Year

2008

Degree Name

Doctor of Philosophy

Department

Faculty of Engineering

Abstract

This work was carried out to address the scope for hybrid laser-GMAW process improvement using controlled dip transfer and a high power diode laser in single and twin spot modes. It is suggested that an optimum combination of the two sources of thermal energy can enhance the speed and quality of single sided butt welds. The objectives of the current work were therefore, to investigate the process control possibilities, performance characteristics and the processes interactions of twin beam hybrid laser-GMAW welding. Since no appropriate twin beam system existed it was also necessary to design and build an experimental system.

This research was made possible by using a power source which enabled flexible computer control of the GMAW current waveform and a 3kW high power diode laser. Weld beads were produced to study the basic operating parameters for the individual arc and laser processes and these were compared with those of combined process with laser in single and twin spot modes. Bead geometry and the current waveforms captured by the data acquisition system were used to evaluate the welding processes performance.

Variables such as groove shape and shielding gas were also found to be critical for full penetration of butt joints on plates. CO2 produced weld bead with deeper penetration than with Ar based gas mixtures.

A novel hybrid welding head was design and implemented to investigate the process using an extended heat source (as in multicathode GTAW and tandem GMAW) to create an elongated weld pool through the use of laser-GMAW with dual laser spots leading and trailing the GMAW heat source.

To understand the process control mechanisms, a 3D finite element model was created and implemented to analyze the temperature distribution resulting from the arc and mutual effects of the arc and laser heat sources.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.