High quality welding of stainless steel with 10 kW high power fibre laser

Abstract

The objectives of this research are to investigate penetration characteristics, to clarify welding phenomena and to develop high quality welding procedures in bead on plate welding of type 304 austenitic stainless steel plates with a 10 kW fibre laser beam. The penetration depth reached 18 mm at the maximum at 5 mm s 21 . At 50 mm s 21 or lower welding speeds, however, porosity was generated at any fibre laser spot diameter. On the other hand, at 100 mm s 21 or higher welding speeds, underfilling and humping weld beads were formed under the conventionally and tightly focused conditions respectively. The generation of spatters was influenced mainly by a strong shear force of a laser induced plume and was greatly reduced by controlling direction of the plume blowing out of a keyhole inlet. The humping formation was dependent upon several dynamic or static factors, such as melt volume above the surface, strong melt flow to the rear molten pool on the top surface, solidification rate and narrow molten pool width and corresponding high surface tension. Its suppression was effective by producing a wider weld bead width under the defocused laser beam conditions or reduction of melt volume out of keyhole inlet under the full penetration welding conditions. Concerning porosity, X-ray transmission in situ observation images demonstrated that pores were formed not only from the tip of the keyhole but also at the middle part because of high power density. The keyhole behaviour was stabilised using a nitrogen shielding gas, resulting in porosity prevention. Consequently, to produce high quality welds in 10 kW high power fibre laser welding, the reduction procedures of welding defects were required on the basis of understanding their formation mechanism, and 10 kW fibre laser power could produce sound deeply penetrated welds of 18 mm depth in a nitrogen shielding gas.

Formation and influence mechanism of keyhole-induced porosity in deep-penetration laser welding based on 3D transient modeling

“…Fujinaga et al observed porosity would generate when laser power decreased rapidly during pulse laser process [7]. Kawahito et al found that pores were not only at the tip of the keyhole but also at the middle due to high power density [8]. All the findings through experimental investigation provide valuable information in understanding the correlation of dynamic keyhole with porosity in deep penetration laser welding.…”

Laser Welding under Vacuum: A Review

“…Due to the availability of a new generation of high brightness multi-kilowatt solid state lasers, high-power laser beam welding became a new stimulus. However, some new problems, for example, the weld defects of sagging and spatter, the intense plasma plume and turbulent molten pool flow, are accompanied during high-power laser beam welding [26][27][28]. That means that the application of high power single pass laser welding encounters a bottleneck.…”

Microstructural evolution and mechanical properties of friction stir welded joint of Fe–Cr–Mn–Mo–N austenite stainless steel

“…It is hard to achieve defect-free HNS joints by conventional fusion welding techniques [4]. The nitrogen loss, welding defects and nitride precipitation in the welding process of HNS result in the loss of corrosion resistance and mechanical properties [5,6].…”