Of particular relevance to this study is the combination of numerical modelling with schlieren imaging to examine the gas distribution during arc welding. Shadowgraphy has been used to visualise the e ﬀ ect of cross-drafts speeds on the shield gas ﬂow proﬁle and coverage during GMAW of mild steel, at a range of shield gas ﬂow-rates and torch nozzle diameters (Beyer et al., 2013). The shadowgraphy revealed an em- pirical ratio of cross-draft speed to shield gas speed < 1.25 to be a re- liable indicator of acceptable weld quality independent of nozzle dia- meter, validated by radiographic measurements of the welds. A model of the shield gas ﬂ ow was reported, but it did not include the plasma jet and so its predictive capability was severely limited. (Dreher et al., 2013) examined a large set of variables numerically, including aspects of the torch geometry, as well as the nozzle stand-o ﬀ and angle. The model conﬁrmed the profound inﬂuence of Lorentz forces (magnetic pinch) on the bulk ﬂow of the shield gas, as coverage quality deterio- rated with an increase in current. Additionally, it was shown that the increased temperature at higher currents causes diﬀusion to play an increasingly important role in the gas dynamics. The shielding gas ﬂow- rate was determined for a range of arc currents and stand-o ﬀ distances, but the calculation omitted temperature-dependent transport properties of the gas mixture; and a somewhat arbitrary O 2 limit of 50 ppm was
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The end plate forces the shielding gas through a reduced cross-sectional area increasing its velocity to 4.05 m/s (9 mph) at the nozzle exit. As a result, this geometry produced the best performance of those investigated. However, a previous study by Ramsey et al.  found that reducing the nozzle exit diameter to 11 mm produced shielding gas exit velocities above 4.5 m/s (10 mph) and consequently out performs those changes that have been investigated in this study. Additionally, spatter build-up on the welding nozzle is unavoidable in practice, and can be minimised by good control of the welding parameters, the 2 mm diameter holes in the end plate may be more susceptible to blockage than a circumferential restriction.
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Abstract: Extensive experimental trials were conducted, emulating the conditions modelled, in order to validate the computational fluid dynamic results. Final results demonstrated that a more constricted nozzle was more effective at creating a stable gas column when subjected to side draughts. Higher shielding gas flow rates further reduce the gas column’s vulnerability to side draughts and thus create a more stable coverage. The results have highlighted potential economic benefits for draught free environments, in which, the shielding gas flow rate can effectively be reduced.
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In the present study gas tungsten arc welding is used to join aluminum TWBs. Aluminum TWBs consist of 6061 aluminum sheets with different thickness of 1 mm and 2 mm. Analyzing the GTAW parameters effect on the formability of aluminum TWBs is the main purpose of present study. Therefore, main parameters of GTAW consist of welding current, pressure of shielding gas, welding speed and diameter of filler material are selected for investigation. Design of Experiment (DOE) based on the Tauguchi method is used to investigate the effect of each parameter and also interaction of parameters. Erichsen formability test (out-of-plane stretching forming test) is used for mechanical and forming behavior investigation of aluminum TWBs. Forming height of Erichsen test is used as a criterion to study the effect of GTAW parameters on the quality of aluminum TWBs. There is no study in the literature which studies the effect of GTAW parameters on the formability of TWBs. Whereas more tailor welded blanks are used in the out of plane forming process such as stamping or deep drawing, uniaxial tensile test which is used in other studies is not a proper test for formability investigation. Therefore, in the present study Erichsen formability test which is out-of-plane test is used for weld quality investigation of welded samples by GTAW. Investigation of GTAW parameters effect and their interaction on the formability of aluminum TWBs using Erichsen formability test is the novelty of present study. The main application of this study is in the aerospace and automotive industry.
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Although a new model to account for the nitrogen behaviour in complex systems such as the plasma of a welding arc is not the objective of the present study, the aim of this experimental programme is to evaluate the effects of different argon, nitrogen, and helium shield- ing gas mixtures in welding AISI 316LN material and, in particular, to determine the outcomes with respect to final nitrogen levels in the completed weld joints. To allow an accurate evaluation to be reported with respect to weld metal nitrogen retention and prop- erties, the experimental programme allowed multiple weldments to be produced under strictly controlled conditions to ensure that repeatability of welding con- ditions were assured. The following error analysis was determined and applied to all mechanical property data to account for experimental variation
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Cracking is the most serious type of weld discontinuity. Weld cracking is extensively discussed in section 9. 10.2 Weld Quality and Process-Specific Influences Some welding processes are more sensitive to the gener- ation of certain types of weld discontinuities, and some weld discontinuities are associated with only a few types of welding processes. Conversely, some welding process- es are nearly immune from certain types of weld discon- tinuities. Contained below are the popular welding processes and their variations, along with a description of their associated sensitivity relative to weld quality. SMAW — The unique limitations of shielded metal arc welding fall into three categories: arc length related dis- continuities, start-stop related discontinuities, and coat- ing moisture related problems. In SMAW, the operator controls arc length. Excessively short arc lengths can lead to arc outages, where the electrode becomes stuck to the work. When the electrode is mechanically broken off the joint, the area where the short has occurred needs to be carefully cleaned, usually ground, to ensure condi- tions that will be conducive to good fusion by subsequent welding. The electrode is usually discarded since a por- tion of the coating typically breaks off of the electrode when it is removed from the work. Excessively long arc lengths will generate porosity, undercut, and excessive spatter. Because of the finite length of the SMAW elec- trodes, an increased number of starts and stops is neces- sitated. During arc initiation with SMAW, starting porosity may result during the short time after the arc is initiated and before adequate shielding is established. Where the arc is terminated, under-filled weld craters can lead to crater cracking. The coatings of SMAW elec- trodes are sensitive to moisture pick-up. While newer developments in electrodes have extended the period for which electrodes may be exposed to the atmosphere, it is still necessary to ensure that the electrodes remain dry in order to be assured of low hydrogen welding conditions. Improper care of low hydrogen SMAW electrodes can lead to hydrogen assisted cracking, i.e., underbead crack- ing or transverse cracking. See 2.1 on care and storage of low hydrogen electrodes.
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Figure 6 shows the back scattered electron (BSE) image and the electron probe micro-analyzer (EPMA) line analyses of the weld metal (WM) in the HDSS tube-to-tube sheet welded using a pure Ar shielding gas with a ﬁller metal. As presented in Fig. 6(a), the weld metal of the tube-to-tube sheet welds obtained by solidiﬁcation after the GTAW forms cells that are composed of the interdendritic regions (IR) and dendritic regions (DR). In the interdendritic region, Cr and Mo were enriched whereas Ni and Fe were depleted. Conversely, in the dendrite core, Cr and Mo were depleted whereas Ni and Fe were enriched (Fig. 6(b)). The content of Cr and Mo in the dendrite core (DC) decreased greatly, compared with that in the other regions. In particular, the
Shielding gases are fundamental to most welding processes; their primary purpose being to protect the molten weld pool from contamination by atmospheric gases. In addition, computational models have shown that the shielding gas implemented in the GMAW process can be selected to tailor the weld to meet a desired specification . There are a number of shielding gases commonly used, each with its own specific properties [1-9], which can have pronounced affects on the arc characteristics, mode of metal transfer, cleaning action, penetration level and weld shape. Consequently, the shielding gas can also have a positive influence on the travel speed as reported by Gillies et al. 
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Welding is a fabrication or sculptural process that joins materials, usually metals by causing coalescence. Md. Ibrahim Khan (2007) stated that the joining of the two or more parts becoming one piece is called welding process.  There are types of welding process such as Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), Manual Metal Arc Welding (MMAW) and etc. In this study, Gas Metal Arc Welding is used and two different gasses which are Carbon Dioxide (CO 2 ) and
Process parameters such as speed, focal position, beam inclination, shielding gas, and joint design, as well as material properties have been examined and studied in efforts to improve beam characteristics such as laser power, beam quality, wavelength, focal diameter and focal length, mode and polarization [32-34]. The key pa- rameters of RLW, that is, boundary conditions, process conditions and process quality, as illustrated in Figure 6, have been researched and reported by Oefele et al. . Figure 5. RLW of limited working zone .
Stainless steel plate was cut in dimensions of 200 X 400mm with a hydraulic saw machine using a cooling liquid then the sample’s edges to be bonded were chamfered at 30 o . Bonding was carried out under different shielding gases mixtures. Which are supplied by gas feeding arrangement. Three different shielding gases were used for each sample. Shielding gases and welding parameters are shown in Table III. Three samples were welded using the same welding parameters. Except the gas mixtures.
Gas Tungsten Arc Welding (GTAW) also referred to as Tungsten Inert Gas (TIG) uses a non-consumable tungsten electrode to produce the weld. Under the correct welding conditions, the tungsten electrode does not melt. It operates by creating an electric arc between the tungsten electrode and the work piece; the electric arc can produce temperatures of up to 19,400˚C  . In GTAW, weld can be made with or without filler metal. When filler metal is used, it is added di- rectly into the molten pool by dipping the end of a filler rod into the leading edge of the molten weld pool, when filler metal is not used, edges of the metal are heated, melted and flowed together by themselves, and as the molten metal cools, coalescence occurs and the parts are joined, resulting in weld requiring minimum finishing  . The common use of GTAW as components assem- bling technique has been linked to its high quality welds, which is attributable to high degree of control of heat input and filler additions. GTAW has found wide appreciation in areas where precision welding is required, notable among which included atomic energy, aircraft, chemical and instrument industries, nuclear industry, food industry, maintenance and repair work and some manufacturing areas . Also, GTA welding is widely utilized for the joining of high strength, reactive metals and alloys such as stainless steel, aluminium and magnesium al- loys  . In addition, copper, brass, titanium, nickel and nickel alloys, stainless steel, inconel, high temperature and hard surfacing alloys like zirco- nium, titanium have been successfully welded with the GTA welding techniques .
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Initially, camera modules, electronic and optics assemblies and components intended to be used in the camera models, were checked for their rad-hard counterparts in the available databases , and tested against radiation. The purpose of these tests is to determine the doses (both neutron and γ ) that the components and modules can withstand. These tests were performed at the JSI TRIGA mark II reactor  (TRIGA) in the existing and newly constructed irradiation facilities. A gas-ﬂow ionization cham- ber in close proximity of the test assembly was used for cumulative dose and dose-rate measurements during the irradiation procedure. A custom assembly-parameter-reader was constructed for each test assembly, which monitored several aspects of the assembly operation. A failure or malfunction would be noted on the parameter reader log, thus determining the radiation tolerance of the component. Activated TRIGA fuel elements were utilized as a γ-ray source, either in an in-core Triangular chan- nel (TriC) irradiation facility, or ex-core, by moving up to 6 TRIGA fuel elements to the fuel element rack on the edge of the reactor tank . A new irradiation facility, an aluminum box with internal dimensions of 20 cm × 20 cm × 30 cm and a cable guide tube, leading to the reactor platform, was designed and constructed to utilize ex-core fuel elements as γ -ray sources. After the irradiations the logged data for both ionization chamber and for electronic components were evaluated and points of failure for each component determined. This process was repeated several times over, using di ﬀ erent components and module designs, until a satisfactory radiation tolerance of the module was obtained. After the irradiations, the measurement data were post-processed, and points of failure determined. An example of an irradiation test data visualization is presented in ﬁgure 1.
The pilot experiment was performed within above mentioned working range. One parameter varied by keeping other two parameters constant. Total 60 numbers of work pieces are welded. The range selected for shielding gas flow with work piece thickness 1 mm and welding current 30A is shown in Table 3.5. Welding parameters such as welding current and work piece thickness are maintained constant whereas shielding gas flow is varied in the range 1 LPM to 5.5 LPM. The range selected for shielding gas flow with work piece thickness 2 mm and welding current 65A is shown in Table 3.5. Welding parameters such as welding current and work piece thickness are maintained constant whereas shielding gas flow is varied in the range 1 LPM to 14.5 LPM. The range selected for shielding gas flow with work piece thickness 3 mm and welding current 110A is shown in Table 3.5. Welding parameters such as welding current and work piece thickness are maintained constant whereas shielding gas flow is varied in the range 1.5 LPM to 10.5 LPM.
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It has been widely publicised that plate distortion is a function of heat input. It has been reported that lower heat input welding processes result in less heat induced distortion [1,26]. The decrease in heat input, which would be as a result of the increased travel speed used to produce the equivalent levels of penetration when using alternating shielding gases, will also have beneficial effects with regards to weld induced distortion.
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The dimensions of the fusion zone at different distances from the sample’s edge are reported in Table 4. Analyzing Table 4, it is observed that in general, there is an increase in the fusion zone dimensions when moving from the sample’s edge towards the end of the melted track. It is observed that nitrogen and helium produced a fusion zone 80-85% wider and 50-85% deeper compared to the fusion zone of the sample protected with argon. This is due to the fact that these gases have a specific heat and thermal conductivity higher than the argon, as seen in Table 2. Also these results are in agreement with previous research , where the influence of the welding parameters on the fusion zone dimensions was highlighted. In this case, it must be noticed that despite the fact that the heat input was constant for all conditions (~ 840J/mm) to achieve this value, the arc current and voltage varied to obtain arc stability, depending on the shielding gas used; as observed, a wider fusion zone was obtained when using nitrogen as the shielding gas, where the value of voltage was the highest (22V). However, a deeper fusion zone was obtained when using helium as the shielding gas. Here, the value of arc current was the highest (97A). Also, it is well established, that adding argon or helium in the shielding gas, reduces defects, due to their higher thermal conductivity, which allows more heat to be transferred to the substrate, providing improved fusion and slower cooling rates, which results in slower freezing rates, allowing more time for entrapped gases to escape .
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After conducted experimental welding and preparation of the specimens for macrograph analysis the bead on plate dimensions are measured (table 3, figure 2). The influence of the two effects: heat input (welding speed) and gas flow on the values of the bead on the plate width are investigated by analysis of variance for two cases: (a) welding with solid wire with gas shielding CO 2 and (b) welding with flux
Satisfactory mechanical properties including yield strength, tensile strength, elongation and bending were obtained for laser welds. Results indicated that heat input has no remarkable effect on mechanical properties, ex- cept elongation that was improved with either increasing laser power or decreasing welding speed that means with increasing heat input. This is related to maintaining pro- per ferrite-austenite balance in fusion zone in this case. Using nitrogen to replace argon as a shielding gas, under same flow rate, has resulted in remarkable decrease in corrosion rate and increase in ductility of welded joint. Improvement in both mechanical and corrosion proper- ties of laser beam welded joints made using nitrogen as a shielding gas is related to maintaining proper ferrite- austenite balance in both weld metal and heat affected zone.
Abstract—Mildsteel is the largely material for industrial and commercial applications. Gas Metal Arc Welding (GMAW) and Gas Tungstan Arc Welding (GTAW) process is the largely used metal joining process for thin gauge milsteel and stainless. This research focus on the on the effect of process welding parameters for acquring greater mechanical properties of weld plates. the Taguchi parametric optimization methodology and regression analysis is identified and used for Acquring the greater welding effectiveness and efficiency. The shielding gas, weld volrage& current is choosen as a process parameters for this research to Acquring the greater welding effectiveness and efficiency. At end of process, the mechanical properties like ultimate tensile strength, toughness and hardness of the weldment. After completion of the experimental work, the S/N ratio and mean S/N ratio were evaluated and the optimum values of each parameters was evaluated through the Taguchi method. Subsequently the significant co-efficient for each input factor of the mechanical properties was evaluated of by using the analysis of variance and prediction on the mechanical properties is evaluated by using regression analysis. In this research, 15 mm IS2062 Mild Steel is welded by GMAW with the shielding gas mixtures of pure(100%) CO2 , Ar+20% CO2, and Ar+10% O2. The tensile strength optimum value was provided by the shielding gas mixture Ar+20% CO2 and also it gives the optimum value for toughness. The superior hardness value is obtained by Pure(100%) CO2 with respect to other shielding gas mixtures. The evaluated values tells that the welding current & shielding gas and have impressive effect on the IS2062 weldment mechanical properties.
The alternating shielding gas technique is a method of achieving transient arc characteristics during arc welding; however the complex flow that occurs through its use has not been investigated previously. A schlieren system was used to image density gradients that arise when alternating argon and helium shield gases, under varying flow parameters, with gas tungsten arc welding (GTAW). A theoretical analysis was carried out to determine the conditions under which the technique facilitates arc pulsing, in particular to avoid mixing of the shield gases in the delivery pipe prior to the welding nozzle. At appropriate pulsing frequency and flow rates, a stable horizontal region of helium was observed in the weld region, maintained in position by the denser argon from the preceding pulse. This higher than average mass fraction of helium when applying the shielding gases alternately, compared to a premixed gas with the same volume of argon and helium, increased the weld penetration by 13% on average, suggesting a modest improvement in heat transfer.
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