Study on Heating Process of Ultrasonic Welding for Thermoplastics

Heating mechanisms of ultrasonic welding for thermoplastics were studied via numerical simulation and experiment. Relationship between dynamic modulus and static relaxation modulus of thermoplastics was theoretically analyzed. Segment time-temperature equivalency equation for different temperature ranges and a method for directly separating viscoelastic heat from strain energy were used in the simulation. Temperature measurement tests with poly(methyl methacrylate) specimens were carried out to verify the simulation results. Results of simulation and experiment reveal that interfacial friction rather than viscoelastic heat initially start the whole welding process. Viscoelastic heating becomes dominant when temperature reaches T-g (glass transition temperature) of the material. And viscoelastic heat provides most required heat during welding.