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CNAA / Theses / 2008 / May /

A Fundamental and Applied Study of Electroerozive Effects in Non-conventional Technologies


Author: Pavel Topala
Degree:doctor habilitat of engineering
Speciality: 05.03.01 - Procedures and equipment for mechanical and physical - technical working (according to branches)
Year:2008
Scientific consultant: Petru Stoicev
doctor habilitat, professor, Technical University of Moldova
Institution:

Status

The thesis was presented on the 23 May, 2008
Approved by NCAA on the 19 June, 2008

Abstract

Adobe PDF document – 0.84 Mb / in romanian

Thesis

CZU 621.0.484.755

Adobe PDF document 8.24 Mb / in romanian
332 pages

Keywords

Adhesve resistance, Alloy, Electrode, Electron, Discharge, Electoerosion, Quenching, Voltage drop, Anode fall, Catod fall, Circuit, Current electric, Electostatic field, Izolant, Alloy plate, Effective size, Variance, Divice, Sabidity, Durability, Reliability, Matrix,Updating, Ion, Ionization, Impulse, Gap, Interval, Electrod spot, Anode spot, Cathode spot, Particle, Dimeisional conformity, Powder, Layer, Breakdown, Current surse, Shunt, Transformer, Thermal processing, Deterioration

Summary

The paper is devoted to the solution of an important problem of modern science that is the elaboration of the physical picture of the phenomenon called electroerosion by applying the results in the development of new techniques for superficial processing (the formation of deposits from compact and powder materials, modification of surface microgeometry, thermal and chemico-thermal treatment of piece surface) and equipment for their realization.

The first chapter of the dissertation is devoted to the influence of different factors on the intensity of electroerosive phenomena development on the international scale. It was proved that the results obtained by different authors are sometimes contradictory, in other cases they surpass what is described by the classical picture. The author specifically emphasizes the recent scientific statements concerning the phenomenon of electroerosion and their application in the technology of material processing. The objectives of the investigation are formulated at the end of this chapter.

In chapter II entitled ”The strategy of the paper” the author determines the entrance and exit parameters of the processes of superficial processing by the application of electric discharges in impulse. He also describes the used equipment and the methodology of the investigations concerning their determination and measurement. He presents the model of mathematical optimization of the processing.

Chapter III “ The Interaction between the plasma canal and the surface of electrodes, powder particles and the working medium” is devoted to the study of the starting processes of electric discharges in impulse under conditions of forming powder deposit layers, to determining the conditions of forming the liquid phase on the processed surface of the piece and melting of powder particles due to the interaction of the plasma canal of electric discharges in impulse and the transmission of the latter by the curent. The regularities of mass transfer on the processed surface in the liquid and solid phases are established.

Chapter IV “ Modifying the piece surface microgeometry by the application of electric discharges in impulse”. This chapter contains a new physical model of transmitting the electrode material during the disturbance of the liquid metal surface in the electric field of electric discharge impulse accompanied by capillary wave development. All this allowed to develop a technique of modifying the surface microgeometry by extracting the cone-type meniscus and to determine the technological regularities of its realization.

Chapter V “Technologies of forming powder deposits by applying electric discharges in impulse” contains an analysis of regularities in the strata formation of deposits from compact and powder materials through the ignition of electric discharges in impulse breaking the contact under a regime of underexcitation. It is demonstrated that the intensity of deposit formation on the processed piece surface depends on the physical mechanic properties of the deposited material, the parameters of the processing regime, the dimensions of powder particles and their rate in their dosator. It is proved that to form a continuous depositing at a high productivity it is recommended to use powder with a diameter equivalent to the micrometer type particles. The procedure of forming the powder deposits by microwelding particles on the surface of the tool-electrode allowed to solve the problem of forming depositing strata on the plane and loomed surface by increasing the efficiency of utilizing the powder within the limits 90-100%. The thickness of the formed strata is limited due to the appearance of remaining voltage of thermal nature.

Chapter VI “Technologies of thermal and chemico-thermal surface treatment by means of electric discharges in impulse” describes the technology of thermal and chemico-thermal treatment of piece surface; it determines the regularities of modifying the structure and chemical composition of piece surface strata when no deposits are formed. In a regime of thermal treatment of pieces, made of building steel and titan alloys their microdurity increases by 2 or 3, their roughness remaining unchanged or sometimes decreasing. The author also describes the technology of oxide strata formation on the piece surface under normal conditions that allow to increase their active resistance from 10 -1 to 106 .

Chapter VII “Contributions to the conceiving, projecting and realization of the equipment and devices necessary for the realization of procedures “.In this chapter the author presents the results concerning his development of some new generators of current impulse, powder dosator, «Razread»-type installation for the realization of deposit forming procedures, modification of surface microgeometry and thermal and chemico-thermal treatment.

Chapter VIII highlights the properties of processed surfaces by means of the procedures described in chapters IV-VII, and respectively the domains of applying them aiming at decreasing their friction factor, increasing the resistance under conditions of wear and corrosion, modification of surface active resistance.

As a result of the fundamental and applying study of electroerosive effects, the author of the paper has presented concrete procedures of superficial processing of pieces applied in machine and apparatus building, formulated the final conclusions, the contributions made in the dissertation and recommendations for their implementation.