When people think of machining, lathes and milling machines may be the first thing they imagine. Still, there are a variety of other machining processes that may be even better suited for certain applications. One such method is electrical discharge machining (EDM).
This article will provide a more in-depth look at the function and capabilities of one particular type of electrical discharge machining — wire EDM.
What is Wire Electrical Discharge Machining?
Wire EDM is a type of EDM that uses a wire running continuously through the workpiece to cut complex shapes with tight tolerances and minimal kerf. This process is particularly useful for cutting precisely through conductive materials that are both hard and thick, with some machines able to cut materials over 300mm thick.
The different varieties of EDM use the same basic operating principles, as we discussed in a previous article. In essence, an electrode and a dielectric fluid work together to disintegrate microscopic pieces of the conductive workpiece using electricity. While each electrical discharge, or spark, may only remove a tiny amount of material, the process happens hundreds of thousands of times per second.
In wire EDM, an incredibly thin wire acts as the cathode while the conductive workpiece acts as the anode. The wire runs between two guides capable of moving independently to create unique shapes. This introduces some limitations on the capabilities of the process however, as the wire must generally pass through the entire workpiece.
Similar to other types of EDM, the cathode and anode do not normally make physical contact. Instead, the high difference in electrical potential (voltage) between the wire and workpiece causes ionization in the dielectric fluid, making it electrically conductive.
Simply put, the result is a spark that melts or vaporizes and detaches tiny pieces of both the wire electrode and the workpiece, called EDM chips. These microscopic EDM chips are then washed away and filtered out in the circulation of the dielectric fluid.
How Does Wire EDM Work?
Example of a “Wire EDM” by LaurensvanLieshout
Public domain, via Wikimedia Commons
Since the wire electrode is damaged during sparking, it needs to be continuously fed through the workpiece and replenished. Likewise, the dielectric fluid, typically deionized water in wire EDM, is circulated, filtered, and deionized to prevent it from causing irregular sparking.
The wire system and the dielectric fluid make up the two main components of wire EDM, which must work in sync to ensure efficient, precision cuts and a high-quality surface finish.
The Wire System
The wire in wire EDM is typically made of brass or copper, sometimes with a zinc coating to improve consistency and efficiency. The wire is very thin, typically 0.3mm in diameter or less, so the constant erosion damage from sparking wears through it quickly. As such, fresh wire must be constantly fed through the workpiece using spools holding several kilometers of wire. The damaged wire is then recycled at the end of the process.
The Dielectric Fluid
The deionized water has three main functions in wire EDM:
- Providing a medium to help control the powerful sparks,
- Rinsing away EDM chips from the workpiece and wire, and
- Cooling the workpiece to prevent excessive thermal stressing.
When it is working properly, the deionized water should act like an insulator between the wire electrode and the workpiece until there is a sufficiently high difference in electric charge between them. This allows for a sort of controlled chaos as the sparks at different points will have similar “strengths”, creating a smooth even cut around the immediate proximity of the wire. Excessive contaminants can weaken the water’s insulating properties, allowing for more erratic and inconsistent sparking.
This is also why the dielectric fluid must be constantly flushed away to prevent the build-up of EDM chips and ions in the water. For this to happen effectively, the workpiece should be submerged and have a steady flow of deionized water directly through the cutting area.
The flowing fluid also pulls heat from the cut area to prevent overheating that could induce thermal stress in the workpiece. Especially in very thick materials, fluid flow must be carefully controlled to manage the heat-affected zone (HAZ) in the workpiece. Excessive thermal stress could cause micro-cracking and altered material properties near the cut surface.
Wire EDM: Benefits and Limitations
With a better understanding of how this manufacturing process works, it’s worth creating a summary of its main strengths and weaknesses.
The main benefits of using wire EDM are that it is:
- One of the preferred methods for cutting very hard materials, especially when the cut angle is not perpendicular to the work surface.
- Capable of achieving very tight tolerances (within ±0.012mm), with minimal kerf, and no taper throughout the cut.
- Suitable for both very thin and very thick materials without significantly impacting cut quality or causing part distortion.
- Excellent for creating very high-quality surface finishes, especially after skimming passes have been used to smooth the fast initial roughing cut.
- A fully CNC process, meaning operators are typically only needed for loading and unloading consumables & parts. Therefore the process can be labor-saving.
The main limitations and shortcomings of wire EDM are that it is:
- Only compatible with conductive materials.
- Generally not efficient for use with heterogeneous materials, like carbon fiber reinforced polymers, and impure materials, like cheap tool steel with large inclusions.
- Sometimes more time-consuming that other suitable processes, depending on the conditions.
- Not capable of drilling holes, which may have to be started by another process, like hole popping EDM, if required by the design.
- Potentially more expensive than alternatives like waterjet cutting, especially when it comes to consumable use.
Another consideration may be that it is possible for wire EDM to introduce thermal stresses into the workpiece, changing the material’s properties or inducing micro-cracks. On the flip side, however, it does not impart any mechanical cutting forces onto the workpiece.
Is Wire EDM the Right Process for You?
If the potential limitations listed above do not apply to your project, wire EDM proves to be an exceptional method for cutting hard materials with high thicknesses. This process is synonymous with precision, accuracy, consistency, and high quality.
This means wire EDM is regularly applied for parts with complex geometries and tight tolerances, especially when using advanced materials. Fragile medical device components, precision aerospace parts, and tooling made from particularly hard materials like titanium are great applications for this manufacturing process.
If you want to find out how wire EDM can produce your precision-cut parts, check out our wire EDM services page to see what Gensun has to offer.