Tailor welded blanks (TWB) afford better utilization of sheet steel for automotive and other applications. However, forming behaviour can be complicated because of the interactions between the different sheet steels comprising the TWB and the welding processes used.At Dofasco we have studied a matrix of different steel types, sheet thicknesses, and welding processes (i.e. mash seam, laser and electron beam) in order to gain an understanding of forming behaviour of tailor welded blanks. Simulative forming tests such as hole expansion, stretch bend, stretch dome and tensile tests were used. Finite element simulations using the FTICASE code were used to determine mechanisms for part failures.In addition, weld “service” characteristics such as corrosion performance and fatigue life were evaluated. Microscopic examinations included microhardness, metallography, and tests for weld porosity and zinc entrapment.Overall, the laboratory results showed that the formability is reduced as the ratio of blank thicknesses comprising the tailor welded blanks increases. Finite element simulations using the FTICASE code agreed with the laboratory results.The paper will discuss test techniques used to obtain the results and key forming issues.