Masters Theses

Date of Award

8-1989

Degree Type

Thesis

Degree Name

Master of Science

Major

Aerospace Engineering

Major Professor

T. Dwayne McCay

Committee Members

Mary Helen McCay, Roger A. Crawford

Abstract

Lasers used for welding contain a series of reflective and transmission optics which if not kept free of contamination results in aberrations in the laser beam and subsequent degradation in the properties of the weld. Downtime is necessary to clean the optics and maintain the weld quality. Particle build-up on the optics may even cause physical damage such as fracture, necessitating replacement with its attendant material costs. Welding of aluminum alloys has been particularly damaging to the optics due to the presence of alloying elements, such as magnesium and manganese, which vaporize and deposit ejecta particles on the optics.

A welding nozzle with an aerodynamic window was developed to protect the laser beam delivery optics by preventing ejecta particles from depositing on the optics. The area and magnitude of the cross-flow through the window was optimized in a cold flow experiment with the nozzle removed from the laser. A series of welds were conducted with the cross-flow nozzle and the existing baseline laser welding nozzle. The degradation of power to the workpiece, particle distribution on the reflective optics and integrity of the Zn-Se transmission optic was noted. The weld structure was examined to ensure that there was IV no interference with the quality of the weld due to the cross-flow.

The aerodynamic window substantially reduced the amount of particle build-up on the reflective optics. Loss in the power delivered to the workpiece was reduced. During the baseline nozzle experiments the Zn-Se optic was destroyed, while during the cross-flow nozzle experiments the optic remained intact. The ratio of deep penetration to conduction limited weld was greater and the percentage porosity was lower for the cross-flow nozzle welds. Comparison of weld penetration and depth-to-width ratio of the welds showed little difference between the two nozzles.

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