Product Code: ICAL08_P149

Development of a Time Resolved Energy Absorption Measurement Technique for Laser Beam Spot Welds
C.V. Robino, Sandia National Laboratory; Albuquerque NM USA
J.T. Norris, Sandia National Laboratories; Albquerque NM USA
Presented at ICALEO 2008

A method is currently being developed to temporally characterize the energy absorption in laser beam spot welds. As a spot weld is created, absorption of laser energy changes with the condition of the weld (initial melting conduction keyhole). By relating the known pulse energy to the energy scattered during welding, a time resolved description of energy absorption can be determined. The method discussed uses a gold plated integrating sphere with a Nd:YAG notch filtered photodiode to capture and detect the scattered laser light. Under various welding parameters (pulse energy, duration, and shape), the level of light scattered changes with the condition of the weld pool during the pulse. For high depth-to-width aspect ratio welds, instantaneous energy transfer efficiency ranges from ~50 to 75% depending on the state of the weld pool. Low aspect ratio welds (conduction mode welds) maintain the same transfer efficiency throughout the welding process (at ~50%). Average transfer efficiencies measured by this method are in good agreement with calorimetric [1] and thermal expansion measurements [2]. Characterizing keyhole formation and transfer efficiency in relation to welding parameters allows optimization of the laser welding process and provides insight into keyhole phenomena needed for developing and improving modeling capabilities.

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