Parameters of thermal power spark machining

Parameters of EDM

Keywords: EDM special machining EDM

the concept of EDM is a special machining method that uses the electric erosion generated by the pulse discharge between the two poles immersed in the working fluid to etch away conductive materials, also known as EDM or electric erosion machining, which is called EDM for short in English

in 1943, the Soviet Union scholar Lazarenko and his wife studied and invented EDM. Later, with the improvement of pulse power supply and control system, some outsourcing enterprises only mastered the size of oil cylinder and developed rapidly. The first pulse power supply used was a simple resistance capacitance circuit. In the early 1950s, it was improved into resistance inductance capacitance circuit. At the same time, the so-called long pulse power supply such as pulse generator is also used to improve the etching efficiency and reduce the relative loss of tool electrode

then came high-frequency pulse power supplies such as high-power electronic tubes and thyristors, which improved the productivity under the same surface roughness. In the mid-1960s, transistor and thyristor pulse power supply appeared, which improved energy efficiency and reduced tool electrode loss, and expanded the adjustable range of rough and finish machining

by the 1970s, high and low voltage composite pulses, multi loop pulses, equal amplitude pulses and adjustable waveform pulses had appeared, and new progress had been made in machining surface roughness, machining accuracy and reducing tool electrode loss. In the aspect of control system, from simply maintaining the discharge gap and controlling the advance and retreat of tool electrode at the beginning, it has gradually developed to using microcomputer to timely control various factors such as electrical parameters and non electrical parameters

during EDM, the tool electrode and workpiece are respectively connected to the two poles of the pulse power supply and immersed in the working fluid, or the working fluid is charged into the discharge gap. The automatic gap control system controls the tool electrode to feed the workpiece. When the gap between the two electrodes reaches a certain distance, the pulse voltage applied on the two electrodes will breakdown the working fluid and produce spark discharge

a large amount of heat energy is instantaneously concentrated in the micro channel of discharge, the temperature can be as high as 10000 degrees Celsius, and the pressure also changes sharply, so that at this point, a small amount of metal materials on the working surface immediately melt, vaporize, and explode into the working fluid, which quickly condenses, forming solid metal particles, which are taken away by the working fluid. At this time, a tiny dent mark is left on the surface of the workpiece, the discharge stops briefly, and the working fluid between the two electrodes recovers the insulation state

then, the next pulse voltage breaks down at another point where the two electrodes are relatively close, generating spark discharge, and the above process is repeated. In this way, although the amount of metal removed by each pulse discharge is very small, because there are thousands of pulse discharges per second, more metal can be removed, with a certain productivity

under the condition of maintaining a constant discharge gap between the tool electrode and the workpiece, while eroding the workpiece metal, it is not only facing the new round of "return to the Asia Pacific" background of the United States with containing China as the core in diplomacy, but also making the tool electrode continuously feed into the workpiece, and finally machining the shape corresponding to the shape of the tool electrode. Therefore, as long as the shape of the tool electrode and the relative movement mode between the tool electrode and the workpiece are changed, various complex surfaces can be machined

tool electrodes are commonly made of corrosion-resistant materials with good conductivity, high melting point and easy processing, such as copper, graphite, copper tungsten alloy and molybdenum. In the process of machining, the tool electrode also has loss, but it is less than the corrosion amount of the workpiece metal, and even close to no loss

working fluid, as the discharge medium, also plays the role of cooling and chip removal in the machining process. Commonly used working fluids are media with low viscosity, high flash point and stable performance, such as kerosene, deionized water and emulsion

according to the form of tool electrode and the characteristics of relative motion between tool electrode and workpiece, EDM can be divided into five categories: EDM with forming tool electrode and simple feed motion relative to workpiece; Using the axially moving metal wire as the tool electrode, the workpiece moves according to the required shape and size, so as to cut the conductive material in WEDM; Using metal wire or formed conductive grinding wheel as tool electrode to carry out EDM grinding of small hole grinding or formed grinding; It is used for EDM conjugate rotary machining of thread ring gauge, thread plug gauge, gear, etc; Small hole processing, engraving, surface alloying, surface strengthening and other kinds of processing that stops (1min~6hour) actively pulling out of the battery

EDM can process materials and workpieces with complex shapes that are difficult to be cut by ordinary cutting methods; No cutting force during machining; No burrs, knife marks, grooves and other defects; The tool electrode material need not be harder than the workpiece material; Direct use of electric energy processing, easy to achieve automation; After processing, there is a metamorphic layer on the surface, which must be further removed in some applications; The purification of working fluid and the treatment of smoke pollution produced in processing are relatively troublesome

EDM is mainly used to process molds and parts with complex shaped holes and cavities; Processing all kinds of hard and brittle materials, such as cemented carbide and quenched steel; Processing deep and fine holes, special-shaped holes, deep grooves, narrow seams and cutting thin sheets; Processing all kinds of forming tools, templates, thread ring gauges and other tools and measuring tools

EDM is a new process completely different from mechanical machining

with the development of industrial production and the progress of science and technology, new materials with high melting point, high hardness, high strength, high brittleness, high viscosity and high purity continue to appear. There are more and more workpieces with various complex structures and special process requirements, which makes the traditional machining methods unable to process or difficult to process. Therefore, in addition to further developing and improving machining methods, people also strive to find new machining methods. EDM can meet the needs of production development and show many excellent properties in application. Therefore, it has been rapidly developed and increasingly widely used

the characteristics of EDM are as follows:

1 The energy density of pulse discharge is high, which is convenient for processing special materials and workpieces with complex shapes that are difficult or impossible to be processed by ordinary machining methods. It is not affected by material hardness and heat treatment

2. The duration of pulse discharge is very short, the range of heat conduction and diffusion generated during discharge is small, and the range of material heating influence is small

3. During machining, the tool electrode is not in contact with the workpiece material, and the macro force between them is very small. The tool electrode material does not need to be harder than the workpiece material, so the tool electrode is easy to manufacture

4. It can reform the workpiece structure, simplify the processing technology, improve the service life of the workpiece and reduce the labor intensity of workers

based on the above characteristics, the main uses of EDM are as follows:

1) manufacturing stamping dies, plastic dies, forging dies and die-casting dies

2) machining small holes, abnormal holes and threaded screw holes on cemented carbide

3) cut the parts on the metal plate

4) process narrow seams

5) grinding plane and circular surface

6) others (such as strengthening metal surface, taking out broken tools, punching on quenched parts, directly machining parts with complex profile, etc.)