Industrial processing of metals includes several dozen methods and techniques for changing the shape, volume and even the molecular structure of a material. Electrospark processing of metals is one of the most common technologies for working with metals, characterized by high accuracy and productivity. Using electric spark machines you can:
- cut metal;
- drill holes of microscopic diameter;
- increase defective areas of parts;
- produce jewelry work with precious metals;
- strengthen the surface of products;
- grind products of the most complex shapes;
- remove stuck broken drills and cutters.
Many industrial machines have been created based on the electric spark method of metal processing. This is high-precision and expensive equipment that only large enterprises specializing in metalworking can afford to buy.
Electric spark machine
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 homemade electric spark machine. This is quite possible even at home, not to mention enterprises that include turning and electromechanical shops or areas.
Operating principle of an electric spark machine
The processing of metals by the electric spark method is based on the property of electric current to transfer a substance during breakdown. At high voltage and direct current (1-60 A), the anode (positively charged electrode) heats up 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.
To prevent a full-fledged electric arc from occurring during operation, the electrodes are brought closer together only for short moments, lasting a fraction of a second. During this time, a spark occurs, destroying the anode and growing the cathode. The treated area is heated and exposed to 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 borderline states does not arise in principle.
If cutting or drilling is required, the working tool serves as the cathode, and the workpiece serves as the anode. When building up, strengthening the surface or restoring the shape of a part, they change places. For these types of processing, special machines have been created, each of which performs its own operations.
The tools used in EDM installations are brass or copper-graphite electrodes, which conduct current well and are inexpensive to manufacture. With their help you can cut and drill the hardest alloys. To prevent the cathode metal from settling on the electrode and increasing its size, the process occurs in a liquid medium - the liquid cools the melt droplets, 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 cannot keep up with the current. The metal settles in the bath as a sediment and does not interfere with the further passage of current.
When increasing the surface of parts or strengthening, metal is transferred from the anode to the cathode. In this case, a positive electrode is fixed to the vibration installation, serving as a metal donor, and the part is connected to the negative pole. No water or oil is used in this process, everything happens in the air.
Electrolytic extension method
Restoring parts using the electrolytic buildup method involves depositing metal from an aqueous solution onto the part. Electrolytic build-up is used to increase the wear resistance and corrosion resistance of a part, restore the dimensions of a part, repair of pipeline systems and ship fittings, and for decorative purposes.
When repairing parts, use:
- chrome plating;
- leaving;
- copper plating and other coatings.
Chrome plating is used both in the repair of mechanical parts and in the manufacture of new parts. Chrome coatings can be smooth or porous. Smooth hard chrome has valuable physical and mechanical properties. Porous chrome plating is used to increase the wear resistance of ship parts operating in conditions of insufficient lubrication.
Bulk carrier Kkaye E. Barker, Lake Michigan
The wear resistance of cast iron coated with smooth chromium increases by 4-7 times, and that of cast iron coated with porous chromium increases by 30-150 times. To eliminate porosity, which limits the use of chromium coatings for ship parts operating in a corrosive environment, a combined coating is used; a layer of chromium is applied to the applied layers of copper, cadmium or nickel, or sequentially copper and nickel.
The thickness of the deposited chromium layer ranges from 15-30 microns. Chrome plating restores parts that have little wear, since the thickness of the chrome coating is practically in the range of 0.05-0.3 mm per side. With a large coating thickness, the strength of the chrome layer decreases, and chrome plating becomes economically unprofitable. The chrome plating process consists of the following operations.
Restore the geometry of the part:
- groove;
- grinding;
- polishing
Electrolytes of various compositions are used for electrolytic polishing:
- a mixture of sulfuric, phosphoric and chromic acids;
- a mixture of sulfuric and citric acids;
- a mixture of various mineral acids and glycerin.
Degrease the part in electric baths with electrolyte (30-50 g of caustic soda per 1 liter of water). To speed up the degreasing process, it is recommended to add sodium silicate (liquid glass) in an amount of 0.5-1 g/l. The electrolytic degreasing process lasts 2-3 minutes. Wash the parts in hot water and running water.
In this case, the part is subjected to pickling in order to remove oxide films that may form during the preparation of the part for chrome plating. Picking involves lightly etching the surface of the part in a 2-3% solution of sulfuric acid. At a solution temperature of 18–20°C, the part is kept for 4–5 minutes to equalize its temperature with the temperature of the electrolyte.
Bulk carrier Edgar B. Speer, Lake Michigan
The most widespread is anodic pickling, which consists in the fact that a part placed in a bath to heat it to the bath temperature and being the anode is held for 30-50 s under a current density of 20-26 A/dm2. Decapitate immediately before chrome plating. Typically, the surfaces of parts that are not subject to chrome plating are coated with varnish.
Suggested reading: Types and organization of ship repairs
Chrome plating is carried out in iron baths with double walls, the space between which is filled with hot water to regulate the constant temperature of the electrolyte in the bath. Water is poured into the bath, heated to a temperature of 70°C, electrolyte components are introduced, and a direct current of 6-12 V is connected. To equalize the electrolyte concentration, the part mounted on the suspension is dipped into the solution 3-4 times and then suspended on the cathode rod .
The current density during chrome plating is 20-50 A/dm2, and the duration depends on the thickness of the coating, the composition of the electrolyte, and the operating mode of the bath. The anode for chrome plating is lead plates, located concentrically relative to the part and having a surface 2 times larger than the surface of the part being chromed.
After chrome plating, the part is subjected to anodic treatment in order to obtain a porous surface at a current density of 25–35 A/dm2 and at a temperature of 30–40°C for 10–20 minutes. Then the part is washed with cold and hot water.
Remaining is the process of electrolytic deposition of iron coatings from aqueous solutions of iron chloride FeCl24H2O or iron sulfate FeSO47H2O. Electrolytic deposition of iron from aqueous salt solutions was obtained by academicians B. S. Jacobi, E. I. Kleiman and E. X. Lenz in 1868-1870. When a direct current passes through a salt solution, iron ions are discharged at the cathode (part), thus covering the cathode with a layer of iron. The anode dissolves and its ions enter the solution.
On the. rice. Figure 3 shows a diagram of an installation for cooling parts, which consists of a bath with electrolyte 1, a ring anode 2, a suspension 3 for fastening the part to be coated, a thermometer 4 for monitoring the temperature of the electrolyte, a generator 5, an electric coil for heating the bath 6, and a rheostat 7.
Rice. 3 Installation diagram for remaining parts
Retaining is a less complex and cheaper process than chrome plating. For example, the current efficiency during cooling reaches 70–90%, the current density is 10–20 A/dm2, the deposit thickness per hour at the applied current density is 0.013–0.26 mm. The thickness of the iron layer with soft coating (140-225 HB) is more than 3 mm, with hard coating (225-600 HB) - up to 2 mm. Low-hardness coatings are used to restore non-friction surfaces of parts, the outer surfaces of bronze bushings of the connecting rod upper head, liners, etc.
The cooling technology is as follows:
- the part is cleaned of dirt;
- washed in gasoline;
- clean the areas covered with sandpaper or sandblasting;
- isolate areas not to be coated with perchlorovinyl varnish or rubber;
- mount the part on hangers;
- degreased with lime;
- washed with cold running water;
- passivated in a special electrolyte at a current density of 10-40 A/dm2 for 2-5 minutes;
- washed with hot water;
- load into a bath with electrolyte and heat the solution.
Taking the part out of the bath:
- washed with hot water;
- neutralized in an alkaline solution;
- washed with hot water;
- dismantle the suspensions;
- remove insulation;
- carry out aging;
- mechanically processed.
When cadmium ions are introduced into a chromium electrolyte, a coating is obtained that has:
- hardness;
- wear resistance;
- complete absence of porosity.
Bulk carrier American Integrity Source: www.shipspotting.com
Cadmium chrome coating is used, in particular, for propeller shaft journals and steel linings.
Copper plating is carried out to increase the protective and decorative properties of steel parts. In this case, multilayer coatings, copper-nickel or copper-nickel-chrome, are used. Copper is deposited on the nickel sublayer. In ship repair, sulfuric acid electrolytes are used for copper plating. Electrolytic copper is used as anodes.
Nickel plating of steel parts is carried out to increase their protective and decorative properties. Nickel protects the base metal from corrosion. Sometimes nickel coatings, due to their significant hardness, are used as wear-resistant coatings. When applying a nickel coating, the surface roughness of the part must be at least Rz = 80 ÷ 20 µm. For bright nickel plating, which does not require precise dimensions, the part is polished, and parts with precise dimensions are processed to Ra = 0.32 ÷ 0.16 µm.
Technological indicators
An electric spark installation, depending on the operating mode, can ensure the accuracy of the result within a wide range. If high performance is required with relatively low requirements for surface condition (class I and II), then currents of 10-60 A are used at voltages up to 220V. In this case, electric spark erosion can remove metal from the cutting or drilling zone in a volume of up to 300 mm3/min. With higher accuracy class values - VI and VII, productivity decreases to 20-30 mm3/min, but lower currents are required, no more than 1 A at voltages up to 40 V.
Such a wide range of adjustments shows that electric spark processing of metal can be used in various fields, 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 ability to strengthen parts of various configurations. A thin layer of a stronger alloy or metal is applied to the surface of the workpiece without heating the base to a greater depth. This allows you to preserve the metal structure of the base product and significantly change the properties of its surface. In some cases, base viscosity and high surface hardness are required, or vice versa. Only an electric spark machine can solve this problem.
Electric spark machine diagram
Metal processing by the electric spark 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:
- DC source;
- capacitor;
- vibrator;
- mode switch.
A design operating in an electric spark mode may differ in a number of characteristics that allow it to work with a particular material, but the general principles of constructing a working circuit are the same.
The battery of capacitors is coordinated with the mechanical movement of the electrode, the discharge occurs at the moment of maximum approach 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 the spark discharge, the capacitor has time to charge fully.
DIY electric spark machine
One of the main parts of an electric spark installation, which you can implement with your own hands, of course, subject to all safety rules, is given below. It should be noted that this is only one of many designs that can be used in machine design.
Approximate diagram of a spark discharge generator
The work table of the machine must be equipped with an oxide removal system (continuous supply of oil or kerosene). They reduce the likelihood of depositing an oxide film on the surface of the part and, as a result, stopping sparking. For breakdown, reliable electrical contact is required. As a basic 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 reciprocating movement of the electrode is selected depending on the characteristics of the material being processed.
All conductive parts and cables must be properly and reliably insulated, and the installation itself must be grounded. You can see how homemade homemade installations work in the video:
It should be noted that homemade machines will never equal the capabilities of industrial ones, for example the ARTA series. They may be suitable for the production of handicrafts or use as one of the types of hobbies, but they are not “up to par” for working in a workshop or metalwork shop. Not to mention that the complexity of the electrical circuit and the need for precise coordination of kinematics and capacitor discharge make them very difficult to adjust.
Abstract on the topic “Electric spark and electric pulse processing of metal”
Department of "MANAGEMENT IN ROAD TRANSPORT"
“Natural Scientific Foundations of Modern Technologies”
Project topic:
"Electric spark and electric pulse processing of metal"
INTRODUCTION
Electrotechnology includes electrical methods of metal processing, which have received great development over the past decade.
Electrical processing methods are those types of processing in which the removal of metal or a change in the structure and quality of the surface layer of a part is a consequence of the thermal, chemical or combined action of an electric current supplied directly (galvanic connection) to the part and the tool. In this case, the conversion of electrical energy into other types of energy occurs in the processing zone formed by the interacting surfaces of the tool and the workpiece.
Electrical processing includes electrical erosion, electrochemical, combined electrical erosion-chemical and electromechanical processing methods (Scheme 1).
With electroerosive processing methods, metal removal and changes in the surface properties of the part are the result of the thermal action of electric current.
In turn, electroerosive methods of processing metals according to their intended purpose differ into the methods by which they are carried out:
a) electroerosive dimensional
metal processing (removing metal and giving the workpiece a given shape and size);
b) electrical discharge hardening
or
coating
(changing the properties of the surface layer).
Currently, the following main methods of electrical discharge machining are known and used: electric spark, electric pulse
and
electrical contact
.
the anodic-mechanical
should also be included in this group , since electrochemical metal removal (anodic dissolution) is used only in finishing modes and, moreover, not in all cases of using this method.
Scheme 1. General classification of electroerosive methods of metal processing.
As can be seen from diagram 1, electric spark
and
electric pulse
methods allow both metal removal and hardening;
anodic-mechanical
and
electrical contact
- only metal removal.
Depending on the method of processing or hardening, we can talk about electric spark, electric pulse
,
electrical contact
or
anodic-mechanical
dimensional processing or hardening.
The given definitions and classification allow us to consider the electrical processing of metals as an independent branch of electrical technology.
With the advent of electrical processing methods, it turned out to be, in principle, possible to carry out using electrical technology methods the entire complex of operations necessary to transform a workpiece into a finished part, including its heat treatment.
Electroerosive methods do not exclude mechanical processing, but complement it, occupying their specific place corresponding to their characteristics, namely: the ability to process conductive materials with any physical and mechanical properties and display the shape of the tool in the product. Consequently, the use of electrical discharge processing methods will develop with an increase in the hardness and viscosity of the processed materials, with the complication of the shape of the part and the processed surfaces (cavities of complex configuration, holes with a curved axis, holes of very small diameter, thin and deep slots of simple and complex shape, etc. .), finally, with the improvement of the technical and economic indicators of electrical discharge processing methods - increasing productivity, surface cleanliness, accuracy, tool life and reducing the energy intensity of the process.
Particularly promising is the use of electrical methods for processing parts made of hard alloys, heat-resistant steels and special difficult-to-process alloys, which are increasingly used due to increasing pressures, temperatures and speeds in machines and devices.
Individual elements of varieties and particular applications of electrical discharge machining of metals have been known for a long time. For example, cutting metals with the application of electric current (the so-called electrofriction
cutting, similar in design and parameters to
electrical contact
processing) was used about 70 years ago; surface hardening with a carbon electrode using electric current according to the method of D.N. Dulchevsky was proposed in 1928, etc.
the electric spark machine in 1943 by B. R. and N. I. Lazarenko
method and V.N. Gusev -
anode-mechanical
method.
These methods were supplemented in 1948 by the new use of electric contact processing (sharpening according to the method of engineer M. E. Perlin), which was further developed in the work of the Kharkov Electrotechnical Institute, Kharkov Bearing Plant (processing of balls according to the method of engineer B. P. Hoffman) , KhTZ named after Ordzhonikidze (processing of tracks), Research Institute of the Ministry of Shipbuilding Industry (processing of propellers), etc.
Development of electric spark
and
anode-mechanical
methods went through the creation of numerous experimental designs of adapted and special electrical discharge machines, automatic regulators and the development of new technological operations. The technical characteristics of these methods - productivity, tool life, energy intensity, ease of use - have not undergone any significant changes for the better during this period.
In electric spark
The method based on the use of dependent (capacitor) relaxation pulse generators has practically exhausted the possibilities for further increasing productivity, reducing tool wear and energy consumption. Fundamentally new technical solutions and the abandonment of capacitor circuits turned out to be necessary. The first steps in this direction were made in 1950 at the Design Bureau of the Ministry of Machine Tool and Tool Industry (KB MSiIP) in the field of creating new pulsed current power supplies (independent pulse generators) for stitching and copying work, and by the Odessa Polytechnic Institute in the field of developing pulsed current sources current for processing with a rotating tool in soft modes (for making needle files).
A new processing method based on the use of independent voltage and current pulse generators is called electric pulse processing.
Since 1951 electric pulse
the method was developed in close collaboration by three organizations: the MSiIP Design Bureau, the Laboratory of Electrical Processing Methods of the Experimental Research Institute of Metal-Cutting Machine Tools and the Department of Electrical Machines of the V. I. Lenin Kharkov Polytechnic Institute.
Electropulse
The processing method when carrying out piercing and copying work made it possible, in comparison with
the electric spark
method, to increase the rate of metal removal under harsh conditions by 5-10 times, with the possibility of its further increase, to reduce tool wear by 5-20 times and energy intensity by 2-3 times.
The information presented in this work generally characterizes the current state of technology, technology and industrial use of electrical discharge machining of metals. The greatest attention is paid to electric pulse
a processing method that has better technical and economic indicators and a wider range of applications than
electric spark
.
Of the various applications of electric pulse
processing, mainly the more studied stitching and copying works are presented, which are the most difficult to implement and are more universal in technological capabilities.
Electrical processing of metals and its variety - electrical discharge machining - represent an independent branch of electrical technology, which is at the initial stage of development.
PHYSICAL CONDITIONS FOR IMPLEMENTING DIMENSIONAL ELECTRO-EROSIVE MACHINING
To ensure high-quality dimensional processing of metals through the use of the thermal effect of electric current, the following three basic conditions must be met:
1. Electric current energy must be supplied to the treated area in the form of a pulse of sufficiently short duration (localization of elementary metal removal in time).
With a continuous supply of energy, the processing accuracy is lost, a defective fused sublayer appears, the surface cleanliness deteriorates and one of the main technological qualities of electrical processing methods is lost - the display
(copying) the tool shape into the part.
An example of processing with a continuous supply of energy is cutting or burning holes with an electric arc; in this case, the accuracy and cleanliness of the surface at the cut site is unacceptable for dimensional processing.
2. The area of the part to which the energy pulse is applied must be small enough (localization of elementary metal removal in space).
In order to remove metal when applying an energy pulse to a large area, it is necessary to correspondingly increase the pulse energy, which will lead to an increase in the elementary removal. The greater the elementary metal removal, the worse, naturally, the surface cleanliness and the lower the processing accuracy.
If the energy impulse is kept unchanged with an enlarged elementary section, then metal removal may not occur at all, since the supplied energy will not be enough to melt the elementary removal.
3. Energy pulses must be supplied to elementary areas of the volume of metal to be removed continuously and with sufficient frequency (localization of the processing process in time). This condition ensures the continuity of the process and obtaining the required productivity.
These three conditions are satisfied to varying degrees by electrical processing methods based on the thermal effect of electric current.
VARIETIES OF ELECTRO-EROSIVE MACHINING OF METALS
Electrical processing of metals can be divided into three groups.
To the first
The group based on purely contact energy supply includes
electromechanical
processing.
Since a purely contact energy supply does not satisfy the three conditions of dimensional processing, as a result of which metal removal is not achieved, with electromechanical
In this method, metal is removed with a cutter, the cutting edge of which is at the same time a contacting surface.
An alternating current is supplied to the cutter and the workpiece, which heats the part at the point of contact. Electrical contact heating serves only the purpose of reducing cutting forces and can be replaced by other heat sources - an arc, an acetylene torch flame, high-frequency heating, etc.
As calculations and experience show, from an energy point of view, introducing an electric current through a cutter is generally impractical and does not increase productivity or increase tool life. The latter is explained by the fact that, due to small voltage drops at the contact point, to create any significant heating it is necessary to introduce very large currents; in this case, the cutter finds itself, from the point of view of heat removal, in much more severe conditions than the workpiece. Therefore, the cutting edge heats up and the durability of the cutter decreases.
At low currents, the heating of the product is so negligible that it has virtually no effect on the magnitude of the mechanical cutting force.
Second
the group includes processing methods that use energy supply through a discharge channel.
This group includes electric spark
and
electric pulse
methods and intermediate varieties, for example, such as processing with aperiodic pulses on a relaxation generator, which includes elements of both methods.
Third
a group that combines
diode-mechanical
and
electrical contact
methods with all varieties, based on the use of a combined contact-arc energy supply.
Scheme 2. Classification of electroerosive metal processing methods according to energy supply methods.
Scheme 2 shows the classification of methods for electrical discharge machining of metals according to energy supply methods and indicates the varieties known in industry, assigned to one or another method based on the principle of similarity of the greatest number of characteristics. The largest number of varieties is obtained by combining pulsed current sources required when supplying energy through the discharge channel with the relative movement of the electrodes used in combined energy supply. These varieties include the so-called low-voltage electric spark
and
electric pulse
processing of bodies of rotation or processing with a rotating electrode,
anodic-mechanical
processing with pulsed power, etc. Depending on which of the methods prevails in this combination, we can speak, for example, of
electrical contact
processing with pulsed power or
electric pulse
processing with a rotating electrode. The same applies to other combinations of the four main EDM methods.
Let us consider the fundamental differences between the types of dimensional electrical discharge machining within the second and third groups.
Electrospark
and
electric pulse
methods differ, as will be shown in more detail below, in the device for generating pulses, the parameters and shape of the pulse, as well as the polarity of the electrodes.
Diode-mechanical
and
electrical contact
methods differ in the type of current used (in the first case - direct, in the second - alternating, and, less often - direct) and in the type of working medium (in the first case - liquid glass, in the second - air, water, oil, etc. )
The consequence of these differences is, in general, a deterioration in the technical characteristics of the electrical contact
method compared to
the anodic-mechanical one
(lower productivity with the same surface cleanliness, greater tool wear, limited range of processed materials), with more favorable operating conditions and greater ease of installation in general. This also determines various areas of their application.
As follows from the above, regardless of the method of supplying energy, the known electroerosive methods of dimensional processing of metals are based on a single physical nature - the metal is removed as a result of the thermal action of electric current.
The differences lie in the mechanism for removing removed metal and in the technical means that ensure the fulfillment of the three conditions of dimensional electrical processing.
A comparison of specific energy consumption for metal removal by various methods shows that the highest energy consumption occurs during electrochemical dissolution (3.85 kWh/kg),
then during melting (0.35
kWh/kg).
During mechanical processing, specific energy consumption largely depends on the type of processing. So, when grinding it is, on average, 2 kW-h/kg,
planing, drilling and milling 0.20-0.25
kWh/kg,
turning 0.045
kWh/kg.
When comparing these data, it should be borne in mind that the specific energy consumption for electrochemical dissolution and melting practically does not depend on the mechanical properties of the materials being processed, while during mechanical processing, an increase, for example, in the hardness of the material being processed sharply increases the specific energy consumption. It should be noted, however, that the actual specific costs in electroerosive and electrochemical installations are significantly higher than the given data due to the inevitable losses of energy during its conversion and transmission.
From an energy point of view, these data determine the feasibility of using electrical methods for processing conductive materials that are difficult to machine.
Taking into account the mapping (copying) property carried out on electroerosive machines using an extremely simple kinematic scheme and without a power drive, and the possibility of performing a number of special operations that are inaccessible to mechanical processing, it is necessary to expand the expedient scope of application of electroerosive methods to parts made of ordinary materials, but with complex shape that makes them difficult to machine.
Consideration of methods for supplying electric current energy to a tool and part shows that to carry out the required physical process of metal removal, special equipment is needed - a machine or installation that includes the following specific elements:
1) pulse generator;
2) automatic regulator;
3) a working fluid supply system (bath, device for working with irrigation, pumping station, etc., depending on the type and purpose of the machine).
ELECTROTECHNOLOGICAL CHARACTERISTICS
The electrical-technological characteristics of electrical discharge machining methods make it possible to determine, based on the given area, configuration and material of the workpiece, which electrical modes and in what sequence they need to be applied in order to obtain a part with the given dimensions and surface finish, and what the machine processing time will be. Electrotechnological characteristics in electrical processing are similar to cutting modes in metal machining.
We will focus here only on the basic fundamental electrotechnological characteristics and methods for their determination. In order to avoid repetition of information known from the literature, we will present only new directions in this issue in relation to electric pulse
processing, although the methodology and quality side are valid for other types of electrical discharge machining. The method of approach to solving the technological problem of processing a part electrically is very important, since the industry has not yet accumulated sufficient experience in creating electrical technology. In order for this experience to be widely used, a unified methodological approach is necessary.
CHARACTERISTICS AND AREAS OF APPLICATION OF DIMENSIONAL ELECTRIC EROSIVE MACHINING
Let us consider the main technological characteristics and areas of primary application of types of electrical discharge machining of metals.
The given data on productivity, surface cleanliness and energy intensity refer to the processing of areas of various sizes in modes that ensure the absence of areas of melting and coating, i.e. at optimal current densities.
Electric spark method
.
removal
rate at maximum conditions when processing steel is on average 600
mm3/min
and is close to the maximum possible for this method of metal processing.
The specific energy consumption in hard modes is 20-50 kWh/kg
of dispersed metal.
Tool wear in relation to the volume of metal removed reaches 25-120 percent or more. Surface cleanliness in soft modes reaches class 4 (Hsr
= 25-30
µm)
at a removal rate of 10-15
mm3/min.
A further increase in surface cleanliness is accompanied by a sharp decrease in the removal rate.
Thus, when obtaining class 5 surface cleanliness (Нср
= 16-19
μm),
the productivity of the electric spark processing method is less than 5
mm3/min.
The specific energy consumption in soft modes is tens and hundreds of times higher than in hard modes.
When processing hard alloys, the productivity of the process in soft modes is approximately two to three times less than when processing steel, but this results in slightly better surface cleanliness. The use of more severe conditions when processing hard alloys is limited by the formation of cracks on them.
Electrospark
The method is currently mainly used for piercing work, manufacturing cavities of complex configurations, etc. operations, as well as for grinding bodies of rotation.
Electropulse method
.
A number of characteristics of this method are outlined above. Electric pulse
processing has significant advantages compared to
electric spark processing
.
The improvement of the technological characteristics of the new processing method is due to the use of special independent pulse generators. The technological characteristics of the method reported below reflect the results of the first works and do not fully characterize the capabilities of the electric pulse
method.
Performance in harsh electric pulse
stitching and copying machine KB MSiIP with a lamp pulse generator exceeds 5000
mm3/min
when obtaining surface cleanliness outside the class.
The indicated productivity can be increased over the corresponding area to several tens of cubic centimeters per minute by increasing the pulse power. The energy intensity in hard modes is 8-12 kWh/kg
of dispersed metal, the relative wear of the tool reaches
0.2 - 20%.
The surface cleanliness obtained on the specified machine in soft modes corresponds to class 4 (
Hsr
= 25-30 µm) with a productivity of: 6-8
mm3/min
, approximately 2-3 times less for hard alloy. Further reduction of the processing mode to obtain greater surface cleanliness leads to an even greater drop in productivity and increases energy consumption. The given technological characteristics of soft modes have now been significantly improved by using new models of machine pulse generators developed by the Lenin Kharkov Polytechnic Institute, ENIMS and KB MSiIP, but still the problem of a sharp increase in the productivity of the processing process in soft modes cannot be solved
