Manual metal arc welding of the thin sheet sidepanel subassemblies of a railway coach shell causes deformation on the exterior surface. Welding creates residual stresses and distortions because of the elastoplastic response of the sheet to the transient, localized thermal expansion and contraction. Various strategies minimize the distortion, but a basic understanding of the mechanism is required. The welding process has been mathematically modelled using a general-purpose finite element code ABAQUS. The transient temperature fields and the associated stress, strain and strain fields have been calculated by a coupled thermomechanical analysis. To improve the exterior appearance of the coach shell, a technique called the magnetic forming process has been proposed. This process is designed to restore the original geometry of the deformed sidepanel sheet. The effectiveness of this process has been studied in detail. The magnetic forming process, simulated to flatten and straighten the thin sheet, is calculated to yield good results.