Heating and bonding mechanisms in ultrasonic welding of thermoplastics

Abstract

An experimental study of the heating and bonding mechanisms in ultrasonic welding is described. Polystyrene specimens were joined under a variety of welding conditions while the temperatures at the interface and within the interior of these specimens were measured. The power input, amplitude of vibrations, and amount of deformation during welding were measured concurrently. In general, the rate of heating at the interface is greatest at the beginning of the weld cycle, but slows markedly after the interface temperature reaches approximately 250°C. The interface temperature peaks well before the weld is completed. Temperatures within the body increase most rapidly at temperatures near the glass transition temperature. Welded specimens were broken on a special testing apparatus under combined torsional and compressional loads to determine the weld strength. The results show that weld strength is dependent on the amount of energy input and the degree to which material flows out of the interface region. Possible mechanisms for heating and bonding during ultrasonic welding are discussed in light of the observed behavior.

Modeling of ultrasonic processing

“…3 The data showed that increasing the static pressure has no observable effect on the heat generation in the material during UTL, suggesting that the viscoelastic heating is dominating the UTL heat generation. This conclusion is in agreement with the results of Tolunay et al, 4 which showed, for soft polymers, the interface did not have a significant effect on the amount of heat dissipated during ultrasonic welding of unreinforced materials. They observed that in this case the heating occurs over the whole volume.…”

“…This temperature most probably corresponds to the glass transition temperature, since, as T g is approached, the level of viscoelastic energy dissipation as measured by loss modulus increases markedly. As the material continues to heat above T g , the loss modulus drops again, and Tolunay et al 4 observed that the heating rate also generally drops until the temperature remains constant. Based on these results, the UTL process model described here focuses on viscoelastic energy dissipation and reaction exotherm as volumetric heat sources rather than frictional heating at the interfaces.…”

Heat generation in an elastic binder system with embedded discrete energetic particles due to high-frequency, periodic mechanical excitation

“…[1][2][3] The utilization of this phenomenon in composite explosives may lead to the development of novel detection methods, 4 or enhance existing vapor-based trace detection systems by raising the vapor pressures of select high explosives. 5,6 In addition, this excitation could generate stress concentrations and/or hot spots within energetic materials, 7 offering unique pathways for explosives defeat.…”

A low temperature ultrasonic bonding method for PMMA microfluidic chips

“…1b and c. It may cause the whole device unusable. Heating mechanisms of ultrasonic welding were intensively studied in the past decades (Shi and Little 2000;Tolunay et al 1983). During the whole welding process, polymer experiences different states of glassy state, rubbery state and viscous flow state.…”