Formability Of Laser Tailor Welded Blanks With Different Thickness

With the demands of environmental protection and energy conservation, increasing resources and improving environment, TWB (Tailor Weld Blank) as one of green re-manufacturing technologies will be a guiding orientation in industry. TWB is a technology that composed of two or more materials with similar or different thickness, strength and surfaces status welded together to produce a single blank sheet before forming process. The TWB allows designers to reduce the weight and the number of components in a structure without compromising to the final strength, stiffness, and durability of the components. Laser welding of the 20th century developed in the 1960s is a precision welding technology, which has been widely used in many industries. The TWB welded by laser can not only increase the quality and efficiency, but also reduce the cost, so the technology of the TWB is very important in future. The formability and welding performance of the TWB for SAPH440 and DP600 with different thickness (1.8mm and2.2.mm) jointed by laser weld were studied in this paper, and the forming process was simulated by the software of Dynaform.The welded joint by laser welding had narrow welded seam, small heat affected zone, and weld deformation. The welding quality was good. The microstructures of weld were acicular ferrite and plate pearlite. The microstructures of HAZ besides SAPH440 were pearlite and grain ferrite, and the microstructures of HAZ besides DP600 were numbly pearlite and plate ferrite. The hardness of welded joints were different,the hardness of weld was bigger than the base materials.The tensile test,fracture surface scanning test,cupping test were carried out to study the formability of TWB with different thickness jointed by laser weld. The tensile test for both base metals and welds that welds were located in different direction were tested. With the aid of the acquired data, the parameters were provided to describe the mechanical properties of plastic deformation, and analyzing the influence of weld location on formability of the TWB. The research results were shown that the forming process of the TWB was stable, the shape of materials after drawing was not easy to be rebounded, the plastic deformation of the blank was very good, when the weld line was paralleled tensile axis. And when the weld was perpendicular to tensile axial, the deformation of the TWB was uneven, the plastic deformation was poor. It was the best to make the weld line parallel the tensile axis, during the drawing.The SEM of fracture morphology showed that when the weld line was paralleled tensile axial, a lot of tensile isometric cavities and obvious traces were on the fracture surface, the fracture was ductile and cleavage, and when the weld line was perpendicular to tensile axial, a lot of isometric cavities were on the fracture surface, it was typical ductile fracture.The cupping tests were carried out to test the bulging formability of the TWB with different thickness jointed by laser weld, analyzing the influence of different weld location for forming specimens on the bulging formability, further compared with base material, eventually the phenomena of weld movement during the cupping test was discussed. The research results were shown that the TWB was smaller than any base materials, the bulging formability of the TWB was worse than the base materials. The weld seam position has an impact on the bulging formability of the TWB. The bigger proportion of the thin blank to the TWB, the better bulging formability of the TWB, because the deformation of the thin blank for the TWB was large, during the drawing, the weld line moved to the thick blank.The forming process of the TWB was simulated by the software of Dynaform, ignoring types of the welded joints, considering the weld position in model. The research results were shown that the simulation results of the single blank was basically the same as the tests, and the simulation results of the TWB was a slight difference from the real tests.The galvanized sheet SGCC with thickness of 0.7mm was welded by Tungsten Inert Gas(TIG) welding, and the performance of weld seam was tested. The test results suggested that the galvanized sheet SGCC welding quality was good.