Pulsed GMAW Parameter Variation to Minimize Interference from Tack Welds
Abstract
This thesis provides a comprehensive analysis of the effect of tack welds on shipbuilding and the possible means by which they can be dealt with more effectively. An overview of the shipbuilding process is provided first, with emphasis on modern shipbuilding techniques and their relation to flexible automation and automated welding and the problem of tack welds. Next is a specific examination of the welding phenomena occurring at tack weld sites in steel butt joints. Experimentally, tack welds are shown to be a major source of defects. Lack of penetration, lack of fusion, and discontinuities at the beginnings and ends of tack welds are prevalent. Underbead temperature profiles are measured and compared to predictions using the Rosenthal solution. Agreement is good, and the differences are discussed in terms of the Rosenthal assumptions and the effects of transient heat flow at the tack weld sites. The third study area is an analysis of pulsed gas metal arc welding as a means of better handling tack welds by increasing penetration. Four mechanisms of penetration are discussed in detail: arc pressure, compound vortex, weld pool convection, and droplet momentum. The effect of current pulsing on each mechanism is analyzed, and strategies are devised for increasing penetration: low frequency pulsing, high frequency pulsing, high duty cycle pulsing, high peak pulsing, and mid-peak drop transfer. All strategies are tested experimentally, and all except high frequency pulsing are found to increase penetration. Theses. (edc)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1987
- Accession Number
- ADA216831
Entities
People
- Gregory C. Kolodziejczak
Organizations
- Naval Postgraduate School