Electrical Discharge Machining (EDM) is a non-traditional method of precision machining that uses thermal energy and a controlled electrical spark to remove material from a workpiece. EDM can also be referred to as spark machining and spark erosion. Electrodes are used to generate an electrical current through non-metal objects. By doing so, they alter objects. Brass, copper and copper alloys, graphite, molybdenum, silver, and tungsten are all examples of electrode components that can be used in the EDM process.
What are the Benefits & Drawbacks of EDM?
If you are contemplating whether or not electrodes for EDM will provide the right service for your project, it’s important to understand the benefits and drawbacks of EDM.
Benefits of EDM Include:
- EDM works on hardened materials
- Tooling does not come into contact with the workpiece, meaning no mechanical stresses, distortion, or burring will occur.
- Complex shapes can be machined.
- Tight tolerances can be achieved.
Drawbacks of EDM Include:
- Electrical discharge machining only works on electrically conductive materials.
- EDM produces heat which can cause tool wear.
- EDM requires power to work, often leading to high power consumption.
- The material removal rate may be slower than alternative methods.
Types of Electrodes
In the field of Electrical Discharge Machining (EDM), the choice of electrode plays a crucial role in determining the efficiency and accuracy of the process. There are several types of electrodes available for EDM, each with its own unique characteristics and applications. In this section, we will explore the different types of electrodes commonly used in EDM and discuss their advantages, disadvantages, and ideal uses.
Graphite Electrodes
Graphite electrodes are used to melt and refine steel, iron, and other metals. They are used in electric arc furnaces (EAFs). Graphite electrodes have great electrical conductivity as well as a high melting point, and high thermal conductivity.
This electrode is essential to components made in the metalworking industry as they lead to the production of high-quality steel.
Graphite electrodes are also popular due to their cost-saving, low-wear characteristics. They can work within the most aggressive machine parameters and produce high-quality processing.
Silver Tungsten Electrodes
Silver Tungsten electrodes, also known as Ag/AgCl electrodes, are commonly used in wiring to harness electrical components of line switches, battery packs, automobiles, aerospace, aviation, sports equipment, and circuit breakers in manufacturing lines. They are also well-suited to high-speed, automated welding applications.
The benefits of using silver tungsten electrodes lie in their strength as they can penetrate the toughest of materials. Silver tungsten electrodes are also excellent conductors, they are in fact, the best-known element for conductivity against any pressure or temperature on Earth.
Low noise is another benefit to using silver tungsten electrodes alongside zero electrode polarisation and impedance effects.
Copper Electrodes
Copper EDM electrode tubes are useful in small cavities as well as complex geometrical shapes. One of their biggest advantages is that they are inert (do not react) to electrolytes in dry cells which is why they are commonly used in wires. Copper tends to work better for EDM machining even if the flushing system is poor.
In comparison to graphite electrodes, copper electrodes are a much harder form of metal and have a much lower heating point. They can often stick or melt if heated quickly. Copper electrodes also need to go through a deburring process (removing sharp edges or fins to smooth out material).
Molybdenum Electrodes
If your project requires an electrode that can withstand challenging conditions, then molybdenum electrodes could be a match for you. Its characteristics consist of being strong, resistant to oxidisation under high temperatures, and they have a long lifespan.
Molybdenum Electrodes are made through isostatic pressing. They can be forged to various specifications after undergoing sintering and shaping in medium-frequency furnaces.
Overall, molybdenum electrodes have excellent electrical properties and high-temperature strength.
Material Selection
Electrode materials have a great impact on discharge erosion, electrode loss, machining speed, machining accuracy, and the stability of machines in EDM. The processing quality is directly affected by your electrode material selection combined with your technical requirements and the condition of your parameters.
Other considerations include:
- Surface roughness
- Dimension
- Tolerance accuracy of the workpiece
Electrode Wear and Maintenance
Electrode wear is dependent on the application process, largely related to factors such as the distribution of power between both electrodes and thermodynamic constants of materials.
Types of Electrode Wear
End wear
The EDM process produces sparks on the leading edge or working surface of the electrode. End wear is the amount of material burned away from the bottom of the material to the depth of the electrode to the cavity.
With many work metals, it is possible to reduce the amount of end wear to one percent or less by adjusting the on-time of your machine.
Corner wear
Corner wear is caused by the increase in sparks generated in the corners of your material due to heat build-up. Corner wear is measured as the length lost of the 90-degree external corner of an electrode to the corresponding internal corner.
The most vulnerable points of the electrode (depending on their shape) are the corners and sharp angles.
Proper flushing and dielectric fluid circulation can help in cooling the electrode and reducing corner wear. Optimising the machining parameters such as the current, voltage, and pulse duration can also help in reducing corner wear.
Side wear
Side wear is caused by your chosen material’s (for example, graphite) particles eroding from the electrode. This causes mechanical abrasion from debris passing along the side of the electrode as it flushes out of the gap.
Large particles, excessive particles or poor flushing systems can cause sparks to increase the amount of overburn which will eventually slow down the speed of the cut, affecting the overall productivity of your project.
You can avoid the negative effects of side wear by removing particles from the bottom of the cavity through vacuum flushing.
Electrode Design Considerations
To make your EDM process more efficient, you must understand the applications needed for your job.
For example, if your job has a large cavity, fast metal removal rate or requires no/minimal critical dimensions, then electrode wear will not become an issue. However, if your job requires intricate detail or thin, deep ribs then the rates of electrode wear will increase.
Check your electrical discharge machines regularly to identify any signs/potential signs of wear to extend the life of your electrodes.
Electrodes For EDM Frequently Asked Questions
Dielectric fluids fill the gap between the tool electrode and the workpiece to control electrical discharges during the material-removal process.
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To see how A&M could support your next complex manufacturing project – simply call us, or use the form below.