History and Types of Electrical Discharge Machining (EDM)
– Electrical discharges were first noted to have an erosive effect in 1770 by Joseph Priestley.
– In 1943, Lazarenko and Lazarenko invented an EDM machine for working difficult-to-machine materials.
– Simultaneously, an American team developed an EDM machine for removing broken drills and taps.
– Lazarenko and Lazarenko’s machine is known as an R-C-type machine.
– Wire-cut EDM arose in the 1960s for making tools from hardened steel.
– Sinker EDM, wire EDM, and fast hole drilling EDM are different types of EDM machines.
Generalities and Advantages of EDM
– EDM is primarily used for hard metals or materials difficult to machine with traditional techniques.
– EDM can cut intricate contours or cavities in pre-hardened steel without the need for heat treatment.
– EDM can be used with metals such as titanium, hastelloy, kovar, and inconel.
– EDM is considered a non-traditional machining method.
– EDM is often grouped with processes such as electrochemical machining, water jet cutting, and laser cutting.
– EDM does not require direct contact between the tool and workpiece, reducing the risk of tool wear.
– It can machine complex shapes and fine details with high accuracy.
– EDM is effective for hard materials that are difficult to machine with conventional methods.
– The process can achieve a good surface finish without the need for secondary operations.
– It is suitable for both small-scale and large-scale production.
Process Description and Wear in EDM
– EDM involves breakdown and restoration of the liquid dielectric between the electrodes.
– Debris removal from the inter-electrode volume is often partial.
– The inter-electrode distance is controlled by machine algorithms.
– Short-circuits and arcing can occur, leading to unwanted changes in shape and damage.
– Small craters on the tool result in gradual erosion of the electrode.
– Wear can be counteracted by continuously replacing the tool-electrode.
– Strategies to address wear include using a rotating disk as a tool-electrode and employing multiple electrode strategies.
Technological Parameters and Measurement of Electrical Parameters
– Two broad categories of generators on EDM machines: RC circuits and transistor-controlled pulses.
– RC circuits offer little control over discharge duration, while transistor-controlled pulses allow control over pulse shape, duration, and amplitude.
– Maximum duration of discharge is equal to pulse duration.
– Parameters may vary depending on the generator manufacturer.
– A framework proposed by Ferri et al. allows for direct measurement of electrical parameters during EDM operations.
– Estimating electrical parameters without relying on machine manufacturers’ claims is possible.
– Electrical parameters vary significantly when machining different materials.
– An oscilloscope can be used to measure electrical parameters externally to the machine.
Applications and Disadvantages of EDM
– EDM is widely used in industries such as aerospace, automotive, and medical.
– It is used for manufacturing molds, dies, and tooling.
– EDM can create intricate features in small and delicate components.
– It is suitable for materials like hardened steel, titanium, and tungsten carbide.
– EDM is also used for removing broken taps and drills.
– Difficulty finding expert machinists and slow rate of material removal are disadvantages of EDM.
– There is a potential fire hazard with oil-based dielectrics.
– Additional time and cost are required for creating electrodes.
– Reproducing sharp corners on a workpiece can be challenging. Source: https://en.wikipedia.org/wiki/Electrical_discharge_machining
Electrical discharge machining (EDM), also known as spark machining, spark eroding, die sinking, wire burning or wire erosion, is a metal fabrication process whereby a desired shape is obtained by using electrical discharges (sparks). Material is removed from the work piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. One of the electrodes is called the tool-electrode, or simply the tool or electrode, while the other is called the workpiece-electrode, or work piece. The process depends upon the tool and work piece not making physical contact. Extremely hard materials like carbides, ceramics, titanium alloys and heat treated tool steels that are very difficult to machine using conventional machining can be precisely machined by EDM.
When the voltage between the two electrodes is increased, the intensity of the electric field in the volume between the electrodes becomes greater, causing dielectric break down of the liquid, and produces an electric arc. As a result, material is removed from the electrodes. Once the current stops (or is stopped, depending on the type of generator), new liquid dielectric is conveyed into the inter-electrode volume, enabling the solid particles (debris) to be carried away and the insulating properties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. After a current flow, the voltage between the electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur to repeat the cycle.
