C. L. Tsai, T. Mert, S. S. Babu, Ohio State University, Columbus, OH
Welding-induced distortion is a result of structural equilibrium between the shrinkage strains, caused by an integrated effect of heat input, material’s thermal/mechanical properties, joint stiffness, and the structural restraints. The fundamental principal of distortion control is to minimize the shrinkage strains by avoiding temperature rise in the base metal beyond its softening temperature. With recent advancements in low-heat welding processes and procedures, it is feasible to reduce the amount of heat flow into the base metal. This would leave the primary distortion cause to weld shrinkage.
In this paper, a conceptual welding procedure using two different welding processes, for filling the joint and strain relaxation of the weld, respectively, is investigated by an integrated experimental and modeling approach. The joint type studied is a double-fillet welded Tee-joint. The low-heat welding process is used for the filling passes and a process that results in a narrow, but deep-penetration weld is subsequently used for strain relaxation. The research methodology takes a two-step approach. The first step is to characterize the strain relaxation due to spring back effect after cutting the weld along its centerline. Heat diffusion into the base metal or in-situ heat removal from the base metal is controlled to minimize base metal softening. This quantifies the amount of strain relaxation from weld without remelting and establishes a baseline for the tandem procedure design. The tandem welding procedure is simulated using the FE modeling technique. Two moving heat source models, spread and focused, are placed at a distance apart along the weld centerline. The optimum process parameters and procedure factors are determined and used in the experimental verification of the tandem procedure.
Summary: A conceptual welding procedure using tandem welding processes is studied to reduce welding distortion. This procedure is simulated using the FE modeling technique and demonstrated by experimental tests. This paper presents the preliminary results derived from this study. Several observations are summarized to demonstrate the fesibility of this new distortion control technique.
