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Hydroforming is a process in which metal parts are pressed into shape under hydrostatic pressure. This means that the finished components are exceptionally rigid. "Work-pieces made of lighter materials can therefore offer the same degree of safety as components made of heavier material machined using conventional methods. This is what makes this process so attractive for lightweight construction, " says Hans Braunlich of the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz.

Hydroforming is not an altogether recent development. It is already being used in numerous industrial applications. "A typical example is the production of T-joints, " states the engineer. "In the past, these components were welded; today, hydroforming is increasingly being used to give pipe fittings their correct shape." In this technique, a straight tubular blank is placed in a T-shaped tool. Axial punches are positioned at both ends of the work-piece in order to seal the component. Then a fluid is pumped into the pipe. Internal pressure builds up in the component and shapes the metal. The pipe yields within the tool's pre-formed cavity - in a similar manner to cake mixture which expands to fit the shape of a cake tin.

The axial punches exert a constant force on the pipe until the component is pressed into the same shape as the T-shaped mould.

Hydroforming is not only suitable for producing simple shapes such as T-joints but also for forming complex geometries, including automotive parts such as side rails, transverse links and cross-members. The advantage over conventional processes is that hydroforming cuts out otherwise needed, additional production stages, such as welding.

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