Study of weld quality in gas metal arc welding under varied welding parameters : Experiments, analyses and optimization

Abstract

Welding of various grades of stainless steel is still a potential area of research. In the present work investigation is carried out through welding of butt joints of i) austenitic to austenitic ii) ferritic to ferritic and iii) austenitic to ferritic stainless steels. MIG welding is used. Parametric studies have been done by planning the experiments suitably, making the butt joints as per plan, conducting visual and X-ray examinations of the welded specimens, tensile testing, hardness measurements at different zones and microstructural studies. The input parameters taken into consideration are current, gas flow rate and nozzle to plate distance. Response parameters in the context of optimization have been: ultimate tensile strength, yield strength and percentage elongation. Thickness of the material welded is 3 mm, width = 50 mm, length of each piece = 60 mm. Inert gas used is Ar+5%CO2. Response surface methodology and Grey-Taguchi method have been applied for process optimization. Optimized conditions for each of the three sets of study have been evaluated. The results of optimization have been validated by confirmatory tests. In the process of doing so, the results of all the tests have been interpreted, discussed and analyzed. Consistency among the results of various tests has been verified. Significance of the input parameters on each of the responses has been identified. Mathematical models have been developed to relate each of the responses with the input parameters. Response surface plots and contour plots are also generated, which help predicting the response(s) at varied levels of any two input parameters, when the third parameter is held constant. The work is, principally, directed to the study of weld quality under varied welding parameters through experiments, analyses and optimization. Based on all these, some useful conclusions are made for each of the three sets of experiments mentioned in the beginning.