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The additional element from the filler wire in the laser beam welding is usually distributed inhomogeneously in the final weld due to the high solidification rate of weld pool. It has been found that the electromagnetic stirring produced by an external oscillating magnetic field can enhance the material mixing in the weld pool to achieve a more uniform element distribution. However, the magnetic field has a highly non-linear and multi-coupled interaction with the weld pool behavior, which makes the quantitative explanation of the physical mechanism difficult. In this study, the effect of electromagnetic stirring on the transport phenomena in the wire feed laser beam welding is investigated by a numerical modelling. A 3D transient multi-physical model considering the magnetohydrodynamics, heat transfer, fluid flow, keyhole dynamics and element transport is developed. The multiple reflections and the Fresnel absorption of the laser on the keyhole wall are calculated using the ray tracing method. The numerical results show that a Lorentz force produced by the oscillating magnetic field and its induced eddy current gives significant influence on the transport phenomena in the molten pool. The forward and downward flow is enhanced by the electromagnetic stirring, which homogenizes the distribution of the additional elements from a nickel-based filler wire in a steel weld pool. The numerical results show a good agreement with the high-speed images of the molten pool, the fusion line from the optical micrograph and the element distribution from the energy dispersive X-ray spectroscopy. This work provides a physical base for the electromagnetic-controlled laser beam welding and some guidance for the selection of electromagnetic parameters.
Offshore wind energy plays an important role for the desired transition towards a carbon dioxide free industry within the next decades. However, the grounding of the offshore wind plants governs the overall installation process besides bureaucratic bottlenecks.
The application of lightweight principles in steel construction, e.g. the usage dissolved load-bearing structures, so called Jackets foundations, offer great potential in reducing the resource consumption, especially with respect to the needed amount of steel.
In this context this paper focuses on a fully digitalization of the welding manufacturing and as well as testing chain to enable a fully automated manufacturing as well as quality assessment of tubular nodes as key element of Jackets foundation structures. Furthermore, the relationship between the seam shape geometry and resulting fatigue strength is evaluated by numerical methods incorporating bionic principles. It is shown that tubular nodes can be welded fully automatically taking geometry tolerances into account. Moreover, the seam shape could be manufactured as requested by the numerical models which offers great potential for an extended lifetime. Subsequently, the improvements in resource efficiency and reduction of carbon dioxide emissions are evaluated by a life-cycle-assessment.
The present work deals with the development of a strategy for the prevention of end crater defects in high-power laser welding of thick-walled circumferential welds. A series of experiments were performed to understand the influence of the welding parameters on the formation of end crater defects such as pores, cracks, excessive root-side drop-through and shrinkage cavities in the overlap area. An abrupt switch-off of the laser power while closing the circumferential weld leads to a formation of a hole which passes through the whole welded material thickness. A laser power ramp causes solidification cracks which are initiated on the transition from full-penetration mode to partial penetration. Strategies with a reduction of the welding speed shows a creation of inadmissible root sagging. Defocusing the laser beam led to promising results in terms of avoiding end crater defects. Cracks and pores in the overlap area could be effectively avoided by using defocusing techniques. A strategy for avoiding of end crater imperfections was tested on flat specimens of steel grade S355J2 with a wall thickness of 10 mm and then transferred on the 9.5 mm thick pipe sections made of high-strength steel X100Q.
Test procedure to characterize the cracking susceptibility of RSW-steels has been developed
During externally loaded test procedure all investigated steels (HDT780CD+Z100, HDT780C+ZE75/75, HX340LAD+Z100, HCT690TD+Z100) showed a cracking behavior
With increased specimen load, the crack length grows for the micro-alloyed-steel and TRIP-steel
Complex phase steels behavior during test procedure:
Crack length growth with increasing force could not be determined
The cracking susceptibility of electro-galvanized steels is less than hot-dip galvanized steels (in this case)
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•Main Welding Technologies in the Automotive: RSW and laserbeam welding
•Light Weight Design leads to increasing use of AHSS and UHSS which results in higher demands for the joining technology
•Joining Multi-Material Structures offers opportunities for “new” Thermal-Mechanical Joining Processes and Hybrid Processes
•In the coming years a trend towards sustainable manufacturing can be seen. Comparison between laserbeam and RSW will be a tight match!
Drop-out of molten material was avoided by EM pressure
Compensation of the hydrostatic pressure of up to 20 mm thick
aluminum and stainless steel (experiment and FEM)
Mitigation of the weld bead dynamics
Significant changes in the velocity distributions in the weld pool
Weld pool geometry shape changes due to Hartmann effect
Significant porosity reduction
Surface quality improvements
Drop-out of molten material was avoided by EM pressure
Compensation of the hydrostatic pressure of up to 20 mm thick
aluminum and stainless steel (experiment and FEM)
Mitigation of the weld bead dynamics
Significant changes in the velocity distributions in the weld pool
Weld pool geometry shape changes due to Hartmann effect
Significant porosity reduction
Surface quality improvements
Through experimental observation and auxiliary numerical simulation, this investigation studies the different types of grain refinement of 5754 aluminum alloy laser beam welding by applying a transverse oscillating magnetic field. Scanning electron microscope results have proved that the application of a magnetic field can reduce the average crystal branch width and increase its number. The interaction between the induced eddy current generated by the Seebeck effect and the applied external magnetic field produces a Lorentz force, which is important for the increase in the number of crystal branches. Based on the theory of dendrite fragmentation and the magnetic field-induced branches increment, the grain size reduction caused by the magnetic field is studied. Furthermore, the effects of the magnetic field are ana lyzed by combining a phase field method model and simulations of nucleation and grain growth. The grain distribution and average grain size after welding verify the reliability of the model. In addition, the introduction of a magnetic field can increase the number of periodic three-dimensional solidification patterns. In the intersection of two periods of solidification patterns, the metal can be re-melted and then re-solidified, which prevents the grains, that have been solidified and formed previously, from further growth and generates some small cel lular grains in the new fusion line. The magnetic field increases the building frequency of these solidification structures and thus promotes this kind of grain refinement.
Experimental study and numerical simulation of hot crack formation for novel laser weldability test
(2015)
Hot cracking susceptibility in laser beam welding was assessed for several stainless steels by means of the CTW test
The strain rate has a significant influence on the formation of the hot crack
It was possible to determine the critical strain and strain rate that led to shot crack formation
A material ranking of hot cracking resistance could be made.A three-dimensional FEM using the contact element technique to simulate hot cracking during LBW under external load conditions was developed.
Good agreement between the strain field measured using the DIC technique and the simulation results
Susceptibility to hot cracking can be predicted by using FEM with the correct mechanical and thermo-physical material properties
Electromagnetic weld pool support system is illustrated successfully for hybrid laser arc welding of 20 -30 mm ferromagnetic Steels Welding of thick-walled steels in flat position and reduced welding velocities is possible Gap and misalignment between welded plates can be tolerated by use of this Technology Opportunity to reduce the laser beam power because of reduced welding velocity respectively increase of weldable material thickness with a 20 kW- fibre laser Mechanical properties of welds are in correspondence with requirements of Standards.