This paper reveals the influences of pulsed current parameters namely peak current, back current, pulse and pulse width on the ultimate tensile strength of Micro Plasma Arc Welded Inconel 625 sheets. Mathematical model is developed to predict ultimate tensile strength of pulsed current micro plasma arc welded Inconel 625 sheets. Four factors, five level, central composite rotatable design matrix is used to optimize the number of experiments. The mathematical model has been developed by using Response Surface Method. The adequacy of the developed model is checked by using Analysis of Variance technique. By using the developed mathematical model, ultimate tensile strength of the weld joints are predicted with 99% confidence level. Validation experiments are conducted to validate the predicted values of the developed mathematical model. From the contour plots, it is understood that ultimate tensile strength is more sensitive to peak current and pulse. Also it is found that peak current is most dominant parameter out of all the selected parameters. The developed mathematical model has been optimized using Response Surface Method to maximize the ultimate tensile strength. The weld joints fabricated using peak current of 7 Amps, back current of 4 Amps , pulse of 40 pulses/sec and pulse with of 50% yielded superior ultimate tensile strength of 833 MPa compared to the other joints.

Micro Plasma Arc Welding (MPAW) is one of the important arc welding process commonly used in sheet metal industry for manufacturing metal bellows, metal diaphragms etc. The present work discusses about the weld quality characteristics of various austenitic stainless steels namely AISI 304L, AISI 316L, AISI 316Ti, AISI 321 which are commonly used for manufacturing of metal bellows. Square butt joint is used in the welding and no filler wire is used. Welding is carried out at fixed values of input parameters and same thickness of 0.25mm for all the steels. Peak current, background current, pulse rate and pulse width are considered as the main welding process parameters of MPAW process, where as weld bead geometry, microstructure, grain size, hardness and tensile properties are considered as weld quality  characteristics. Results reveal that out of all the materials considered in the study AISI 304L attains better weld quality characteristics for same welding conditions.Keywords: Pulsed current micro plasma arc welding, microstructure, grain size, hardness, tensile properties.