EXPERIMENTAL AND NUMERICAL INVESTIGATIONS ON FORMABILITY OF TAILOR WELDED BLANKS PREPARED BY FRICTION STIR WELDING PROCESS

Abstract

With the advent in technology, the automotive parts makers are particularly interested in the utilization of new manufacturing concepts and modern materials. The phrase "tailor welded blank (TWB)" refers to a blank in which two or more sheets of material are welded together to form a single blank before the forming process. TWBs have considerable benefits in terms of lowering manufacturing costs, reducing vehicle weight, and enhancing part performance. Experimental and numerical investigations on the formability of longitudinally buttwelded tailor welded blank of the same thickness prepared by friction stir welding is presented in the thesis. The friction stir welding technique involves a solid-state stirring mechanism to butt weld the two blanks of aluminium alloy AA5083 and AA6082 both in annealed state. This study employs a Taguchi approach to systematically explore and optimize critical FSW parameters such as tool rotational speed and traverse speed, while keeping axial force as constant. The influence of each parameter on weld quality metrics, such as tensile properties (strength and ductility), hardness distribution, and defect formation, is assessed using an appropriate orthogonal array (L9) and signal-to-noise (S/N) ratio analysis. The Taguchi approach identifies the most significant parameters and their optimal levels with fewer experimental trials, boosting joint efficiency, increasing material flow in the stir zone, and ensuring a defect-free weld. This optimization framework offers a reliable and cost-effective way for creating different FSW joints between AA5083 and AA6082 alloys. In order to study the effect of welded region on formability, experiments are performed on tailor welded blanks with and without the annealing operation. The tensile properties of the parent sheets, welded blanks and welded region are determined by performing standard uniaxial tension tests. The formability of tailor-welded blanks was investigated by performing limiting dome height (LDH) tests vii and measuring major and minor strains along and across the weld line in deformed samples. The elastic properties, true stress-true strain and anisotropic data sets are used in the material model for the prediction of failure strains to develop forming limit plots. The predicted results from finite element analysis are validated with the experimental results obtained from limiting dome height test and are found to correlate well with experimental data. The annealing is observed to enhance the formability of the FSTWB by almost 13% in plane strain and equibiaxial stretch conditions.