Assessment of Weld Bead Performance for Pulsed Gas Metal Arc Welding (P-GMAW) Using Acoustic Emission (AE) and Machine Vision (MV) Signals Through NDT Methods for SS 304 Material

To gain high cost effective products along with quality and productivity, Pulsed Gas Metal Arc Welding (P-GMAW) process is used in many highly developed industries for fabrication of welded joints. The input parameters are the most important factors which affects the productivity, quality and cost effective for the welding process.  The processes enable low net heat input, stable spray transfer and with low mean current. To enhance efficiencies with constant voltage GMAW process, P-GMAW is an outstanding substitute for those industries which are looking to improve quality of welds since the process helps over varying operator’s skills. It is essential to determine the input/output relationship parameters, in order to recognize and control the P-GMAW welding process. P-GMAW applies waveform control logic to fabricate a very precise control of the arc during speed range and a broad wire feed. The power source switches between low background current and a high peak current between 30 to 400 times per second to obtain modified spray transfer process. The peak current pinches off wire droplets and drive it to the welded joints over this period. The process produces low heat input allowing weld pool to solidify, that metal transfer cannot occur but by the mean time, background current maintains the arc with stable spray transfer. Trials have been conducted on SS 304 material using copper coated filler wire of size 1.4 mm based on the Taguchi’s L₂₇ standard orthogonal array. Current, Gas Flow Rate (GFR) and Wire Feed Rate (WFR) with a constant speed are the input parameters considered to carry out trials. The output parameters are Yield strength (YS, N/mm²), percentage of elongation and Ultimate Tensile Strength (UTS, N/mm²). Indirect response parameters are Viz., AE signals such as welding AE_RMS, welding AE_ENERGY, tensile AE_RMS and tensile AE_ENERGY along with MV signals like area and height of the weld bead are considered to assess the performance of the weld bead joint. It is clearly observed from the obtained results that an excellent relationship exists between welding AE_RMS welding AE_ENERGY with tensile AE_RMS and tensile AE_ENERGY along with MV signals which were taken at the time of tensile test to evaluate the performance of the weld bead joint. Verification of the results are carried out through performing different NDT testing methods on weld bead joint Viz., X – radiography, Scanning Electron Microscope (SEM) images to analyse external defects in the welded joints. On different zones of welded joint, Energy dispersive analysis (EDX) examination is carried out for elemental composition.