What Is Wire EDM?

What is Wire EDM?

1.What is the Principle of Wire EDM?

Wire Electrical Discharge Machining (Wire EDM) is a non-traditional machining process based on the principle of electrical discharge machining. It is commonly used for cutting hard materials, such as hardened tool steel and cemented carbide, and can produce metal parts with complex geometric shapes.

    The basic working principle of Wire EDM can be illustrated with a diagram.

    The cutting wire [2] is fed from a wire spool [1] through guide rollers [3] and a guide assembly [4]. To resist wear, the guide assembly is typically made of diamond. The cutting wire is eventually collected on a take-up spool [5] or cut into small pieces as it is consumed. Through a power supply connection, the cutting wire acts as the cathode and the workpiece acts as the anode. When the electrode (in this case, the cutting wire) is brought close to the workpiece, a spark discharge occurs, causing material to be removed from the workpiece. The discharge is supported by a dielectric fluid [6], which helps cool the material; the process can also be fully submerged in the dielectric fluid. The spark gap [7] results in the machined profile being slightly larger than the diameter of the wire [8]. The machining path is typically controlled by the movement of the workpiece in the horizontal plane.

    The Wire EDM process can be divided into three stages.

    1.Arc Formation Between Electrode and Workpiece: In Wire EDM, a thin, conductive metal wire is used as the electrode. The distance between the electrode and the workpiece is very small, but there is no direct physical contact. By applying a high voltage, an arc discharge is formed.

    2.Arc Creates a High-Temperature, High-Pressure Region: The energy generated by the arc discharge is very high, causing the metal on the workpiece surface to be heated to a high temperature instantaneously. This high-temperature and high-pressure region enables evaporation and corrosion of the metal surface.

    3.Metal Corrosion and Removal: In the high-temperature and high-pressure region, the metal begins to corrode and dissolve. The corroded metal particles are washed away by shock waves, thereby achieving the removal of material from the metal workpiece. The arc continuously moves between the electrode and the workpiece, allowing the entire cutting process to form the desired shape on the metal surface. Material removal in Wire EDM occurs due to the effect of sparks on the workpiece surface. These sparks are not a continuous current but rather short-lived electrical discharges that occur millions of times per second. When machining enclosed areas, the workpiece for a Wire EDM machine has a through-hole as the starting point for cutting, and the wire needs to be threaded through this hole before cutting begins;

    The process of inserting the wire from the top guide to the bottom guide is called threading. Wire EDM machines may have an automatic threading system or may require manual completion. Additionally, the system generally has a sensor to detect wire breakage during the EDM Wire Cutting process.

What Materials are Suitable for Wire EDM?

Wire EDM is very practical for machining hard and brittle materials, such as tool steel, hardened tool steel, cemented carbide, Inconel, and other materials that are difficult to machine using traditional methods. It is also used for machining parts with complex contours in the aerospace or medical industries.

In addition to these, Wire EDM can also be used to cut any conductive material, including copper, brass, aluminum, Hastelloy, etc.

Can Graphite be Cut with Wire EDM?

Yes, Wire EDM machines can cut graphite. However, graphite is brittle and requires careful handling, and the cutting speed is very slow. Furthermore, it is best to machine graphite conventionally through milling, using Wire EDM for complex contours. In this way, the process can be made more economical and faster. After EDM, the graphite needs to be dried to remove moisture.

Can Titanium be Machined with EDM?

Yes, Wire EDM machines can cut titanium alloys. Zinc-coated brass cutting wire (electrode) can be used to achieve better speed and surface finish. In addition, wire breakage can be an issue during the cutting process, which can be minimized by adjusting the current value and the length of the "pulse off-time".

Advantages, Disadvantages, and Limitations of Wire EDM

Advantages: Wire EDM is a precise cutting process that can be used to cut difficult profiles with tight tolerances, and even small-sized workpieces that cannot be cut by traditional machining processes. It can easily cut soft metals such as brass and copper, brittle materials such as graphite, and hard materials such as cemented carbide and Inconel. Wire EDM can cut workpieces with a height of up to 300mm or a weight of up to 1000 kilograms. It can be used to cut sharp corners (with negligible radius) without leaving burrs or tool marks. The electrode is a simple wire in the Wire EDM machine, so the tool cost is relatively low.

Disadvantages and Limitations:Wire EDM can only be used to cut conductive materials. The cutting speed or material removal rate of Wire EDM is low and uneconomical, so it is often used for machining very hard materials or difficult-to-machine profiles. Wire EDM may leave a recast layer on the workpiece surface, which requires secondary operations such as polishing to remove. Wire breakage is a problem in Wire EDM, resulting in loss of time and some wire material. The wire (electrode) in Wire EDM cannot be reused and is discarded after one use, which increases costs.