Micro thin film sensor embedded in metal structures for in-situ process monitoring during ultrasonic welding

The objective of this research is to develop an effective method, i.e., ultrasonic metal welding (USMW), to-embed micro thin film sensors for metal tooling, and use micro thin film thermocouple study the heat generation during USMW. A complete understanding of the fundamental mechanisms of USMW does not yet exist, and the function of heat generation on weld formation is especially in argument due to the lack of the method to measure the temperature at the welding interface. Continuing on the previous preliminary study [I] which proved that thin film sensors can survive ultrasonic welding process, significant advances were made to improve sensor reliability as well as sensor fabrication effectiveness. These include the development of a new approach for batch production of the sensor units, improvement of the adhesion between metal encapsulating layers for the sensor, as well as the adhesion between the sensing layer and the dielectric layer. Welding experiments are conducted using a series of welding parameter settings with the in-situ data acquisition of temperature 50 mu m away from the welding interface. Attempts are then made to correlate the heat generation to welding parameters. With the mechanical testing of the weld strength, the possibility of using heat generation as a weld strength indicator is explored.