Date of Award

Winter 1996

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

First Advisor

Gail Ulrich

Abstract

This investigation studied fume generated from Gas Metal Arc Welding (GMAW). Through an extensive literature review, experimental measurements and analytical reasoning this dissertation answers four questions. Why and how does oxygen content of the shield gas effect fume generation? Why is more fume generated with helium than with argon as a shield gas? Why and how does welding mode affect fume rate? Why and how does pulsing the current lower fume generation rate?

An extensive literature survey was conducted. The current view of GMAW indicates that four modes exist in metal transfer across the arc. Each mode selects from several mechanisms of fume creation. These mechanisms are drop evaporation, arc root evaporation, explosive evaporation, fine spray and spatter and burning of spatter.

GMAW heat transfer was analyzed to include radiation effects. Convective heat transfer was found to be much less important than previously thought. A new model for mass transfer of fume with chemical reaction explained the increase in fume with both oxygen and helium in the shield gas. For the first time a force balance along with the heat transfer was used to explain the effects on fume formation.

The new heat and mass transfer analysis showed that in past and present data, mode effected fume by using more/fewer of the possible mechanisms noted above. The magnitude and severity of the effect on each mechanism depended not only on current and voltage, but was clearly effected by which mode was operating.

A fume collection box was built. Analysis of fume generated in this box confirmed many past findings, as well as the theoretical mechanisms behind them. Particle size measurements were attempted using nitrogen adsorption. Unfortunately the size measurements were inconclusive.

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