EDM machines operate on the principle of the effect of electric charges on the workpiece surface in an electrically conductive medium.

Due to this, electrical erosion occurs in a given direction, which makes it possible to obtain a specific shape or dimensions of the part.

1 WORKING PRINCIPLE

EDM cutting occurs during the occurrence of a pulse of a gaseous electric discharge, which has a directional effect. The scheme is such that in this case, the destruction and removal of part of the material in the impact zone occurs.

Under the influence of high temperature in the area of ​​the occurrence of discharges, the metal melts(brass or copper wire) with its partial evaporation. In order to obtain the required temperature, the circuit uses a pulse generator to concentrate a large number of energy.

The electrodes between which the discharge occurs are the part itself, on the one hand, and the tool, on the other. The space between them is filled with a working fluid, which is constantly supplied during the operation of the machine through a supply tube (brass or copper), if the processing does not take place in a special bath.

EDM machines, which use electrical discharges of various types and methods for their production, can produce several types of EDM metal processing:

• electrospark circuit;
• electrocontact scheme;
• electrical impulse circuit;
• anode-mechanical (combined circuit).

When working with various materials, a piercing electroerosive CNC machine has one limitation They must have good electrical conductivity. If the material does not have this property, then the piercing machine will not be able to work.

1.1 The process of the EDM machine (video)

2 Main types of electrical discharge machining

Electroerosive wire cut machine is used for the following types electroerosive machining of metal parts:

• stitching;
• bulk copying;
• cutting/cutting;
• grinding;
• fine-tuning;
• marking;
• hardening.

Electrocontact processing possible while doing:

• cutting;
• work with bodies of revolution;
• processing of internal cavities;
• gear surfaces;
• processing of flat and conical surfaces;
• hardening.

2.1 Sodick machines

The Japanese manufacturing company Sodick Co LTD, which began operations in 1976, is today the world leader in the production and sales of EDM machines.

Representative offices of Sodick are located in Asia, the USA, Europe and its products are well-deservedly popular with industrial enterprises who deal with the processing of materials such as titanium and tool steel.

Sodick is the only manufacturer in the world that produces a CNC EDM piercing machine with linear motors and a working area made of ceramic. Sodic specialists developed a revolutionary electrospark mirror polishing technology processed material.

The scheme of Sodick equipment works on the principle of direct action of thermal energy on the treated metal surface. At the same time, there is no force effect on the material, which significantly improves the quality of the work performed.

Parts made on Sodick EDM machines receive additional strength and resistance to conventional corrosion, as they undergo a change in the course of work on them. physical characteristics metal.

2.2 Copy-stitching machine 4l721f1

The piercing machine 4l721f1 has an adaptive CNC and is used in the processing of holes and cavities in workpieces made of metal that is difficult to process. With it, you can also make dies, molds, dies, etc.

The ShGI-80-440M2 pulse generator, high-speed drive, digital display device, quick-release devices installed in the 4l721f1 piercing machine make it possible to significantly increase its productivity and processing quality.

Machine 4l721f1 does not require a particularly strong foundation in industrial premises as it is installed on vibration-resistant supports.

On the machine 4l721f1, it is possible to process parts that have maximum dimensions in length, width and height - 280 × 250x120 mm.

2.3 P&G machines (dk7732, dk7740, dk7725)

Machines dk7732, dk7740, dk7725 are designed for the manufacture measuring tools, tooling, parts for machines and mechanisms (gears, cogwheels, etc.).

For wire cutters dk7732, dk7740, dk7725 there are several features:

• when working, molybdenum wire is used, which allows it to be used repeatedly. For the operation of the machine during the week, 200 meters are enough;
• machines are equipped with a convenient CNC. It is enough to make a drawing of the part in the CAD program and load it into the CNC of the machine using removable media;
• they have high productivity - processing up to 160 sq. mm surface per minute.

2.4 Do-it-yourself machine

A homemade EDM machine can be assembled with a spark generator. This is the most complex element in the design of a do-it-yourself instrument. In a short period of time, sufficient electrical energy must be collected for its instantaneous release.

Many components for the EDM machine that you plan to do with your own hands can be found in an old TV. For example, a 1000uF capacitor. All necessary parts are placed in a box made of PTFE, which must be completely insulated. The electrode guide sleeve can be made from the grounding pin of a European-type socket.

The electrode is a molybdenum wire, which, as it evaporates, is advanced using a screw clamp. The sleeve must have a hole for the passage of coolant and at the same time working environment along the axis coinciding with the location of the electrode.

It is necessary to connect a drive to the electrode (a starter that has a 230 V coil). The piercing element is adjusted according to the depth of the hole by the value of the stroke of the rod.

When the capacitors are charging, the lamp is on, and the starter rod is inside. As soon as the capacitors are charged, the lamp goes out, the rod moves down to the workpiece and, upon contact with it, a spark discharge occurs. The impact on the workpiece (part) occurs cyclically, and the frequency of cycles depends on the power of the lighting lamp.

The main components that make up a do-it-yourself EDM machine:

• electrode;
• screw for fixing the electrode;
• positive contact clamp;
• guide sleeve;
• fluoroplastic housing;
• recess for the inflow of working fluid (oil)%;
• tripod.

EDM machine diagram

See page 154 for more information about the device and information about the ratings of electrical components.

2.5 Consumables

In order to perform high-quality work on the manufacture of parts from especially durable metal, the following consumables are required for electroerosive machines:

• brass wire for electroerosive machines (option with zinc coating), brass wire with a diameter of 0.1, 0.2, 0.25 mm;
• molybdenum wire with a cross section of 0.14 mm (supplied in coils of 200 m each, weighing 32 kg);
• brass or copper tube (electrode) with a cross section of 0.5 to 6 mm and a length of 30 to 40 cm. Brass can have from one to three holes;
• modular coolant pipes, which are made of high quality polymers.

1. Essence and purpose of electroerosive machining

electroerosion- this is the destruction of the surface of the product under the action of an electric discharge. The founders of the technology are Soviet technologists B.R. Lazarenko and N.I. Lazarenko.

Electrical discharge machining (EDM) is widely used to change the size of metal products - to obtain holes of various shapes, shaped cavities, profile grooves and grooves in hard alloy parts, to harden tools, for electroprinting, grinding, cutting, etc.

Rice. 1.9. 1 - tool electrode, 2 - workpiece, 3 - environment in which the discharge is performed, 4 - capacitor, 5 - rheostat, 6 - power source, 1p - electric spark processing mode, 2p - electric pulse processing mode

The scheme of electroerosive processing of materials is shown in fig. 1.9. The circuit is powered by a pulsed voltage of different polarity, which corresponds to the electric spark mode (1p) and the electric pulse mode (2p). The supply voltage charges the capacitor (4), parallel to which is the discharge gap between the electrode-tool (1) and the workpiece (2), which are placed in a liquid with a low dielectric constant. When the voltage on the capacitor exceeds the ignition potential of the discharge, breakdown of the liquid occurs. The liquid is heated to the boiling point and a gas bubble is formed from the vapors of the liquid. Further, an electric discharge develops in a gaseous medium, which leads to intense local heating of the part, the near-surface layers of the material melt and the melt products in the form of balls solidify in the flowing liquid and are removed from the processing zone.

2. Stages of electroerosive machining Electrospark machining mode

The workpiece is an anode (+), that is, in this case, the workpiece is processed by an electron flow, that is, the electronic streamer works, melting the volume of the anode-workpiece in the form of a hole. In order for the ion flow not to destroy the tool electrode, voltage pulses with a duration of no more than 10 -3 s are used. The electric spark mode is used for finishing, precise machining, since the metal removal in this case is small.

Electropulse processing mode

The workpiece is a cathode, that is, a negative pulse with a duration of more than 10 -3 s is applied to it. During electropulse processing, an arc discharge is ignited between the electrodes and the processing of parts is carried out by an ion stream. This mode is characterized by a high metal removal rate, which exceeds the productivity of the electrospark mode by 8–10 times, but the processing cleanliness is much worse. In both modes, kerosene or insulating oils are usually used as the working fluid.

3. Physics of EDM

The phenomena occurring in the interelectrode gap are very complex and are the subject of special studies. Here, the simplest scheme for removing metal from the processing area by means of electrical erosion will be considered.

As shown in fig. 1.10, a voltage is applied to the electrodes 1, which creates an electric field in the interelectrode gap. When the electrodes approach a critical distance, an electric discharge occurs in the form of a conductive channel. To increase the intensity of the discharge, the electrodes are immersed in a dielectric liquid 2 (kerosene, mineral oil, etc.). On the surface of the electrodes there are microroughnesses of various sizes. The electric field strength will be greatest between the two protrusions closest to each other on the surface of the electrodes; therefore, it is here that conductive bridges from impurity liquid particles arise. The current through the bridges heats the liquid until evaporation and a gas bubble (4) is formed, inside which a powerful spark or arc discharge develops, accompanied by a shock wave. There are flows of electrons and ions (positive and negative streamers) that bombard the electrodes. A plasma discharge channel is formed. Due to the high concentration of energy in the discharge zone, the temperature reaches thousands and tens of thousands of degrees. The metal on the electrode surface melts and evaporates. Drops of molten metal as a result of the movement of the liquid flow in the working area are thrown out of the electrodes and solidify in the liquid surrounding the electrodes in the form of small spherical particles (5).

From the interaction of liquid with sections of electrodes heated to a temperature of 100-400 0C, pyrolysis of the dielectric liquid occurs at the boundaries of the plasma channel of the discharge. As a result, gases are formed in the liquid, as well as asphalt-resinous substances. Carbon is released from the gaseous medium, deposited on the heated surfaces of the electrodes in the form of a thin film of crystalline graphite. At the site of action of the current pulse, small depressions remain on the surfaces of the electrodes - holes formed as a result of the removal of a certain amount of metal by the discharge.

In table. 1.2 shows the dependence of the erosion of the steel electrode on the energy and duration of a single pulse.

Table 1.2

Dependence of the erosion value of the steel electrode (anode) on the energy and duration of a single pulse

Rice. 1.10. 1 - electrodes, 2 - liquid, 3 - wells, 4 - gas bubble, 5 - erosion products

After the discharge, for some time, the channel column cools down and the plasma substance in the interelectrode gap deionizes. The electrical strength of the interelectrode gap is restored. The deionization time of the liquid dielectric is 10 6 -10 -2 s. The next discharge usually occurs already in a new place, between the other two nearest points of the electrodes.

The duration of the intervals between pulses should be sufficient to remove erosion products from the discharge zone, as well as a gas bubble, which is the main obstacle to the next discharge. In this regard, the frequency of discharges decreases with increasing energy.

This happens until the discharges remove from the surface of the electrodes all parts of the metal that are at a breakdown distance at the magnitude of the applied voltage. When the distance between the electrodes exceeds the breakdown distance, the electrodes must be brought closer to resume the discharges. Usually, the electrodes are brought together during the entire treatment time so that the electrical discharges do not stop.

Parameters of working impulses owls. The main parameters of electrical pulses applied to the interelectrode gap are their repetition frequency, duration, amplitude and duty cycle, as well as the shape, which determine the maximum power and energy. The shape and parameters of the pulses have a significant impact on the wear of the tool electrode, productivity and roughness of the machined surface.

Let us denote the pulse repetition rate, i.e., their number per second, through f. Then T = 1/f will be a period. It determines the time interval after which the next impulse follows.

The pulse is characterized by the amplitude value (or amplitude) of the voltage and current Um and Im. These are the maximum values ​​that the voltage and current acquire during the pulse time. During electroerosive machining, the voltage amplitude varies from a few volts to several hundred volts, and the current amplitude varies from a fraction of an ampere to tens of thousands of amperes. The range of duty cycles of the pulse during electroerosive machining is in the range from 1 to 30.

Polar effect and pulse polarity. The high temperature in the discharge channel and the ongoing dynamic processes cause erosion of both electrodes. The increase in erosion of one electrode compared to the other electrode is called the polar effect. The polar effect is determined by the material of the electrodes, the energy and duration of the pulses, and the sign of the potential applied to the electrode.

The processes of voltage and current changes have an oscillatory character relative to their zero value. In electroerosive machining, it is customary to consider the working or direct polarity of the pulse to be that part of it that causes the greatest effect of erosion of the workpiece being machined, and the reverse is the part of the pulse that causes increased erosion of the tool electrode. The workpiece to be processed is attached to that pole, the effect of erosion of which is greater under given conditions. An electrode-tool is attached to the opposite pole. For example, with short pulses of electrospark processing, energy is predominantly supplied to the anode, which should be used here as a workpiece (straight polarity). With an increase in the duration of the pulses, a redistribution of the heat flux on the electrodes occurs. This leads to the fact that under certain modes of electropulse processing, the anode erosion becomes less than the cathode erosion. In this case, reverse polarity should be used, using the workpiece as the cathode.

Electrical discharge machinability. The effect of erosion of various metals and alloys, produced by electric pulses of the same parameters, is different. The dependence of the intensity of erosion on the properties of metals is called electroerosive machinability.

The different influence of pulsed discharges on metals and alloys depends on their thermophysical constants: - melting and boiling points, thermal conductivity, heat capacity. If we take the electrical discharge machinability of steel as a unit, then the electrical discharge machinability of other metals (under the same conditions) can be represented in the following relative units: tungsten - 0.3; hard alloy - 0.5; titanium - 0.6; nickel - 0.8; copper - 1.1; brass - 1.6; aluminum - 4; magnesium - 6 (the indicated data are valid only under specific conditions: pulse energy 0.125 J, duration 1.4-10 -5 s, frequency 1200 1/s, current amplitude 250 A).

Workspace. Most EDM operations are carried out in a liquid. It provides the conditions necessary for the removal of erosion products from the interelectrode gap, stabilizes the process, and affects the dielectric strength of the interelectrode gap. Fluids suitable for electrospark processing must have the appropriate viscosity, electrical insulating properties, and chemical resistance to discharges.

With an increase in the pulse frequency and a decrease in the operating current, the stability of the working process deteriorates. This makes it necessary to increase the duty cycle of the pulses. The use of rectangular pulses significantly improves performance.

Processing productivity can be increased if forced removal of erosion products from the interelectrode gap is applied. To do this, liquid is injected into the interelectrode gap under pressure (Fig. 1.11).

Rice. 1.11.

Good results are obtained by applying vibrations to the tool electrode, as well as rotating one or both electrodes. The liquid pressure depends on the depth of the hole and the size of the interelectrode gap. Vibrations are especially necessary for electrospark processing of deep holes of small diameter and narrow slots. Most EDM machines are equipped with a special vibrating head.

Surface quality and machining accuracy. The metal of the electrodes is subjected to a local, short-term, but very intense electrothermal effect. The highest temperature exists on the treated surface and decreases rapidly at some distance from the surface. Most of the molten metal and its vapors are removed from the discharge zone, but some remains in the hole (Fig. 1.12). When the metal solidifies, a film is formed on the surface of the hole, which differs in its properties from the base metal.

Rice. 1.12. 1 - the space left after the melting of the metal; 2 - white layer; 3 - roller around the hole; 4 - processed workpiece; BL, NL - diameter and depth of the hole

The surface layer in the molten state actively enters into chemical interaction with vapors and decomposition products of the working fluid formed in the high temperature zone. The result of this interaction is an intense saturation of the metal with the components contained in the liquid medium, as well as with the substances that make up the tool electrode. Thus, titanium, chromium, tungsten, etc., can be introduced into the surface layer. When electroerosive machining of steel billets in a medium consisting of liquid hydrocarbons (kerosene, oil), the surface layer is saturated with carbon, i.e., iron carbides are formed. Therefore, during electroerosive machining, the surface of the part is hardened.

Intensive heat removal from the discharge zone through the masses of cold metal adjacent to it and the working fluid creates conditions for superfast hardening, which simultaneously with carburization leads to the formation of a very hard layer. The hardened surface layer of steel has an increased resistance to abrasion and a lower coefficient of friction than that of non-heat-treated steel. The structure of the surface layer differs significantly from the structure of the base metal and is similar to the structure of the chilled layer that occurs on the surface of some cast irons. Therefore, this layer is called the "white layer". The depth of the white layer depends on the energy of the pulses, their duration and the thermophysical properties of the processed material. With long current pulses of high energy, the depth of the white layer is equal to tenths of a millimeter, and with short pulses - hundredths of a millimeter and microns.

Hardening of the surface layer of metals (electroerosive alloying). One of the advantages of the electrospark method of processing materials is that, under certain conditions, the strength properties of the workpiece surface increase sharply: hardness, wear resistance, heat resistance, and erosion resistance. This feature is used to increase the wear resistance of cutting tools, dies, molds and machine parts by strengthening metal surfaces using an electrospark method.

In electrospark alloying, reverse polarity is used (the workpiece is the cathode, the tool is the anode); processing is usually carried out in air and, as a rule, with electrode vibration. The equipment with which the hardening process is carried out is small-sized and very easy to operate. The main advantages of the electrospark coating method are as follows: the coatings have a high adhesive strength with the base material; surfaces to be coated do not require preliminary preparation; it is possible to apply not only metals and their alloys, but also their compositions. The processes occurring during electrospark hardening are complex and are the subject of thorough research. The essence of hardening is that during an electric spark discharge in air, a polar transfer of the electrode material to the workpiece occurs. The transferred electrode material alloys the workpiece metal and, chemically combining with dissociated atomic air nitrogen, carbon and the workpiece material, forms a diffusion wear-resistant hardened layer. In this case, complex chemical compounds, highly resistant nitrides and carbonitrides, as well as quenching structures appear in the layer. According to experts, during electrospark hardening in the surface layer, for example, steel, the processes listed in Table 1 occur. 1.3.

Table 1.3

During electrospark hardening, the microhardness of the white layer in carbon steels can be increased to 230 MPa, the height of the microroughness of the treated surface is up to 2.5 microns. The thickness of the coating layer obtained on some installations is 0.003-0.2 mm.

4. Basic technologies of electroerosive processing of metals

Technologies for dimensional processing of metal parts.

The shaping of parts by the electroerosive method can be carried out according to the following schemes.

1. Copying the shape of the electrode or its section. In this case, the processed element of the workpiece in shape is an inverse reflection of the working surface of the tool. This operation is called stitching. There are direct and reverse copy methods. With direct copying, the tool is above the workpiece, and with reverse copying, it is below it. The stitching method is simple to perform and widely used in industry. On fig. 1.13 shows a diagram of electrical discharge machining by copying the shape of the electrode-tool. In the course of electroerosive machining, the electrode (1) is introduced into the part, providing copying of the electrode.

2. Mutual movement of the workpiece and the electrode-tool. With this scheme, the operations of cutting out complex profile parts and cutting blanks with electrodes, electroerosive grinding and boring of parts are possible.

Rice. 1.13. : 1 - electrode-tool, 2 - workpiece, 3 - liquid, 4 - vessel

Sewing windows, cracks and holes. This operation is carried out on universal machines. Slots with a width of (2.5-10) mm and a depth of up to 100 mm are stitched by the electroerosive method. To ensure the removal of erosion products from the interelectrode gap, the electrode-tool is made T-shaped or the thickness of the tail part is reduced compared to working part by a few tenths of a millimetre. The speed of flashing the slots is (0.5-0.8) mm/min, the roughness of the treated surface is up to 2.5 microns.

Processing of parts such as nets and sieves. EDM machines have been created that allow processing mesh parts with up to several thousand holes. The machines can simultaneously process more than 800 holes with a diameter of (0.2-2) mm in sheets of corrosion-resistant steels, brass and other materials up to 2 mm thick. Processing capacity up to 10,000 holes per hour.

Electroerosive grinding. This is one of the varieties of electrical discharge machining, which is used for processing high-strength workpieces made of steels and hard alloys. Removal of metal in this case occurs under the influence of pulsed discharges between the rotating electrode-tool and the workpiece being processed, and not as a result of mechanical action, as in abrasive grinding.

The methods of direct and reverse copying have a significant drawback, which consists in the need to use complex shaped tool electrodes. The wear of the electrodes affects the accuracy of the manufacture of parts, therefore, with one electrode-tool, it is possible to produce no more than 5-10 parts.

The electric spark method of complex contour wire cutting compares favorably with copying methods in that here the tool is a thin wire made of copper, brass or tungsten with a diameter of several microns to 0.5 mm, which is included in the electrical circuit as a cathode (see Fig. 1.14).

Rice. 1.14. : 1 - wire, 2 - workpiece, 3 - guide rollers, 4 - device for adjusting the wire drawing speed

To eliminate the influence of wire wear on the accuracy of processing, the wire is rewound from one coil to another, which allows all new elements to participate in the work. When rewinding, there is a slight tension. Near the workpiece to be processed, rollers are installed that orient the wire relative to the workpiece. Complex contour wire cutting is used for precision cutting of workpieces, cutting of precise slots, cutting of semiconductor materials, processing of cylindrical, conical outer and inner surfaces.

The main advantages of electrical discharge machining with a wire electrode-tool include high accuracy and the possibility of wide automation of the process.

Electrocontact method of processing. Electrocontact processing of materials is a kind of electroerosive processing. Its difference lies in the fact that electrical energy pulses are generated as a result of the mutual movement of the electrodes or the interruption of the electrical discharge when pumping liquid under pressure. Electrocontact processing can be carried out at direct and alternating current, in air or liquid (water with anti-corrosion additives). During processing, the electrode-tool and the workpiece are completely immersed in a liquid, or liquid is sprayed into the interelectrode gap. Processing is carried out at significant currents (up to 5000 A) and open-circuit voltages of the power source 18-40 V. Semi-finish turning of bodies of revolution, fine cutting, flashing of cylindrical, shaped holes and volumetric cavities, milling, grinding are performed using the electric contact method. The electrocontact method is especially effective in processing workpieces made of hard-to-cut steels and alloys, as well as high-hardness cast irons, single crystals, and materials with high thermal properties.

circuit diagram installation for electrocontact processing is as follows. The workpiece and the electrode-tool, having an axis of rotational symmetry and included in the circuit with a power source, after contact, perform rotational motion relative to each other.

Under the conditions necessary for the implementation of electroerosive processes, metal is removed from the workpiece.

Hardening of the surface layer of the metal (electroerosive alloying)

One of the advantages of electroerosive machining of metals is that, under certain conditions, the strength properties of the surface of the workpiece sharply increase. This feature is used to improve the wear resistance of cutting tools, dies, molds, etc. In electroerosive alloying, reverse polarity is used (the workpiece is the cathode, the tool is the anode), processing is usually carried out with the atoms of the tool-electrode in the electric pulse mode (see Fig. 1.15) in the air and, as a rule, with electrode vibration.

Rice. 1.15 Scheme of electroerosive alloying: 1 - alloying electrode-tool, 2 - alloyed part

The main advantages of electroerosive alloying are as follows: coatings have a high degree of adhesion to the base material; surfaces to be coated do not require preliminary preparation; it is possible to apply not only metals and alloys, but also their compositions.

The processes occurring during electroerosive hardening are complex and are the subject of thorough research. However, the essence of hardening is that during an electric spark discharge in air, the electrode material is transferred to the workpiece (see Fig. 1.15). The transferred electrode material alloys the workpiece metal and, chemically combining with air nitrogen ions, carbon and the workpiece material, forms a wear-resistant hardened layer consisting of nitrides, carbonitrides and other hardening structures.

With electrospark alloying, the microhardness of the white layer in carbon steels can be increased to 230 MPa. The thickness of the coating layer obtained on some installations is 0.003-0.2 mm. When hardening the surface of machine parts (for example, at the IE-2M installation), it is possible to obtain a layer depth of up to 0.5–1.6 mm with a microhardness of 50–60 MPa (when hardened with ferrochrome).

There is a distinction between clean processing, which corresponds to high voltages and low short-circuit currents (up to 20 A), and rough (coarse alloying) at low voltages of 50-60 V and short-circuit currents over 20 A.

Work on electroerosive machines. Preparation of electroerosive machines for work consists in installing the workpiece and the tool electrode and aligning their relative position, preparing the bath for work and the working fluid pumping system, selecting and setting the generator modes. The workpiece is installed and fixed directly on the machine table or in the fixture. The tool electrode is installed with its tail into the head spindle. When aligning, indicators, optical instruments, devices are used that allow you to change the position of the tool in relation to the workpiece and the angle of inclination.

After adjusting the position of the electrode tool, fill the bath with working fluid, check the operation of the pumping system, set the required pumping pressure. The pulse generator mode is set (polarity, pulse shape, duty cycle, pulse repetition rate, average current), using the appropriate tables and nomograms. Changing the polarity of the voltage of the pulse generator is carried out by switching on the plug connector of the current leads to the machine. When working with direct polarity (electric spark mode), a negative potential is applied to the electrode, and a positive potential is applied to the workpiece. To work with reverse polarity (electropulse mode), reverse switching is performed. The installation of electrical parameters and operating modes is carried out using switches located on the control panel. Adjust the supply regulator by setting the recommended regulator voltage.

Industrial processing of metals includes dozens of methods and methods for changing the shape, volume, and even the molecular structure of a material. Electrospark processing of metals is one of the widespread technologies for working with metal, characterized by high precision and productivity. With the help of electric spark machines you can:

• cut metal;
• drill holes of microscopic diameter;
• build up defective areas of parts;
• to carry out jewelry work with precious metals;
• harden the surface of products;
• grind products of the most complex shape;
• remove stuck broken drills and cutters.

Many machine tools for industrial use have been created on the basis of the electrospark method of metal processing. It is high precision and expensive equipment that can only afford to buy large enterprises specializing in metalworking.

But sometimes electric spark machines are also required in workshops or workshops, where their services are required from time to time. To do this, you can buy an industrial device with somewhat limited capabilities (functionality within the most popular operations), or build a home-made electric spark machine. This is quite possible even at home, not to mention enterprises that include turning and electromechanical workshops or sections.

The processing of metals by the electrospark method is based on the property of an electric current to transfer a substance during a breakdown. At high voltage and direct current (1-60 A), the anode (positively charged electrode) is heated to a high temperature in the range of 10-15 thousand degrees Celsius, melts, ionizes and rushes to the cathode. There, due to electrical interactions, it settles.

So that a full-fledged electric arc does not occur during operation, the electrodes approach each other only for short moments, lasting a fraction of a second. During this time, a spark occurs that destroys the anode and builds up the cathode. The treated area is subjected to heating and electric current for milliseconds, while the neighboring areas and the underlying layer do not have time to warm up and their structure is not disturbed. The problem of boundary conditions does not arise in principle.

If cutting or drilling is required, the working tool serves as the cathode, and the workpiece is the anode. When building up, strengthening the surface or restoring the shape of the part, they change places. For these types of processing, special machines have been created, each of which performs its own operations.

Brass or copper-graphite electrodes, which conduct current well and are inexpensive to manufacture, serve as tools in electroerosion installations. With their help, you can cut and drill the most hard alloys. So that the cathode metal does not settle on the electrode and does not increase its size, the process takes place in a liquid medium - the liquid cools the melt drops, and it cannot settle on the electrode, even if it reaches it. The viscosity of the liquid determines the speed of movement of material particles, and they do not keep up with the current. The metal settles in the bath in the form of a precipitate and does not interfere with the further passage of current.

When building up the surface of parts or strengthening, the metal from the anode is transferred to the cathode. In this case, a positive electrode, which serves as a metal donor, is fixed on the vibration unit, and the part is connected to the negative pole. No water or oil is used in this process, everything happens in the air.

Technological indicators

The electric spark installation, depending on the operating mode, can provide the accuracy of the result over a wide range. If high performance is required with relatively low requirements for the surface condition (I and II class), then currents of 10-60 A at voltages up to 220V are used. In this case, electrospark erosion can remove metal from the cutting or drilling zone in a volume up to 300 mm 3 /min. At higher accuracy classes - VI and VII, the performance is reduced to 20-30 mm 3 / min, but the currents are also required less, no more than 1 A at voltages up to 40 V.

Such a wide range of adjustments shows that electrospark machining of metal can be used in various areas, both for the production of large series of parts, and for one-time work, including jewelry.

A feature of the use of electric spark installations can be considered the possibility of strengthening parts of various configurations. The thinnest layer of a more durable alloy or metal is applied to the surface of the workpiece without heating the base to a great depth. This allows you to save the metal structure of the base product and significantly change the properties of its surface. In some cases, a tough base and a high surface hardness are required, or vice versa. Only an electric spark machine can solve this problem.

Diagram of an electric spark machine

The processing of metals by the electrospark method is very common, so it is very difficult to consider all types of equipment and models of specific installations. They are all united by common structural elements:

• direct current source;
• capacitor;
• vibrator;
• mode switch.

A design operating in the electrospark mode may differ in a number of characteristics that allow it to work with one or another material, but general principles the construction of the working scheme is the same.

Capacitor bank matched with mechanical movement electrode, the discharge occurs at the moment of maximum convergence of the working surfaces. Relaxation pulse generators determine the maximum charge of the capacitor at the maximum amplitude of deviation from the approach point. After a spark discharge, the capacitor has time to fully charge.

The difference between spark erosion and arc welding and cutting

The use of pulsed electric current is different from the effect of an arc. The impulse works in a very limited space, not having time to warm up the neighboring areas. Even on the most complex alloys in terms of thermal oxidation, an inert atmosphere is not required - the interaction occurs on areas of no more than 0.05-1 mm 2 at an impact depth of 0.05-0.3 mm. Even in the most aggressive atmosphere, conditions for active oxidation do not have time to arise.

Do-it-yourself electric spark machine

One of the main details of the electric spark installation, which can be implemented by one's own hands, of course, subject to all safety regulations, is given below. It should be noted that this is only one of many schemes that can be used in the design of the machine.

The working table of the machine must be equipped with an oxide removal system (continuous supply of oil or kerosene). They reduce the likelihood of oxide film deposition on the surface of the part and, as a result, the termination of sparking. Breakdown requires reliable electrical contact. As the main option, you can use a bath filled with liquid.

The electrode is a brass or copper wire of the required diameter, which is fixed in a clamp. The clamp, in turn, is a part of the vertical rod of the crank mechanism, which is driven by an electric motor. The frequency of the reciprocating movement of the electrode is selected depending on the characteristics of the material being processed.

All conductive parts and cables must be insulated with high quality and reliably, the installation itself must be grounded. You can see how household home-made installations work on the video:

It should be noted that homemade machines will never be equal in capabilities to industrial ones, for example, the ARTA series. For the production of handicrafts or use as one of the types of hobbies, they may be suitable, but they do not “hold out” for work in a workshop or locksmith shop. Not to mention that the complexity of the electrical circuit and the need to precisely match the kinematics and discharge of the capacitor make them very difficult to adjust.

To obtain elements with a complex profile from hard-to-cut metals, an electroerosive machine is used. Its work is based on the impact of electric current discharges, which create a high temperature in the processing zone, due to which the metal evaporates. This effect is called electrical erosion. Industry has been using machines based on this principle for more than 50 years.

Types of equipment and processing methods

The operation of an EDM machine can be described as follows:: take a charged capacitor and bring it with electrodes to a metal plate. During a short circuit, the capacitor discharges. A bright flash is accompanied by the release of energy (high temperature). A recess is formed at the closure site due to the evaporation of a certain amount of metal from high temperature.

On the technological equipment implemented different kinds receiving electrical discharges . The main schemes are:

• electrospark;
• electrocontact;
• electropulse;
• anode-mechanical.

Implementing one of the schemes in practice, machines are manufactured. On the principle of electrical erosion, the following machines were produced in various modifications:

• cut;
• wire;
• firmware.

To obtain accurate dimensions and automate the process, the equipment is equipped with a numerical program management(CNC).

The electric spark machine is powered by a spark generator. A generator is an energy storage device that gives an electrical impulse. For a constant supply of pulses, a capacitor bank is organized.

To organize an electrical circuit, the cathode is connected to the executive tool, and the anode to the workpiece. The constant distance between the electrode and the workpiece guarantees a uniform process. When the electrode is lowered vertically onto the part, the metal is pierced and a hole is formed, the shape of which is determined by the shape of the electrode. This is how the EDM machine works.

For the manufacture of parts from carbide and hard-to-cut parts, an electroerosive wire machine is used. A thin wire acts as an electrode in it. When the metal evaporates, oxides with a high melting point are formed on the surface of the workpiece. To protect against them, the process is carried out in a liquid medium or oil. During sparking, the liquid begins to burn, taking oxygen and other gases from the working area.

Machines of this type are sometimes the only possible way manufacturing of a structural element. But buying EDM equipment for infrequent jobs is a waste of money. Therefore, if the need arose, then you can make an electroerosive machine with your own hands.

Features of a homemade device

Before you start making a homemade EDM machine, you need to understand its device. The main structural elements include:

Making a spark generator

For the manufacture of a spark generator, parts can be found everywhere (in old TVs, power supply monitors, etc.). The principle of its work is:

Work Safety Measures

Since organized electrical erosion with their own hands is associated with the possibility of defeat electric shock, safety must be approached with all responsibility. The workpiece must not be grounded. Otherwise, a state of emergency will occur - a short circuit in the supply network. Capacitors rated at 400V can be lethal at only 1000uF.

Connecting devices excludes contact with the body. To connect the capacitor to the electrode, a copper wire with a cross section of 6–10 square meters is required. mm. A large volume of oil used to prevent the formation of oxides may ignite and cause a fire.

Rice. 1. Electric spark pencil: 1 - working electrode; 2 - core; 3 - cheek; 4 - tube; 5 - insulating tape; 6 - electromagnet winding; 7 - spring; 8 - cork; 9 - connecting wire; 10 - clamp

ki. Near the front (according to the figure) cheeks, the end of the coil wire (PELSHO 0.5-0.6) is soldered to the tube and the wire is wound round to round over the entire surface of the tube in 7-8 layers. The second output of the coil is made with a stranded mounting wire (for example, ^ brand MGShV) with a cross section of at least 1 mm "to the end of which a crocodile clip is soldered. The coil is protected from accidental damage with a layer of varnished cloth, over which a layer of insulating tape is wound. After that, into the tube insert a spring (15-20 turns), screw in a plug (M5 screw), and firmly insert an electrode into the split end of the core - a steel needle with a diameter of 1 mm. (5-10V) of the transformer winding, and the other output of the winding - with a crocodile clip on the output of the coil. Having moistened the surface of the part with kerosene, touch it with the tip of the needle. This closes the power circuit of the coil, and the resulting magnetic field draws the core into the tube. Circuit then the core returns to its original state under the action of the spring, and the needle touches the metal again. oh detail, a spark arises, which leaves a clear mark on the metal.

Small-sized electric spark installation

A simple electric spark machine allows you to easily and quickly process small parts made of electrically conductive materials of any hardness. With its help, it is possible to obtain through holes of any shape, remove a broken threaded tool, cut thin slots, engrave, sharpen a tool, etc. The essence of the electrospark machining process is the destruction of the workpiece material under the action of a pulsed electric discharge. Due to the small area of ​​the working surface of the tool, a large amount of heat is released at the discharge site, which melts the substance of the workpiece. The processing process is most effectively carried out in a liquid (for example, in kerosene), which washes the place of contact between the vibrating tool and the parts and carries away the erosion products. The tool is brass rods (electrodes), repeating the shape of the intended hole. The circuit diagram of the installation is shown in fig. 3. The installation works as follows. The discharge capacitor Ci is connected to its positive