Parametric Optimisation of Spot Welding of 17-4 Ph Stainless Steels Using the Analytic Hierarchy Process

Resistance spot welding is traditionally employed for joining thin sheet metals. However, flawless resistance spot welding of steels with large amount of alloying elements is a challenge to the welding engineers and scientists. In this work, resistance spot welding is done on 17-4 precipitation hardened stainless steel sheets that are widely applied in aerospace industries. Effect of variation of set weld current and welding time on the weldment is investigated. First, welding time is varied keeping weld current constant, and then, under a constant welding time, weld current is varied. Weld nugget diameter and its form are observed macroscopically, and tensile shear load tests are done to determine the spot strength. Metallographic observation is made to compare the heat affected zone and the weld zone. Details of the experimental conditions and procedure are presented in this paper. The Analytical Hierarchy Process (AHP) is then applied to optimize the process parameters within the experimental domain. The optimal condition to have a quality weld is found at 5 cycles of welding time and 8 kA of set weld current under a load of 4 kN.