Principle of EDM Processing

The fundamental tenet of  EDM Processing is the electro-corrosion phenomenon that occurs during pulsed spark discharge between the tool and the workpiece electrode (positive and negative electrodes), which is used to remove extra metal. Instantaneously after the electric spark is discharged, a significant quantity of heat is produced in the spark channel, reaching a high temperature sufficient to melt and gasify any metal substance locally and etch away material to create a discharge pit.

The principle of EDM processing is that the workpiece and the tool are respectively connected to two different polarity output ends of the pulse power supply, and the automatic feed adjustment device keeps a nearly equal discharge gap between the workpiece and the electrode. After the pulse voltage is applied between the two electrodes, the medium of the working fluid will be broken down at the place where the gap is the smallest or where the insulation strength is the lowest, forming a discharge spark.

The instantaneous high temperature of the plasma in the discharge channel causes a small part of the material to be etched away on the surface of the workpiece and the electrode, forming a tiny discharge pit. After the pulse discharge ends, after some time, the working fluid restores its insulation, and the next pulse voltage is applied to the two poles, and another cycle is also performed to form another small pit. When this process is repeated at a fairly high frequency, the tool electrode adjusts its relative position to the workpiece without any plans to process the required parts. From a microscopic point of view, the processed surface is composed of many small pulse discharge pits.

EDM Processing Conditions

EDM Processing is typically performed in liquid media, and the initial stage of pulse discharge is the breakdown of the medium between electrodes. Different contaminants can be found in the liquid medium used between the two electrodes. These impurities are drawn to the region with the strongest electric field intensity when there is an electric field. To minimize the breakdown voltage of the gap and shorten the actual distance between electrodes, a specific contact bridge is built along the power line. As a result, the electric field intensity is significantly boosted while maintaining the same voltage.

EDM Processing Characteristics

Under the action of an electric field, electrons move toward the anode at high speed, and hit neutral molecules and atoms in the medium during the motion, resulting in impact ionization, forming negatively charged particles (mainly electrons) and positively charged particles (positrons), resulting in charged an avalanche of particles.

When the electrons reach the anode, the medium is broken down, spark discharge is generated, and a conductive channel is formed, and then the energy accumulated in the power supply is injected into the discharge point and the gap between the two poles along the discharge channel. The electric erosion effect when the spark discharge is generated between the two electrodes is used to etch away the excess metal material, so as to meet the predetermined processing requirements for the size, shape and surface quality of the parts.

Characteristics of EDM Processing

1. It is convenient to process workpieces that are difficult or impossible to process by mechanical cutting (such as hardened steel mold parts, hard alloy mold parts, etc.)

2. Since the tool electrode and the workpiece to be processed are not in contact during the processing, the macroscopic force between the two is very small, so it is convenient to process the small holes, deep holes, and narrow slots of the workpiece without being affected by the tool electrode and the workpiece. stiffness limit. For various holes, three-dimensional curved surfaces, and complex shapes of the mold, the EDM method can be used to complete the processing at one time. The material used for the tool electrode does not have to be harder than the workpiece.

3. Directly use electric energy and thermal energy for processing, which is convenient for automatic control of the processing process.

4. The duration of the pulse discharge is short, and the heat-affected zone generated by the discharge is small, which can ensure good processing accuracy and watch quality.

5. Rough and finish machining can be performed on the same machine tool by adjusting the pulse parameters.

Basic Conditions of EDM Processing

1. There must be a certain distance between the tool and the workpiece, usually a few microns to hundreds of microns, and this distance can be maintained.

2. There must be a large enough energy density at the pulse discharge point, that is, the discharge channel must have a large current density, generally 105~106/cm2, so that a large amount of heat generated during discharge is enough to locally melt and vaporize the metal, and Under the action of the explosive force of the discharge, the molten metal is thrown out.

3. The discharge should be a short-term pulse discharge, and the duration of the discharge is 10-7~10-3 S, so that the heat generated by the discharge has no time to conduct and spread to the rest, and each discharge is distributed in a small range. It will not generate a lot of heat like continuous arc discharge, which will melt and burn the metal surface.

4. Pulse discharge needs to be repeated many times, and each pulse discharge is dispersed in time and space, that is, each pulse discharge is generally not performed at the same point to avoid local burns.

5. EDM processing must be carried out in a liquid medium with certain insulating properties. The liquid medium, also known as the working fluid, must have a high dielectric strength, and the general resistivity is 103~107Ω·cm, to facilitate the generation of pulsed discharge sparks. At the same time, the working fluid should remove the small metal chips, carbon black, and other electric corrosion products produced in the EDM processing in time, and have a more effective cooling effect on the tool electrode and the surface of the workpiece to ensure that the processing can continue normally.