Titanium is a material that offers many excellent properties; it is a practically unlimited resource that is stable and lightweight, but at the same time enormously malleable as well as corrosion and temperature resistant. Nonetheless, this lustrous white-silver metal is still less used than steel, chrome, nickel and aluminum when it comes to manufacturing.
The reason for titanium’s under-usage is that metal forming processes such as deep drawing or hydroforming can only be used in a limited way. “Titanium tends to adhere to the forming tools. This leads to major damage which can cause components to fail in the worst case. This effect is amplified by the extremely high temperatures of up to 800 °C, at which titanium has to be formed“, according to André Albert of the Fraunhofer for Machine Tools and Forming Technology IWU.
Fraunhofer Institute researchers are now giving this multi-purpose metal another chance, having developed a new technology for hydroforming titanium car exhaust systems at elevated temperatures. The new method enables forming to be undertaken in a single process stage. Researchers presented the initial results of the joint project at the EuroBlech trade fair.
Titanium Process Improvements
Previously, a minimum of three stages were required, utilizing intermediate heat treatments that partly required processing at different locations. The scientists have now developed a process, and a custom tool which can survive temperatures of over 800 °C.
“Forming titanium at room temperatures leads to severe cold work hardening of the processed pipe. In order to prevent cracking, the metal requires frequent treatment by means of recrystallization processes. This leads to extremely complex multi-stage forming processes which are not economically viable in large-volume production of exhaust systems. This microstructural change can be avoided at extremely high temperatures“, explains Albert.
The roughly 1.40 x 1.20 meter forming tool is manufactured from high-performance materials like nickel-base alloys which remain stable without oxidizing at temperatures over 800 °C. A specialized coating, only a few micrometers thick, prevents titanium from adhering to the tool, which can lead to component cracking and severe damage to the surface.
“At temperatures from approximately 500 °C, titanium exhibits a strong tendency to combine with oxygen and nitrogen from the surrounding atmosphere. For this reason, it is necessary to work with shielding gases at extremely high temperatures, such as argon, in order to prevent oxidization of the titanium. After extensive testing with various materials, we were able to develop the ideal coating for the special conditions encountered within the various temperature ranges,“ Martin Weber, expert in new tribological coatings at IST explains.
Wide Range of Uses for Titanium
Titanium is exceptionally versatile. Something like 40 percent of the metal’s worldwide production is used in the aerospace industry. Typical applications include window frames, hydraulic lines and jet engine components. Additional usages are in seawater-resistant components for offshore wind farms, pipes and containers for the chemicals industry, bio-compatible implants, pacemakers or surgical instruments as well as consumer items such as bicycle frames and items of piercing jewelry.
In the automotive industry, this multipurpose metal has only been used for high-end vehicles and motor sport applications up until now. Nevertheless it offers a great deal of potential, particularly for mass production of exhaust systems. Because of the lack of cost-effective forming technologies for titanium, currently manifolds, exhaust pipes, catalytic converters and mufflers are primarily manufactured from high-alloy stainless steel.
Titanium would not only be lighter , with a total weight advantage of 40 percent achievable per component, but it is also more available. Titanium belongs to the ten most frequently occurring substances in the earth‘s crust.