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Products of thin-sheet copper are widely used in radio electronics, instrumentation, power engineering, etc. This article considers micro-plasma and TIG welding of copper with a thickness of 0.2 mm in argon and helium. As a result of the conducted research, it was established that in case of using helium as a shielding gas, the welding speed increases by more than 2 times compared to the microplasma process and by almost 5 times compared to TIG welding in argon. At the same time, the width of the weld and heat-affected zone (HAZ) decreases to 1.4…1.6 mm and 1.0…1.5 mm, respectively. Metallographic examinations of the welds did not reveal defects such as pores, cracks or lack of fusion. The weld microstructure consists of a set of equiaxed crystallites with a grain size of 4…8 μm without clearly expressed crystallization direction and with a smooth transition of the fusion line. The mechanical properties of the welded joints such as temporary resistance and microhardness were determined. Ref. 8, Fig. 7, Tab. 2 [ABSTRACT FROM AUTHOR]

The main direction of improving the operational characteristics of titanium alloys is the creation of heat resistant and high temperature titanium alloys. The high specific strength and corrosion resistance of this type of alloys, at temperatures up to 500…600 °С, enables making them the main structural material for aircraft and rocket engineering. However, their widespread use is associated with the problem of precipitation of brittle phases during welding, which requires the use of additional technological operations, such as local heat treatment or pre-heating. In this paper, the finite element modeling method was applied to study the influence of the TIG welding thermal cycle of the high temperature titanium alloy of Ti‒6.5Al‒5.3Zr‒2.2Sn‒0.6Mo‒0.5Nb‒0.75Si system with and without the use of pre-heating and to plot the cooling rates diagrams of the produced welded joints. Ref. 10, Tabl. 2, Fig. 12. [ABSTRACT FROM AUTHOR]

Results of mathematical modeling of an argon arc with refractory cathode in case of a deformed surface of the weld pool (arc anode) are described. It is assumed that there is a depression (crater) on the anode surface, the shape and size of which are preset; arc plasma has axial symmetry, and it is in a stationary state; metal evaporation from the anode surface is ignored. A mathematical model of the processes of energy, momentum, mass and charge transfer in the arc column and anode region is briefly described. A numerical study was conducted of thermal, electromagnetic and gas-dynamic processes in the arc column with a curved surface of the anode, as well as conditions of electric, thermal and force interaction of the arc with the anode surface, depending on the crater depth. Results of computational experiments are illustrated by the fields of isotherms, isobars and current lines in an arc with a curved surface of the anode, which are compared with similar fields in the case of an anode with a plane surface. A procedure for calculation of normal components of the vectors of electric current density and specific heat flux into the anode with a curved surface is described, and results of calculation of radial distributions of these characteristics, depending on the depth of the crater on the anode surface, are given. These results are complemented by numerical studies of the influence of the crater depth on arc pressure distribution over the anode surface. A conclusion was made that sagging of the weld pool surface in TIG welding can significantly change the conditions of electric and thermal interaction of the arc with the metal being welded, namely it can influence the thermal and hydrodynamic processes in the liquid metal, which determine the penetrability of the arc with the refractory cathode. [ABSTRACT FROM AUTHOR]

A self-consisted mathematical model is presented, describing nonstationary processes of energy, momentum, mass and charge transfer in plasma column and anode boundary layer of an electric arc burning in atmospheric pressure inert gas at pulsed modulation of current. A numerical study of distributed and integrated characteristics of 2 mm long argon arc was performed in the case of current modulation by rectangular pulses at 10 kHz frequency and different values of the duty cycle (0.3; 0.5; 0.7) under the condition that the average current value remains unchanged and equal to 140 A. Calculated time dependencies of plasma temperature, velocity and current density in the arc column centre, as well as axial values of plasma temperature and pressure near the anode surface, anode current density and heat flux into the anode are given for the selected values of duty cycle. Radial distributions of averaged over the current modulation period heat flux, introduced by the arc into the anode, pressure and force of friction of arc plasma flow on its surface were calculated, which are the determinant ones for simulation of thermal and hydrodynamic processes in the metal being welded in TIG welding with high-frequency pulsed current (HFPC) modulation. Results of simulation of nonstationary arc characteristics are compared with the respective results for a direct current (DC) arc, at current equal to average value of modulated current. Analysis of the obtained results leads to the conclusion that in the case of HFPC TIG welding at 10 kHz frequency decrease of duty cycle (increase of pulse current) at constant value of average current leads to greater force impact of such an arc on weld pool metal and to increase of its penetrability, respectively. 20 Ref., 2 Tabl., 6 Fig. [ABSTRACT FROM AUTHOR]

A device was designed that allows inserting a tungsten dart probe into the plasma of arc column during TIG welding. The operation of the device envisaged that a metal string with a diameter in the range of (0.25…0.4) · 10–3 m was elastically deformed (twisted) under the action of torque. During the movement of the arc column plasma, the probe was subjected to a pressure force, the string was elastically deformed and this allowed establishing the velocity of the arc column plasma rotating around its axis during TIG welding under a constant longitudinal magnetic field. The arc burned between the tungsten electrode and a copper plate with a thickness of 6,0 · 10–3 m on the direct polarity without mixing the electrode (vw = 0). The length of the arc was 4.0 · 10–3 m. It was found that at a welding current of 200 A, an increase in the induction of the magnetic field from 18 to 45 mT leads to an increase in the azimuthal velocity of the arc column plasma at a distance within (3…4) · 10 -3m from its axis in the range from 17 to 20 m/h, and the angular speed of rotation is in the range from 750 to 940 rps. The plasma probings of the arc column were performed with a double probe during TIG welding with the effect of a constant longitudinal magnetic field. In capacity of probes, tungsten darts with a diameter of 0.3 ∙ 10–3 m served. According to the results of measuring voltage drop, between the probes the values of longitudinal and azimuthal current densities at a set point during TIG welding were established. It was found that at the level of magnetic field induction within 18…45 mT and arc current of 200 A, the values of the azimuthal component of current density in the arc column are approximately the same as the values of the longitudinal component of current density in the arc column. 14 Ref., 6 Fig. [ABSTRACT FROM AUTHOR]

The presented study involved mathematical modelling of single pass TIG welding of duplex stainless steel S32205. The temperature fields, the fusion zone and HAZ dimension, the cooling rate fields, residual stresses taking into account kinetics of dissolution of austenite during heating and kinetics of precipitation of austenite during cooling were obtained. The comparative analysis of residual stresses with/without phase transformations showed the difference of residual stresses distribution due to different amounts of austenite and ferrite and due to volumetric changes during phase transformations. 24 Ref, 1 Тabl., 9 Fig. [ABSTRACT FROM AUTHOR]

Structural pseudo-β-titanium alloys attract a lot of interest in fabrication of critical structures. This alloy class includes alloys with the structure represented by one β-phase after hardening or normalizing in the β-region. The alloy weldability is an important factor at application of pseudo-β-titanium alloys in aircraft and rocket engineering. By their mechanical characteristics, the welded joints of modern pseudo-β-titanium alloys should match the level of base metal mechanical properties. In this work, the impact of argon arc welding, as well as further heat treatment on the phase composition, structure and mechanical properties of welded joints of pseudo-β-titanium alloy was studied. It was established that as a result of the impact of thermal cycle of welding predominantly β-phase in the amount of 77% is recorded in the weld metal of joints of pseudo-β-alloy V19. Application of VT1-00sv filler wire enhances the quantity of dispersed α-phase particles and reduces the quantity of β-phase in the weld metal to 60%, respectively. Annealing results in formation of a uniform, homogeneous finely-dispersed two-phase (α+β)-structure with ultimate tensile strength values of welded joints on the level of σt = 1010 MPa, that exceed the respective base metal values by 12%. [ABSTRACT FROM AUTHOR]

A review of investigations devoted to the processes of inert-gas nonconsumable electrode welding with welding current modulation was performed. The third part of the review is devoted to analysis of the works, dealing with theoretical study and mathematical modeling of the processes of heat-, mass- and electric transfer in arc plasma and welded metal in TIG welding by modulated current. Different approaches to theoretical study of the above-mentioned processes are described, as well as respective mathematical models, allowing for the conditions of nonconsumable electrode welding with low-frequency (up to 10 Hz) and high-frequency (above 10 kHz) pulsed modulation of welding current. Results of numerical analysis of the distributed and integral characteristics of an argon arc with refractory cathode at pulse variation of current are given. It was performed on the base of models of a non-stationary arc with distributed and concentrated parameters. Results of computer modeling of thermal, hydrodynamic and electromagnetic processes in the welded metal (also at self-consistent accounting of the processes that proceed in arc plasma) were analyzed for the case of spot TIG welding with low-frequency pulse modulation of current. Presented are the analytical dependencies that describe the impact of the shape and parameters of welding current pulses on the characteristics of dynamic action of an arc with a refractory cathode on weld pool metal. [ABSTRACT FROM AUTHOR]

Technology of welding and recovery of performance of the shaft of regulator of limiting number of revolutions in overspeed governor of turbo feed pump in No.1 power unit of Trypillya TPS is presented. Operating conditions of overspeed governor regulator shaft and causes for its damage have been analyzed. Parameters of the mode of welding and heat treatment of the regulator shaft from steel 40Kh were optimized. Microstructure and mechanical properties of witness-samples were studied, and optimum technological conditions of producing a sound repair welded joint were determined. Obtained results were confirmed by successful operation of the turboset for 2743 h. [ABSTRACT FROM AUTHOR]

A review of studies, devoted to the processes of nonconsumable electrode inert-gas welding with welding current modulation was performed. The second part of the review is devoted to analysis of the works, dealing with the features of metal penetration (aluminium alloys, stainless steel, high-temperature nickel-chromium alloys) and weld formation in TIG welding with modulated current. [ABSTRACT FROM AUTHOR]

Works devoted to the processes of inert-gas nonconsumable electrode welding with current modulation were reviewed. In the first part of the review attention is focused on studies, dealing with the features of running of thermal, gas-dynamic and electromagnetic processes in non-stationary arcs with refractory cathode at different modes of arc current modulation. [ABSTRACT FROM AUTHOR]

The experience of the E.O. Paton Electric Welding Institute in creating a metal-cored wire for helium arc TIG welding of copper and its alloys was described. The deposited metal of the wire contains not more than 0.35 wt. % of alloying additives and is characterized by a high electrical and heat conductivity. Examples of the effective use of the developed wire in welding rotors of electric machines and in repair of gas-oxygen copper chambers are given. [ABSTRACT FROM AUTHOR]

The paper considers an approach for selection of filler material in TIG welding of titanium alloy VT22. It is shown that weld metal obtained using pilot flux-cored wire PPT-22 is a representative of transient class of titanium alloys, to which VT22 alloy is referred to (coefficient of β-stabilizing of such metal equals 1). This wire can be used for argon-arc welding of high-strength titanium alloys VT22. Mechanical properties of such welded joints after heat treatment reach the level of base metal indices. Application of PPT-22 wire in restoration argon-arc surfacing of VT22 alloy parts provides their high service characteristics. 15 Ref., 4 Tabl., 5 Fig. [ABSTRACT FROM AUTHOR]