The concept of Tailor Welded Blanks is well known in the automotive industry, but it is new for the aerospace industry. Main reasons for the delayed introduction of the concept are the different materials, forming processes and joining methods. Nevertheless, the concept could be very beneficial for the branche. TWB concept is based on reversing the sequence of forming and joining: for the TWB concept, two or more sheets are welded together first (to create the TWB), and than formed into a part. This offers advantages with respect to weight, costs, and lead time.
For the aircraft industry, Tailor Made Blanks is a better word, since the metal sheets (aluminum alloys) are joined using adhesive bonding, friction stir welding or the TMB are (chemically) machined from thick sheets. The high potential of the concept is based on the combination of these TMB and the forming processes used in the Aircraft Industry. Universal processes like rubber forming and air bending are ideal for forming of TMB, because the different material/thickness combinations of TMB do not require adjustment of the tooling.
Research performed at the faculty of Aerospace Engineering (TU Delft) has proven the feasibility of this concept for the industry. The TMB have been tested to explore the forming limits, the spring back, and models have been made to predict the behavior of the TMB during forming processes. Due to the transition lines (weld lines or thickness steps), the formability of a TMB is usually less than of the parent materials, in particular when the major strain is perpendicular to the transition line. Therefore, the orientation of the transition line with respect to the direction of major strain is important and should be carefully designed. For some parts a “separation” of strong and stiff elements or features within a part could further decrease the weight which is very important for aircraft.
In addition to the scientific research, a demonstrator to investigate the manufacturability of the TMB in an industrial setting showed that a suitable product (a wing rib – see figure) can be made having lower costs (-50%), shorter lead time (-25%), and a lower weight (-15%), when compared to the current manufacturing method: machining of a thick plate.
Wing rib made of TMB – courtesy Stork Fokker Aerospace
