Heating mechanisms involved in the ultrasonic welding of oriented polypropylene using tie-layers

The conventional ultrasonic welding technique was used to join oriented polypropylene sheets using tie-layer film.;For phase II, the heat conduction equation showed that the bulk of the tie-layer is not affected by the heat flux from the interface while the viscoelastic heating equation significantly overestimated the temperature rise. Phase III heating rates depended on the molecular weight of the tie-layer where vibrational energy was absorbed to a greater extent for increasing molecular weight. However, voids were more prevalent in the bondline with higher molecular weight tie-layer materials and with increasing contact pressures.;The results suggest that molecular weight and pressure are important variables in ultrasonic welding using tie-layers. Inadequacies in the dynamic moduli and strain distribution in the tie-layer are also reported. (Abstract shortened by UMI.).;The process was comprised of four phases: (I) the temperature rapidly increased to the melting point of the tie-layer; (II) the interface region and tie-layer started to melt; (III) the polymer melt exhibited intense heating from the stressing of inhibited chain segments; and (IV) the weld zone cooled and solidified.