Lightening the load for car makers
EU-funded researchers have developed and tested an innovative new method for producing tailor-made steel parts of variable thickness and shape. This could hugely benefit car manufacturers interested in incorporating flexible lightweight components in future designs - reducing costs and boosting their competitiveness.
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Circular steel tubes are used extensively in car components such as the chassis and exhaust pipes. Hydroforming technology is an efficient means of altering the shape of these tubes through the application of water pressure, allowing for more complex shapes to be created without the need to weld parts together.
The EU-funded STT project successfully developed an efficient manufacturing process based on a known technology called flowforming, which harnesses the full potential of hydroforming. Project partners were able to deliver a tailored tube with variable thickness, before hydroforming it to achieve final specifications.
The end result is a one-piece component with a high strength-to-weight ratio, says STT project coordinator Amaia Arroyo Llanos from Tecnalia, an applied research and technology organisation in Spain. The technique enables the automotive industry to achieve weight reduction through more efficient section design, improved structural strength and stiffness and lower tooling costs as a result of fewer parts.
Arroyo believes that there will be huge commercial opportunities in the expected roll-out of electric vehicles in the very near future. The success of electric cars will to some extent be reliant on lightweight parts that enable vehicles to be superefficient. Another sector that that could take advantage of STTs technology is aeronautics, which already makes use of hydroforming to produce certain components.
Making the process viable
Despite its advantages, however, hydroforming is a relatively new technology that requires scaling up in order to achieve necessary processing efficiencies. It also faces stiff competition from the traditional stamping industry, which forms shapes using a stamping press. This sector has plenty of production capacity.
In fact, recent price pressures associated with excess stamping capacity have caused a slight shift in the industry, notes Arroyo. A number of high-volume hydroformed parts have reverted to stamping, resulting in a lost market for both hydroformers and tube manufacturers.
Therefore, in order to succeed in this competitive environment, the hydroforming sector needs to find ways of making stronger, lighter and less expensive products in the most efficient way possible. This was the overriding objective of the STT project, which was funded by the European Commissions Research Fund for Coal and Steel.
The projects flowforming and hydroforming processes were evaluated in laboratory scale tests on different thicknesses and steel grades. The influence of different thickness reduction was analysed and variations in mechanical properties, hardness, microstructure and formability measured. From this, two industrial prototypes were redesigned and constructed to produce tailored exhaust pipes and twist beam prototypes.
The prototypes demonstrators showed good dimensional stability and improved mechanical properties in terms of hardness, resistance and fatigue strength, says Arroyo. Concerning the functionality, both tailored demonstrators passed the validation tests performed.
The STT project will therefore also benefit metal tube suppliers to the automotive sector, as well as flowforming processing machine manufacturers.
Moving towards industrialisation
Moving forward, Arroyo notes that further investment and research will be needed to fully scale up and industrialise the process pioneered by the STT project. There are still issues to be ironed out, such as slow cycle time, expensive equipment and the excessive material hardening.
It will be necessary to involve the entire value chain, including pipe manufacturers, in order to take this step towards commercialisation, says Arroyo.Nonetheless, the STT project shows that this can be done.
The complementary nature of the projects consortium meant that we were able to overcome most manufacturing challenges that came up, Arroyo notes. Project partners covered the complete process, from tube makers and flowforming manufacturers through to final customers and technology centres.