Why is Graphite the most preferred electrode material in EDM?
Opinions are indeed divided when it comes to whether copper or Graphite is a more suitable material as electrodes used in EDM electrical discharge machining equipment. The primary reason behind the former dominance of copper as EDM electrode material was the clean manner in which it let the EDM process be executed. But with the forward march of technology, a whopping 70% of all global users of EDM instruments prefer and use graphite EDM electrodes. In the US, the figures are further tilted towards Graphite. An overwhelming 95% of all EDM electrodes being used are made from Graphite. These technical experts know precisely what they are doing. They choose Graphite as their EDM electrode material for some solid reasons. Some of such reasons are as follows:
The Long-Term Costs Associated With The Electrode-
In general perception, copper is known to be more affordable than graphite right. But while doing such innocent calculations, we often forget to consider the concerned graphite grade. When you factor in this aspect, you will often find plenty of graphite grades that are more affordable than their copper counterparts.
Another additional factor that we often miss out on while assessing the cost of graphite electrodes is the expense associated with machining the electrode. If you choose graphite electrodes over copper, you potentially save a significant amount. Such savings result from:
- A reduction in machining time
- Less speed of cut
- Decreased electrode creation production time
- Faster EDM times
- Getting enhanced throughput from the EDM equipment
We can illustrate such savings using how soft and malleable copper is, which makes it gummy. Such properties of copper make it necessary to alter traditional machining process elements like speed and feeds. Doing so considerably increases the machining period, and along with it, the costs spiral upwards too. Compare this with the ease and swiftness with which you can conventionally machine Graphite. Even if you choose more expensive graphite grades, the reduced machining expenditure will offset potential savings.
Graphite Provides More Material Variety-
EDM Graphite is specially created to possess several material properties that are especially useful as an electrode material to EDM applications during the production process itself. Some such features necessary for applications that are relatively less critical are as follows:
- Open tolerance
- Large radius
- Minimum EDM requirements
For such requirements, the electrode material needs to be:
- Contain large particles
- Relatively low strength
- And an affordable cost
If, however, the EDM requirements are rigorous, then the EDM electrode would need to be:
- Highly detailed
- Exceptional tolerance levels
- Critical features
To meet such requirements, you will likely need a premium graphite electrode to complete the application needs.
In contrast, copper is limited to only a few varieties being available in the market. It limits the ability to match the electrode's physical characteristics with the particular EDM application's needs, negatively affecting the performance significantly.
The Electrode Details-
Graphite is well known for its superior handling of current density, which is far more effective than copper. Additionally, Graphite does a great job at adequately maintaining complex geometry even when the current density is unusually high. It lets you create a variety of complex machine details by using the same electrode. It translates to a significantly less electrode number being required to carry out the same EDM task.
The leading EDM manufacturing firms provide you with an array of options regarding the graphite material you want to use in your EDM. There is a vast diversity in:
- The lifespan of the electrode
- Surface finish
- Cut speed
- Job metallurgy
If you choose copper as your electrode material, on the other hand, you are stuck with one single form. You don't have the option to precisely select the material specification for optimum use in your EDM application.
The EDM Performance-
People familiar with EDM operations' workings only know too well that excess wear requires additional electrodes or its only other alternative, i.e., redressing it frequently. Graphite as an electrode material boasts of keeping electrode wear to less than 1% compared to how deep it cuts when used with particularly aggressive parameters. That translates to high ampere levels and greater on-times, which help to preserve the electrode. It is something that copper conspicuously lacks as an electrode material.
We can take the example of EDM use in aerospace, where their thinness and fine details characterize the electrodes. If we use copper in such situations, the applied pressure will result in often unnoticed movements. Copper is relatively fragile and doesn't tolerate rough handling, and is vulnerable to physical damage. The copper movements resulting from pressure are likely to create significant issues with performance further down the line. EDM Graphite electrode material, in contrast, can easily be identified as being work-ready or being damaged. Such a characteristic dramatically reduces the production risks posed by the electrode.
Please don't hold the misconception that it is not possible to wire erode Graphite. It is a fallacious view as many leading graphite electrode companies have indeed wire eroded Graphite without breaking it. Even the wire erosion process timings are comparable to that of copper EDM electrodes.
The Surface Finish-
It must be admitted that the fineness of their surface finish characterizes copper electrodes. The EDM technology that is present with us has evolved to a high level of sophistication. As a result, the gap between copper and graphite electrode materials' surface finish has decreased to negligible levels. For instance, you can get a copper-like surface finish when you use fine-grained graphite electrodes. Graphite electrodes additionally provide vastly faster speed and a significant reduction in the wear of the electrode.
If you are looking for a suitable material for your EDM electrode, it would not be very smart to let preconceived notions cloud your choice. We hope this post brings the facts before you so that you can judge for yourself!