Experiments on formation mechanism of root humping in high-power laser autogenous welding of thick plates with stainless steels

Zhang, Mingjun; Zhang, Yingze; Mao, Cong; Hu, Yongle; Chen, Genyu; Bi, Zhuming

doi:10.1016/j.optlastec.2018.09.029

Cited by 18 publications

(3 citation statements)

References 24 publications

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“…Moreover, possible reasons more in-depth were discussed with solutions to these challenges. The negative focal point position and faster welding speeds was found to mitigate humping with stably keyhole conditions in LAHW of 12 mm stainless steel according to Zhang et al [19]. The recoil pressure, surface tension, and gravity were identified as main forces to be involved in humping development during experimental and numerical studies in single-pass autogenous LBW of 12 mm thick stainless steel [20].…”

Section: Introductionmentioning

confidence: 96%

Root formation and metallurgical challenges in laser beam and laser-arc hybrid welding of thick structural steel

Bunaziv

Dørum

Nielsen

et al. 2021

Int J Adv Manuf Technol

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Single-pass laser beam welding (LBW) of steel components with wall thickness of > 10 mm is of high interest due to enhanced productivity. Deep penetration LBW provides excessive hardness and certain quality issues such as root humping in flat position, which is associated with disability of surface tension to sustain melt dropout. High hardness is associated with fast cooling rates and shortage of filler wire transportation to the root of the fusion zone. Use of laser-arc hybrid welding (LAHW) can promote acicular ferrite by adding filler metal and additional heat input from the arc. However, LAHW may promote humping and adjustment of many parameters is required hindering its application. In this work, a 16 kW disk laser was used in butt welding of 12 mm and 15 mm thick plates with different bevelling geometries. Root humping occurred within a wide range of process parameters providing narrow process window. Twelve millimeter thick plates were successfully welded with a single-pass technique providing good quality of root by using zero air gap regardless bevelling geometry. Welding of 15 mm plates was more challenging, and the process was sensitive even with a slight parameter change. Improved results were achieved with application of small air gap. Acceptable hardness in both weld metal and heat affected zone (< 290 HV) was achieved for both plate thicknesses providing good toughness of minimum 27 J at −50°C.

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Section: Introductionmentioning

confidence: 96%

Root formation and metallurgical challenges in laser beam and laser-arc hybrid welding of thick structural steel

Bunaziv

Dørum

Nielsen

et al. 2021

Int J Adv Manuf Technol

View full text Add to dashboard Cite

show abstract

“…From that, process windows for defect-free welds could be derived with special focus on drop-out [5] and macropososity formation due to keyhole collapse [6]. The formation of root humps in high-power laser beam welding was also investigated in [7]. The authors show that specific combinations of welding speed, defocus, and the presence of bottom shielding gas could help to suppress the humping phenomena.…”

Section: Introductionmentioning

confidence: 99%

High-power laser beam welding for thick section steels – new perspectives using electromagnetic systems

Rethmeier

Gumenyuk

Bachmann

2022

Science and Technology of Welding and Joining

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In recent years, it was shown that the introduction of additional oscillating and permanent magnetic fields to laser beam and laser-arc hybrid welding can bring several beneficial effects. Examples are a contactless weld pool support for metals of high thickness suffering from severe drop-out when being welded conventionally or an enhanced stirring to improve the mixing of added filler material in the depth of the weld pool to guarantee homogeneous resulting mechanical properties of the weld. The latest research results show the applicability to various metal types over a wide range of thicknesses and welding conditions. The observations made were demonstrated in numerous experimental studies and a deep understanding of the interaction of the underlying physical mechanisms was extracted from numerical calculations.

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“…Welding of thicker sections poses further challenges due to the higher laser powers required to achieve full penetration welds. Defect formation in high laser power and thick section welding such as cracking, root humping and sagging, surface underfill, undercuts, and root porosity, have been investigated by several authors [7][8][9][10][11]. The higher solidification stresses and material shrinkage associated with thicker plate thicknesses can lead to crack formation.…”

Section: Introductionmentioning

confidence: 99%

Study on effect of laser keyhole weld termination regimes and material composition on weld overlap start-stop defects

Lai

Ganguly

Suder

2020

Journal of Manufacturing Processes

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The effects of two different laser termination regimes; laser power ramp-down and laser defocusing, on the weld overlap start-stop region, have been studied on three different compositions of S355J2+N grade steel plates. The plates have varying amounts of deoxidisers, such as manganese and silicon, to allow for the effect of dissolved oxygen on melt pool dynamics and defect formation to be studied. Observations show that gas entrapment, manifesting as porosity, is the main issue in both the laser termination regimes studied, due to melt pool instabilities related to keyhole termination. However, it is more severe during laser defocusing due to the formation of porosity clusters below a specific power density and melt pool size. The percentage of dissolved oxygen and deoxidisers was found to be vital and could be correlated to the response of the melt pool during laser processing. Steel, with a higher percentage of deoxidisers, such as manganese and silicon, would combine with the dissolved oxygen in the weld pool and thereby affect the surface tension and melt pool dynamics. The effect of lower dissolved oxygen would lead to a reduction in penetration depth, but more importantly, porosity and porosity cluster formation, as observed for both laser termination regimes. Successful laser termination with defect-free weld overlaps at the start-stop region could be achieved using both termination regimes for the steel with a higher proportion of deoxidising elements.

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Experiments on formation mechanism of root humping in high-power laser autogenous welding of thick plates with stainless steels

Cited by 18 publications

References 24 publications

Root formation and metallurgical challenges in laser beam and laser-arc hybrid welding of thick structural steel

Root formation and metallurgical challenges in laser beam and laser-arc hybrid welding of thick structural steel

High-power laser beam welding for thick section steels – new perspectives using electromagnetic systems

Study on effect of laser keyhole weld termination regimes and material composition on weld overlap start-stop defects

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