What is Wire EDM Cutting, its advantages & limitations?

Electrical discharge machining, or the EDM wire cutting process, uses controlled and rapidly repeating electrical charges to remove material from electrically conductive materials such as metals. EDM is a process of metal machining in which a tool discharges thousands of sparks to a metal workpiece to be cut. Being a non-conventional process, but a new one, wire EDM works on parts impossible to cut by conventional machining processes, but only if these parts are electrically conductive ( for example steel); usually, they are non-ferrous & mostly metals, and include steel, copper, brass, and many other metals. Instead of cutting the material like conventional cutting processes, EDM melts or vaporizes it, producing comparatively small chips and providing a very accurate cut line.

e see the wire EDM cutting in terms of how the strategy stacks up against laser cutting, 3D fabricating, or conventional machining for multi-axis forming of metal.

Advantages of EDM

Precise for 2-axis cutoff of small parts

Wire EDM cutting could be an exceptionally exact strategy for the proper applications, such as for 2-axis cutting of little parts with tight resiliences at tall volumes. For illustration, for mass generation of pins, tests, and other little, strong metal parts with distances across beneath 0.010” (0.25 mm), the focal points of EDM incorporate:

  • High dimensional control with repeatbility in the dimension without any material shape change.
  • Cost effective compare to other cutting process such as laser cutting.

High Ppk/Cpk

For small diameter solids, wire EDM cutting also offers extremely high measures of central tendency, for remarkably high Ppk/Cpk values. For example, EDM not only can cut a precious metal wire of 0.004″ (0.1 mm) diameter to a length of 1″ (25 mm), but also can do so while achieving a length tolerance of ±0.001″, radiused ends, and a Ppk well over the standard minimum of 1.33.

Burr-free cutting of a range of diameters

Wire EDM can cut diameters ranging from a few thousandths of an inch to several inches, to lengths from 0.5” (12 mm) to 18.0” (450 mm) and with high dimensional accuracy. Because it does not involve a wheel or saw teeth, the EDM wire cut procedure generally does not leave any burrs, and the kerf width is usually 0.004” to 0.012” (0.1 to 0.3 mm).

Different material hardnesses and radiused end cuts

Wire EDM cutting is also versatile in the hardness of the conductive metals it can cut with relative ease, ranging from copper to the hardest materials including molybdenum and tungsten. EDM also gives a natural radius to the end cut; this may or may not be an advantage, depending on the application.

Disadvantages of Wire EDM Cutting

Slow speed

The most widely known negative is that wire EDM cutting is still an extremely slow method. Modern EDM machines with AWT (automatic wire threading) and CNC capability can be programmed to work “lights out,” to help mitigate the slow cutting speed. However, for very high volumes of parts with diameters larger than 0.020″ (0.5 mm), a method such as thin-wheel abrasive cutting might be preferred.

Conductive materials only

Due to the nature of wire EDM cutting — removing material by using rapidly repeating, controlled electrical charges along a strand of metal wire — the method is limited to electrically conductive materials. Therefore, any material that is a composite or coated with a dielectric is not feasible for EDM.

Effects of a charged environment

The total EDM environment — including the wire, deionized water, and workpiece — is charged. The wire’s repeated electrical discharges can heat the target area of the workpiece to thousands of degrees. This can result in thermal stress to neighboring portions and cause some amount of waste. The wire itself also suffers damage, so the EDM machine must constantly feed new wire.

Depending on the metal being cut, another disadvantage of wire EDM cutting is that an oxide layer can form on the cut surface. This may require secondary cleaning, which adds to cost.

Not ideal for tubing cutoff

Wire EDM cutting is best for materials that are solid, so the method is not a good choice for cutoff of tubing. To maintain conductivity, the parts to be cut using EDM must be held firmly in place. This creates significant risk of deformation to tubing. It can also cause the cutting wire to contact the workpiece — shorting out the cut, causing the cutting wire to break, and possibly causing a “step” in the workpiece.

Although you can fixture a tube so that it rotates in the machine, the wire EDM cutting method is optimized for more complex shapes and not cost-effective for simple 2-axis cutoff of tubing. In addition, the wire EDM cannot do very short cutoffs (under 0.125”, or 3.175 mm) and does not produce quality cut end surface finishes. In fact, wire EDM cutting can result in surface roughness that is often characterized as “craters of the moon”!

So for applications such as medical device tubing that must be cut to very short lengths and have a very smooth end finish, a method such as thin-wheel abrasive metal cutting would deliver the necessary tight tolerance, burr-free results and a clean end cut without tube wall deformation.

What is the differences Between Wire Cut and Conventional EDM?

There are two main types of EDM: conventional, or sinker, and wire, or wire cut. Conventional EDM, as described above, uses a tool to disperse the electric current. This tool, the cathode, runs along the metal piece, the anode, and the electrical current reacts to melt or vaporize the metal. As a result of the dielectric fluid, usually a hydrocarbon oil into which both the cathode and the workpiece are immersed, the minute chips produced by the process wash away from the piece. Wire cut EDM (or WCEDM) discharges the electrified current by means of a taut thin wire, which acts as the cathode and is guided alongside the desired cutting path, or kerf. The dielectric fluid in this case—usually deionized water—is flushed through the cut as it proceeds, again serving to carry off particles and control the sparks. The thin wire allows precision cuts, with narrow kerfs (~0.015 in. routinely, with finer kerfs available) and tolerances of +/- 0.0001 in. possible. This heightened precision allows for complex, three-dimensional cuts, and produces highly accurate punches, dies, and stripper plates. 

Wire cut EDM equipment is run by computer numerically controlled (CNC) instruments, which can control the wire on a three-dimensional axis to provide greater flexibility. Simple cuts are done by varying the x-y coordinates of the cutter with more complex cuts achieved by adding axes of motion to the wire guides. Both four- and five-axis wire EDM machines and services are available. Whereas conventional EDM cannot always produce tight corners or very intricate patterns, wire EDM’s increased precision allows for intricate patterns and cuts. Additionally, wire EDM is able to cut metals as thin as 0.004 in. and thicker materials upwards of 16 in. routinely, with thicker sections possible. At a certain material thinness, wire EDM will simply cause the metal to evaporate, thereby eliminating potential debris. The wire of a WCEDM unit emits sparks on all sides, which means the cut must be thicker than the wire itself. In other words, because the wire is surrounded by a ring of current, the smallest and most precise cutting path possible is the added diameter of the ring and wire; technicians easily account for this added dimension. Manufacturers continue to produce thinner and thinner wire to allow for smaller kerfs and even finer precision.

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