Effects of adaptive GMAW processes: Performance and dissimilar weld quality

摘要

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 improvefuel consumption. Moreover, in construction of lifting and handling systems and bridgebuilding, dissimilar welds can provide lightweight solutions and good performance. Inpower plants, dissimilar weld is often used to comply rapidly changing from low to highertemperature. Although the dissimilar weld has many application, failure was observednear 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 andpropagation of the cracks. Adaptive GMAW is characterized by the ability of the processto adjust the welding parameter such as length of the electrode, the current waveform, gasflow and wire feed rate as required by the workpiece.The objectives of this research are to conduct a critical analysis of various techniquesapplicable to adaptive control of gas metal arc welding processes, to categorize controlparameters and identify benefits and drawbacks of the available processes, and to suggestinnovative techniques and scientific approaches that could significantly improveproductivity and the quality of dissimilar metal welds.The thesis is an article-based dissertation that includes in its second part eight publicationsrelated to the subject under study. The methods used in the works include both criticalliterature review and empirical experiments. Samples and data are analyzed in order todetermine the controllability of welding parameters at the shielding gas unit, drivensystem performance, and the quality of the welded joints produced. The study alsoanalyses the influence of control of gas metal arc welding process systems on dissimilarwelding of high-strength steels and high manganese steels, welding of non-ferrous andferrous metals (i.e. steel and aluminium) and non-ferrous dissimilar welding (i.e.aluminium of different grades). The microstructures formed, the deposited weld geometryand the physical and mechanical characteristics of the welded joints are evaluated.The results show a considerable variation in the formed microstructures with differencesin the presence of acicular ferrite, grain boundary ferrite, Widmanstätten ferrite or bainite,polygonal ferrite, and lower bainite or martensite depending on the current waveformparameters. Control of heat input and shielding gas (e.g. pulsed flow rate, alternativeshielding gas) is seen to enable improvements in weld shape geometry and a reduction incoarse grain in the heat affected zone, and such dissimilar welds exhibit limited dilution and a reduction in intermetallic compounds. When alternative shielding or pulsedshielding are used, savings in gas usage are possible without undermining the quality ofthe welds.On the basis of the results of this study, it is concluded that enhanced adaptive control ofgas metal arc welding processes with real-time adjustment can provide improvement inwelding productivity and stability, support consistent welded joint quality, and givegreater autonomy to automated welding processes.