Electrical Discharge Machining (EDM)

One of the most recent developments in electric discharge machining (DM) drilling is fast hole EDM drilling, which was developed to facilitate quick hole making jobs. With this latest EDM technology, it is possible to drill precision holes up to 70 percent faster than any other available drilling method, no matter what the type of metal or how hard it is.

Since workpieces intended for industries like aviation, power engine turbines, and aerospace require techniques for core competency that revolve around vanes and blades produced to tolerate intensely high-heat in certain crucial sections, it is necessary to transform EDM drilling hardware from solid airfoil to hollow airfoil configurations. Such cooling holes in the airfoil—the cross-sectional shape of a blade, wing, propellor, rotor or turbine—have become the industry standard, as engine manufacturers have started to design an increasing number of components using them. The cooling holes keep these vital parts safe from exceedingly high temperatures for most materials. Temperatures often rise far above the materials' own melting point. Further, blades and vanes are often cast from cobalt and nickel alloys, making laser machining or EDM drilling processes necessary in creating the necessarily small holes in such materials.

What is EDM?

EDM is the process that makes it possible to create a desired workpiece shape in the manufacturing using electrical discharges, or sparks, which is why it is sometimes referred to as spark machining. In this process, the material is removed from the workpiece by a series of recurring current discharges between two separate electrodes that remain separated by a dielectric liquid undergoing targeted electric voltage. One of the electrodes in the process is called the tool electrode, or sometimes the "tool" or "electrode," while the other electrode is referred to as the workpiece-electrode, or "workpiece."

As the time and point at which the electric voltage between the two electrodes increases and grows closer, the intensity of the electric field in the volume between the two electrodes becomes greater than the strength of the dielectric fluid field—at least in some spots—breaking down and allowing current to flow freely between the two electrodes. One key to success for this process relies on the tool and the workpiece never making actual physical contact.

This phenomenon is similar to the breakdown of a capacitor, or condenser, which is also known as breakdown voltage and shares the same result in removing material from electrodes to achieve the desired shape for other purposes. Once the current between the two electrodes stops—or is stopped, which depends on the type of generator used—new liquid dielectric is generally conveyed into the inter-electrode volume. This step enables the solid particles, or debris, to be flushed and carried away so the insulating properties associated with the dielectric fluid can be restored. The process of adding new liquid dielectric to the inter-electrode volume is typically known and referred to as "flushing." After a current flow, the difference of potential—also known as the difference of potential between two points—between the electrodes is restored to its pre-breakdown condition, allowing for a new liquid dielectric breakdown process to occur.

The Three Types of EDM Machines

There are many specialized forms of EDMs, industrial EDM machines generally fall into one of the following three main categories.

Die Sinker or RAM EDM

More commonly referred to as sinker EDM, which is a task created for difficult-to-machine materials such as tungsten since erosion is more precisely controlled if the electrodes are immersed in a dielectric fluid. The sinker EDM machining process uses an electrically charged electrode, which is configured to a specific geometrical shape. The process burns the geometry of the electrode into the metal component. This process is commonly used in the mass production of dies and molds.

Wire EDM

In the wire EDM process, the tool electrode is a wire that is frequently made of a thin, single strand of brass. The wire is fed through the workpiece then submerged in a tank of dielectric fluid, which is most often composed of deionized water. To protect the wire from erosion, which could cause it to break, the wire is wound between two spools to allow for the active part of the wire to constantly change.

Fast Hole Drilling EDM

This type of hole drilling relies on an energized rotating tube electrode, along with high-pressure flushing, to produce fast and accurate machining that results in small, deep holes in conductive metals.

Each EDM type operates on the same principle of erosion or wearing via electrical discharge.

What are the Key Benefits of Fast Hole EDMs Over Conventional EDMs?

Fast hole EDMs delivery precision drilling results at a high speed and with a high rate of accuracy, which are important for a wide range of highly specialized industries today, such as aviation and power engine turbine manufacturing. In these industries, parts must undergo extreme conditions, such as extreme heat and fast rotation, making it imperative that all parts have a high tolerance and can withstand those conditions and more. EDM allows manufacturers to cut and drill the necessary shapes that would not be possible with traditional machinery.

Following are additional benefits that fast hole EDMs have over conventional EDMs:

• Features 6-axis machining capability

• Capable of creating round holes from .010" diameter to .080"

• Holes are created very quickly with very good surface finishes and low recast layers

• Can produce round, conical and shaped airfoil holes to accommodate the designs of today’s major OEMs

• A single point electrode can EDM mill shaped hole geometries while producing a round hole through the airfoil wall in a single step