Visualization and acoustic monitoring of laser weld pool oscillatory behavior

Various welding positions need be used in laser welding of structures with complex configurations. Therefore, it is necessary to gain knowledge of how the welding positions can influence the keyhole and weld pool behavior in order to better control the laser weld quality. In the present study, a computational fluid mechanics (CFD) model was constructed to simulate the laser-welding process of the titanium alloy Ti6Al4V, with which the keyhole stability and the fluid flow characteristics in weld pool were studied for four welding positions, i.e., flat welding, horizontal welding, vertical-up welding, and vertical-down welding. Results showed that the stability of the keyhole was the best in flat welding, the worst in horizontal welding, and moderate in vertical welding positions. Increasing heat input (the ratio of laser power to welding speed) could increase the keyhole stability. When the small heat input was used, the dimensions and flow patterns of weld pools were similar for different welding positions. When the heat input was increased, the weld pool size was increased, and the fluid flow in the weld pool became turbulent. The influences of gravity became significant when a large heat input was used, especially for laser welding with vertical positions. Too high a heat input in vertical-up laser welding would lead to oscillation and separation of molten metal around the keyhole, and in turn result in burn-through holes in the laser weld. Based on the present study, moderate heat input was suggested in positional laser welding to generate a stable keyhole and, meanwhile, to guarantee good weld quality.

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Dual Process Welding of Steel Plate

21st International Conference on Offshore Mechanics and Arctic Engineering, Volume 3 ◽

10.1115/omae2002-28587 ◽

2002 ◽

Author(s):

Clint Wildash ◽

Steve Webster

Keyword(s):

Laser Welding ◽

Weld Pool ◽

Welding Speed ◽

Welded Joint ◽

Laser Beam Welding ◽

Dual Process ◽

Dual Processing ◽

Laser Weld ◽

Stage 1 ◽

Welding Processes

Large scale fabrication and welding industries, such as those involved in offshore construction, are continuously striving to improve productivity, while maintaining quality levels required by the applicable design codes and standards. To achieve this, new improved welding technologies are regularly being evaluated. One area of development is to combine different welding processes to produce a welded joint exhibiting properties and productivity benefits that neither process could achieve individually. One promising combination is the use of both arc and laser beam welding for products such as pipeline. The welding procedure development work described, was carried out in two stages. Stage 1 (discrete dual processing) investigated the production of a welded joint using both arc and laser welding at separate times. The welds produced for this work, demonstrate that significant increases in welding speed are achievable in comparison to using either process individually. Stage 2 (simultaneous dual processing) investigated arc and laser welding of the joint at the same time from opposing plate faces, with the laser weld pool trailing the arc weld pool so that the former was positioned in the area of highest preheat temperature. The use of arc preheat significantly reduced the hardness of the laser welds to more acceptable levels. The main disadvantage identified for both stages of work was that fit up of the laser welded part of the joint needed to be good to accommodate the autogenous laser weld. Both Stages were shown to be capable of producing full penetration welds at higher productivity than using either process individually. It has been demonstrated that for 19 mm thick plate, an overall doubling of welding speed could be achieved using dual process as opposed to submerged arc welding, which is currently widely used to weld fabricated products such as pipeline. Future work to be carried will include extensive destructive testing on the welds to assess the benefits of Stage 1 and 2, which will be reported in another paper.

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