High-power Fiber Laser Welding Research Articles

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

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−1. At 50 mm s−1 or lower welding speeds, however, porosity was generated at any fibre laser spot diameter. On the other hand, at 100 mm s−1 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.

10 kW高出力ファイバーレーザ・マグアークハイブリッド溶接による厚さ12 mm鋼板の突合せ溶接部形成に関する研究

10 kW高出力ファイバーレーザ・マグアークハイブリッド溶接による厚さ12 mm鋼板の突合せ溶接部形成に関する研究

ステンレス鋼の高出力ファイバーレーザ溶接時におけるレーザ吸収特性

A tightly-focused high power fiber laser beam can produce a narrower and deeper penetration weld than a conventional laser weld of wine-cup shape, which is expected to improve laser absorption. The objective of this research is to assess laser absorption in a wide range of conditions such as laser powers of 2 kW to 10 kW or welding speeds of 17 mm/s to 250 mm/s in bead-on-plate welding of Type 304 austenitic stainless steel with a laser beam of 200μm spot diameter by water-calorimetric method. Furthermore, the relationship between the laser absorption and the keyhole formation location to a focused laser beam was revealed by using X-ray transmission in-site observation system and high-speed video camera with diode-laser illumination. It was found that the absorption at 10 kW laser power and 17 mm/s welding speed was 89% high. Compared X-ray transmission observation images of the keyhole with the focusing feature of the fiber laser beam, the center part of the incident beam with a bell-shape profile were delivered directly to the tip of a keyhole. Moreover, the increase in the welding speed from 17 mm/s to 250 mm/s reduced the absorption from 89% to 65%. The high-speed observation pictures indicated that the incident fiber laser beam was partially exposed out of the keyhole inlet at higher welding speed, which led to the decrease in the laser absorption. Consequently, it was confirmed that the tightly-focused high-power fiber laser welding was high-efficiency process at the maximum of about 90% in laser absorption at low welding speeds, owing to the irradiation of almost all the incident laser beam into the keyhole inlet. It was also assessed that the energy loss due to evaporation was smaller than 1%.

Characterisation of plasma induced during high power fibre laser welding of stainless steel

The objective of this research is to obtain a fundamental knowledge of generation behaviour and ionised state of a plume or plasma induced during bead on plate welding of a 20 mm thick type 304 stainless steel plate with a 10 kW fibre laser beam of 0˙9 MW mm–2 power density, on the basis of 10 000 to 40 000 flames s–1 high speed video observation and spectroscopic analysis. The high power fibre laser produced a partial penetration weld of 12 mm in depth at 50 mm s–1 welding speed. According to the high speed observation pictures, the laser induced plume was repeatedly generated from a keyhole at the interval of about 0&dot5 ms period to reach 12 mm in maximum height. The spectroscopy indicated the line spectra of neutral atoms of alloying elements of type 304 such as iron (Fe), chromium (Cr) and manganese (Mn). However, ionised spectra of alloying elements and line spectra of argon (Ar) neutral atom were not apparently detected under these welding conditions. Furthermore, the temperature and the ionisation degree of the laser induced plume were calculated to be approximately 6000 K and 0&dot02 respectively, by the Bolzman plots and Saha's equation. Consequently, the plume induced with the 10 kW fibre laser beam of the ultra high power density was judged to be weakly ionised plasma from these experimental results.

ステンレス鋼の10kW高出力ファイバーレーザ溶接時の欠陥形成機構と防止法

ステンレス鋼の10kW高出力ファイバーレーザ溶接時の欠陥形成機構と防止法

High-power fiber laser welding and its application to metallic glass Zr 55Al 10Ni 5Cu 30

Fiber laser has been receiving attention due to its advantages of high-power and high-beam quality to produce narrow and deep penetration welds at high-welding speeds. Therefore, fiber laser welding is expected to apply to the joining of metallic glass which has unique properties such as high-mechanical strength or small solidification shrinkage, because extremely rapid quenching for the laser weldment or heat-affected zone (HAZ) is possible to remain amorphous. In this research, fiber laser welding was first performed with the objective of obtaining a fundamental knowledge of weld property produced in bead-on-plate welding for common marital such as Type 304 stainless steel with 6 kW fiber laser beams of several peak power densities. Deeply penetrated weld beads with narrow widths were produced with small spots of tightly focused laser beams and full-penetration welds in 8 mm thick plate could be obtained at the high-welding speed of 4.5 m/min. Subsequently, the tightly focused 2.5 kW fiber laser beam was applied to 72 m/min ultra-high-speed welding for metallic glass Zr 55Al 10Ni 5Cu 30 in order to keep amorphous metals. Consequently, the weldment and HAZ remained desirably amorphous at ultra-high-welding speed with a tightly focused fiber laser beam.

Elucidation of high-power fibre laser welding phenomena of stainless steel and effect of factors on weld geometry

The fibre laser has been receiving great attention due to its advantages of high efficiency, high power and high beam quality, and is expected to be one of the most desirable heat sources for high-speed and deep-penetration welding. In this study, therefore, in bead-on-plate welding of Type 304 stainless steel plates with 6 kW fibre laser, the effects of laser power, power density and welding speed on the formation of sound welds were investigated with four laser beams of 130, 200, 360 and 560 µm in spot diameter, and their welding phenomena were clarified with high-speed video cameras and an x-ray transmission real-time imaging system. The weld beads showed a keyhole type of penetration at any diameter, and the maximum penetration of 11 mm in depth was obtained at 130 µm spot diameter and 0.6 m min−1 welding speed. It was found that the laser power density exerted a remarkable effect on the increase in weld penetration at higher welding speeds, and sound partially penetrated welds without welding defects such as porosity, underfilling or humping could be produced at wide process windows of welding speeds between 4.5 and 10 m min−1 with fibre laser beams of 360 µm or 560 µm in spot diameter. The high-speed video observation pictures and the x-ray images of the welding phenomena at 6 m min−1 welding speed and 360 µm spot diameter show that a sound weld bead was formed owing to a long molten pool suppressing and accommodating spattering and a stable keyhole generating no bubbles from the tip, respectively.

High-Power Fiber Laser Welding and Its Phenomena

High-Power Fiber Laser Welding and Its Phenomena