The mathematical description of the relationship between the process torque MP and the welding temperature TS allows for the determination or control of the welding temperature using the process torque. Employing this relationship, expensive and sensitive sensors used to measure the welding temperature are not needed and weld seam defects caused by inadequate welding temperatures can be avoided.
The properties of friction stir welds are mainly determined by the welding temperature, which depends both on the process parameters and on the thermal conductivity of the joining partners. A constant welding temperature and consequently a constant weld quality is difficult to achieve on components with a complex geometry. This is due to heat accumulation in zones of low thermal conductivity. This leads to a varying welding temperature, even though constant process parameters are employed.
One solution to ensure a constant weld quality is the use of a control system that maintains a constant welding temperature by adjusting the process parameters. The major challenge in temperature-controlled FSW is the measurement of the welding temperature. This is tedious, since sensitive measuring equipment is required. In preliminary investigations at iwb, a relationship between the process torque and the welding temperature could be observed.
The aim of the research project is to describe the relationship between MP and TS mathematically, and to employ it to determine and control the welding temperature. This simplifies the application of temperature-controlled FSW, since it eliminates the need for additional measuring equipment. The torque-based temperature control system is implemented ona real-time system, which is integrated into an FSW welding machine and validated experimentally.
Results and benefits
The torque-based temperature control maintains a constant welding temperature and therefore ensures constant weld properties. The complex parameterization of the welding process is simplified because the welding temperature is valid for different welding tasks of the same material. The use of the torque-based temperature control system will increase the competitiveness of companies producing small batches of their products and manufacturers of FSW systems in particular.
The IGF project 19516 N of the German Welding Society e.V. is funded by the AiF within the framework of the program for the promotion of industrial joint research (IGF) and the Federal Ministry for Economic Affairs and Energy on the basis of a decision by the German Bundestag.