EDM 101: Electrical Discharge Machining Basics

EDM (electrical discharge machining) has long been the answer for high accuracy, demanding machining applications where conventional metal removal is difficult or impossible. Conceptually, it is very simple; electrical current passes between an electrode and a workpiece.  The spark discharge erodes it to form the desired final shape.


The whole process takes place in a dielectric bath such as oil or deionized water. EDM was developed during the Second World War by the Lazarenko Brothers in the Soviet Union and has since evolved into a major industry with several types of machinery. Electrical spark discharges have long been a method for achieving extremely high temperatures. In EDM processes, the plasma-like 10,000 C temperatures can create a complex environment at the microscopic level on the workpiece surface.


While it is generally understood to be a high temperature melting process, what is actually happening on the workpiece surface is still a subject of research. The major challenge in efficient EDM processing is control of electrode. There are other parameters, including electrode shape for some processes – issues which made computer numerical control a breakthrough technology for widespread adoption of EDM.


Three major types of EDM machines


While there are numerous specialty forms of electrical discharge machining, industrial machines are commonly grouped into three categories:


  • Wire EDM
  • Die sinker or ram EDM
  • Hole drilling or “hole popper” machines


As the name implies, wire EDM uses a thin wire as the electrode, which carries the spark inducing electrical potential. It is programmed to move in a carefully controlled pattern roughly analogous to a woodworker’s scroll saw. Control of the wire movement in an XY plane is similar to other CNC-driven technologies, but with the unique conditions of EDM and special requirements. Logical discharge erodes the electrode as well as the workpiece, so typically a spool of wire is used for the electrode, passing continuously by motor drive to present a fresh discharge path in the cut.


Also, during the process an unstable discharge can be created if the dielectric breaks down in the cut region, or wear debris contaminates it. Control electronics can compensate to a certain extent, but clean dielectric fluid must be pumped continually to flush the cutting zone.


The “cheese cutter” wire EDM technology is popular, but has one important limitation: wire must pass entirely through the workpiece, making essentially a two-dimensional cut in a three-dimensional part. Complex cavity shapes that are needed in many tool and die applications, such as metal stamping dies and plastic injection mould can be EDM processed using “die sinker”  (sometimes called “ram”) EDM.


In this process, an electrically conductive graphite electrode is machined precisely to form a “positive” of the desired cavity that is carefully plunged into the workpiece. Logical spark occurs over the surface of the graphite electrode. The ability to produce complex, three-dimensional cavities is a major advantage. Disadvantages include the need to machine the electrode, more complex electrode wear control issues and occasional difficulties in flushing the cut.


EDM can also be used in hole-making operations. If a small pilot hole is pre-drilled in the workpiece, wire can be threaded through, and conventional wire EDM used. Where this is impossible – in blind hole applications, for example – a specialized EDM hole making machine can be used. Commonly called a “hole popper,” these machines use a rotating conductive tube as the electrode, with a continuous flow of dielectric (usually deionized water) to flush the cut.


This technology is also used with wire EDM machines to create the pilot hole necessary for wire threading. Accurate, precise holes are possible and have allowed for several advanced technologies. Perhaps the most important is the use of EDM created cooling holes in high temperature alloy turbine blade sections. This permits a “film cooling” process, which allows jet engines to operate at higher temperatures for greater durability and efficiency.


Why EDM?


In practical terms, Electrical Discharge Machining overcomes a major issue with conventional machining: hardness.


In traditional machining processes, metal workpieces are typically made from special grades of hard enable tool steels, which are machined in an annealed or soft state to facilitate cutting.


After the desired shape is machined, the parts are then hardened by one or more heat treatments. This adds time, cost and can alter the finished parts’ dimensions, especially if a poorly controlled heat treatment process is used. EDM, however, can cut hardened materials and exotic metal alloys and as a bonus produces excellent surface finishes, frequently reducing the need for post machining grinding or surface treatment steps.


Like all machining processes, EDM is a balancing act between speed and surface finish. In wire EDM processes for example, it is common to use a faster, rough-cut followed by the finishing or skimming cut, which uses a less aggressive flushing profile to minimize wire deflection. Material removal can be precisely controlled, typically measured in “tenths.”


If you need further details about electrical discharge machining, welcome to visit our website and feel free to contact OCEAN Technologies Co., Ltd. – the professional EDMs manufacturer in Taiwan.


Article Source: http://www.engineering.com/AdvancedManufacturing/ArticleID/10100/EDM-101-Electrical-Discharge-Machining-Basics.aspx


What is Electrical Discharge Machining (EDM)?

Electrical discharge machining (EDM) is a type of machining operation used for shaping conductive workpieces into geometrically complex parts. Electrical discharge machines are particularly ideal for machining components that have complicated contours or subtle cavities that would be difficult to produce with other conventional machining equipment. The process involves supplying electricity to both the shaping tool as well as the workpiece and then bringing the tool into close proximity with the workpiece, which is completely immersed in a dielectric fluid bath. This proximity causes the electrical field intensity between the tool and workpiece to overcome the strength of the dielectric fluid, and produces a series of electrical discharges between them. These electrical discharges remove material from the workpiece, and the pattern or shape of material removed is dependent on the shape of the tooling electrode. After the machining operation, the dielectric fluid is replaced between the electrodes. Apart from acting as a dielectric between the two electrodes, the fluid also plays a key role in the machining process, as it is used to flush away the removed material and cool the machined area. The nature of the process is such that, while material is being removed from the workpiece; the tooling electrode is also gradually eroded, making periodic replacement necessary.


The electrical discharge machining process is extremely precise and generally used in the production of components that are typically complex and require extreme accuracy. In addition, another area of application that EDMs perform above par is in the machining and shaping of hard or exotic materials such as titanium, Hastelloy, Kovar, Inconel, as well as hardened steel. However, the only caveat with the electrical discharge machining process is that it can be only be used with conductive materials.


There are essentially two types of electrical discharge machines, which differ in the type of tooling electrode that they are outfitted with. They are sinker EDMs and wire EDMs. The sinker EDM, also known as a ram EDM uses a shaped tooling electrode to facilitate the machining process. This tooling electrode is formed by conventional machining into a shape that is specific to the application it is used for and an exact reverse of the shape to be machined into the workpiece. The tooling, typically machined from graphite, is used with an insulating fluid such as oil or other dielectric fluids. This shaped tooling is connected to a power supply and made to approach the workpiece electrode, creating electrical discharges between them, which cause erosion in the desired shape. This type of EDM is typically used for precise machining of complex 3D parts, such as injection molding, die tooling, and other components that require exceptional accuracy.


The wire EDM, on the other hand, is an electrical discharge machine that uses a fine metallic wire, usually made from brass, which acts as a cutting electrode to accurately shape intricate, complex components from thick metal plates. The wire and workpiece are both supplied with electricity and when the wire approaches the workpiece, electrical discharges occur between them. These discharges remove material from the workpiece in a shape that is similar to a cutting or slicing action. As the wire electrode is eroding along with the workpiece, it is continuously fed into the workpiece from a spool to ensure uninterrupted cutting operation. The wire is fed through two guides, typically made from diamonds, each placed above and below the workpiece electrode. These guides are movable on a 2-axis x-y plane and are CNC controlled for cutting. The cutting operation occurs on a workpiece that is completely immersed in a dielectric fluid bath, normally de-ionized water, which is used as a coolant and to flush away the removed material. This machining process is used to cut complex and intricate 2D shapes on thick metal parts, especially components from hard and exotic metals such as Inconel and titanium. Some components commonly machined using wire EDMs are stripper plates, custom gears, and other parts that need to be intricately cut out. However, the advent of upper guides and multi-axis freedom of movement in the newer wire EDMs, allows these machines to cut intricate tapers and transitional shapes as well.


Welcome to visit EXCETEK, the leading manufacturer of wire cutting machine, established in 2006 specializing in various series of wire cutting EDM machines (Electrical Discharge Machining). We insist to provide only the best electrical discharge machines and related accessories to our clients around the world, and we have also earned well reputations by high quality wire cut machines we manufactured. For more specification, please browse our product list and feel free to contact us, the superior EDM machine manufacturers to get more wire cutting machines and electro discharge machining.



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