Date

December 1986

Document Type

Thesis

Degree Name

M.S.

Department

Dept. of Materials Science and Engineering

Institution

Oregon Graduate Center

Abstract

Aluminum alloys, while readily weldable with other techniques, are very difficult to weld using the laser beam welding (LBW) process. The purpose of this investigation was to examine the use of the arc-augmented LBW process as a possible technique for successful LBW of structural aluminum alloys. LBW parameters were examined using an industrial type 1200 watt continuous wave CO2 laser. Because of the high surface reflectivity and thermal diffusivity of aluminum, power densities of greater than 10[superscript 6] W/cm2 were necessary to initiate and continue deep-penetration mode welding. Beam focusing optics capable of producing this high power density were limited by short depth of field which makes thick section welding impossible. Surface preparations including anodizing and grit blasting proved helpful while using longer focal length lenses. Synergy resulting from the combined action of the laser beam and the gas tungsten arc produced a far greater volume of molten metal than the individual contributions of each process added separately. This synergistic effect was seen when the laser beam was augmented with an arc produced by a conventional gas tungsten arc welding (GTAW) electrode. Evidence was obtained showing this increase in melted volume to be related to an increase in the efficiency of the gas tungsten arc. Measured changes in arc column resistance and current coupled with high speed videography results showing the arc rooting to the laser induced hot-spot confirm an overall increase in applied power density (mainly from the GTAW arc). Weld preheating temperatures close to the melting point of aluminum was found to promote thermal coupling of laser energy. The increase in absorption of the laser beam by aluminum was proposed as a possible mechanism of the observed arc-laser synergism in the combined process. Results from arc-augmented LBW of mild steel are provided which show the increase in melted volume to be similar to that obtained for aluminum, and based on this, the dominant mechanism of arc-laser synergism was proposed to be an increase in the GTAW efficiency. Relative to the engineering significance of this work, possible benefits from the arc-augmented LBW technique (on aluminum) would include coupling a GTAW torch to an already existing LBW application with increased quality or productivity as an aim. It would not make economical sense to do the reverse because of the high cost of a LBW system relative to the increase in welding velocity or penetration depth one might gain from a GTAW system.

Identifier

doi:10.6083/M4JW8BTP

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