Effects of adaptive GMAW processes: Performance and dissimilar weld quality
Mvola Belinga, Eric Martial (2017-06-21)
Väitöskirja
Mvola Belinga, Eric Martial
21.06.2017
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-335-096-0
https://urn.fi/URN:ISBN:978-952-335-096-0
Tiivistelmä
The last decades have seen growing demand for welding of dissimilar steels, in particular,
as a part of efforts to improve transportation safety and, by weight reduction, to improve
fuel consumption. Moreover, in construction of lifting and handling systems and bridge
building, dissimilar welds can provide lightweight solutions and good performance. In
power plants, dissimilar weld is often used to comply rapidly changing from low to higher
temperature. Although the dissimilar weld has many application, failure was observed
near the fusion line and in the heat affected zone. Adaptive gas metal arc welding
(GMAW) can improve the formation of the microstructure and reduce the initiation and
propagation of the cracks. Adaptive GMAW is characterized by the ability of the process
to adjust the welding parameter such as length of the electrode, the current waveform, gas
flow and wire feed rate as required by the workpiece.
The objectives of this research are to conduct a critical analysis of various techniques
applicable to adaptive control of gas metal arc welding processes, to categorize control
parameters and identify benefits and drawbacks of the available processes, and to suggest
innovative techniques and scientific approaches that could significantly improve
productivity and the quality of dissimilar metal welds.
The thesis is an article-based dissertation that includes in its second part eight publications
related to the subject under study. The methods used in the works include both critical
literature review and empirical experiments. Samples and data are analyzed in order to
determine the controllability of welding parameters at the shielding gas unit, driven
system performance, and the quality of the welded joints produced. The study also
analyses the influence of control of gas metal arc welding process systems on dissimilar
welding of high-strength steels and high manganese steels, welding of non-ferrous and
ferrous metals (i.e. steel and aluminium) and non-ferrous dissimilar welding (i.e.
aluminium of different grades). The microstructures formed, the deposited weld geometry
and the physical and mechanical characteristics of the welded joints are evaluated.
The results show a considerable variation in the formed microstructures with differences
in the presence of acicular ferrite, grain boundary ferrite, Widmanstätten ferrite or bainite,
polygonal ferrite, and lower bainite or martensite depending on the current waveform
parameters. Control of heat input and shielding gas (e.g. pulsed flow rate, alternative
shielding gas) is seen to enable improvements in weld shape geometry and a reduction in
coarse grain in the heat affected zone, and such dissimilar welds exhibit limited dilution and a reduction in intermetallic compounds. When alternative shielding or pulsed
shielding are used, savings in gas usage are possible without undermining the quality of
the welds.
On the basis of the results of this study, it is concluded that enhanced adaptive control of
gas metal arc welding processes with real-time adjustment can provide improvement in
welding productivity and stability, support consistent welded joint quality, and give
greater autonomy to automated welding processes.
as a part of efforts to improve transportation safety and, by weight reduction, to improve
fuel consumption. Moreover, in construction of lifting and handling systems and bridge
building, dissimilar welds can provide lightweight solutions and good performance. In
power plants, dissimilar weld is often used to comply rapidly changing from low to higher
temperature. Although the dissimilar weld has many application, failure was observed
near the fusion line and in the heat affected zone. Adaptive gas metal arc welding
(GMAW) can improve the formation of the microstructure and reduce the initiation and
propagation of the cracks. Adaptive GMAW is characterized by the ability of the process
to adjust the welding parameter such as length of the electrode, the current waveform, gas
flow and wire feed rate as required by the workpiece.
The objectives of this research are to conduct a critical analysis of various techniques
applicable to adaptive control of gas metal arc welding processes, to categorize control
parameters and identify benefits and drawbacks of the available processes, and to suggest
innovative techniques and scientific approaches that could significantly improve
productivity and the quality of dissimilar metal welds.
The thesis is an article-based dissertation that includes in its second part eight publications
related to the subject under study. The methods used in the works include both critical
literature review and empirical experiments. Samples and data are analyzed in order to
determine the controllability of welding parameters at the shielding gas unit, driven
system performance, and the quality of the welded joints produced. The study also
analyses the influence of control of gas metal arc welding process systems on dissimilar
welding of high-strength steels and high manganese steels, welding of non-ferrous and
ferrous metals (i.e. steel and aluminium) and non-ferrous dissimilar welding (i.e.
aluminium of different grades). The microstructures formed, the deposited weld geometry
and the physical and mechanical characteristics of the welded joints are evaluated.
The results show a considerable variation in the formed microstructures with differences
in the presence of acicular ferrite, grain boundary ferrite, Widmanstätten ferrite or bainite,
polygonal ferrite, and lower bainite or martensite depending on the current waveform
parameters. Control of heat input and shielding gas (e.g. pulsed flow rate, alternative
shielding gas) is seen to enable improvements in weld shape geometry and a reduction in
coarse grain in the heat affected zone, and such dissimilar welds exhibit limited dilution and a reduction in intermetallic compounds. When alternative shielding or pulsed
shielding are used, savings in gas usage are possible without undermining the quality of
the welds.
On the basis of the results of this study, it is concluded that enhanced adaptive control of
gas metal arc welding processes with real-time adjustment can provide improvement in
welding productivity and stability, support consistent welded joint quality, and give
greater autonomy to automated welding processes.
Kokoelmat
- Väitöskirjat [1036]