Wire arc additive manufacturing (WAAM) is one of the metal additive manufacturing methods in which rapid fabrication is possible for components of big size. A significant amount of heat energy is transferred to the workpiece during this process, with a defined idle period so that the workpiece cools down between each layer of deposition. This variable cooling rate technique keeps the workpiece from collapsing and crack growth by maintaining a proper inter-pass temperature. The main challenge is to choose an inter-pass ambient cooling time to mitigate the residual stresses and distortions induced in the workpiece. A numerical model is developed to study the variation of residual stress with respect to change in the cooling time of WAAM process. The material’s thermal and mechanical behaviour was instigated using finite element analysis, by introducing DFLUX SUBROUTINE within ABAQUS 6.20 SOFTWARE. The simulation results were analyzed and the optimum inter-pass cooling time obtained was 800 sec.