Have you ever seen a video or GIF where a metal part slides into another and simply disappears? Don't know what we're talking about? Take a look at the GIF below.
Parts like this aren't produced using traditional machining practices, rather they are made using a process called electrical discharge machining or EDM.
EDM allows for incredibly high precision parts with insanely low tolerances.
The process is a non-traditional machining method as material is removed from the workpiece not through drilling or milling, but rather through thermal energy. You can think of this process much like laser cutting, but if it were used on machine objects.
One of the key use cases for this material is tool and mold-making as it can be incredibly accurate on metals that are relatively hard, like titanium. So how exactly does it work?
The EDM machining process
Before we get into EDM machining, how it's different from mechanical machining, and how it works, take a look at the video below if you need a refresher on mechanical machining processes.
With that out of the way, let's dive into how EDM exactly works.
Electrical discharge machining is the machining of a material through the direction of high-frequency electrical spark discharges from a tool, usually made of graphite. This graphite tool acts as an electrode that disintegrates conductive materials in the machining process.
Bascially, there's an electrode that passes a current through a material that causes it to melt or vaporize, and that's how the machining is accomplished. However, this process can't happen just anywhere, in fact the workpiece and the electrode have to be submerged in a dielectric fluid.
When it comes to technical processes, often the best way to understand how they work is to see them in action. Take a look at this short educational video on EDM below.
The different types of EDM
Under the main process of EDM, there are three subprocesses. Those are Wire EDM, Sinker EDM, and Hole Drilling EDM.
Sinker EDM is a type of machining that allows users to produce highly complex shapes. The reason it is called sinker EDM is because in this process, the electrodes have to be highly precise and pre-machined so that they can be sunk into the workpiece to create a negative version of it's shape.
Wire EDM on the other hand involves a thin wire used to cut the work piece, acting as an electrode. The wire is fed through an automatic feed and cuts are made around the piece. In this apparatus, the wire is held with diamond guides and the wire itself is generally made from brass or copper.
Finally, there's hole drilling EDM, which is a process specifically designed for drilling holes in materials. Hole drilling EDM is able to drill incredibly tiny holes that otherwise wouldn't be possible with mechanical machining. The electrodes in this instance are tubular with the dielectric fluid flowing through the electrode nozzle.
Now that we've covered the basics of the processes, what can you use this technique on? Any conductive material.
When you would use Electrical Discharge Machining
The biggest advantage that EDM poses to modern machining is how versatile it is for use with metals, particularly with harder metals that are harder to mechanically machine. Metals like tungsten carbide or titanium can be easily machined with EDM. Another advantage of this technique is the ability to produce highly precise outlines on parts without having to deburr, or clean up the edge.
Due to the nature of the machining process being purely based on electrical current, EDM can make long depth cuts that would otherwise be impossible. Designs like slots or ribs are particularly suited for EDM.
Finally, EDM can be done after a piece has been heat-treated, meaning that the process doesn't mess up any of the metal's tempering or treatment like mechanical machining does.
So then, if EDM can do all of that, then what can't it do?
Well, it is not a particularly fast machining method so it's not great at scale. It also takes an immense amount of electrical energy, far more than any mechanical machining process.
EDM electrodes also frequently need to be replaced, just like bits in mechanical machines, but EDM electrodes are sometimes custom made for each job. This would mean additional steps in the process.
Applications of EDM
We've discussed when EDM would be used and some of the pros and cons, but let's talk about specific examples where it would be a good fit. EDM is great for incredibly small volume production batches or one-off parts that need an intense degree of precision.
EDM is largely used in the mold-making industry, but also in the aerospace and automotive industries. These industries also see mechanical machining processes that are on the cutting edge as well.
At the end of the day, while you may just be learning about what EDM it, it's actually a process that's become fairly standard in the industry. Chances are it's had an impact on the products in your life in some way – and it certainly is a fascinating machining process to see in action.