Mastering Plunge EDM: The Ultimate Guide to Precision Electrical Discharge Machining

What Is Plunge EDM?

Plunge EDM (electrical discharge machining) goes by many names, but is most commonly known as sinker EDM or conventional EDM. This process contains the electrodes and a workpiece submerged in an insulating liquid, usually oil or other dielectric fluids. Plunge EDM utilizes a custom machined electrode that “plunges'' a shape into a material, creating extremely precise cavities in the material capable of conducting electricity. The electrodes, which are commonly made of copper, graphite, or tungsten, appear as a reverse of the required shape. Just like other EDMs, the tool-electrode degrades with use, and additional electrodes are required for subsequent sinker applications long-term.
 

How Does Plunge EDM Work?

The plunge EDM utilizes an electrically charged electrode to burn a desired geometry into a metal component. The process is commonly undertaken in production of dies and molds. During the process, two metal components submerged in dielectric fluids are connected to a source of current that switches on and off automatically based on the variables set on the controller. When the current is switched on, an electric tension is established between the two metal components.

Once the two components are joined together within a fraction of an inch, the electrical tension is discharged, and sparks jump across. The metal is heated up so much as a result that it starts to melt. The use of spark spray will gradually shape the desired form in the piece of metal depending on the shape of the electrode. Tons of sparks should jump across per second before erosion can happen.
 

Plunge EDM Machines

The equipment for plunge EDM has many uses. It can make starting holes for wire EDM to mirror an electrode shape into the desired shape in a part. There is only so much, for example, a milling machine can do, especially when you need to create intricate holes or cavities. The plunge EDM machine can take advantage of all movable axes to produce the cavity without damaging the rest of the part. This will also allow plunge EDM to reach the parts where there is no other way to get to them. Tool changers for the machine are also available because sometimes multiple electrodes are required for some parts, which makes lights-out production very probable. 
 

Plunge EDM Electrodes

Electrodes of plunge EDM can be made of a variety of materials, such as brass or graphite. In some cases, the upper mold cavity can be used as the electrode. When creating the electrode, it can take the shape of something as simple as a round or square tip, or a more complex, three-dimensional shape that is burnt in the workpiece as a reverse image. With the vast development in controls and programming, these complex shapes are typically made on vertical machining centers with high spindle speeds at which the desired finishes are achieved to make the electrodes and vacuum systems that are needed to remove the graphite dust produced. That said, some sinker EDMs have been honed to be able to make the shape in the part direction by using simple electrodes as well.
 

What Are the Applications of Plunge EDM?

Plunge EDM machining, as with its prevailing counterpart wire EDM, uses spark erosion to machine blind cavities. This process finds its use in many applications, such as blind cavities, intricate details, sharp corners, fine surface finishes to 10 micro inches, thin walls and cross sections, blind keyways, machining threads into hardened parts, internal squares or hexes, tolerances that need to be held to 0.001”, and the machining of a number of conductive materials including aluminum, carbide, copper, brass, steel, titanium, etc. In a nutshell, the superb in-house electrode manufacturing capabilities make plunge EDM technologies a desirable counterpart to wire EDM. Depending on the machining and wear requirements, the electrode materials of plunge EDM machining will vary as well.
 

What Are the Differences between Plunge EDM and Wire EDM?

The difference between plunge EDM and wire EDM primarily lies in the different spark erosion techniques. Wire EDM, as the name suggests, uses wire as the electrode to burn a predetermined contour through the part. Plunge EDM, as we’ve touched base above, sinks the shape into the workpiece. 

Another difference is that plunge EDM machining is designed for maximum reliability and precision. Over the course of its advancement, plunge EDM machines have created a wide spectrum of high-precision products, such as satellites, rocket engines, and other space crafts. Wire EDM machining, on the other hand, is known for its ease of production, speed, and low maintenance. The automatic wire feeding ensures that the cutting remains consistent and wire is never worn, which results in recurring accuracy. During the cutting process, debris is washed away to help operators determine the suitable maximum feed rate for any material. And being the state-of-the-art EDM process, wire EDM also offers reliable, robust, and cutting-edge performance while remaining user-friendly.