A study was conducted on the arc and melting efficiency of the plasma arc, gas tungsten arc, gas metal arc, and submerged arc welding processes The results of this work are extended to develop a quantitative method for estimating weld metal dilution in a companion paper Arc efficiency was determined as a function of current for each process using A36 steel base metal Melting efficiency was evaluated with variations in arc power and travel speed during deposition of austenitic stainless steel filler metal onto A36 steel substrates The arc efficiency did not vary significantly within a given process over the range of currents investigated The consumable electrode processes exhibited the highest arc efficiency (084), followed by the gas tungsten arc (067) and plasma arc (047) processes Resistive heating of the consumable GMAW electrode was calculated to account for a significant difference in arc efficiency between the gas metal arc and gas tungsten arc processes A semi-empirical relation was developed for the melting efficiency as a function of net arc power and travel speed, which described the experimental data well An interaction was observed between the arc and melting efficiency A low arc efficiency factor limits the power delivered to the substrate which, in turn, limits the maximum travel speed for a given set of conditions High melting efficiency is favored by high arc powers and travel speeds As a result, a low arc efficiency can limit the maximum obtainable melting efficiency

Thermal efficiency of arc welding processes

The effects of pulsed gas tungsten arc welding parameters on the morphology of additive layer manufactured Ti6Al4V has been investigated in this study. The peak/base current ratio and pulse frequency are found to have no significant effect on the refinement of prior beta grain size. However, it is found that the wire feed rate has a considerable effect on the prior beta grain refinement at a given heat input. This is due to the extra wire input being able to supply many heterogeneous nucleation sites and also results in a negative temperature gradient in the front of the liquidus which blocks the columnar growth and changes the columnar growth to equiaixal growth.

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Morphology investigation on direct current pulsed gas tungsten arc welded additive layer manufactured Ti6Al4V alloy.

The thermal or process efficiency in gas metal arc welding (GMAW) is a crucial input to numerical models of the process and requires the use of an accurate welding calorimeter. In this paper, the authors compare a liquid nitrogen calorimeter with an insulated box calorimeter for measuring the process efficiency of Fronius cold metal transfer, Lincoln surface tension transfer and RapidArc, Kemppi FastRoot and standard pulsed GMAW. All of the controlled dip transfer processes had a process efficiency of ∼85% when measured with the liquid nitrogen calorimeter. This value was slightly higher when welding in a groove and slightly lower for the RapidArc and pulsed GMAW. The efficiency measured with the insulated box calorimeter was slightly lower, but it had the advantage of a much smaller random error.

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Measuring the process efficiency of controlled gas metal arc welding processes

An innovative method for estimating the actual cooling rate in a welded section is presented. The method is based on applying a weighting factor to the Rosenthal analytical solutions for thick and thin plates. The factor is determined from the heat-affected zone (HAZ) width, obtained from etched sections, and reflects the actual response of the plate to the heat flow condition. Previous formulations in the literature are based on the assumption of either thin-plate or thick-plate conditions, while most actual conditions lie somewhere between the two extremes. Limited experimental measurements of cooling rate, carried out by instrumented welding, showed good agreement with predicted values. The model was further used to predict the peak temperature profile across the HAZ.

Estimation of cooling rate in the welding of plates with intermediate thickness

A mathematical model is developed to describe the heat transfer and fluid flow in stationary keyhole plasma arc welding. Using the volume of fluid method, the processes of heating, melting, collapsing and subsequent solidifying in the molten pool are dynamically studied. The predicted results have been compared with the experimental weld and keyhole shape. Using the LaserStrobe video system, the captured images of the upper surface of the weld pool are used to verify the predicted transient development of the weld pool. It is indicated that theoretical predictions and the experimental results are in close agreement.

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Keyhole formation and collapse in plasma arc welding

A study of melting efficiency in plasma arc and gas tungsten arc welding : a method for selecting optimal weld schedules to minimize net heat input is derived frm calorimetric measuremts

P. W. Fuerschbach

Papers

A study of melting efficiency in plasma arc and gas tungsten arc welding : a method for selecting optimal weld schedules to minimize net heat input is derived frm calorimetric measuremts