Showing papers on "Shielding gas published in 2012"

Welding Duplex Stainless Steels — A Review Of Current Recommendations

Abstract: A steel will not become widely accepted and used unless it can be successfully welded without too many limitations. Contemporary duplex stainless steel grades fulfil these requirements with some grade dependent differences. The duplex stainless steel family has, during the last decade, been extended with new lean grades and recently also highly-alloyed hyperduplex grades. Most welding recommendations are very similar to those of the 1990’s. However, the introduction of new grades and the increased use of newer welding methods has somewhat changed the perception of what is possible. This paper discusses the state-of-the-art and trends in welding of duplex stainless steels. It is based on input from the worldwide welding community, including users and producers of steel and welding consumables as well as literature. In most cases, there is consensus on recommendations but variations reflecting differences in practices exist in particular for newer steel grades where limits in e.g. allowable energy inputs are less well documented.

Effects of Activating Flux on Weld Bead Geometry of Inconel 718 Alloy TIG Welds

Abstract: The purpose of this work is to investigate the effects of activating fluxes and welding parameter to the penetration and depth-to-width ratio (DWR) of weld bead of Inconel 718 alloy welds in the tungsten inert gas (TIG) welding process. In the activating flux with TIG (A-TIG) welding process, the single-component fluxes used in the initial experiment were SiO2, NiO, MoO3, Cr2O3, TiO2, MnO2, ZnO, and MoS2. Based on the higher DWR of weld bead, four fluxes were selected to create six new mixtures using 50% of each original flux. The A-TIG weldment coated 50% SiO2 + 50% MoO3 flux and 75° of electrode tip angle were provided with better welding performance. In addition, the experimental procedure of flux-bounded TIG (FB-TIG) welding with the same welding conditions and flux produced full penetration of weld bead on a 6.35 mm thickness of Inconel 718 alloy plate with single pass weld.

Laves Phase Control in Inconel 718 Weldments

Abstract: The detrimental laves formation in fusion zone during welding of Inconel 718 is controlled with compound current pulsing technique along with helium shielding gas. Also solid solution filler wire is used to minimize the niobium segregation. Welds were produced in 2mm thick sheets by GTA welding process and subjected to the characterization techniques. The results show, refined fusion zone microstructure, reduced amount of laves phase, minimum niobium segregation and softer fusion zone in the as welded condition.

Local Exhaust Ventilation for the Control of Welding Fumes in the Construction Industry—A Literature Review

Abstract: Arc welding is a common unit operation in the construction industry, where frequent changes in location and welding position make it more difficult to control fume exposures than in industries where fixed locations are the norm. Welders may be exposed to a variety of toxic airborne contaminants including manganese (Mn) and hexavalent chromium (CrVI). Local exhaust ventilation (LEV) is a well-known engineering control for welding fumes but has not been adopted widely in the construction industry. This literature review presents data on the performance of a variety of LEV systems for welding fume control from the construction (five references), shipyard (five references), and other industries. The studies indicate that LEV can reduce fume exposures to total particulate, Mn, and CrVI to levels below currently relevant standards. Field studies suggest that 40-50% or more reduction in exposure is possible with portable or fixed LEV systems relative to natural ventilation but that correct positioning of the hood and adequate exhaust flow rates are essential. Successful implementation of extraction guns for gas metal arc welding (GMAW) and flux core arc welding has been demonstrated, indicating that a successful balance between extraction airflow and shielding gas requirements is possible. Work practices are an important part of achieving successful control of fume exposures; in particular, positioning the hood close to the arc, checking exhaust flow rates, and avoiding the plume. Further research is needed on hood size effects for controlling welding fume with portable LEV systems and identifying and overcoming barriers to LEV use in construction.

Study on the periodic oscillation of plasma/vapour induced during high power fibre laser penetration welding

Abstract: High power fibre lasers have recently received much attention because of their inherent advantages such as high output power, high beam quality, compact size, and flexible fibre delivery. Studies on the mechanism behind fibre laser welding systems may further promote their practical application. In this paper, high speed video observations were used to study the characteristics of the plasma/vapour induced during the bead-on-plate welding of ZL114 using a high power CW fibre laser. We also analysed the cause of the periodic oscillation of the plasma/vapour. The results revealed that plasma/vapour induced from high power lasers oscillate periodically at 450–600 μs cycles above the weld pool surface. The use of a shielding gas has little effect on the oscillation cycle. The plasma/vapour absorption is not the main reason for the periodical oscillation of plasma/vapour induced during fibre laser welding. The periodic oscillation of the plasma/vapour can be attributed to the oscillation of the keyhole.

Artificial neural network prediction of weld geometry performed using GMAW with alternating shielding gases

Abstract: An Artificial Neural Network (ANN) model has been applied to the prediction of key weld geometries produced using Gas Metal Arc Welding (GMAW) with alternating shielding gases. This is a recently developed method of supplying shielding gases to the weld area in which the gases are discretely supplied at a given frequency. The model can be used to predict the penetration, leg length and effective throat thickness for a given set of weld parameters and alternating shielding gas frequency. A comparison between the experimental and predicted geometries matched closely and demonstrates the effectiveness of this software approach in predicting weld outputs. The model has shown that the application of alternating shielding gases increases the penetration and effective throat thickness of a fillet weld whilst the leg length is reduced. A sensitivity analysis was performed which showed that the travel speed is the most influential input parameter when predicting weld geometries, this is to be expected for any given welding set-up due to the influence of the travel speed on the heat input. The sensitivity analysis also showed that the shielding gas configuration had the lowest influence on the output of the model. The output from the model has demonstrated that the use of alternating shielding gases during GMAW results in a step change in the weld metal geometry. This suggests that, in the case of alternating shielding gases, an increased travel speed is required to produce a similar weld geometry to that of the conventional Ar/20%CO2 technique.

Optimal design for laser beam butt welding process parameter using artificial neural networks and genetic algorithm for super austenitic stainless steel

Abstract: Laser welding input parameters play a very significant role in determining the quality of a weld joint. The joint quality can be defined in terms of properties such as weld bead geometry, mechanical properties and distortion. Therefore, mechanical properties should be controlled to obtain good welded joints. In this study, the weld bead geometry such as depth of penetration (DP), bead width (BW) and tensile strength (TS) of the laser welded butt joints made of AISI 904L super austenitic stainless steel were investigated. Full factorial design was used to carry out the experimental design. Artificial Neural networks (ANN) program was developed in MatLab software to establish the relationships between the laser welding input parameters like beam power, travel speed and focal position and the three responses DP, BW and TS in three different shielding gases (Argon, Helium and Nitrogen). The established models were used for optimizing the process parameters using Genetic Algorithm (GA). Optimum solutions for the three different gases and their respective responses were obtained. Confirmation experiment has also been conducted to validate the optimized parameters obtained from GA.

Effects of temperature-dependent material properties and shielding gas on molten pool formation during continuous laser welding of AZ91 magnesium alloy

Abstract: Laser welding processes are widely used for fabrications in many engineering applications such as aerospace and automotives. In this paper, a moving distributed heat source model based on Goldak's method [1] has been implemented into finite volume thermal simulations in order to predict temperature distributions during the welding process of a magnesium alloy and to study the effects of variations in thermal properties, absorption coefficient and gas shielding on the computed temperature distributions and weld pool dimensions. The main conclusion is the significant effects of varying the thermal conductivity and absorption coefficient of magnesium. Also, it has been seen that the shielding gas, besides its main role of protection against oxidation, has a significant effect on the width of the weld pool. Finally, the obtained results have been compared to the experimental ones and a satisfactory correlation has been observed, indicating the reliability of the model developed in this study.

New Findings On The Efficiency Of Gas Shielded Arc Welding

Abstract: A study was carried out to measure the effective efficiency of different gas shielded arc welding processes and investigate the role of influence coefficients on the process efficiency. A new system to measure the integrated heat flow in welding processes was developed and further investigated. By this system, it can be shown how e.g. electrical and welding torch parameters, as well as material and gas parameters directly influence the efficiency of the welding process. Through this, it is possible to raise the efficiency of welding (processes for example by reducing the wire speed, using helium gas or increasing the distance of the welding torch to the metal plate. Contrary, increasing the current, welding speed or voltage reduces the process efficiency. The difference between the lowest and highest achievable value of efficiency can be more than 15 % for one specific welding process. In addition to the conventional welding processes like gas tungsten arc welding (GTAW), gas metal arc welding (GMAW) and plasma welding also latest technologies, such as heat reduced processes (for example controlled dip arc with or without wire pullback) and high performance welding processes were analysed. In this manuscript, primarily the new technology for measuring the efficiency is presented. Furthermore, different influence coefficients and their effects on the overall efficiency of welding processes are described. Finally, the differences between measured efficiencies and fixed values of efficiencies for welding processes given in standards are discussed. The efficiencies of the latest heat reduced and high performance welding processes are given. The results verify that the parametrical influence on the efficiency of welding processes is huge, so that it is not recommended to work with fixed efficiency values for example in modeling and simulation.

Gas-shielded arc welding method

Abstract: PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method by which weld metal having a superior strength and toughness is obtained, even in multi-layer welding with high heat input and high interpass temperature, and by which improved weldability is demonstrated by reducing the mount of the occurrence of spatter and of formation of slag at welding SOLUTION: Welding is performed by using: a welding steel wire composed of a steel wire stock containing by mass 001-010% C, 02-12% Si, 10-25% Mn, 005-020% Ti, 0003-0020% S, ≤0020% P, 005-05% Mo, 005-03% Cr, ≤05% Cu, 0005-002% Al, and 00005-00050% B; and gaseous mixture containing 10-50 volume % Co 2 and 50-90 volume% Ar as a shielding gas, thereafter time required until the bead of the final pass is cooled from 800°C to 500°C is adjusted to 15-450 seconds COPYRIGHT: (C)2005,JPO&NCIPI

Electron beam welding of ceramic to metal using fore-vacuum plasma electron source

Abstract: The possibility of creating ceramic-metal joints by electron beam welding is considered. The welding of alumina ceramic to aluminum and titanium was performed in the fore-vacuum pressure range (5–20 Pa) using a plasma electron source. The structure and composition of the ceramic-metal transition layer are investigated. It is shown that the transition-layer thickness exceeds substantially the microroughness size of the initial ceramic, which confirms that intermixing of materials, i.e., welding, has occurred. The dependence of breaking strength of the obtained joints on the electron-beam power is measured. A sharp difference in the strength depending on the metal selection is found: the ceramic-aluminum weld strength is an order of magnitude higher than the strength of the ceramic-titanium system.

Visualization and Optimization of Shielding Gas Flows in Arc Welding

Abstract: GMA welding is one of the most frequently applied welding techniques in industry. Particularly the joining of aluminium, high alloyed steels or titanium requires a cover of shielding gas in order to provide a low PPM concentration of oxygen. The result of the welding process depends essentially on the chemical and thermophysical properties of the process gas used. Consequently, it is necessary to be able to describe and to analyse its flow with respect to various influencing variables. However, it is very difficult to realize this during arc welding processes; a poor access is predominant due to the covered areas inside the welding torch and temperatures of up to 20 000 K cause the strong radiation of the arc and electromagnetic fields. This paper deals with experimental and numerical methods for visualization and quantification of process gas flows in arc welding and gives examples for their technical applications. Unlike previous work, the described methods consider the arc as a dynamic element which determinates the gas flow. Advanced Particle Image Velocimetry (PIV) and Schlieren measurement were used for characterization of the flow field in the direct vicinity of the arc in GTA and GMA welding. Furthermore, a numerical model including magneto-hydrodynamics and turbulence models was used for a detailed visualization of the flow in the free jet and in the hidden interior of the torch. It is based on a commercial CFD code which allows to model complex 3-D geometries of torch and workpiece design. Mixing effects and turbulence model were validated by oxygen measurements in the gas shield.

Effect of High-Strength Filler Metals on Fatigue

Abstract: Fatigue life of welded joints is in general independent from the material strength. High-strength materials are only beneficial in the low-cycle-fatigue region due to their increased yield limit. This property leads to their application, for instance, in welded mobile crane structures. The high-cycle fatigue limit, however, depends mostly on the geometry and the metallurgy of the notch. Therefore, an optimized weld process is required to achieve a certain fatigue strength. This paper contributes to the obtainable fatigue limits for thin-walled, high-strength joints regarding an optimization of the gas metal arc weld process for fillet welds without additional post-treatment. A methodology is designed to manufacture welded specimens with minimized production scatter. The specimens were carefully analysed by metallographic studies, hardness, distortion and geometric weld toe measurements. The detailed analysis enables a profound link between experimental fatigue life and weld process settings. For the assessment of the fatigue life of thin-walled specimens, the nominal stress approach and the notch stress method are used. The thin wall thickness is considered in the nominal approach by a thickness correction factor. The experimental results showed that the highest fatigue strength for the specific specimen design in ‘as-welded’ condition can be obtained when using a high-strength metal-cored wire filler in combination with a three-component mixed gas.

Weld metal characterization of 316L(N) austenitic stainless steel by electron beam welding process

Abstract: Electron beam welding (EBW) is a fusion joining process that produces a weld by impinging a beam of high energy electron to the weld joint. EBW has been used widely due to its advantages like narrow weld zone and heat affected zone, low distortion and contamination etc. The present work is focused on EBW of 316L(N) austenitic stainless steel varying the welding parameters such as beam power and welding speed. This study is carried out by analyzing the mechanical and metallurgical properties of the welded material. The mechanical properties have been evaluated using tensile, impact, hardness and bend test in accordance with the ASTM standards. The metallurgical characteristics are further investigated through optical microscopy. The mechanical properties of the weld material are better than the parent material. The variations of the mechanical properties were related with the variations in the cooling rate of the weld metal. The change in the cooling rate has influenced the grain size which has in turn influenced the mechanical properties. The metallurgical factors such as the presence of the ferrite and its percentage were also considered to substantiate the variation in the characteristics of the weld metal. Keywords: electron beam welding, 316L (N), beam current, gun voltage.