Electrical Discharge Machining (EDM)
Electrical Discharge Machining or as it is more commonly referred to EDM, is a technology for subtractive manufacturing that uses a controlled release of electrical current in the form of sparks to slowly remove material from a part.
EDM machining goes by many other common industry names, such as die sinking, wire burning, wire erosion, EDM cutting, EDM drilling, spark machining and spark eroding, among others. The principle of EDM is that the spark is transmitted from a tool electrode on the machine to the workpiece which is held in close proximity. The spark is passed through a dielectric fluid which helps to control the spark and acts as a secondary electrode. The electricity starts to erode and re-shape the electrically conductive workpiece (typically metal). There are several different technologies that fall under EDM, and each has its own use and value to the machining process. Three of the most common are detailed below.
Wire EDM works by passing a conductive single stranded metal wire (usually brass) through the part to be machined. It may be easiest to think of this process as working like a band saw. Electricity is passed through the wire and the wire strand is constantly cycled through the machine (fed from a spool), as it runs down through the part to be cut, the machine table traverses perpendicular to the blade therefore feeding the part into the wire as it cuts. As the electricity passes through the wire it jumps off to the workpiece, creating a spark and starting to erode the material. For this to function properly a very small gap must be maintained between the wire and the surface to be machined. This gap is what the spark jumps across. As in all Electrical Discharge Machining technologies, the bed that the workpart sits on is submerged in a dielectric fluid, usually deionized water in the case of wire EDM. The aids in controlling the resistivity and electric pathway as well as washing away any debris created by the machining process. Wire EDM machines are CNC controlled and use wires as thin as .001” so they can manufacture intricate parts and complex shapes and do so in a repeatable fashion. The wire angle can be tilted so cuts can be made on an angle (typically up to 45 degrees), and cut parts in thicknesses of up to 24” or even more.
Sinker Electrical Discharge Machining is also often referred to as Conventional EDM, Die-sinking EDM, Plunge EDM or Ram EDM. A sinker EDM functions more like a drilling or milling machine as it ‘rams’ an electrode down onto the part. As in wire EDM a very small gap is left between the electrode and the part, which is the area the electricity jumps across thus creating a spark. The entire table, part and electrode are submerged in a dielectric fluid, commonly oil, which both flushes debris and helps control (through electrical resistance) the flow of electricity. The electrode can be machined to various different shapes and sizes to create different sized features in the workpiece. One common example is a hex shape which can produce a hex shaped blind hole in the part. As the electrode is lowered close to the surface of the part thousands of sparks per second are sent between the electrode and the part. The electrode works in a pecking motion, as it raises and lowers in short, small travel intervals to give clearance and flush away debris.
Hole Drilling EDM
The process of drilling holes with EDM or as it is sometimes called, Small Hole EDM, Fast Hole EDM Drilling or Hole Popping, is used to (as the name suggests) drill very small and accurate holes in metal materials. The process operates similarly to Sinker EDM, however with Hole Drilling EDM the electrode is made up of a round, hollow rod. High pressure dielectric fluid is passed through the center of the electrode, serving to both stiffen it (enabling higher external forces that are applied through process) and to flush away particulate generated. The electrode is also rotating at a high rate of speed as it is mounted in a rotary spindle, thereby functioning similar to a drill. Like other EDM types, the electrode is extended to very close proximity of the workpiece, but never actually makes contact. The gap is what allows the spark to ‘jump’ and create the erosion process. Hole Drilling EDM typically utilizes an electrode made of copper or brass.
Our EDM Process and Approach
EDM Technologies provide significant advantages to traditional machining approaches, and as such certainly have their place in industry. At Alle-Kiski we leverage EDM techniques to supplement our capabilities and fill gaps that traditional machining cannot fill. In some cases a project requirement or design may require a part to be completely machined via EDM and in some cases there may be segments or features of the work that are completed with EDM. In addition to in house capabilities we have a strong partner network that enables to round out our Electrical Discharge Machining capability.
Our approach is focused around flexibility. We thrive in projects that range from low volumes or even single piece such as prototyping, to high volume production runs. We can support a variety of materials, from steel to stainless steel to aluminum to plastics to exotic metals and everything in between. We cover industries from medical, to energy to defense to instrumentation and robotics and more.From small high precision parts to large part requirements, our goal is to service a wide range of needs for our customers. To supplement our internal capabilities, we have built out a strong partner network that allows us to fill in any gaps, and maximize response time.
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EDM technologies are generally ideal for greater levels of intricacy then traditional machining processes. Features or designs with very tight internal corners or radius or require superior finishes on internal features, are generally good candidates. Some example operations include but are not limited to-
- Machining of internal features of die shoes for making punched parts
- Machining of moulds for various moulding processes
- Machining of blind holes
The Advantages of EDM
Electrical Discharge Machining is Computer Numerical Controlled (CNC) machining process, so like CNC Machining discussed above, EDM machines can achieve very tight control and consistency over the manufacturing process. They also require programming of the machine in advance of part creation. Generally speaking EDM machines can hold tighter tolerances and improved finish specifications over traditional machining technologies. EDM is also an ideal solution for metals with higher hardness properties, as the cutting rate is often un-affected by hardness of the work material. This means that raw materials can be machined fully-hard and therefore do not require post-processing heat treat to harden the part. This can improve cost and manufacturing lead time. EDM machines can also be used to cut very intricate surface contours which are more challenging for traditional machining technologies.