Shape up

A process for heat-forming aluminium alloys could help meet the growing demand from the automotive industry for lightweight materials.

A process for heat-forming aluminium alloys could help meet the growing demand from the automotive industry for lightweight materials.

Researchers at Imperial College London, in a project supported by Aston Martin and Lotus Engineering, will investigate a process called solution heat treatment, forming and cold-die quenching (HFQ).

It will be used for shaping components such as bonnets and side wing panels out of sheet aluminium alloys in a single operation.

Imperial’s Prof Jianguo Lin said: ‘Lightweight automotive parts are very important for energy and reducing emissions, so many components are made from aluminium alloys. For example, Jaguar doors were previously formed in one piece from mild steel because it is more ductile and has higher formability, which means we can have larger deformation without failure.

‘But then the company changed to aluminium alloy, which is difficult because the formability is very low. So the panel had to be redesigned so it could be made with a number of fibre components that are welded and joined together to form one piece. That would be much lighter, but it is very expensive.’

Traditional methods of shaping aluminium alloy components — cold forming (carried out at room temperature) and hot stamping — are said to have problems that the HFQ process would overcome.

Cold forming, for example, causes low ductility and high springback (the metal returns to its original shape after undergoing stress). And hot stamping destroys the desirable microstructure of the material, which may distort the final formed panels.

‘Aston Martin gave us a sample aluminium alloy component design and they have proved that it is not possible to form the alloy using traditional technology. We are trying to test it out using HFQ technology to see whether we can form it or not,’ said Lin.

In Lin’s HFQ process, the material is put in a furnace where it is solution heat-treated before being moved to the press and formed, within a second or even less, using a cold die.

‘We hold the material within the cold die for about five to six seconds to let the temperature of the work piece drop very quickly from about 525ºC to around 100ºC. That means the whole process takes less than 30 seconds,’ said Lin.

He said forming the material at high temperature makes it possible to achieve higher levels of ductility, which means more complex components can be formed in a single procedure. ‘The ductility, compared with current cold forming processes, can be increased about six times,’ he said.

Also, springback is minimised because stress relaxation takes place when the material is held in the die.

The timescale of the process is significant. At 30 seconds it is much faster than superplastic forming, an existing technique used to shape sheet aluminium alloys, in which the material is deformed beyond its normal breaking point.

Lin said this expensive technique, which requires at least an hour to form a component, is suitable for aerospace applications because only a few parts need to be formed. However, it is not suitable for cars where large-scale production is required.

Another of the project’s partners uses superplastic forming to manufacture aluminium alloy components for aerospace firms but hopes to exploit Imperial’s research to expand into the automotive sector.

‘For superplastic forming, you heat it up to 500ºC or so and then you have to use high gas pressure to deform the material. You have to deform the material very slowly otherwise you cannot observe the superplastic behaviour of the material,’ said Lin.

‘Having formed the components, the material has to cool down to room temperature within the furnace, when it is removed. Normally one production cycle takes over an hour.’

HFQ is based on a process Lin developed for forming boron steel components as part of a project with a Japanese company that produced safety-critical components for Toyota.

Also supporting this project are Wagon Automotive, Innoval Technology and the Confederation of British Metalforming.

Anh Nguyen