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Multi-thickness blanks (MTB) enable the dimensional optimization of steel parts by modulating thickness and mechanical properties. Traditionally, this is done by the addition of reinforcement to the basic part after the drawing of both. With MTBs, we first assemble the two flat blanks to obtain a single blank, which is then drawn without further assembly. MTBs comprise the Tailored Welded Blank (TWB), already widely used in automobiles, and a new category “Patchwork”. The TWB is a butt-welded assembly of two blanks with neither overlap nor superimposition. The patchwork blank is made by either the adhesive bonding or welding of a blank onto the surface of the base blank, at the point to be reinforced. These products enable the increase of performance objectives (impact, rigidity, vibration and fatigue resistance, etc.) whilst permitting weight reduction and thus adding to the potential of high resistance steels. They also enable, in numerous cases, the reduction of overall costs.

The Research Centre of Cockerill Sambre (R.D.C.S.), together with Cockerill Sambre Tailored Blanks (C.S.T.B.) has developed a new technique, Patchwork, for the optimization of parts in the automotive industry. Patchwork means optimized and economical parts made from two or more superposed and spot welded flat blanks deep-drawn together at the same time. The technique avoids the problems of precise cutting of blanks and precise and specific clamping devices. Moreover, the use of spot welding instead of classical laser welding leads to a reduced operating cost. In this paper, we are presenting different applications where this technique has been successfully used. Such a technique has been introduced at an industrial scale on the new Peugeot 206 model. The use of the patchwork technique for the front members leads to a reduced production cost together with a high target for safety.