What are EDM Electrode Materials and how are they classified?
EDM or Electric discharge machining is the machining process of choice when you need high precision beyond the scope of other conventional machining methods. It does not use force to remove material and put it into shape. Instead, wires that discharge electricity in a way cut through the workpiece material. The EDM process uses thermal energy to achieve the machining requirements. Its characteristic of absence of mechanical force gives it the epithet of being a non-conventional machining process.
The materials used for manufacturing EDM electrodes need to have the twin and slightly contradictory properties of quickly allowing the flow of charges while resisting the resultant eroding characteristics. In other words, while the workpiece must get eroded by the electrical discharges, the electrode itself should not. Several metallic alloys have properties especially suited for various applications of the EDM process. We will briefly examine the main options open to you for the same:
This zinc and copper alloy is used as the constituent materials of EDM wires and smaller tube-shaped electrodes. While as an electrode material, brass is comparatively less resistant to wear than tungsten and copper. It does make machining easy. Additionally, you can also extrude or die-cast brass for special EDM applications. The EDM wires used in the process itself need not be resistant to arc erosion or wear. During the procedure, a new wire is continuously provided.
- Copper And Copper Alloys
While electrodes made from copper and copper alloys exhibit better wear than brass, the advantage is downplayed significantly by lesser machinability than graphite and brass. Additionally, electrode materials of copper and its alloys happen to cost more too. Still, copper is widely used as a base material due to its strength and high-conductivity levels. Suppose you want to machine workpieces made of tungsten carbide or need an excellent finish. In that case, copper is a good choice as your electrode material.
- Copper tungsten
Composite materials made from copper and tungsten are another option open to you as the electrode material. Made using powder metallurgy methods, copper tungsten is significantly costly compared to the other materials mentioned here. But if you require to machine tungsten carbide or need to reproduce deep slots in bad flushing conditions, then it might be your best choice. They are also suitable for machining circuit breakers or resistance welding electrodes.
Graphite is perhaps the most popular EDM electrode material and is characterized by its cleaning effect even at low speeds. The very initial brush material grades produced were made from carbon graphite. It is commonly found in various aging generators and motors. Its amorphous structure also characterizes graphite.
This material is usually put into use in manufactured the wire component of EDM equipment. You want to prefer it over all other materials if your machining calls for small slots or tiny corners in terms of radii. The high levels of tensile strength characterize the material it exhibits as well as exceptional conductivity. It is best suited where the application requires wires with minimal diameters.
- Silver tungsten
This name refers to a material made up of tungsten carbide particles, which remain spread in a silver matrix. The material combines the best properties of the high electrical conductivity levels of silver and tungsten’s characteristic of resisting erosion. Additionally, it also has the high anti-welding properties required by applications that need high power. It is best suited for situations where you want maximum conductivity.
- Tellurium copper
If your applications need an excellent finish, you might want to consider this material as your electrode material. It displays high machinability comparable to that of brass and works better than pure copper.
EDM Electrode Specifications
The two significant factors to consider while choosing your electrode material in terms of both form and function are its resistance to erosion and its high-conductivity. Conductivity is critical. Electric current is the tool used by EDM equipment, and it depends on the cutting efficiency of the electrode significantly.
On the other hand, the erosion resistance properties of a material depend on the combination of hardness, melting point, and structural integrity. Materials that resist erosion most have an extended service life. The determining factors that we mentioned, of course, vary from one material to another.
The EDM Process
In a straightforward explanation, the EDM manufacturing process can achieve extremely high precision levels while removing material from substances that conduct electricity. It achieves this goal through the help of an electrode. You can compare how this electrode works to forming shapes out of soft materials. The electrode works by leaving behind a negative stamp on the workpiece you want to machine.
However, the physical process that takes place is indeed a bit more complicated. An electric discharge is let out in the minute gap between the electrode and the workpiece. Such discharges remove the material by melting or vaporizing it. Note that it is necessary for both the workpiece and electrode to remain immersed in a dielectric fluid for the process to function correctly.
The underlying principle which drives machining through electrodes is how you can erode material by exposing it to controlled sparks. During the EDM machining process, no actual physical contact between the electrode and the workpiece takes place. Instead, there a minute gap as thick as a single strand of hair of a human being. Indeed, the amount of material you can remove with a single spark is small and negligible. But the excellent discharge frequency helps to cut down the workpiece relatively quickly. For people fascinated with figures, the discharge takes place several hundreds of thousands of times every second.