Visualization and quantification of melt flow dynamics for laser welding with superimposed intensity distributions analyzed by synchrotron radiation imaging

Lasers in Manufacturing and Materials Processing, vol. 13, pp. 831–855

Abstract

Abstract Modern solid-state lasers enable a continuous increase in welding speed due to higher possible laser beam powers. However, welding speeds above 8 m/min for high-alloy steels lead to altered melt flow dynamics and increased spatter formation, resulting in spatter adhesion and particularly in undercuts along the weld seam. In contrast to the cost- or time-intensive methods described in the state of the art to reduce these effects, modifying the intensity distributions appears to be a simple and effective approach that is independent of the welding direction. In particular, using a superimposed intensity allows a detailed investigation by adjusting the intensity with varying spot sizes or laser powers. Using a superimposed intensity to widen up the melt pool is especially effective in reducing the velocity of the melt flow around the keyhole and, consequently, spatter formation. However, its effect on other melt pool flows, especially the upward directed melt flow along the keyhole rear wall, remains largely unknown. To investigate these effects, high-speed synchrotron X-ray imaging in combination with tungsten carbide tracer particles was used to visualize the melt flow dynamics. Generally, two melt vortices are observed in the area behind the keyhole, one in the upper and one in the lower part of the melt pool. The backward melt flow at the melt pool bottom is unaffected by the additional energy input due to the limited penetration depth of the second laser. Furthermore, the upward directed flow along the keyhole rear wall remains unchanged. When increasing the second laser power, the keyhole widens and fluctuates at the rear wall. As a result, the upward melt flow at the rear wall is not discernible. In general, the superimposed intensity alters the melt flow behind the keyhole. However, these changes appear to be minor significant for spatter formation compared to the flow around the keyhole.

Authors 13

1. Christian Diegel corresponding

   Technische Universität Ilmenau

   Affiliation as printed

   Production Technology Group, Technische Universität Ilmenau, Gustav-Kirchhoff-Platz 2, Ilmenau, 98693, Germany

2. Leander Schmidt

   Technische Universität Ilmenau

   Affiliation as printed

   Production Technology Group, Technische Universität Ilmenau, Gustav-Kirchhoff-Platz 2, Ilmenau, 98693, Germany

3. Klaus Schricker

   Technische Universität Ilmenau · Brandenburg University of Technology Cottbus-Senftenberg

   Affiliation as printed

   Chair of Joining and Welding Technology, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus, Germany

   Production Technology Group, Technische Universität Ilmenau, Gustav-Kirchhoff-Platz 2, Ilmenau, 98693, Germany

4. Marc Seibold

   Technische Universität Ilmenau

   Affiliation as printed

   Production Technology Group, Technische Universität Ilmenau, Gustav-Kirchhoff-Platz 2, Ilmenau, 98693, Germany

5. Felix Zaiß

   University of Stuttgart

   Affiliation as printed

   Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Stuttgart, Germany

6. Christian Hagenlocher

   University of Stuttgart

   Affiliation as printed

   Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Stuttgart, Germany

7. Christoph Spurk Aachen Chair for Laser Technology LLT

   RWTH Aachen University

   Affiliation as printed

   Chair for Laser Technology LLT, RWTH Aachen University, Aachen, Germany

8. Marc Hummel Aachen Chair for Laser Technology LLT Fraunhofer Institute for Laser Technology ILT

   Fraunhofer Institute for Laser Technology · RWTH Aachen University

   Affiliation as printed

   Chair for Laser Technology LLT, RWTH Aachen University, Aachen, Germany

   Fraunhofer Institute for Laser Technology ILT, Aachen, Germany

9. Alexander M. Olowinsky Aachen Fraunhofer Institute for Laser Technology ILT

   Fraunhofer Institute for Laser Technology

   Affiliation as printed

   Fraunhofer Institute for Laser Technology ILT, Aachen, Germany

10. Felix Beckmann

    Helmholtz-Zentrum Hereon

    Affiliation as printed

    Institute of Material Physics, Helmholtz-Zentrum Hereon, Geesthacht, Germany

11. Julian P. Moosmann

    Helmholtz-Zentrum Hereon

    Affiliation as printed

    Institute of Material Physics, Helmholtz-Zentrum Hereon, Geesthacht, Germany

12. Thomas G. Graf

    University of Stuttgart

    Affiliation as printed

    Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Stuttgart, Germany

13. Jean Pierre Bergmann

    Technische Universität Ilmenau

    Affiliation as printed

    Production Technology Group, Technische Universität Ilmenau, Gustav-Kirchhoff-Platz 2, Ilmenau, 98693, Germany