914 research outputs found

    Nitrogen retention/enrichment of 316LN austenitic stainless steel welds

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    The development of nitrogen enriched austenitic stainless steels has been a source of recent interest due to the abundant availability of nitrogen and by the manner in which nitrogen contributes several beneficial material property effects over a wide service temperature range. It is widely recognised that, in the case of nitrogen enriched 316L, improvements in mechanical property and corrosion resistance are derived from the interstitial influence of nitrogen within the matrix. Consequently, having the best combination of strength, toughness and corrosion resistance relationships found in any group of steels, nitrogen strengthened austenitic stainless steels have tremendous scope for application in areas as diverse as the cryogenic, nuclear, power generation and chemical transportation industries

    Thin plate buckling mitigation and reduction challenges for naval ships

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    Thin plate buckling or distortion on ship structures is an ongoing issue for shipbuilders. It has been identified that a significant number of factors can be put in place based on prior knowledge and good practice. Additionally, research work aimed at reducing thin plate distortion has been relatively prolific, particularly in the area of simulation modelling. However, the uptake in the research findings by industry has been relatively low. A number of these findings are discussed and their application considered. For any further reductions in thin plate distortion to be generated there is a clear need for better interaction between the research institutes and the industry

    An evaluation of weld metal nitrogen retention and properties in 316NL austenitic stainless steel

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    A series of tests were conducted using varying levels of nitrogen and helium in a conventional argon shielding gas when welding 316LN austenitic stainless steel. The outcome was that a 15 per cent nitrogen addition to the argon shielding gas had the most significant effect on increasing the weld metal nitrogen. Subsequent additions of helium to the argon 15 per cent nitrogen shielding gas had very little overall benefit. Increasing the nitrogen content of the weld metal had the consequential effects of decreasing the ferrite content and the hardness. As a result of solid solution strengthening, the yield strength increased with increase in nitrogen content. There was an increase in impact toughness as the nitrogen content increased. This was related to the decreased ferrite content associated with the strong austenetizing potential of nitrogen. It was also shown that an almost fully austenitic weld metal could still have very good toughness. In combination with these effects there was no loss in corrosion resistance. The addition of nitrogen to a conventional argon shielding gas presents attractive cost and quality benefits over the established requirement to over alloy the weld filler material with expensive alloys such as nickel

    Helium additions to MIG shielding gas - an economic option?

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    An investigation has been carried out to establish the technical and economic benefits of adding two levels of helium to a normal shielding gas. Technically no adverse issues were established using the two levels of helium, and the most significant positive one was the highly beneficial effects on travel speed increase and heat input decrease. Although helium gas carries a significant cost premium, the economic evaluation showed that overall this was a beneficial approach as the man-hour reduction associated with the welding process dominated the process cost effects

    Arc pressure and weld metal fluid flow whilst using alternating shielding gases Part 2 : arc force determination

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    The transient variation of the shielding gas present in the alternating shielding gas process produces a dynamic action within the liquid weld metal. Flow vectors opposite in direction have been reported due to the various forces acting on the weld metal when argon and helium are present, however no data has been provided to substantiate this claim. This part of the study evaluates the various forces acting on the liquid weld metal when using argon and helium and their effects discussed. It was determined that argon produces a greater vertically downward force in the central region than helium for both the arc force and Lorentz force. While helium produces a greater radially outwards force at the pool surface than argon due to plasma shear stress and Marangoni convection. In addition, the buoyancy force, i.e. the vertically upward force in the central portion of the weld metal, was greater for helium

    Arc pressure and weld metal fluid flow whilst using alternating shielding gases Part 1 : arc pressure measurement

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    As part of an ongoing process to fully evaluate the effects of an alternating shielding gas supply on gas shielded welding processes, a comparison between the arc pressures generated using argon, helium, alternating shielding gases and pulsed GTAW has been conducted. Arc pressure variation and peaking are two of the fundamental phenomena produced during the alternating shielding gas process and are said to help create a stirring action within the liquid weld metal. However, there is no published data on arc pressure measurements during an alternating shielding gas supply and, consequently, these phenomena are based solely on theoretical assumptions. The experimental measurements made have shown that alternating shielding gases produces considerably higher arc pressures than argon, helium and pulsed GTAW due to a surge at weld initiation. The transient arc pressure measurements made when using alternating shielding gases are also considerably different from the theoretical assumptions previously reported

    Derivation of forces acting on the liquid weld metal based on arc pressure measurements produced using alternating shielding gases in the GTAW process

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    As part of an ongoing process to fully evaluate the effects of an alternating shielding gas supply on the gas tungsten arc and gas metal arc welding processes, a comparison between arc pressures produced using argon, helium, alternating gases and GTAW-P has been conducted. The alternating shielding gas process is reported to create a dynamic stirring action within the liquid weld metal as a result of three independent phenomena: a) variation in weld pool fluidity, b) arc pressure variation, and c) arc pressure peaking. These effects have been the basis of previous advantages associated with the process, however these phenomena have not previously been verified and are based solely on theoretical assumptions. Arc pressure measurements are presented which allowed for the numerical derivation of various forces acting on the liquid weld metal in order to estimate the flow vectors present when each shielding gas is present

    Evaluation of gas metal arc welding with alterating shielding gases for use on AA6082T6

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    Studies have been carried out to determine the effects of implementing alternating shielding gases for 6082T6 aluminium alloy welding. Alternating shielding gases is a newly developed method of supplying shielding gases to the weld area to enhance the efficiency of the standard Gas Metal Arc Welding (GMAW) process. This method involves discretely supplying two different shielding gases to the weld zone at a pre-determined frequency which creates a dynamic action in the weld pool. Several benefits have been identified in relation to supplying shielding gases in this manner including increased travel speed, reduced distortion, reduced porosity and, in the case of specific alternating frequencies, marginal improvements in mechanical properties. All in all, this method of shielding gas delivery presents attractive benefits to the manufacturing community, namely the increased productivity and quality in addition to a reduction in the amount of post-weld straightening required. However, the literature available on this advanced joining process is very scant, especially so for aluminium alloys. For this reason, an evaluation has been carried out on the application of alternating shielding gases for the GMAW process on 6082T6 aluminium alloys

    A potential solution to GMAW gas flow optimisation

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    A number of self-regulating shielding gas valves have been developed to synchronise the shielding gas flow rate to the welding current being used in the gas metal arc welding process (GMAW). These valves make claims to reduce the shielding gas consumption by up to 60%. One such system, the RegulaÂź EWR Pro, has undergone detailed evaluation in an effort to fully understand the benefits that could be obtained. This electromagnetically controlled system necessitates around an extremely fast response valve, which opens and closes continually throughout the welding process. This creates a pulsing of the shielding gas, further reducing consumption whilst maintaining optimal shielding gas flow. The unit has been identified to reduce the initial gas surge at weld initiation and results in a virtually instant decay of gas flow at weld termination. These particular characteristics have been found to be ideally suited to saving shielding gas when carrying out intermittent or stitch welding. It was established that the use of this valve generated deeper penetration in fillet welds, which in turn has highlighted the potential to increase the welding speed, therefore further reducing gas consumption. In addition, a computational model has been developed to simulate the effects of cross drafts. The combination of reducing the gas surge and slow decay with faster welding has been shown to meet the drive for cost savings and improving the carbon footprint

    Artificial neural network optimisation of shielding gas flow rate in gas metal arc welding subjected to cross drafts when using alternating shielding gases

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    This study implemented an iterative experimental approach in order to determine the shielding gas flow required to produce high quality welds in the gas metal arc welding (GMAW) process with alternating shielding gases when subjected to varying velocities of cross drafts. Thus determining the transitional zone where the weld quality deteriorates as a function of cross draft velocity. An Artificial Neural Network (ANN) was developed using the experimental data that would predict the weld quality based primarily on shielding gas composition, alternating frequency and flowrate, and cross draft velocity, but also incorporated other important input parameters including voltage and current. A series of weld trials were conducted validate and test the robustness of the model generated. It was found that the alternating shielding gas process does not provide the same level of resistance to the adverse effects of cross drafts as a conventional argon/carbon dioxide mixture. The use of such a prediction tool is of benefit to industry in that it allows the adoption of a more efficient shielding gas flow rate, whilst removing the uncertainty of the resultant weld quality
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