Stretch forming is widespread in the aerospace industry. It allows the manufacture of large parts, most often made of aluminum, with lower tooling costs than those of the drawing tools, as only a single run is required to form the part, on a single die.
The sheet to be formed is stretched around a tool through a traction force (thanks to gripper jaws) applied on the sheet. This force induces a traction stress in excess of the yield point of the material.
Two processes can then be used, the draping and the wrapping:
- Stretch drape forming process: the sheet to be formed is first draped around the tool and then stretched
- Stretch wrap forming process: the sheet to be formed is first stretched and then wrapped around the tool
A metal sheet can be stretched in 2 directions according to the direction of rolling:
- Transversal direction (the jaws clamp the lenght sides on the sheet) with FET Presses
- Longitudinal direction (the jaws clamp the width sides of the sheet) with FEL Presses
Transversal mode is suitable for deep single or double curve parts (leading edges, saddles). It is a more versatile process
Longitudinal mode offers the possibility of very long parts and is generally limited to shallow shapes