Laser weld pool optical diagnostics: Topography and visualization used for surface contour analysis and process monitoring
Voelkel, David Daniel
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Permalink
https://hdl.handle.net/2142/23604
Description
Title
Laser weld pool optical diagnostics: Topography and visualization used for surface contour analysis and process monitoring
Author(s)
Voelkel, David Daniel
Issue Date
1992
Doctoral Committee Chair(s)
Mazumder, Jyotirmoy
Department of Study
Engineering, Mechanical
Engineering, Metallurgy
Discipline
Engineering, Mechanical
Engineering, Metallurgy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Engineering, Metallurgy
Language
eng
Abstract
This experimental investigation into shallow laser welding describes new techniques for visualizing, measuring dimensions, and mapping the deformation of the weld pool free surface. The first known measurements of the molten surface contour have been obtained, analyzed, and compared with predicted surface contours from five models in order to ascertain what phenomena are most important in determining the molten pool topography. Accurate prediction of the weld pool surface by a model is one indication of whether the welding process is correctly understood. The surface contour was found to be convex when the CO$\sb2$ laser beam was relatively defocused. It gradually changed to a concave surface as the beam was focused more. Only one model predicted a surface shape similar to any of those measured. Seven factors were considered for their influence on the surface contour: density change, porosity, thermocapillary flow, radiation pressure, cover gas flow, recoil pressure, and mass loss. Analysis shows the volume change associated with density change, the volume change associated with mass loss, and recoil pressure are the most important phenomena to incorporate into the thermocapillary flow models of the weld pool in order to more accurately consider the surface contour. In addition to measuring the molten surface contour of the weld pool, progress has been made in two other areas of laser welding: visualization and on-line monitoring. Visualization of the pool has been greatly improved by illumination with both diffused and focused argon laser light. On-line measurement of the weld pool surface dimensions, detection of piece mismatch, and indication of non-fusion have been performed by projecting fine Ronchi rulings onto the workpiece surface. Altogether, these advances serve the multiple objectives of increasing understanding of the welding process, providing data for comparison with models, and providing on-line monitoring of welding in an industrial environment.
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