EDM is a thermoelectric process used to remove metal via a series of discrete sparks between the metal and workpiece. In EDM an electric spark is used as the cutting tool to cut (erode) the workpiece and produce the finished part to the required shape. Electricity flows through the electrode in the form of a square wave attacking the points of least resistance on the workpiece, similar to a bolt of lightning hitting a tree before it hits the ground (http://www.polecraft.com.) The basic principle is shown in Figure 5.1.
Figure 5.1. Principle of the electric discharge machining process
In EDM, material removal is performed by applying a pulsating (ON/OFF) high-frequency current through the electrode to the workpiece. This removes (erodes) very tiny pieces of material from the workpiece at a controlled rate. The electrode and the workpiece are both immersed in a liquid called dielectric fluid. The workpiece is normally the anode and the tool is the cathode. A thin gap of about 0.025 mm is maintained between the tool and the workpiece by a servo system. A suitably shaped tool with feed mechanism is used to get the proper shape and size of the work. The dielectric used in the system is continuously circulated and filtered. No grinding or finishing is required after the EDM operation. A schematic diagram of the EDM process is presented in Figure 5.2.
Figure 5.2. Schematic of an electric discharge machine
EDM is basically of three types according to the electrode used, namely die sinking EDM, wire-cut EDM and micro EDM mill. Die sinking EDM consists of an electrode and the workpiece is submerged in an insulating liquid. The electrode and the workpiece are connected to a power supply in which the electrode is made according to the required shape. The machine uses the shape of the electrode to erode the inverse shape in the workpiece. This is one of the important accurate processes normally used for making mould cavities. The die sinking EDM arrangement is presented in Figure 5.3. In this form of EDM, the electrode is configured like the cavity desired in the workpiece. The machining speed depends upon the type of material, area of the material to be machined and the machining condition.
Figure 5.3. Conventional die sinking EDM
Source: www.materion.comIn wire EDM the electrode is a wire and is fed through an upper and lower diamond guide. The wire diameters usually range from 0.05 to 3.0 mm. The electrode is used only once and is discarded after it is used. Wire control is carried out by computer numerical control, which programs the path of the wire. This form of EDM is the most accurate and can be used for both rough and finish machining. A schematic of travelling wire EDM is presented in Figure 5.4. A third type of EDM recently developed is micro EDM mill in which the electrode has diameters of 50 μm to 10 mm. The complex electrode is replaced by a set of moving standardized electrodes. The process is similar to the conventional die sinking EDM. Micro EDM complements wire EDM by providing the ability to drill pilot holes through heat-treated materials and carbide. It can be used for machining deep cavities up to 10 mm with nearly vertical walls of 1.5° taper, and also for machining of very thin (< 0.1 mm) ribs. This technology is an important application in micro machining.
Figure 5.4. (a) Wire EDM, (b) micro EDM mill
Source: www.materion.comThe EDM process is used for making different kinds of workpieces. The EDM machine is programmed for vertical machining, orbital, vectorial, polygon, spherical, circular, directional, helical, conical, spin and indexing machining cycles. These different machining cycles are used for making parts, and are presented in Figure 5.5.
Figure 5.5. Tools of different cross sections and produced workpiece
Courtesy: Electronica Machine Tools Ltd, IndiaEDM has many advantages over conventional machining. Using EDM, electrically conductive material can be cut and has been used for machining hardened and heat-treated workpieces. Complex and intricate profiles can cut accurately, faster and at lower costs. Thin, fragile sections have been made easily and without burrs. EDM is mainly used in the tool and die industries. Today, EDM is an integral part of the process for making prototypes and production parts. Some of the applications of EDM are presented in Figure 5.6.
EDMs, or electronic discharge machines, are computer controlled machine tools that use electrical discharges or sparks to create a desired shape in a metal. An EDM machine may be interchangeably called spark machinery, die sinking, spark eroding or wire erosion since metals are subjected to different electrical process to obtain the desired design or shape. https://www.taguti.net/collections/view-more
