The State of the Art of Short Pulsed CO2 Laser for Materials Processing.

et al. 2006

A comprehensive survey of high speed weld bead defects is presented with strong emphasis on the formation of humping and undercutting in autogenous and non-autogenous fusion welding processes. Blowhole and overlap weld defects are also discussed. Although experimental results from previous studies are informative, they do not always reveal the physical mechanisms responsible for the formation of these high speed weld bead defects. In addition, these experimental results do not reveal the complex relationships between welding process parameters and the onset of high speed weld bead defects. Various phenomenological models of humping and undercutting have been proposed that were based on observations of events in different regions within the weld pool or the final weld bead profile. The ability of these models to predict the onset of humping or undercutting has not been satisfactorily demonstrated. Furthermore, the proposed formation mechanisms of these high speed weld bead defects are still being questioned. Recent welding techniques and processes have, however, been shown to be very effective in suppressing humping and undercutting by slowing the backward flow of molten metal in the weld pool. This backward flow of molten weld metal may be the principal physical phenomenon responsible for the formation of humping and undercutting during high speed fusion welding.

Section: Effects Of Weld Process Parameters On High Speed Welding Def...mentioning

confidence: 95%

Section: Effects Of Weld Process Parameters On High Speed Welding Def...mentioning

confidence: 95%

Section: Effects Of Weld Process Parameters On High Speed Welding Def...mentioning

confidence: 99%

Section: Mapping Of Various Weld Bead Regionsmentioning

confidence: 99%

Section: Techniques and Processes For Higher Welding Speedsmentioning

confidence: 99%

See 3 more Smart Citations

High speed fusion weld bead defects

Nguyen¹,

Weckman²,

et al. 2006

The humping phenomenon during high speed gas metal arc welding

Nguyen¹,

Weckman²,

et al. 2005

118

A commonly observed welding defect that characteristically occurs at high welding speeds is the periodic undulation of the weld bead profile, also known as humping. The occurrence of humping limits the range of usable welding speeds in most fusion welding processes and prevents further increases in productivity in a welding operation. At the present time, the physical mechanisms responsible for humping are not well understood. Thus, it is difficult to know how to suppress humping in order to achieve higher welding speeds. The objectives of this study were to identify and experimentally validate the physical mechanisms responsible for the humping phenomenon during high speed gas metal arc (GMA) welding of plain carbon steel. A LaserStrobe video imaging system was used to obtain video images of typical sequences of events during the formation of a hump. Based on these recorded video images, the strong momentum of the backward flow of molten metal in the weld pool that typically occurred during high speed welding was identified as the major factor responsible for the initiation of humping. Experiments with different process variables affecting the backward flow of molten weld metal were used to validate this hypothesis. These process variables included welding speed, welding position and shielding gas composition. The use of downhill welding positions and reactive shielding gases was found to suppress humping and to allow higher welding speeds by reducing the momentum of the backward flow of molten metal in the weld pool. This would suggest that any process variables or welding techniques that can dissipate or reduce the momentum of the backward flow of molten metal in the weld pool will facilitate higher welding speeds and productivity.

Predicting onset of high speed gas metal arc weld bead defects using dimensional analysis techniques

Nguyen¹,

Weckman²,

2007

The onset of geometric defects such as humping or discontinuous weld beads during gas metal arc welding (GMAW) frequently limits the use of higher welding speeds and increased productivity. In the present study, a dimensional analysis of the GMAW process was performed in order to identify a number of dimensionless groups formulated based on various GMAW process parameters and material properties that could be used to predict when humping or discontinuous weld beads would occur. Experimental data from bead on plate GMA welds in plain carbon steel plate made using argon and two different reactive shielding gases, welding powers between 5 and 12 kW and a range of welding speeds were then used to create dimensionless process maps. These maps showed the limiting welding speed above which the high speed weld defects occurred as a function of all influential process parameters. It was shown that all experimental data for limiting welding speeds could be collapsed onto two collinear dimensionless curves. Also, the transition from spray to rotational metal transfer was found to occur at a well defined value of one of these dimensionless parameters. The effects of workpiece preheat temperature on humping were correctly predicted and there was a good correlation between the dimensionless GMAW process map and experimental data from other independent studies. These results suggest that the occurrence of high speed weld bead defects such as humping and discontinuous weld beads as well as the transition from spray to rotational metal transfer can be predicted using these new dimensionless GMAW process maps.