Investigations on autogeneous joining of thin stainless steel sheets by pulsed micro plasma trnsferred Arc

Abstract

There are wide varieties of applications of thin sheets (thickness < 2 mm) in day-to-day life. Some of the applications of thin sheets are: air plane fuselages skin (2 mm), automobile body panels (1 mm), duct works (0.45 to 2 mm), sheet bellows (0.15 mm) etc. Joining of thin sheets is very challenging due difficulty in maintaining the localized melting and subsequent solidification. This is compounded while joining thin sheets of stainless steel due to its poor weldability. This thesis is focused on autogeneous joining of thin (0.4mm thickness) sheets of AISI 316L austenitic stainless steel using pulsed micro plasma transferred arc process. Effects of pulse-on time, pulse-off time, peak current and torch travel speed were investigated to determine their optimum levels for joint tensile strength and its microstructure. To evaluate the effects of the input variable parameters on the joint strength, analysis of variance (ANOVA) with a confidence interval of 95% was done. Based on ANOVA results, contribution of each process parameter and their interaction on the joint strength was evaluated. It also provides an indication of which process parameters are statistically significant.It was found that 50% duty cycle, 10% pulse frequency, 3.5 A peak current and torch travel speed 250 mm/min yielded maximum joint strength 553 MPa. The fusion zone was found to have finer grain size. Absence of heat affected zone was confirmed by very small variation in Vickers microhardness values across the fusion zone. This study establishes capability of pulse micro plasma transferred arc process for joining thin sheets of stainless steel without any filler material and producing very good quality joint using much less power as compared to conventional fusion joining processes.