Forschung für den Mittelstand - Die IGF-Projektdatenbank

Methode zur Umsetzung von Rührreibschweißprozessen auf konventionellen Fräsmaschinen mittels eines empirischen Ansatzes

The empirical methodology proposed in this project will assure the transfer of nominal FSW processing parameters developed in optimal conditions to a parameter window that can be implemented on any milling machine. This goal will be accomplished by (a) choosing the milling machine whereon the process will be implemented, (b) characterizing only its FSW process relevant static, dynamic and thermal features, (c) robustifying the processing conditions and (d) using the measurement data to convert the nominal parameter window into a capable FSW activity on the milling machine. The same strategy has been used in the past for other technologies. The threshold for the introduction of high speed milling (HSM) in the 1990’ was also lowered by using standard CNC machines, instead of using expensive and highly dynamic new machines, only modifying them by adding a high speed spindle. This “intermediate but cost effective solution” helped the access to and wider implementation of the HSM technology.

Implementing the FSW process on milling machines should enable small and medium-sized companies to increase the machine efficiency through diversification. FSW can also be considered an important technology for “greener” manufacturing because the process does not emit any harmful waste or radiation, it is also energy efficient and supports lightweight aluminum or hybrid design for transportation means etc.

The project consortium is composed of 3 research partners (CEWAC, ISF and WZL). CEWAC and ISF have a lot of expertise in the field of materials and welding in general, and FSW in particular. In the field of FSW both partners are complementary because they work on different TRL’s so that the research and industrial applications are of a different nature, they also have complementary (auxiliary) equipment and different industrial stakeholders. WZL is renowned for its knowledge of machine building and yearlong tradition in research on current and future machine technologies.

Ergebniszusammenfassung:

Within the framework of the Mill-FSW research project, key machine parameters influencing the friction stir welding process could be identified and quantified depending on machine and machine build type. Furthermore, strategies for the extension of the machine spectrum usable for friction stir welding were shown.

- The basic suitability of different types of milling machines for friction stir welding could be shown.

- The dynamic properties of the tested machines show no influence on the formation of the joining zone, even with excitation at natural frequencies, due to the damping properties of the plasticized material of the joining zone.

- No critical vibration behaviour could be proven for any examined machine tools during friction stir welding.

- The static machine properties, especially in the axial direction, have a significant influence on the formation of the weld seam.

- The influence of the axial stiffness can be compensated by compensation of the plunge depth in case of known compliance.

- The temperature flow into the machine tool can be reduced by forced cold air flow cooling until it is not critical for the spindle- and bearing-systems.

- The maximum welding speed can be increased up to 7 m/min by electrically assisted friction stir welding.

- The axial force acting during the process can be reduced by up to 50% by conductive support of the process.

The proposed methodology and lessons learned during the project severely reduce the economical hurdles preventing SMEs from adding FSW capabilities into their processing portfolio. Eliminating the need for dedicated and expensive (>500k €) friction stir welding equipment offers the option to conveniently access a reliable joining technology. At the same time friction stir welding on milling machines allows for the combination of both processes widening the manufacturing options as well as reducing non-productive times and utilizing full machining capacity.