Search academic texts

Information × Registration Number 0218U003280, 0117U007259 , R & D reports Title New high-tech power-saving energy source for precision welding, brazing and surface treatment of materials popup.stage_title Head Bolotov Maksym Hennadiyovych, Registration Date 30-01-2018 Organization Chernigiv National University of Technology popup.description2 The project is pointed at the solving of the actual scientific problem of creation the new high-technological resource-saving and resource-saving power source for diffusion welding and brazing on basis of the distributed gas-discharge plasma of glow discharge. The object of the scientific work is low-temperature distributed gas-discharge plasma as power source for diffusion welding and brazing processes. The subject of the scientific work is the physical-technological and energy characteristics of glow discharge and the methods of their control under welding heating conditions. The aim of this project is the determination and improvement of technological properties and energy rates of medium pressures glow discharge plasma and controlling means of them under high-temperature heating and metal processing. The main tasks of the work are: 1. The investigation of the stable existence high-current glow discharge area under welding heating conditions; 2. The investigation of the energy and thermalphysic characteristics of glow discharge plasma under welding conditions; 3. The development of methods and controlling means of energy and thermalphysic characteristics of glow discharge in welding, brazing and surface treatment technological processes. During execution of the project complex approach with usage of the theory of gas discharge physics, electrodynamics, electromagnetism and transitional process in electric fields is provided. The main idea of the development of such power source is the ensuring of high energy efficiency and manufacturability of diffusion welding and brazing. It is achieved by realization in the vacuum camera of the high-current medium pressures glow discharge with (1.3…13.3 kPa) as surface heating source which allows to implement the heating both metal and non-metal products in different variations of their combinations with energy coefficient of efficiency at level of 75-80 %. On the basis of the diffusion welding specifics analysis and available data about medium pressures glow discharge (1.3…13.3 kPa), as a working hypothesis during the development of the new heat source for diffusion welding the next propositions: 1) massive cathodes (which are products) are the active heat flow towards discharge plasma and influence on the plasma heating process; 2) the state of gas-discharge and its transitions into contrary mode (electric arc) are determined by the processes on the cathode; 3) discharge plasma as a heating means possesses high technological adaptability; 4) existence of gas-discharge plasma in the wide range of gas pressures allows to realize in the sole technological cycle the operations of purification and activation of the joined surfaces, diffusion welding and thermal or chemical-thermal treatment of welded products; 5) the main parameters of glow discharge are regulated by electric signals which is the base for the process automation; 6) usage of quasi-impedance voltage inventors in the structure of mean power sources for diffusion welding by glow discharge will allow to raise the coefficient of efficiency of the system and improve consumption current quality. It has been established, that under the diffusion welding conditions when the gas pressure in the chamber is 2.66...To 26.6 kPa and above, the heating of the joining parts is provided by two energy sources: the bombardment of its surface by the accelerated ions of the gas in the near-cathode zone and heat removal from the plasma of the positive column of the discharge. It has been determined, that the heat transfer from the positive column through the near-cathode layer of 10-3...10-5 m thickness is carried out according to the mechanism of heat conduction. Such mechanism provides from 20% up to 60% of the energy on the surface of the parts that emitted in the positive column of the discharge. The magnitude of this energy is 20...40% of the total energy that emitted on the surface of the cathode and could be smoothly adjusted by the changing of the gas pressure. Due to the total influence of two heat sources at the cathode, the value of the effective efficiency of heating of the glow discharge is reached 0,85...0,9. Such effective efficiency is determined by the characteristics of the shielding gas environment, gas pressure, interelectrode gap and characteristic range of modes of welding at discharge currents of 2...15 A, at the gas pressure of 4...15 kPa and interelectrode gap of 0.004...0.01 m that vary more than 30%. It also should be considered when the technological processes of welding, brazing and surface treatment are designing. The analytical models of the process of surface heating by the glow discharge during the welding process of hermalphysic "thin" and "thick" bodies of similar and dissimilar metals have been created. These models as a function of parameters of the heating mode and characteristics of the joining parts allow to define the dynamics of temperature changing at any point of connection. The obtained results will allow to predict the thermal state in the contact zone of welded joints with an error at 4...7%. The advantages of the obtained results are that the thermal models developed during the first phase of the research work allow to predict thermal condition of the welded samples that considerably differ in thermal-physical properties with an error not exceeding 4...7% at different stages of heating. It is testifies to its sufficient adequacy. It is very important espesially under the conditions of high temperature heating during the diffusion welding with application of gas-discharge plasma of glow discharge as a source of surface heating, since direct monitoring of the thermal state of the surfaces of the welded parts is restricted or impossible by the contact (using a thermocouple) or noncontact (using pyrometers) ways. It is due to the sufficiently high temperature of the welded samples and high levels of radiation of gas-discharge plasma. In addition, the surface control does not allow to determine the character of temperature field distribution inside the details, in particular in the connection area, which is especially important under the conditions of diffusion welding. It has been also proposed the calculation methods of determination of the optimal position of the axis of the heat source (glow discharge) relatively to the connection are of parts which are substantially differ by the thermal resistance in the radial direction. Such calculation methods allows to prevent the overheating and high thermal deformations of thin-walled parts during the welding pressure. Results obtained after implementation of the first stage of the research effort will allow raise considerably the productivity of the diffusion welded joints receiving process made of materials with substantially different physical-mechanical properties and have limited or unsatisfactory welding ability. Such products are hard-alloy punches and cutting tools which are widespread for renovation and renewal of technical equipment, including military one, which is used in implementation zone of ATO. Results obtained after implementation of the first stage of the research effort, in particular defined areas and optimal modes of the stable existence of the medium pressures glow charge under conditions of diffusion welding and brazing, entered into tutorial of discipline "Welding power sources". Product Description popup.authors Іскрижицька Надія Миколаївна Бадай Марія Володимирівна Болотов Геннадій Павлович Гречка Володимир Миколайович Деркач Олег Леонідович Нагорна Ірина В'ячеславівна Петрушинець Лідія Вячеславівна Пустовойт Христина Михайлівна Ющенко Світлана Михайлівна popup.nrat_date 2020-04-02 Close