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AP&T involved in European research project that could result in lighter, stronger vehicle parts
July 2006
Many industries are searching for lighter metal materials. Not least of these is the automotive industry, where lighter components mean lower fuel consumption. At the same time, the requirements in terms of high strength still remain. Demands for metal materials that are lighter but also strong or stronger may sometimes seem irreconcilable. One of the solutions is known as thixoforming, a technology that is already being used on aluminum. AP&T is involved as a partner in an EU project that is now testing the method on steel as well.
Thixoforming is a technique in which the piece to be formed is heated to a temperature just below its melting point. The material then becomes soft without flowing, and is thus very easy to form. Given the right material composition it is also possible to achieve, in comparison with traditional forming techniques, higher strength at the same thickness and weight.
The technique resembles forging in some respects, but offers a number of comparative advantages. In addition to the fact that the finished part is lighter when thixoformed, it also comes substantially closer to its final finish, and the number of production steps is thus reduced. There is very little or no scrap, and the thixoforming process also uses considerably less energy.
Thixo window presents a problem
However, thixoforming is encumbered by one particular problem that is intrinsic to the process and must be solved to achieve a successful result. The forming process must take place within a specific temperature range in order for it to work as intended. If the material is too hot, it cannot be formed. If it is too cold, the desired properties will not be achieved, since the molecular structure of the piece is determined by the temperature at which it is formed. For example, the strength of an individual part can vary dramatically if it is formed at the wrong temperature.
This temperature range is known as the thixo window and imposes special demands on the forming equipment and process. 'The material has to be at the right temperature in the tool. We have to deal with the time factor, and with keeping the material at the right temperature,' says AP&T Technical Manager Bengt Walkin. Thixoforming is currently being used commercially to form aluminum. Aluminum is relatively easy to handle using this process, since its thixo window is roughly 500 - 650 degrees C.
Steel heated to 1400 degrees
To broaden the applicability of the process, it must be possible to use it on other materials as well. In the EU Project 'Development of steel parts forged under semi-solid conditions for the industrial market,' IFUM (Institut für Umformtechnik und Umformmaschinen) at the University of Hannover has studied potential ways of thixoforming steel. AP&T is a partner in the project, with responsibility for the presses and automation process used during forming (read more about this project in separate fact box).The biggest problem that has to be solved in order to thixoform steel has to do with the high temperatures that are required. The thixo window for steel is between 1370 and 1400 degrees C.
Fast servo-control decisive
This also means that the temperature of the material must be maintained reliably. 'For the actual press process, we have been able to use a control system that we normally use for hydroforming, HNC. The most important thing is that the axes are servo-controlled, which results in rapid forming. This is essential to coping with the restrictions imposed by the thixo window,' says Mikael Karlsson, AP&T Project Manager in the EU project.
'Servo control also gives us high precision. The cylinder has to move fast, up to three meters per second, but we must, at the same time, also be able to control the positioning very precisely, given the state of the material. The HNC system delivers positional precision down to hundredths of a millimeter.'
In the European thixoforming project, another partner has been responsible for heating and maintaining the temperature of the material. AP&T's task has been to find a way to enable the piece to move from the heating process down into the tool without losing too much temperature.
The solution is based on traditional AP&T automation combined with a new design with respect to the handling process in immediate proximity to the hot material.
A reality within a few years?
It is not yet entirely certain that steel thixoforming will become commercially feasible. The EU project will be wrapped up in June 2006, at which time many of the results can be published. 'It will presumably become reality within a few years, even if a number of issues are still left to be resolved,' says Bengt Walkin. Participating in the project has been an extremely positive experience for AP&T. 'It has been both informative and fun to work in close cooperation with other companies in Europe, and we have also learned a great deal that we can apply in our regular operations,' says Bengt Walkin.
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