In order to combine those demands, the parts are subjected to a single over- pressure to deform the hollow parts. This deformation leads to a specific stress distribution which can be used to increase the strength of the components without using additional material. For the so-called Autofrettage process, engineers at the Saarland University calculate how the deformed parts behave along the complete manufacturing process chain.
Autofrettage is the French word for self-shrinking. It describes a process where materials are subjected to such a high pressure, that they will deform permanently. "Using an oil-based fluid, an internal pressure of several thousand bars is generated inside the components. This leads to a permanent deformation and induces stresses." says Dirk Bähre, Professor for Production Engineering at the Saarland University. The materials are getting stronger and less vulnerable for cracks. But at the same time the further processing becomes more difficult.
"When single layers of these stress-loaded materials are removed or holes are machined to produce bores, the residual stress distribution is significantly disturbed and may lead to deformations" says the engineer from Saarbrücken. Therefore, he and his staff develop models to predict how the components will deform and where additional material may be saved. "The simulation helps to better coordinate the single manufacturing steps", says Bähre. This would lead to shorter manufacturing times and would also help to save costs.
The engineers from Saarbrücken work together with the company Maximator from Zorge (Harz), a manufacturer of testing and high pressure equipment. They apply the Autofrettage process in different industrial areas. "This leading edge technology is not only interesting for the automobile industry, but also for all large-scale hydraulic machines, e.g. used in refineries and the chemical industry" says Bähre. With his research team he develops design and manufacturing recommendations for different applications. In shared industrial projects he can help SME's without own research departments to introduce the Autofrettage process in their production portfolio.