Forming of tailor-welded blanks
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I.
INTRODUCTION
A tailor-welded blank (TWB) is comprised of two or more sheets that have been welded together in a single plane prior to forming. The sheets can be identical or they can have different thicknesses, mechanical properties, or surface coatings. They can be joined by various welding processes, i.e., laser welding, mash-seam welding, electronbeam welding, or induction welding. The advantages of such a process are numerous. Thirty to 50 pct of the sheet metal purchased by some stamping plants ends up as scrap; scrap which can be used for new blanks with TWB technology, m Alternatively, TWBs can be constructed leaving unused area open, thus minimizing offal directly. Part consolidation, made possible by distributing material thickness and properties, allows for reduced costs and better quality, stiffness, and tolerances. Tailorwelded blanks also provide greater flexibility for component designers. Instead of being forced to work with the same gage, strength, or coating throughout an entire part, different properties can be selected for different locations on the blank. In some cases, for example, differential coating thickness is employed. There have been only a few published results on the formability of TWBs. Azuma et al. [21 studied the behavior of TWBs in three standard forming operations: stretch forming, stretch flangeability, and deep drawability. In stretch forming, the weld bead ductility is the limiting factor when the weld is oriented parallel to the major stretch
F.I. SAUNDERS, formerly Graduate Research Associate, Department of Materials Science and Engineering, The Ohio State University, is with the Metallurgy Department, General Motors Corporation, Warren, MI 48090-9055. R.H. WAGONER, Professor and Chair, is with the Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210-1179. Manuscript submitted March 27, 1995. METALLURGICAL AND MATERIALSTRANSACTIONS A
axis, while the formability of the weaker base material is the limiting factor when the weld is normal to the stretch axis. Stretch flangeability dropped by 25 to 30 pct because of the presence of the weld, while the deep drawability was unaffected. As an extension of this work, Nakagawa et aLt3~ and Iwata et al. tal used the finite element method (FEM) to analyze a similar stretch-flange geometry. Their model accurately predicted the failure modes corresponding to different weld positions. Radlmayr and Szinyu~5j evaluated the formability of TWBs using the Nakazima test (100-mm hemispherical dome stretch) and the uniaxial tensile test. The results of the Nakazima test were very similar to the projection results of Azuma et al. Radlmayr and Szinyur also investigated the influence of welding speed on formability, and they found that increasing the welding speed increased the formability. Tensile tests showed that the presence of the weld increased the strength of the tensile specimen. After wire eroding away the base material, the mechanical properties of the weld bead were measured. The yield streng
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