Andrey Gumenyuk

Single-Pass Laser-Gma Hybrid Welding of 13.5 mm thick duplex stainless steel

Single-pass solid-state laser welding of plates in the thickness range of 10 to 20 mm became possible with the invention of the fibre laser. This new technique provides excellent beam quality at powers as high as 20 kW or more, and has proved applicable in several industrial applications. By replacing conventional methods with the fibre laser, it is possible to avoid multiple-pass welding that requires time-consuming bevelling. The high energy density of the fibre laser beam also reduces the heat input and consequently the distortion. However, the rapid solidification and cooling associated with laser welding can cause imbalance of the microstructure of duplex stainless steel weldments, where excessively high ferrite contents may reduce the corrosion resistance and the ductility of the material. The solution is normally to add nickel-based filler wire and to increase the heat input. By using a hybrid welding process where the laser beam and the gas metal arc (GMA) process act in a common process zone, filler metal can be added to the molten pool at higher heat input and at the same time, higher welding speed and deeper penetration can be achieved. In this work, 13.5 mm thick 2205 (EN 1.4462, UNS S31803) was fibre laser-GMA hybrid welded in a single-pass using 14 kW of laser power and ISO 22 9 3 N L as filler wire for the GMA process. The resulting welds were free from defects, with smooth surfaces and full penetration. The investigation examines the weld metal microstructure and the effect on corrosion resistance and mechanical properties. The option to add nickel foil, when hybrid welding, was also investigated, as comparison, and the effect on austenite formation was evaluated.

Characteristics of weld pool behavior in laser welding with various power inputs

This paper investigates the numerical simulations of multi-kilowatt disk laser and fiber laser welding, ranging from 6 to 18xa0kW to study the behavior of molten pool in 20-mm-thick steel plate by using Volume-Of-Fluid (VOF) method and several mathematical models like Gaussian heat source, recoil pressure, Marangoni flow, buoyancy force, and additional shear stress and heat source due to the metallic vapor. Vortex flow pattern is observed for higher laser power except for 6-kW case, and the higher the laser power, the bigger the vortex flow pattern. Welding speed has an influence on molten pool in terms of depth of penetration and size of molten pool, but overall shape of molten pool remains the same. The reasons for the vortex flow pattern in high-power laser welding are the absorption of more energy at the bottom of keyhole, which promotes more liquid metal at the bottom, while for lower power with lower speed, the melt formation is more uniform in the thickness direction and most of the molten metal in the lower part of keyhole reaches the top of molten pool, and consequently, no vortex flow pattern is observed in the keyhole bottom.

Spectral diagnostics of a vapor-plasma plume produced during welding with a high-power ytterbium fiber laser

We have conducted spectroscopic studies of the welding plasma formed in the process of welding with an ytterbium fiber laser delivering output power of up to 20 kW. The influence of shielding gases (Ar, He) on different parts of the welding plume is investigated. The absorption coefficient of the laser radiation by the welding-plume plasma is estimated. Scattering of 532-nm probe radiation from particles of the condensed metal vapor within the caustic of a high-power fiber laser beam is measured. Based on the obtained results, conclusions are made on the influence of the plasma formation and metal vapor condensation on the radiation of the high-power fiber laser and the stability of the welding process.

Experimental investigation of the laser-plume interaction during high power fiber laser welding

The effect of the well-known plasma absorption and refraction in CO2-laser metal welding plumes is incase of high power solid state laser welding negligibly small. By contrast, the diffraction effects of shorter wavelength laser radiation are considerable. According to the results of preliminary studies, the fine condensed metal particles in the welding plume can lead to essential worsening of the laser beam quality.This work is devoted to the investigation of the laser-matter interaction during up to 20 kW ytterbium fiber laser welding of thick mild steel plates. The plume attenuation of a probe 1.3u2005µm wavelength diode laser beam as well as of continuous radiation in 250-600u2005nm wavelength range was measured during welding with and without Ar shielding gas supply. The measured results allow it to calculate average size and concentration of fine condensed metal particles in different plume areas using the multi-wavelength method and the Mie scattering theory. The plume temperature, whichdetermines the condensation conditions, was measured by means of Fe I atom spectral line emission registration.The obtained results can be also of interest for remote metal treatment with high-power fiber or disc lasers.The effect of the well-known plasma absorption and refraction in CO2-laser metal welding plumes is incase of high power solid state laser welding negligibly small. By contrast, the diffraction effects of shorter wavelength laser radiation are considerable. According to the results of preliminary studies, the fine condensed metal particles in the welding plume can lead to essential worsening of the laser beam quality.This work is devoted to the investigation of the laser-matter interaction during up to 20 kW ytterbium fiber laser welding of thick mild steel plates. The plume attenuation of a probe 1.3u2005µm wavelength diode laser beam as well as of continuous radiation in 250-600u2005nm wavelength range was measured during welding with and without Ar shielding gas supply. The measured results allow it to calculate average size and concentration of fine condensed metal particles in different plume areas using the multi-wavelength method and the Mie scattering theory. The plume temperature, whichdetermines the cond...

Numerical simulation of electromagnetic melt control systems in high power laser beam welding

The availability of laser sources with a power of 20 kW upwards prepared the ground for laser beam welding of up to 20 mm thick metal parts. Challenges are the prevention of gravity-driven melt drop-out and the control of the dynamics mainly due to the Marangoni flow.Coupled numerical turbulent fluid flow, thermal and electromagnetic simulations and experimental validation with aluminum AlMg3 and stainless steel AISI 304 were done for alternating and steady magnetic fields perpendicular to the process direction. The first can prevent melt sagging in full-penetration welding by Lorentz forces in the melt induced by an AC magnet located below the weld specimen counteracting gravitational forces. The latter controls the Marangoni flow by Lorentz braking forces in the melt by the so-called Hartmann effect.The simulations show that the drop-out of aluminum and stainless steel can be avoided for 20 mm thick full-penetration welds with moderate magnetic flux densities of 70 mT and 95 mT at oscillation frequencies of 450 Hz and 3 kHz, respectively. The experiments are in good agreement but show somewhat larger values for steel, whose weakly ferromagnetic properties are a possible reason. The investigations with steady magnetic fields reveal the possibility to mitigate the dynamics significantly beginning with around 500 mT at laser penetration depths of approximately 20 mm.The availability of laser sources with a power of 20 kW upwards prepared the ground for laser beam welding of up to 20 mm thick metal parts. Challenges are the prevention of gravity-driven melt drop-out and the control of the dynamics mainly due to the Marangoni flow.Coupled numerical turbulent fluid flow, thermal and electromagnetic simulations and experimental validation with aluminum AlMg3 and stainless steel AISI 304 were done for alternating and steady magnetic fields perpendicular to the process direction. The first can prevent melt sagging in full-penetration welding by Lorentz forces in the melt induced by an AC magnet located below the weld specimen counteracting gravitational forces. The latter controls the Marangoni flow by Lorentz braking forces in the melt by the so-called Hartmann effect.The simulations show that the drop-out of aluminum and stainless steel can be avoided for 20 mm thick full-penetration welds with moderate magnetic flux densities of 70 mT and 95 mT at oscillation frequencie...

Hot cracking in high power laser beam welding of thick high strength structural steels under restraint conditions

High power laser beam welding represents a cost-effective alternative for fast joining of thick components. However, the reliability of the welded structures can be severely affected by solidification crack formation, caused by constructional restraints. Experimental investigations using 15u2005mm thick plates of the fine grained structural steel S690, welded with a 20 kW fiber laser under different restraint conditions revealed a relationship between hot cracking susceptibility and restraint intensity. Systematic laser welding experiments were conducted in the IRC (Instrumented Restraint Cracking)-test facility, under both free shrinkage as well as defined restraint intensities. In order to assess the stress-strain condition of the weld during solidification which is crucial in the hot crack formation process but also difficult, if not impossible to acquire experimentally, a two-dimensional thermo-mechanical finite element model of the IRC-Test was developed. The results constitute a good approach to explain and understand the detrimental effects of high restraints on hot cracking phenomena during laser beam welding.High power laser beam welding represents a cost-effective alternative for fast joining of thick components. However, the reliability of the welded structures can be severely affected by solidification crack formation, caused by constructional restraints. Experimental investigations using 15u2005mm thick plates of the fine grained structural steel S690, welded with a 20 kW fiber laser under different restraint conditions revealed a relationship between hot cracking susceptibility and restraint intensity. Systematic laser welding experiments were conducted in the IRC (Instrumented Restraint Cracking)-test facility, under both free shrinkage as well as defined restraint intensities. In order to assess the stress-strain condition of the weld during solidification which is crucial in the hot crack formation process but also difficult, if not impossible to acquire experimentally, a two-dimensional thermo-mechanical finite element model of the IRC-Test was developed. The results constitute a good approach to explain...

Strategien zur Erreichung eines konstanten Volumenaufbaus bei der additiven Fertigung mittels Laser-Pulver-Auftragschweißen / Strategies to achieve constant build-up with laser metal deposition

Der Einsatz von Hochleistungswerkstoffen verlangt nach einer hohen Endformnahe der zu fertigenden Bauteile, um den Aufwand und somit die Kosten fur Materialeinsatz und Nachbearbeitung moglichst gering zu halten. Der additive Einsatz in Form des Laser-Pulver-Auftragschweisens bietet hierfur durch den gezielten Materialauftrag ein hohes Potential. Herausforderungen bestehen in Bereichen der Vorhersagbarkeit und der Reproduzierbarkeit des Materialauftrages, sowie der Fertigungszeit. Unterschiedliche Einflusse bei der Schichterzeugung fuhren dabei zu Abweichungen von der Soll-Geometrie. Die vorliegenden Untersuchungen behandeln den Einfluss von Spurgeometrie, Spuruberlappung, Verfahrweg und Aufbaureihenfolge auf die entstehende Bauteilform. Die Teilung einer Lage in Rand- und Kernbereich ermoglicht einen konturangepassten Verfahrweg und eine Erhohung der Endformnahe innerhalb einer Ebene. Die Verwendung unterschiedlicher Spurgrosen bei der Bauteilerzeugung verdeutlicht die Moglichkeiten einer hohen Auftragsrate bei gleichzeitig hoher Formgenauigkeit. Bereits kleine Unterschiede beim Materialauftrag zwischen Kern- und Randbereichen, Start- und Endpunkten sowie in Bereichen des Richtungswechsels fuhren aufgrund von Fehlerfortpflanzung nachmehreren Lagen zu Abweichungen in der Aufbaurichtung. Kompensierungen mittels angepasster Baustrategien werden aufgezeigt und diskutiert. Die Nickelbasislegierung Inconel 718, die Titanlegierung Ti-6Al-4V sowie der austenitische Stahl 316L sind Bestandteil der vorliegenden Untersuchungen. Die gewonnenen Erkenntnisse verdeutlichen das Potenzial einer angepassten Aufbaustrategie zur reproduzierbaren Erzeugung von Bauteilen am Beispiel unterschiedlicher Korpergeometrien.

Weld seam formation and mechanical properties of girth welds performed with laser-GMA-hybrid process on pipes of grade X65

With the recent introduction of multi-kilowatt fiber lasers combining high beam quality with an impressive energy efficiency, it was possible to broaden the spectrum of laser beam and laser-hybrid welding applications widely. Application of these lasers for welding thick-walled structures in different branches of industry (e.g. power generation, shipbuilding, wind power, pipeline construction) is interesting, because the fiber lasers offer sufficient penetration depth to allow economically efficient welding of thick sheet metal, i.e. with a reduced number of welding passes and with a lower amount of filler material. A girth laser-hybrid process using a 20 kW fiber laser and a gas metal arc welding (GMAW) process was examined at BAM, Federal Institute for Materials Research and Testing, Berlin. The aim of this research was to obtain a stable and crack free girth process and to demonstrate the possibility of its application in pipeline construction. The experiments were carried out on 16u2005mm thick pipe rings with 914u2005mm pipe diameter of X65. As it could be shown in previous publications the rings can be welded using a girth hybrid process that is divided into two steps each in 5G position downhill. This paper will focus on imperfections of the weld seams in the different welding positions and on the methods for their avoiding. Influences of forming gas and scanner optic parameters on the appearance of the weld root were analyzed. A serie of welding experiments with preheating was performed. Mechanical properties and weld metal microstructure for the pipe segment welds were examined for different preheat temperatures.With the recent introduction of multi-kilowatt fiber lasers combining high beam quality with an impressive energy efficiency, it was possible to broaden the spectrum of laser beam and laser-hybrid welding applications widely. Application of these lasers for welding thick-walled structures in different branches of industry (e.g. power generation, shipbuilding, wind power, pipeline construction) is interesting, because the fiber lasers offer sufficient penetration depth to allow economically efficient welding of thick sheet metal, i.e. with a reduced number of welding passes and with a lower amount of filler material. A girth laser-hybrid process using a 20 kW fiber laser and a gas metal arc welding (GMAW) process was examined at BAM, Federal Institute for Materials Research and Testing, Berlin. The aim of this research was to obtain a stable and crack free girth process and to demonstrate the possibility of its application in pipeline construction. The experiments were carried out on 16u2005mm thick pipe rings...