The EDM is derived from Electrical Discharge Machining.
The EDM process as we know it today started in 1770 with the observations of Joseph Preistly. He noticed that electrical discharges had removed material from electrodes used in his experiments. This is also known as electro-discharge erosion.
Later on in the 1940’s Soviet researchers developed a machining process that formed the foundation for modern day EDM.
Electric Discharge Machining
The basic EDM process is an electrical spark that is created between an electrode and a work piece. The spark is visible evidence of the electro-discharge. This electric spark produces intense heat with temperatures reaching 8000 to 12000 degrees Celsius, melting almost anything.
The spark is very carefully controlled and localized so that it only affects the surface of the material. The EDM process usually does not affect the heat treat below the surface. With wire EDM the spark always takes place in the dielectric of deionized water. The conductivity of the water is carefully controlled making an excellent environment for the EDM process. The water acts as a coolant and flushes away the eroded metal particles.
If you’ve been inside a mold shop, you’ve likely seen a few electrical discharge machines (EDM). They are widely used in the industry and come in a few different styles. We’re going to go over the different types of machines and how they are used in the injection molding industry, as well as general machining. There are three types of EDMs: Ram, Wire, Drilling.
RAM EDM
The Ram EDM, sometimes called sinker, die sinker, or plunger uses an electrode to produce the desired shape in material via electrical current.
First, a machinist will use 3D data of the desired part and design various electrodes around the part. As you can see in the video, the electrode is the opposite of the desired shape in the material. For more on this machining process, check out this post on graphite milling.
Once the electrode is made, it’s placed into the the Ram EDM. A dielectric oil then surrounds the material and electrode. The oil is a critical component in the process as it serves as an ionizer for the current, flushes out the material being removed, and cools the electrode and workpiece.
Compared to a CNC Mill or Lathe material is moved relatively slowly when common/soft steels are used. The advantages of the EDM compared to standard CNC machining are the ability to machine extremely hard materials with ease, produce features that are either difficult or impossible on other equipment, and produce an array of textures.
WIRE EDM
Like the Ram EDM, the wire EDM uses electrical current to remove material. The difference is that instead of using a machined electrode, a wire is used to cut a narrow channel through material. The wire is continuously moving so that it does not wear and break due to the corrosive nature of the EDM process. The wire EDM is extremely accurate and used for making inserts, insert pockets, precision holes, tapered pockets, and small holes. Like the Ram, the wire can cut hardened material with ease.
DRILLING EDM
Often called a “Hole Popper,” the drilling EDM functions using a spinning electrode rod to “drill” into materials. In the most simple form, workpieces are manually moved and the hole popper is manually aligned to location. However, much more advanced multi-axis CNC hole poppers have been developed.
Since Wire EDMs require a starting hole, these machines are often used in tandem, where the hole popper creates a small starting hole that wire EDM can work from as a starting point. Hole poppers can also create relatively accurate holes. They are also great for removing broken drills and taps (not that I have ever done that).
These three types of EDMs are used extensively for injection mold building. At Basilius, we have an entire room dedicated to this process. Not only for own tool building but also for other production machining applications. We also offer each process as a service to other tool builders or machine shops.
When comparing Electrical Discharge Machining (EDM) and conventional machining methods, each technique has its strengths and applications. Here’s a look at how they differ in seven key situations:
1. Material Hardness
EDM: Ideal for hard materials such as carbide, titanium, and hardened steel. The process relies on electrical discharges rather than cutting forces, making it effective for machining tough materials that would wear down conventional tools.
Conventional Machining: Struggles with extremely hard materials, often requiring special tooling and leading to rapid tool wear.
2. Complex Geometry
EDM: Excels in creating intricate shapes, sharp internal corners, and complex contours that are difficult or impossible to achieve with conventional machining. It can produce detailed features like thin slots or fine holes.
Conventional Machining: Limited when it comes to producing highly detailed parts with complex internal geometries. Sharp internal corners often require additional processes.
3. Tolerance and Precision
EDM: Known for its ability to achieve high precision and tight tolerances, often within microns. This is essential in industries like aerospace and medical devices where accuracy is critical.
Conventional Machining: While capable of good precision, it generally cannot match the micrometer-level accuracy of EDM, especially for very fine details.
4. Surface Finish
EDM: Produces a superior surface finish, especially in fine applications. The process allows for a smoother finish with fewer imperfections, reducing the need for secondary finishing processes.
Conventional Machining: Surface finish varies depending on the tool, speed, and material. Achieving a high-quality finish often requires additional polishing or grinding.
5. Tool Wear and Longevity
EDM: Since there’s no direct contact between the tool (electrode) and the workpiece, tool wear is minimized. This leads to longer tool life, especially when machining hard materials.
Conventional Machining: Tool wear is a significant issue, especially when cutting abrasive or hard materials. Frequent tool changes are often necessary.
6. Heat and Mechanical Stress
EDM: Generates minimal mechanical stress because it doesn’t exert physical force on the material. It’s also well-suited for applications where heat-induced distortion must be minimized.
Conventional Machining: High cutting speeds generate friction and heat, which can cause warping or stress in the workpiece, especially in thin or delicate parts.
7. Speed and Cost
EDM: Typically slower than conventional machining due to the nature of the process. While it’s more precise, the longer machining time can increase costs, making it less suitable for high-volume production runs.
Conventional Machining: Generally faster and more cost-effective for simple parts or large production runs. It’s ideal for operations requiring high-speed material removal.
This practice is when material is removed from a project using thermal energy. Like laser cutting, this method does not use mechanical force throughout the removal process when CNC machining in Missouri does. This practice is popular in use with difficult shapes and materials. It is versatile and able to work on a variety of projects.
In more complicated terms, this machine uses a process that takes out material by using an electrode. The electrode leaves behind a negative imprint on the project, initiating a discharge that removes material through melting or vaporizing.
Every conductive material can be worked on with an EDM machining . That list includes titanium, steel, and other hardened composites. This makes it an ideal tool to use on projects that include those materials, as other machines cannot work on them efficiently. Another benefit of this practice is that it results in less mechanical force used in the shop. Compared to other practices like CNC machining, where cutting tools are used, this method becomes a more versatile option. It can allow for shapes and depths that are not possible with cutting tools alone. Another benefit of this practice is that the surface finish of the project is much higher quality than other end results.