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Abstract of thesis of master's degree work
theme :
"Improvement of treatment of details from materials which are difficult to process with the use of EAP"
Leader: associate professor, candidate of engineering sciences Boltyan Andrey Vladimirpvich
1 Introduction. Ground of actuality
2 Aims and tasks of work
3 Supposed scientific novelty
4 Description of process of elektroarc process
4.1 Stages of flowline.
4.2 Working environments
4.3 Applied electrode-instruments
5 Conclusion
6 Literature
1 Introduction. Ground of actuality
Presently transition from treatment by a blade to treatment without the removal of shaving begins to be carried out. One of such types of process is the method of elektroerosion process, which was invented by the scientists B.R. Lazarenko and N.I. Lazarenko.
Elektroerosion process has received wide application at making products from the materials which are hard to cutting or in generally not accessible for tooling. It allows to process surfaces in the difficult places of access, treatment of which by an instrument with a blade is impossible or requires the special adaptations additionally.
Elektroarc treatment of materials is the variety of elektroerosion treatment.
It is the purpose of master's degree work to define the rational modes of elektroarc process.
Tasks:
- to give description of elektroarc process;
- to analyse the formation and distribution of temperature and thermal tensions on the surface of a detail;
- to analyse the technological indexes of process of elektroerosion process;
- to determine of the rational modes of elektroarc process;
- to compare the quality of surfaces of the details treated by an instrument with a blade and elektroarc process.
One of perspective directions of new technologies allowing to multiply considerably productivity of process, and firmness of instruments is elektroarc process, essence of which is the creation of artificial source of heat in the area of treatment from the input of technological current, that increases the productivity of process.
It is also necessary to mind that elektroarc process not only allows to get the surfaces of high exactness and low roughness but also if it is necessary to consolidate the superficial layer of detail. To receive a similar quality of surface at treatment with a blade additional heat treatment of surfaces was required.
4 Description of process of elektroarc process
Elektroarc process is based on mechanical destruction or change of form of metallic surfaces, occurring simultaneously with heating or melting of these surfaces by an electric current. At this method in the place of contact of two conducting current surfaces the heat is dissipated because of the increased resistance, and electric discharge.
The hasp of interelectrode interval as a result of formation of area with high tension of the field is the first stage of erosion process. Under the action of a discharge there is a ionization of interval, through which electric current begins to flow between the electrodes 1 and 2, i.e. a conducting current channel appears - comparatively narrow cylindrical region, filled by the heated matter (by plasma) containing ions and electrons. There is melting of metal on the border of channel, forming small holes.
Edges gas bubble formation from steams of liquid and metals near the channel of conductivity is the second stage. Because of high pressure (to Pa) the channel of conductivity aims to broaden, squeezing a gas phase surrounding it. Because of inertia a gas bubble and liquid surrounding it is immobile at first, their expansion begins later. The border of channel of conductivity moves with high speed (150…200м/с) in radial direction. The so-called front of compression appears on an outward border, in which pressure uneven changes by steps from initial to high values on a border.
Stopping of current tearing off of shock wave from a gas bubble and continuation of the inertia expansion will be the third stage. At the beginning of this stage in an interelectrode interval there is meted metal (2) in deepening’s of the electrodes (1) and (6); a gas bubble (3), steam 4 metals of detail and instrument is present liquid dielectric (5). Where a gas bubble reaches the biggest size pressure drops sharply inside of it. The molten metal contained in small holes boils up and is thrown out in an interelectrode interval.
Fig.1 - Processes what is going on in an interelectrode interval
The output technological parameters elektroarc are: the Q productivity; specific expense of electric power of q; quality of the treated surface of detail, which is characterized by the parameter of the Rz(mkm) roughness, thermal affected zone, the HV(MPa) micro hardness, numeral value and sign of remaining tensions ooh(MPa).
Working environment of elektroarc has the following influence: 1) physical is localization of a charge ability to change potential of ionization and regulate the parameters of arc charge; 2) chemical is creation of absorptions films providing a heat-resistance and electrode-instrument wear proof on the products of erosion, to accompanying anode dissolution; 3) thermal localization of thermal influence, cooling of the electrode-instrument and detail; 4) mechanical is delete of products of erosion; 5) lubricating influence.
Working liquids must meet the following requirements:
- providing of the high technological indexes of elektroerosion;
- thermal stability of physical and chemical properties under the influence of electric charges with parameters proper to applied at elektroerosion process;
- low corrosive activity to the electrode-instrument materials and the processed detail;
- high temperature of flash and low evaporation;
- good ability to be filted;
- absence of smell and low toxic.
The low molecules hydrocarbon liquids of different viscosity have been used; water and in an insignificant degree silicon organic liquids, and also water solutions of diatomic alcohols at elektroerosion process.
For every kind of elektroerosion working liquids providing the optimum mode of treatment are applied. On the rough modes it is recommended to apply working liquids with viscosity (mixture kerosene-oil industrial), and on clean (kerosene, raw material hydrocarbon).
4.3 Applied electrode-instruments
As electrodes-instruments at elektroarc disks, profiled instruments, wire with some structural features depending on the terms of treatment are applied. The working surface of electrodes-instruments can be made variants: smooth, with radial slots, with openings of small diameter, with or without coverage
Materials, which an electrode-instrument is made of, must have high erosion firmness (copper, composition-metal, tungsten, aluminium, graphite and graphite materials).
Electrodes-instruments must provide stable work in all range of the operating conditions of elektroarc and best performance at small wear.
As a result of implementation of this work the process of elektroarc process has been studied. All stages of flow line of processes taking place in an interelectrode interval are considered in detail. Thermal processes, flowing in the detail, and thermal tensions, occurring while this, are considered. Their influence on the received quality of surface is described.
It is further planned to produce the calculation of the rational modes of elektroarc process and to make comparison of roughness and quality of the surfaces treated by elektroarc and instrument with a blade. It is also planned to make economic comparison of data from types of rocess.
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1 Introduction. Ground of actuality
2 Aims and tasks of work
3 Supposed scientific novelty
4 Description of process of elektroarc process
4.1 Stages of flowline.
4.2 Working environments
4.3 Applied electrode-instruments
5 Conclusion
6 Literature
| Autobiography | List of references | Report | Electronic library | Individual task |