Technology forms titanium car exhausts at high temperatures

Titanium could become more widely used in automotive manufacturing thanks to a new forming technique that overcomes some of the metal’s problems.

Researchers from Germany have found a way to prevent the strong, lightweight metal from sticking to forming tools at high temperatures, meaning it can be formed without the lengthy manufacturing processes it requires at room temperature.

The technique, which has been tested by making hydroformed car exhausts, could make titanium manufacturing economically viable outside the high-end automotive sector and reduce the weight of components such as exhaust pipes, catalytic converters and mufflers by around 40 per cent.

‘With this work we want to show that an apparently expensive warm-forming process could be cheaper at last, if you look at the whole process chain,’ researcher Benedikt Domes from the Fraunhofer Institute for Machine Tools and Forming Technology (IWU) told The Engineer by email.

It has traditionally been very difficult to form titanium with processes such as deep drawing (where the metal is stamped into shape) or hydroforming (where high-pressure water is used to form metal around a tool) because it tends to stick to the forming tools, especially at high temperatures.

But forming at room temperature deforms the structure of the material in a process known as work hardening and it has to undergo expensive and time-consuming multi-stage recrystallising in order to prevent it from cracking.

To counter this, the Fraunhofer researchers have created a tool with a special coating that can be used at 800°C without the metal sticking to it.

At this temperature range the titanium alloy has the right formability with an acceptable wall thickness at the process end, said Domes.

‘The most important fact was the material selection for this tool. For the active components we need a stable and hard alloy at elevated temperatures — so we chose a nickel-based alloy.

‘For the isolation plates we need a material with a very low thermal conductivity but with a very high fracture toughness. And for the cooling plates nearly the opposite — now we need a material with a very high thermal conductivity. For both we chose a powder metallurgical steel.’

The researchers are now looking to work with manufacturers to develop the process and help reduce their costs.