Temperature Measurements of Weld During Friction Stir Welding Using Ultrasonic Time of Flight

Temperature measurements of the weld during friction stir welding (FSW) have previously been carried out using various methods including infra-red imaging/ thermometers, embedded thermocouples in the parent metal as well as direct contact thermometers. These methods usually only measure the temperature of the surface of the metal or requires the drilling of holes and the addition of foreign material into the weld. Using ultrasonic time of flight (TOF), it is possible to measure the average temperature of the weld as the weld is being made.

Two ultrasonic transducers will be mounted in tandem, facing each other and positioned at an offset behind the FSW tool. The transducers are fixed with respect to the FSW tool and will continuously transmit and receive ultrasound along the tool path as the weld is being made.One transducer acts as a transmitter and the other as a receiver and due to the fact that acoustic velocity changes with temperature, it is possible to measure the average temperature of the material where the sound passes through. Furthermore, we are also implementing a method whereby knowing the ultrasonic time of flight, and using energy balance and finite element analysis, we are will able to determine the temperature gradient of the weld.