Electrical discharge machining is innovative manufacturing technique different industries use to create custom parts. It utilizes electrical discharges instead of mechanical force to cut/erode excess material from a workpiece to form the desired shape.
Manufacturers in various industries often turn to EDM machining processes when traditional methods like CNC turning and milling fail to achieve preferred features. It helps create features like deep hollows, sharp internal corners, and many more.
The EDM machining process is highly compatible with various electrically conducting materials. Thus, this process delivers high-accuracy cuts.
This article discusses the EDM process, its working principle, and the basic construction of an electrical discharge machining system. You will also learn the advantages and applications of the process to help you decide if it’s the best choice for your projects.
What Does EDM Manufacturing Mean?
EDM manufacturing is a subtractive technique that extracts excess material from a workpiece using electrical discharges.
The electrical discharges transform into thermal energy that melts workpiece material. EDM uses this surface eroding to make desirable shapes out of the material. It is a perfect alternative to choose whenever all conventional manufacturing processes have reached their limits.
EDM is a highly specialized process that does not use a tool on the raw workpiece. Moreover, it is the best option whenever you need to fabricate hard materials like titanium, Inconel, and tungsten carbide and complex structures.
Most manufacturers refer to EDM as spark machining due to its use of electrical discharges.
EDM Working Principles
Although the definition of EDM seems straightforward, its physical procedure is a bit complicated. Electrical discharge machine working principles involve repeating discharges of currents/sparks between electrodes. The machining EDM process comprises two main electrodes – the workpiece and the pole head.
The workpiece is connected to the positive side of the charge (anode), while the tool electrode takes the negative terminal (cathode). A white-hot electrical spark leaps from the electrode to the workpiece when near due to its high potential difference.
This close contact generates extreme temperatures between 8,000 and 12,000 degrees Celsius in the spark gap, causing the conductive material to melt and erode.
Machinists often use insulating or dielectric fluid because of the high temperatures that occur during the EDM machining process. The workpiece and the electrode are submerged in the dielectric liquid throughout the process.
The dielectric fluid dictates the electric spark, acting as the coolant and a flushing mechanism for washing off tiny particles eroded in the process.
Also, it would help to note that the whole metal-removal process is fully automated with no personnel involvement. You can generate the process for a part automatically using 3D CAD programs.
Components of the EDM System
This section discusses the basic structure of an electrical discharge system:
DC Pulse Generator
It is a primary component of the EDM system. This component is responsible for converting the AC power supply to an active DC supply high enough to create a spark between the workpiece and the eroding tool.
Generally, this tool remains linked to the cathode and. At the same time, it is mounted on the tool post. The electrode tool and the component maintain a very tiny gap /arc gap between them. Suitable electrode materials include cast iron, copper, steel, graphite, and Tungsten alloy.
Servo Motor Mechanism
The servo motor mechanism is another component in the electrical discharge system to guide the tool’s feed and movement. Likewise, this mechanism helps to automatically maintain the accurate arc gap of about the thickness of a human hair (± 20 microns) between the tool electrode and the workpiece electrode.
The servo mechanism moves the electrode into the workpiece. It also helps detect the work-wire spacing and regulate it to maintain the proper arc gap. This is crucial to the success of the machining operation.
This component produces the adequate voltage required for spark creation and discharge maintenance. It can generate one hundred thousand sparks per second. This ability helps to remove significant amount material needed from the workpiece.
This fluid flows in at the gap between the electrode and the workpiece. The most commonly used dielectric fluids are silicone oil, deionized water, and glycol. It is important to set the dielectric fluid to circulate at a stable pressure to wash away particles.
However, you should note that high fluid pressure may lead to the quick removal of metal chips. This could result in a slower cutting action. Likewise, extremely weak fluid pressure may lead to short circuits in the system. This is due to the unremoved chips during erosion.
More importantly, if you notice red sparks during the process, it results from an inadequate water supply. Therefore, increase the flow of water until the sparks turn blue to rectify the machining error.
The material/workpiece completes the EDM basic construction. The electrically conductive workpiece is paired with the anode to achieve the desired results.
Various Electrical Discharge Machining (EDM) Processes
There are different EDM processes, and they can be classified according to their approach and the structure of the tool they use. Here are the three standard EDM processes:
The sinker EDM process is also known as ram, cavity-type, or die sinking EDM. This process uses pre-machined graphite or copper electrodes to machine a positive of the desired shape.
Afterward, it produces a negative of the original workpiece shape by pressing the electrode into the workpiece.
Cavity-type EDM is the perfect option for machining molds for casting and injection molding when you need complex cavity shapes. However, certain factors may determine your choice of electrode material in sinker EDM. The major ones are the conductivity of the electrode and its ability to withstand erosion.
This technique uses a wire as tiny as hair instead of a die as an electrode. The wire attracts the electrical charge to the material, resulting in a microscopic erosion of the material at desired regions.
Wire EDM works similarly to the blade in a bandsaw because the wire moves through the material making vertical cuts in two dimensions. Note that the wire’s diameter ranges from 0.05 mm to 0.35 mm.
The wire is usually brass or copper and machinists place it between the diamond guides. The CNC EDM machine consistently pulls a new wire from a spool during operation to control the precision and accuracy levels of the final product because the wire also burns during the cutting process.
Furthermore, this process makes it difficult to achieve sharp internal corners due to the spark margin/gap between the material and the wire. It creates inner corners with a small radius of 0.15mm instead of an ideal perpendicularity. You can use wire EDM machines to create miniature components for watches and other applications.
Hole drilling EDM helps to cut/drill thin and deep holes into compatible materials. It maintains the same operating principles as the other EDM methods; however, in the case of hole drilling EDM, it is the electrode that supplies the dielectric fluid to the machining area.
Machinists often use the hole drilling EDM to prevent burrs which is a significant benefit of this process. Additionally, this technique is often preferred in applications where complex holes are required in a product. For example, manufacturers choose it for designing complex cooling channels in high-temp turbine blades.
Benefits of Using Electrical Discharge Machining
Here are some benefits of using EDM for your project:
No Mechanical Force
EDM is a non-contact process. As a result, it does not involve using mechanical forces on the workpiece. Also, there is no excessive cutting force in removing materials. Thus, you don’t have to worry about fabricating fragile products. In addition, you can machine incredibly soft materials through electrical discharge machining without complications.
Compatible With Any Electrically Conductive Material
One of the many benefits of EDM manufacturing is that it is compatible with an extensive list of electrically conductive materials.
It is always the ideal process for machining parts that conventional machining methods cannot create. Parts made from tungsten carbide and titanium are good examples of these parts.
Encourages Excellent Surface Finish
EDM also encourages excellent surface finishes than conventional methods. It achieves this due to the slow rate of material removal in the process. It is a high-precision process with refined finishes that are according to specifications. It removes material leaving a smooth surface without the need for post-processing treatments.
EDM manufacturing allows the highest accuracies that modern manufacturing techniques offer. A standard setup can provide about 0.025 mm; specific special EDM machines can offer up to 0.0005 mm.
However, the accuracy of any particular component may be affected by factors such as machining time, degree of the desired surface finish, and material characteristics.
Applications of the EDM Manufacturing Process
This is an efficient method of manufacturing complex shapes and geometries. As a result, it is a more suitable process for applications requiring high precision when conventional machining fails. Here are some of the typical applications:
Die and Mold Making
Due to its extreme accuracy, EDM machining is commonly used as a supportive technique for conventional machining in creating molds and dies. Generally, dies are made from hard steel alloys, which are difficult to make with conventional methods.
Also, you can use hole drilling EDM to create a pressure release hole. The wire cut type is ideal for forming blanks for the molds, while the sinker type is the excellent choice for forming complex shapes of the cavities.
Drilling Small Holes
EDM manufacturing is your best option for accurate deep small holes in materials, regardless of their hardness. Machinists use the hole-drilling technique to create small deep holes of various small dimensions and in complex areas.
You can remove metals stuck within a workpiece using EDM machines. Disintegrating the stuck parts means destroying the material.
Examples include a pin attached to a precious component, sheared bolts on threaded holes, or suck tooling on machined parts. You can remove the stuck metal within a work part by disintegrating the component without destroying it.
Engineers find it challenging to machine several features of aerospace components using standard cutting tools.
EDM machining allows you to achieve certain complex features with essential turbine rotor discs, sharply squared holes, very tight deep holes, and thin slots requirements.
This machining process helps manufacturers in the medical sector prevent burrs on machined medical equipment. As a result, it is a perfect manufacturing process for making different medical devices and implants.
Why Is EDM Preferred?
Electrical discharge machining is a reliable process that most machinists adopt due to its positive outcomes in contrast to traditional machining. Here are a few reasons why manufacturers prefer EDM machining:
The CNC EDM machine can manufacture parts with high precision requirements and the smallest tolerance used in the metal manufacturing sector.
This is possible because the working principles of EDM manufacturing do not apply high stress on the workpiece, which ultimately avoids likely cases of aggressive chattering or vibration.
Highly Capable of Machining Complex Profiles
The EDM machining process has machining flexibility than traditional machining operations. Using the EDM process, you can easily cut several almost impossible features such as fine deep holes, intricate pockets, thin walls, and other irregularly shaped geometries with end mills and drills.
Burr-Free Surface Finish
Various workpieces made with EDM are generally burr-free. In this case, the eroded metal from the workpiece nearly disintegrates into tiny particles that are then washed away.
Also, machined parts often bear high-quality surfaces because EDM cutting does not use sharp cutting tools like saws, end mills, and drills which can form any burrs on the workpiece.
Capable of Cutting Hard Metals
As much as a metallic workpiece has good electrical conductivity, EDM manufacturing can cut hard metals with low force and minimal effort. However, the hardness of the material used for a workpiece does not determine/influence the overall process.
Highly Scalable Manufacturing
EDM manufacturing processes are very effective and flexible regarding manufacturing volume. In any case, it is perfect for low to high-volume production. Likewise, these EDM processes have high repeatability. As such, it allows the production of multiple parts with consistent quality.
Electrical discharge machining is a versatile and reliable complementary process in addition to conventional CNC machining.
It offers solutions for machining applications with complex requirements, including special features nearly impossible to create using CNC milling and turning techniques.
More importantly, EDM is ideal when machining extremely hard electrically conductive metals because it offers excellent accuracy and applies low strain/mechanical force. Contact us at Kemal today to help you get the best out of your project.