Manufacturing processes, particularly welding, play a crucial role in inducing imperfections such as residual stresses and distortions in workpieces. This paper investigates welding-induced residual stresses in normal strength steel (NSS), high strength steel (HSS), and hybrid box sections composed of both NSS and HSS plates. Advanced manufacturing simulations are performed using deterministic uncoupled transient thermomechanical analysis with a double ellipsoidal heat source model to determine residual stress distributions in weldments applying different steel grades, geometrical dimensions, and welding parameters (e.g., heat input, welding speed, preheat temperature, etc.). The welding simulation employs 8-node solid elements, with material models adjusted for very high temperatures, extending beyond the liquidus temperature, as per EN 1993-1-2 standards. In addition, probabilistic finite element analyses are conducted to develop a residual stress model for box sections considering manufacturing technology specialities. Parameters of this unified model are identified through Monte Carlo simulations using Latin hypercube sampling and a quadratic response surface method. The study also evaluates the applicability of existing recommendations and standardized residual stress models, contributing to the development of a comprehensive residual stress model that directly incorporates welding and fabrication characteristics.