How are EDM Electrodes made?
EDM electrodes are meant to transmit electrical impulses that help in machining materials. The electrode can be made from various materials, and copper and graphite are the most popular. When such electrical discharge is transmitted, the workpiece gets eroded without significant erosion of the electrode itself. The electrode material itself must have the following characteristics:
- Substantial levels of material removal
- Low levels of wear of the actual electrode
- Affordable fabrication costs
- Ability to be machined accurately
An electrode material's performance will often vary due to factors like the particular application and the workpiece's material. Some electrode materials offer extremely effective metal removal quantity and will show negligible amounts of wear resistance. Sometimes other electrode materials while doing the same work will have excellent resistance to wear but low levels of actual metal removal. The exact amounts of both these factors are decided by electrode materials properties and characteristics. Another critical factor is the minute gap between the electrode and the workpiece, referred to as the work-gap.
The five most popular materials used as an electrode are as follows:
- And Graphite
Electrode materials can be broadly classified into two primary categories viz:
- And Metallics.
The latter can again be sub-divided into three categories:
- Tungsten and Tungsten Composites
- Common metals
Graphite can belong to one of the six following classes as per the size of the particle:
- Angstrofine – Less than 1 micron
- Ultrafine- Between 1 to 5 microns
- Superfine- Between 6 to 10 microns
- Fine- Between 11 to 20 microns
- Medium- Between 21 to 100 microns
- Coarse – Greater than 100 microns
Keep in mind that the coarse graphite varieties can't be used as EDM Graphite electrode materials.
Conventional Machining Of Graphite Electrodes
It is possible to machine graphite EDM electrodes through the equipment you will find in almost all typical machine shops. However, remember that a large amount of dust is involved. Accordingly, make adequate provisions for controlling the same. There are a variety of methods at your disposal that perform admirably for the task. Two major factors will determine the particular procedure you choose eventually- the type of machining and its size. It is crucial not to machine graphite without putting in place a dust collection method at first.
As the bullet mentioned above points have informed you, graphite is known for its diversity. This diversity is not merely the size of the particles. Other similarly diverse graphite characteristics that the graphite EDM graphite suppliers have to provide happen to be:
- Compressive strength
- Flexural strength
Such characteristics have a significant bearing on the various grades and graphite brands' machinability as other aspects like the wear and pressure on the tool. One primary determining factor of the graphite grade and brand used for machining EDM electrodes is the size and shape. Finely detailed graphite electrodes are paired with close tolerance levels made possible by using the combination premium graphite grades and CNC design and machining.
General Guidelines For Machining Graphite EDM Manufacturing
While machining graphite, it is vital to observe standard machining procedures. Such procedures include:
- Making sure there is a positive rake angle and that you use relief angles
- Maintain rigidity
- Ensure sharpness of the tools
- Maintain low levels of tool pressure
Graphite Electrode EDM Manufacturing Methods
Remember that the particular applications might call for slightly modified settings than the ones laid out below. Specific applications may require slightly different locations than the following general guidelines.
Graphite is comparatively brittle compared to other metals, and the abrading machining process leverages this characteristic to its full advantage. Abrading works for all EDM Graphite classes. The abrading machining process consists of several methods that you may choose to employ. This process of manufacturing graphite electrodes owes its popularity due to the following factors:
- It is dependable
- You can repeat it
It is cost-effective, especially when you want to produce larger molds and dies. By using flushing, you can get rid of graphite dust created by the machining process. You can restore and create graphite electrodes easily with this process. Additionally, the process does not usually require benchwork.
- Ultrasonic Machining
Ultrasonic graphite machining is yet another method that uses the unique characteristics of graphite to its advantage. While it is technically speaking an abrasive process, it uses a different principle that results in the abrasion. The equipment used in this EDM manufacturing process is quite similar to the ultrasonic devices used to clean small parts and jewelry. It stands out from other similar equipment is the far greater power of the machine.
The ultrasonic machining of graphite EDM electrodes is a proven method for reproducing details and the radii down to the levels as minute as 0.002. Additionally, it gives you the ability to achieve surface finishes to 8 µin Ra. Another advantage of ultrasonic graphite machining is that it doesn't require much manual intervention. It is repeatable, and it can restore electrodes with ease. However, ultrasonic electrode machining does indeed come with the limitation of creating only 4" in diameter as per current technology capabilities. Deep cavities are not practically possible with electrodes.
If you need your EDM electrodes to have precise and fine details and close tolerance levels, then wire-cut graphite machining is the method you want to use. It comes with the additional advantages of affordability and lack of human intervention in the operating process. The theory behind the operations of the wire-cut method is the same as the ram-type EDM process. Still, the natural way of putting into practice the approach is quite different. This method is gaining popularity by the day due to its multiple advantages. In wire-cut, the dust control factor does not come into the picture. However, it is possible to effectively wire-cut only a few graphite grades provided by EDM graphite suppliers on the flip side. Additionally, you can't create electrode cavities through this method.
I hope this helps!