Combined effects of temperature field and ultrasonic vibration on bubble motion in laser joining of plastic to metal

A previous study has found that applying ultrasonic vibration in laser joining of Polyethylene terephthalate (PET) plastic to Ti metal can greatly reduce bubbles formed in the joint. In this study, the theoretical basis on the combined effects of pressure and temperature fields on the trajectory of bubbles was analyzed using finite element simulation. A non-uniform temperature field influences the evaporation momentum pressure acting on a bubble, causing it to travel from a low to a high temperature region. A properly designed ultrasonic transducer tool, however, can create an unbalanced pressure field around a bubble. Under the combined effects of these elements, bubbles in the molten pool can be made to escape from the joint. The predicted results and obtained experimental outcomes matched well, which were also supported by the evidence of captured high-speed camera images.