Weld Bead Performance Assessment of P-GMAW Using Acoustic Emission (AE) Signals Through NDT Methods for MS ASTM A 106 B Grade Material

Abstract

Abstract Pulsed Gas Metal Arc Welding (P-GMAW) process is used in many industries to gain high quality, productivity and cost effective products in fabrication of welded joints. The input process parameters will affect the quality, productivity and cost of the welding and are considered to be the most important factors. P-GMAW is an excellent alternative to constant voltage GMAW process for those industries which are looking to boost efficiencies since the process helps to improve quality of welds over varying operator’s skills. The process enables low mean current and low net heat input with stable spray transfer. To produce a very precise control of the arc, P-GMAW applies waveform control logic through a broad wire feed and speed range. In order to understand and control the P-GMAW welding process, it is necessary to determine the input and output relationship parameters. The process is modified spray transfer in which the power source switches between low background current or voltage and a high peak current or voltage between 30 to 400 times per second. Over this period, the peak current pinches off droplets of wire and drive it to the welded joints. By the mean time, background current maintains the arc but produces low heat input that metal transfer cannot occur allowing weld pool to solidify. The process enables low mean current and low net heat input with stable spray transfer. The objective of the present study is to assess the weld bead performance and joint strength by carrying out the destructive testing using AE signals. Experiments have been conducted on MS ASTM A 106 material using 1.2 mm copper coated filler wire based on the Taguchi’s L27 standard orthogonal array. Input parameters considered to carry out the experiments are current, gas flow rate and wire feed rate with a constant speed. The direct response parameters are Ultimate Tensile Strength (UTS, N/mm2), Yield strength (YS, N/mm2) and % of elongation. Indirect response parameters signals are Viz., Acoustic Emission (AE) signals such as welding AERMS, welding AEENERGY, tensile AERMS and tensile AEENERGY are considered to assess the performance of the weld bead joint. From the obtained results, it is clearly observed that a good relationship exists between welding AERMS welding AEENERGY with tensile AERMS and tensile AEENERGY to evaluate the performance of the weld bead joint. The results are validated through carrying out different NDT testing methods on weld bead joint Viz., macro test examination, X–radiography, scanning electron microscope images to analyse external and internal defects in the welded joints. EDX investigation is performed for elemental composition on welded joint in different zones.