Gtaw

The main objective of today’s manufacturing market is quality and productivity. Demands for improved productivity, efficiency and quality pose challenges to the welding industry. The paper considers process systematization and corresponding advances of welding technology. TIG welding is most vital and common operation use for joining of two similar or dissimilar part with heating the material or applying the pressure or using the filler material for increasing productivity with less time and cost constrain. In this paper a deep comprehension is made to understand the effect of TIG welding parameters such as welding current, gas flow rate, welding speed, that are influence on responsive output parameters such as hardness of welding, tensile strength of welding, by using optimization philosophy. The effort to investigate optimal machining parameters and their contribution on producing better weld quality and higher productivity. This paper is also aimed at, to give a brief idea about the research works done in the past, on TIG welding by various researchers, by highlighting the important conclusions and results arrived at and thereby providing the right direction for future research in this particular area.

Reflecting the estimated increase in natural gas demand, there has been a recent interest in the development of cost-effective materials to be used for the transportation and storage of liquefied natural gas (LNG). Mn could be used in high concentration (between 20~28 wt%) as an alloying addition to create an austenitic steel with mechanical properties similar to traditional LNG tank materials. In this study, microstructural analysis of welded joints in elbow of high-Mn steel was carried out. The samples that were studied were cut from elbows of LNG transportation pipes that were welded by Gas Tungsten Arc welding (GTAW) and Flux Cored Arc Welding (FCAW). This work is concentrated on the analysis of defects and the microstuctural changes at various region of the weldments. A comparative study was done between the GTAW and FCAW weldment of high-Mn steel. It was found that the most of the defects were found in the FCAW weldments. Defects were present at the fusion zone and the reheated fusion zone. Fusion zone of FCAW weldment had the dendritic microstructure, where as fusion zone of GTAW weldment had the equiaxed microstructure. It was also observed that the grain size of heat-affected zone (HAZ) is larger than the other regions. Internal defects, present in the FCAW welded samples, were responsible for lowering the impact energy.

Robotic welding is commonly viewed as one of the most effective ways to reduce costs and increase competitiveness in welding production. However, several requirements need to be taken into account when exploiting welding robotics. The main issues to be considered are the construction of the item to be welded, for example, the joint types, and accessibility to weld sub-assemblies such as stiffeners and cross supports. Furthermore, the type of base material places some restrictions upon the sensing technology applied. This work studied the robotic welding of an aluminum boat. Several sensor technologies were examined and welding experiments undertaken to clarify their potential. Redesign of sub-assemblies of the aluminum boat through modularization and selection of suitable welding processes for aluminum welding are found to provide the optimal solution for the adoption of sensor guided robotic welding.

1.ABSTRACT To meet the energy requirements from the world economic development and the environmental protection, the development direction of power stations is becoming into supercritical and ultra-supercritical high parameter unit. And the corresponding materials such as P91 and P92 are widely used in these projects. P92 is a new material based on P91 which is added W 1.5~2% and reduced the Mo by half, they are all belong to the ASME P No.15E materials. So, in the P92 welding study, especially for GTAW, because its lowest heat input and wide applicability, we can refer to the P91 welding process. 2. INTRODUCTION The need for increasing of the thermal efficiency of advanced power plants and environmental protection leads to worldwide effort of the development of modified 9-12% Cr steels with very high creep resistant strength. (2) To increase thermal efficiency and decrease emissions of carbon dioxide, thermal power plant designers wish to raise the operating temperature and pressure of boilers. This drives the development of new creep resisting steels. Table 1 shows the various grades that are now being used in thermal power plant. (5) The current aim of the coal power plant is to increase the thermal efficiency from 42% to 45%, this can be achieved by increasing the steam temperature to 600 ℃ and a pressure to 30 MPa. Therefore, it is necessary to develop new ferritic high-alloy chromium steels with improved creep resistant properties and improved oxidation resistant properties in steam at temperatures exceeding 600 ℃. New 9% chromium martensitic steel marked P92 was developed for these operating parameters. (4) Table 1: Chemical Compositions as per ASTM A335 (3) The T/P91 alloy allowed typical operating parameters up to 290 bar pressure, main steam temperature 580 ℃. Compared to T/P91 steel, T/P92 has 25%-30% higher creep strength. That is why with the usage of T/P92, design parameters can be increased to 300 bar, 610 ℃-630 ℃. (6) In 9% Cr steels, creep resistance is due to Cr,Mo,V and Nb which act as precipitation strengtheners. In P92, the addition of W further improves creep resistance by strengthening the material. These elements which increase creep resistances are known to be detrimental for toughness in weld metal. (5) Molybdenum in P91 has been partially replaced by tungsten (W) for P92. P92 has creep strength approximately 30% higher than the currently widely used steel P91. (1) Nitrogen addition to the weld decreases toughness significantly. Same effect on toughness exists for Boron also but that effect is not as much as Nitrogen effect. W-containing welds have a consistently worse toughness than W-free welds. Titanium addition to the

— The paper presents results of a study on the effect of welding technique and heat treatment on structure and creep resistance of welded joints made on thin (0.5–1.2 mm) Inconel 718 sheet with the use of GTAW and laser method without filler metal. Technological high-temperature creep tests consisted in measuring the time to rupture for sheet metal without and with welded joints under constant stress σ = 150 MPa and at constant temperature t c = (860 ± 2)°C. Sheet metal joints made with the use of GTAW method and laser-welded are characterized with a three-zone macrostructure, including the weld with size of dendritic grains depending on welding method, the heat-affected zone (HAZ), and the base material (BM). For GTAW method, with increasing sheet metal thickness, the observed values of parameter λ 2s (distance between axes of second-order branches of dendritic grains) decrease from about 12 µm to 8 µm, and similarly, in case of laser welding, λ 2s values decrease from about 9.6 µm to 5 µm with increasing sheet metal thickness. Thin sheet Inconel 718 in as-delivered condition high-temperature creep-tested have the time to rupture on the level of 12 h at elongation of about 48%. Similar time-to-rupture values characterize the joints made by laser welding. GTAW joints are characterized by about 30% shorter time to rupture and elongation less by about 45%. The microstructure change induced by heat treatment (solution treatment and two-stage ageing) resulted in significant increase of creep resistance properties of both base metal and laser-welded joints. The time to rupture of heat-treated specimens of thin Inconel 718 sheet and laser-welded joints creep-tested at 860°C ± 2°C under stress of 150 MPa was about 19.5 h with elongation ranging from 23% to 33%.

Arc interruptions and, therefore, oscillation in the amount of energy and molten wire delivered to the plate have been observed during tandem pulsed gas metal arc welding (GMAW). It appears that these instabilities are related to the magnetic interaction between the arcs. In order to clarify the possible mechanisms involved, this paper tries to mimic the tandem GMAW arc interruptions. External magnetic fields were dynamically applied to GTAW arcs in constant current mode to verify their resistance to extinction as a function of current level and direction of deflection. High-speed filming was carried out as an additional tool to understand the extinction mechanism. The influence of the welding current level on the arc resistance to extinction was established: The higher the welding current, the more the arc resists to the extinction. The arc deflection direction has minor effect, but arcs deflected backward have more resistance to extinction.

Pulsing of the welding current is one approach for refining the fusion zone grain structure in α–β titanium alloy welds. In this study, gas tungsten-arc welds were produced in Ti-6Al-4Fe-0.25Si Titanium Alloys under direct current (d.c.) pulsing. Current pulsing enhances fluid flow, reduces temperature gradients and causes a continual change in the weld pool size and shape. These effects are believed to be responsible for refining the solidification structure in d.c. pulsing. The observed grain refinement was shown to result in an increase in tensile properties.

This study focuses on the simulation of a plasma arc heat source in the context of electric arc welding. The simulation model was implemented in the open source CFD software OpenFOAM-1.6.x, in three space dimensions, coupling thermal fluid mechanics with electromagnetism. Two approaches were considered for calculating the magnetic field: i) the three-dimensional approach, and ii) the so-called axisymmetric approach. The electromagnetic part of the solver was tested against analytic solution for an infinite electric rod. Perfect agreement was obtained. The complete solver was tested against experimental measurements for Gas Tungsten Arc Welding (GTAW) with an axisymmetric configuration. The shielding gas was argon, and the anode and cathode were treated as boundary conditions. The numerical solutions then depend significantly on the approach used for calculating the magnetic field. The so-called axisymmetric approach indeed neglects the radial current density component, mainly result...