

Brass is an alloy of copper and zinc, used widely in EDM due to its excellent conduction of electricity. It is also resistant to wear and tear, and easy to machine, making it the go-to metal for EDM.

In wire EDM brass wires could act as the electrode used to cut complex geometries into a workpiece. Brass finds use in wire EDM due to its efficient spark generation, ability to maintain good tensile strength, and ability to produce parts with a smooth surface.

In die sinking, where the shape of the electrode determines the shape of the machined part, brass electrodes offer the added advantage of detailed work. This is due to their high machinability, which facilitates the creation of parts with a high degree of intricacy.

In drilling EDM systems that involve making small holes using tubular electrodes, brass’s ease of fabrication and high conductivity make it ideal for use with these tubes. Its good thermal conductivity also facilitates effective heat removal and debris evacuation, making the drilling process cleaner and more efficient.

Aluminum

Aluminum is one of the most abundant metals on earth. However, it is quite difficult to machine using traditional machining techniques. The difficulty of this process is due to its deformation upon exposure to frictional heat. However since EDM is a non-contact method, this heat does not occur, consequently maintaining the structural integrity of the material.

This material finds use in wire EDM for machining fine details and complex geometries. When used in die sinking, aluminum acts as both the workpiece material and electrode. Its high thermal conductivity facilitates efficient heat removal, ensuring minimal heat damage during the EDM process. Aluminum is also very easy to erode, which results in efficient material removal and the creation of parts with intricate and complex geometries.

In drilling EDM, aluminum finds use in the production of small holes with high precision. Its excellent heat and electrical attributes make drilling very efficient.

Steel

Steel is very hard, and this poses a challenge to conventional machining, as it often causes tool wear and tear. But when machining steel using EDM, its hardness is no longer a challenge since the process easily machines materials with precision EDM and accuracy regardless of toughness.

Steel’s excellent mechanical properties and availability make it ideal for use in EDM. Wire EDM is often used to machine steel due to the metal’s ability to achieve tight tolerances while maintaining dimensional stability. Its high melting point allows for the creation of parts with excellent surface finishes and intricate details.

Steel’s hardness and strength make it ideal for use in die-sinking EDM as it facilitates the creation of molds and dies that are durable. It also finds use as an electrode during the process, but only when specific thermal properties are needed.

Copper

Copper is an extremely ductile metal that conducts electricity excellently. Nonetheless, it is difficult to machine due to its low hardness. But with EDM, it becomes possible to machine intricate parts from copper without compromising its quality or conductivity. In wire EDM, copper guarantees efficient spark generation, which results in accurate cuts. Their resistance to wear makes them perfect for use in Die-sinking EDM where they find use in the production of dies and molds. Copper electrodes dissipate heat effectively, making them perfect for use in drilling EDM where clean and precise holes are important.

Nickel

Nickle is quite difficult to machine using conventional means due to its resistance to high temperatures and corrosion. Nonetheless, EDM cuts through nickel easily, creating parts that are highly intricate and precise. Nickel is a hard material, and when used in wire EDM, it helps in cutting other materials that are hard and heat-resistant. Also, the durability of the material gives it application in die-sinking as it facilitates the creation of parts with intricate details.

Tungsten

Tungsten has a high melting point and hardness, which makes machining it with traditional methods difficult. But with EDM’s ability to machine very hard materials, making parts from tungsten becomes easy as EDM does not induce heat stress on the material. Tungsten’s ability to maintain stability even at high temperatures makes it perfect for use in die-sinking EDM for the production of molds and dies that are wear-resistant.

When to Choose EDM Machining

EDM performs a variety of tasks, such as drilling long or fine holes in any metal, extracting precise 2D shapes from difficult-to-work materials, and creating complex cavity shapes, which are essentially 3D relief shapes cut into the bottom face of 2D blind cavities. One can also use EDM for cutting extrusions, rotary forms, and sharp internal corners. Looking to engrave on a hard material like tungsten? EDM is also ideal. It is important to note that with virtually no tension applied to the workpiece, EDM can create flawlessly finished one-step drilled holes in any cross-section.

Advantages and Limitations of EDM

Benefits of Using EDM

Typically, EDM is used to machine pieces that traditional machining methods are not able to produce. The following are a few benefits of EDM:

Design Freedom and Flexibility

EDM allows the creation of complex and intricate geometries of materials that are difficult to machine using conventional machining techniques. It also easily machines hard materials, such as tungsten and nickel, that conventional methods and machines find difficult or impossible to work on efficiently. Not only does it machine these materials, it does so efficiently, allowing machinists to make parts with intricate features using these materials.

Deformation-Free Parts

In EDM cutting tools do not make direct contact with the workpiece being machined, thus limiting the tendency for distortion as there is no frictional force acting it. The lack of contact ensures there are no distortions or breaks, especially when machining parts with extremely thin features.

Efficient Machining Regardless of Material Hardness

Machining tough materials like tungsten and carbide using conventional machining gives machinists a lot of problems, as it involves a lot of tool replacements and incorrectly machined parts. But with EDM machining components, using these materials becomes easier, as all it requires is the passage of an electric charge.

High Accuracy and Precision

This process produces parts accurately and with higher precision than conventional machining. EDM is a contactless process that cuts parts using electrical pulses. Being contactless, there is zero risk of mechanical deformity due to contact with the cutting tool, which increases the accuracy of the process. The high accuracy of this machining method makes it applicable in the automotive and aerospace industries, where extreme precision is important.

High-Quality Surface Finish

Post-machining finishing is necessary to eliminate the machining marks left on the workpiece by conventional machining techniques. Due to EDM’s zero-directionality about surface smoothness, consistently smooth surfaces can be achieved without the need for additional attention. However, it is important to note that a faint bead blast-like texture may remain after rapid EDM processing.

Limitations and Challenges

With all its benefits, there are some limitations experienced when working with EDM. These limitations include:

Less Versatility in Materials Machined

The prerequisite for materials to be machined using this process is electrical conductivity. This requirement excludes non-conductive materials, thereby restricting the range of materials suitable for this machining method. Although the process is generally considered to be stress-free, it’s crucial to acknowledge that the heat generated can still modify the metallurgical properties of the workpiece.

Time-Consuming Process

When compared to the material removal rate of conventional machining processes, the removal rate of EDM is poor. Also, due to the high power consumption of the production process, longer manufacturing times raise overall costs. Because of this, EDM is not a useful technique for undertaking large-scale projects, and as such, it is frequently ignored in favor of other methods.

Cost of Purchasing an Electrode

Die-sinking EDM requires a unique electrode that is the opposite of the feature, and this type of electrode is expensive. Nonetheless, it is important to note that machining with an electrode may seem costly at low manufacturing levels, but at larger volumes, the extra expense can spread over a larger number of components.

Higher Carbon Footprint

EDM is not an environmentally friendly form of machining because of the amount of electricity needed for it to function, which results in a higher carbon footprint. Other machining techniques that do not use up as much electricity are often preferred over EDM as they do not degrade the environment as much.

Specific Industries and Examples of EDM in Manufacturing

EDM is a versatile machining process used by a diverse range of industries. These industries use EDM due to its high precision in making EDM parts. These industries include:

Medical Industry

EDM is a critical technology in the medical sector, known for its high precision and accuracy—essential attributes for manufacturing medical devices where even slight deviations can have serious consequences. This technique produces intricate components such as cochlear implants, pacemakers, and neurostimulators. Additionally, EDM plays a significant role in dental manufacturing, crafting precise parts like abutments, crowns, and bridges, which are vital for patient care and treatment outcomes.

Aerospace Industry

EDM is invaluable in the aerospace sector for its capability to fabricate parts with complex geometries that are critical for aircraft construction. Dimensional precision is crucial for maintaining the balance and performance of aircraft, and EDM provides this level of exactitude reliably. This technology produces various aerospace components, including stator vanes, turbine discs, and compressor discs. Besides, it is instrumental in manufacturing landing gear components, fuel system parts, dies, aero blades, and metallic molds, all of which are essential for the safe and efficient operation of aerospace vehicles.

Manufacturing Industry

The manufacturing industry values part precision, which is why EDM is the go-to process for making parts in this industry. EDM in the manufacturing sector helps create plastic die molds, extrusion dies, and die sinking. It also facilitates the production of gears, threads, and other intricate machinery parts.

Electronics Industry

Electronic parts have to fit to function optimally, this is especially true for the parts that conduct electricity. This makes the electronics industry one of the major beneficiaries of EDM since the technique only deals with conductive metals. EDM facilitates the production of connectors, sensors, and switches used in this industry. It also produces components such as electrodes, dies, and masks.

EDM vs Traditional Machining Process

While both EDM and traditional machining processes facilitate the production of parts, they differ considerably from each other. The difference between them lies in their mode of operation. For instance, while EDM uses electrical sparks to cut through materials, conventional machining requires the use of a cutting tool, that has to make contact with the material. When these cutting tools cut through the workpiece, it creates heat as a result of the friction between materials, which could result in part deformation and consequent reduction in accuracy.

Besides, EDM parts are more dimensionally accurate, which is why most industries use them for fabricating parts. This higher dimensional accuracy is because the process is contactless, which reduces the risk of deformity and surface imperfections.

The no-contact cutting used by EDM ensures products have a better surface finish and dimensional stability than those made using conventional methods. Nonetheless, it is important to note that conventional machining methods are quicker, more versatile in materials machined, and often less expensive than EDM.

Cost Considerations When Choosing Electrical Discharge Machining

When deciding whether to choose EDM for your machining, here are some cost considerations to keep in mind:

Machine Investment

The initial investment into a machine is on the high side for EDM machinery. This is particularly true for more advanced models. So, keep this in mind when considering EDM machines for making your parts. The cost of the machine makes EDM impractical for short production runs, as it would impact the cost of production greatly.

Operational Costs

Operational cost goes a long way in determining the total cost of production and, by extension, product profitability. The operational costs of EDM are quite high because the technique involves the use of different components such as electrodes, wires, and dielectric fluid. Also, the process runs purely on electricity, and the energy consumed adds to the overall operational costs.

Material Costs

Material costs impact production costs greatly, as the higher the material consumed, the higher the cost of production. Since there is minimal material waste when machining using EDM, the material cost is lower than that incurred when machining traditionally. The lower material costs also translate to lower operational costs.

Machine Maintenance and Upkeep

As with every machine, routine maintenance is important when using EDM too. Also, remember that the higher the frequency of maintenance, the higher the production costs. Nonetheless, it is important to carry out routine maintenance on the EDM machine to ensure its optimal accuracy and effectiveness.

Labor Costs

Acquiring the services of skilled labor costs more, depending on the qualifications of the laborer. EDM machines are complex to operate and often require the services of an expert EDM operator, which would impact operational costs. It is also important to note that the exact labor cost often depends on the EDM technology’s complexity.

Productivity and Turnaround Time

With EDM, it is possible to manufacture complex and intricate parts in a single setup as opposed to traditional machining, where multiple setups are necessary. This considerably increases productivity and turnaround time, reducing the time spent making parts and, by extension enhancing time to market. However, it is best to remember that EDM machines are slower than their CNC counterparts.

Tool Replacement and Design

Replacing worn-out tools costs money and when done frequently, impacts operational and total production costs. EDM cutting tools wear down at a substantially lower rate than their traditional machining counterparts. This helps save money on tool replacement and repairs and also improves the accuracy of parts.

Choosing the Right EDM Services

When choosing the right EDM service provider, it is best to look for providers with experience in the industry. Go for a service that provides different EDM techniques like sinker, wire, and hole drilling. It is also best to verify their machining capabilities, comparing their EDM equipment to the size and complexity of your project.

Also, when choosing an EDM service for your needs, consider communication as it is essential to make sure your parts get to you when they are due. Then consider their pricing about other service providers as well as turnaround time.

Conclusion

EDM is a productive machining technique that makes it easier to produce highly accurate products. We discussed its benefits, which include high precision and quality surface finish, as well as its limitations, which include material versatility, speed, and cost of manufacturing. This article also touched on the different types of EDM technologies, including hole drilling, sinker, and wire, and delved into the sinker EDM vs. wire EDM debate, ensuring you make informed decisions when picking one for your needs.

Looking to make parts using EDM? Then RapidDirect is just the company for you. We are a versatile manufacturing company offering a comprehensive range of services, including EDM, CNC machining, sheet metal fabrication, 3D printing, and more. Regardless of your production scale, whether prototyping, small-scale, or large-scale manufacturing, we guarantee high-quality parts with one of the fastest lead times in the industry.

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