Hydroforming of drawn parts
Hydroforming is ideal for producing deep-drawn parts with undercuts. This is a process in which the sheet metal is formed against a drawing die by a pressurized fluid.
Cup-shaped deep-drawn parts are brought into a tub shape by forming with fluid. In the case of small series, the deep-drawn goods are filled manually. In order to enable the formed deep-drawn part to be removed from the mold, the mold half must be divided into two.
To generate an internal pressure pi, the deep-drawn material must be filled with fluid ④. The seal holder ③ seals the fluid from the atmosphere. At the same time, the die holder ⑨ presses on the two drawing dies mold halves ⑥. Now the punch ① penetrates the fluid ④, causing the internal pressure to increase until the metal is in contact with the forming dies ⑥. These must be at least divided into two parts to ensure that the undercut can be removed from the mold.
If a polymer gasket ⑦ is used for sealing on the flange , material can flow from the flange into the cavity during forming, making the achievable bottom radii smaller. However, if a ring-prong seal ⑧ is used, the flow of sheet metal is hindered and larger base radii must be taken into account.
In order to be able to carry out this procedure on a single-acting press, a drawing cusion must be positioned between the IHU tool and the press.
The maximum internal pressure pi must not lead to a constriction of the deep-drawn part wall. To estimate the permissible internal pressure, the membrane equation can be used as a first approximation.66
| Maximum internal pressure | pi max | = | MPa |
| Sheet thickness | s0 | = | mm | |||
| Tensile strength | Rm | = | MPa | |||
| Punch diameter | d0 | = | mm |