Experimental and numerical investigation of the formation mechanisms of the bulging effect and its influence on the development of centerline cracking defects in high power laser beam welding of low-alloyed steels of high thickness

• Applicant: Dr.-Ing. Marcel Bachmann
• Subject Area: Joining and Separation Technology
• Term: from 2019 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 411393804

• Final Report Year: 2023

Final Report Abstract

The correlation between the weld pool shape and the formation of defects has been long known in the welding field. The aim of the project was the experimental and numerical study of the significant and yet poorly understood influence of the so-called bulging region, defined as an elongated and a widened weld pool shape at approximately half penetration depth, on the formation of centerline solidification cracks. In particular, a coupled multiphysics numerical model has been developed enabling the analysis of the formation mechanisms of the bulging-region. In addition, numerous experimental measurements, and observations such as drilling time, weld pool length, temperature, process efficiency, and metallographic cross-sections were used to validate the numerical findings. In both the physical and numerical experiments, various factors such as the laser power, the welding speed, and the focal position were varied to assess the occurrence of the bulging over a wide process window. It was discovered that a bulging region forms once the two main circulations in the longitudinal section of the weld pool are separated by a necking region. The necking and bulging regions were found to occur transiently but always together since the former causes the latter and vice versa. Moreover, based on the experimental results it was expected that the formation of a bulging-region is strongly dependent on the penetration depth. Although, in the studied process window, none of the varied process parameters could be identified as dominant based on the experimental results, this expectation was confirmed by the numerically obtained results. The various computations suggested that a transition from a slight bulge to a fully developed bulging occurs approximately in the range between 6 mm to 9 mm penetration depth. The results of the research project have been published in several journals and presented at conferences on welding and laser processing. The "IIW Kenneth Easterling Award" at the "13th International Seminar - Numerical Analysis of Weldability" in Seggau, Austria deserves special mention.

Publications

• Assessment of thermal cycles by combining thermo-fluid dynamics and heat conduction in keyhole mode welding processes. International Journal of Thermal Sciences, 145, 105981.
  Artinov, Antoni; Karkhin, Victor; Khomich, Pavel; Bachmann, Marcel & Rethmeier, Michael
  
• Lamé curve approximation for the assessment of the 3D temperature distribution in keyhole mode welding processes. Journal of Laser Applications, 32(2).
  Artinov, Antoni; Karkhin, Victor; Bakir, Nasim; Meng, Xiangmeng; Bachmann, Marcel; Gumenyuk, Andrey & Rethmeier, Michael
  
• Numerical study of additional element transport in wire feed laser beam welding. Procedia CIRP, 94, 722-725.
  Meng, Xiangmeng; Artinov, Antoni; Bachmann, Marcel & Rethmeier, Michael
  
• On the relationship between the bulge effect and the hot cracking formation during deep penetration laser beam welding. Procedia CIRP, 94, 5-10.
  Artinov, Antoni; Bachmann, Marcel; Meng, Xiangmeng; Karkhin, Victor & Rethmeier, Michael
  
• "Numerical study of the bulging effect in deep penetration laser beam welding". In: Lasers in Manufacturing (LiM), (online conference), 2021, pp. 1–8
  M. Bachmann, A. Artinov, X. Meng & M. Rethmeier
  
• Numerical Analysis of the Partial Penetration High Power Laser Beam Welding of Thick Sheets at High Process Speeds. Metals, 11(8), 1319.
  Artinov, Antoni; Meng, Xiangmeng; Bachmann, Marcel & Rethmeier, Michael
  
• The bulging effect and its relevance in high power laser beam welding. IOP Conference Series: Materials Science and Engineering, 1135(1), 012003.
  Artinov, Antoni; Meng, Xiangmeng; Bakir, Nasim; Üstündağ, Ömer; Bachmann, Marcel; Gumenyuk, Andrey & Rethmeier, Michael
  
• Elucidation of the Bulging Effect by an Improved Ray‐Tracing Algorithm in Deep Penetration Wire Feed Laser Beam Welding and Its Influence on the Mixing Behavior. Advanced Engineering Materials, 24(6).
  Bachmann, Marcel; Meng, Xiangmeng; Artinov, Antoni & Rethmeier, Michael
  
• Evaluation of narrowed weld pool shapes and their effect on resulting potential defects during deep penetration laser beam welding. Journal of Laser Applications, 34(4).
  Bachmann, Marcel; Meng, Xiangmeng; Artinov, Antoni & Rethmeier, Michael
  
• High-power laser beam welding for thick section steels – new perspectives using electromagnetic systems. Science and Technology of Welding and Joining, 27(1), 43-51.
  Rethmeier, Michael; Gumenyuk, Andrey & Bachmann, Marcel
  
• Study on the transition behavior of the bulging effect during deep penetration laser beam welding. International Journal of Heat and Mass Transfer, 184, 122171.
  Artinov, Antoni; Meng, Xiangmeng; Bachmann, Marcel & Rethmeier, Michael
  
• The detrimental molten pool narrowing phenomenon in wire feed laser beam welding and its suppression by magnetohydrodynamic technique. International Journal of Heat and Mass Transfer, 193, 122913.
  Meng, Xiangmeng; Artinov, Antoni; Bachmann, Marcel; Üstündağ, Ömer; Gumenyuk, Andrey & Rethmeier, Michael
  
• "A numerical study of the suppression of detrimental weld pool profile in the wire feed laser beam welding by magnetohydrodynamics". In: Mathematical Modelling of Weld Phenomena. Ed. by C. Sommitsch, N. Enzinger, and P. Mayer. Vol. 13. Verlag der Technischen Universität Graz, 2023.
  X. Meng, A. Artinov, M. Bachmann, Ö. Üstündag, A. Gumenyuk & M. Rethmeier
  
• "Numerical analysis of the dependency of the weld pool shape on turbulence and thermodynamic activity of solutes in laser beam welding of unalloyed steels". In: Mathematical Modelling of Weld Phenomena. Ed. by C. Sommitsch, N. Enzinger, and P. Mayer. Vol. 13. Verlag der Technischen Universität Graz, 2023
  A. Artinov, P. Kising, M. Bachmann, X. Meng & M. Rethmeier
  
• "Numerical analysis of the influence of the auxiliary oscillating magnetic field on the suppressing the porosity formation in deep penetration laser beam welding of aluminum alloy". In: Mathematical Modelling of Weld Phenomena. Ed. by C. Sommitsch, N. Enzinger, and P. Mayer. Vol. 13. Verlag der Technischen Universität Graz, 2023.
  F. Yang, M. Bachmann, X. Meng, A. Artinov & M. Rethmeier
  
• "Numerical study on the formation of a bulging region in partial penetration laser beam welding". In: Mathematical Modelling of Weld Phenomena. Ed. by C. Sommitsch, N. Enzinger, and P. Mayer. Vol. 13. Verlag der Technischen Universität Graz, 2023.
  A. Artinov, X. Meng, M. Bachmann & M. Rethmeier
  
• A General Analytical Solution for Two-Dimensional Columnar Crystal Growth during Laser Beam Welding of Thin Steel Sheets. Applied Sciences, 13(10), 6249.
  Artinov, Antoni; Karkhin, Victor; Meng, Xiangmeng; Bachmann, Marcel & Rethmeier, Michael