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

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

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

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

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

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 Regula® 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

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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Performance of a Brief Assessment Tool for Identifying Substance Use Disorders

Objective: Evaluation of the performance of a brief assessment tool for identifying substance use disorders. The Triage Assessment for Addictive Disorders (TAAD) is a triage instrument that provides professionals with a tool to evaluate indications of current substance use disorders in accordance with the DSM-IV diagnostic criteria. The TAAD is a 31-item structured interview that addresses both alcohol and other drug issues to discriminate among those with no clear indications of a diagnosis, those with definite, current indications of abuse or dependence, and those with inconclusive diagnostic indications. Methods: Employing a sample of 1325 women between the ages of 18 and 60, reliability estimates and problem profiles produced by the TAAD were evaluated. Results: The Cronbach alpha coefficients for internal consistency for both the alcohol and drug dependence scales were .92. The alpha coefficients for the alcohol and drug abuse scales were .83 and .84 respectively. The diagnostic profiles elicited from the TAAD indicate that alcohol and drug dependences are the more definitive and distinct syndromes compared with the abuse syndromes. Conclusions: The diagnostic profiles from this sample are consistent with previous research. The Cronbach alpha coefficients suggest that the TAAD provides an internally consistent index for alcohol and drug dependence and abuse. Implications for use in clinical practice and the need for further research regarding the psychometric properties of the TAAD are discussed

Systematic study of effect of cross-drafts and nozzle diameter on shield gas coverage

A shield gas flow rate of 15–20 L min21 is typically specified in metal inert gas welding, but is often adjusted to as high as 36 L min21 by welders in practice. Not only is this overuse of shield gas wasteful, but uncontrolled high gas flows can lead to significant turbulence induced porosity in the final weld. There is therefore a need to understand and control the minimum shield gas flow rate used in practical welding where cross-drafts may affect the coverage. Very low gas coverage or no shielding leads to porosity and spatter development in the weld region. A systematic study is reported of the weld quality achieved for a range of shield gas flow rates, cross-draft speeds and nozzle diameters using optical visualisation and numerical modelling to determine the shield gas coverage. As a consequence of the study, the shield gas flow has been reduced to 12 L min21 in production welding, representing a significant process cost saving and reduced environmental impact with no compromise to the final weld quality