**1.1. Background: identification and significance of the innovation**

#### *1.1.1. General information*

Sheet hydroforming is a process that was primarily developed for the needs of the aircraft industry. In sheet hydroforming, formed tooling blocks are placed in the machine's loading tray and pre-cut sheet metal blanks are placed over the blocks. Throw pads are then placed over the blanks to cushion sharp edges. The tray is then fed into the pressing chamber as a thick elastic blanket is unrolled over the tool and sheet metal. The pressure chamber is a thickwalled cylinder wound with high tensile strength metal wire that is engineered to handle the extremely high forming pressures. Once the part is loaded, immensely high fluid backfill pressure is applied to the membrane. The elastic blanket diaphragm expands and flows downward, over and around the metal blank. The sheet metal is then pressed to follow the contour of the die block, exerting an even, positive pressure at all contact points. As a result, the metal blank is literally wrapped to the exact shape of the die block. The press is then depressurized for unloading the tray. This process is ideal for prototyping and low volume production in aluminum, titanium, stainless steel, and other aerospace alloys such as matrix metal panels in low volumes [1, 2].
