Modeling of the heating phenomena in ultrasonic welding of thermoplastic composites with flat energy directors

Abstract

A model for the mechanics (oscillating deformation), heat transfer including viscoelastic heat generation and friction dissipation, and degree of adhesion (intimate contact and healing) is proposed for the initial transient heating phase. 10Numerical resolution was performed using a multi-physical finite element code. The predicted dissipated power evolution exhibits a good correlation with previous experimental measurement of delivered power, and shows that the apparatus has a global efficiency of 13%. The predicted degree of adhesion also confirms the experimental observation that adhesion starts at the edge of the contact area, and progressively extends to the whole contact area. 15The numerical model was further used to investigate the physical mechanisms occurring during the welding process. As suggested in the literature, the first heating mechanism is confirmed to be due to interfacial friction. Bulk viscoelastic dissipation becomes predominant when the interface reaches higher temperatures. The dissipated power is suddenly increased when the whole interface reaches the glass transition temperature.

On avoiding thermal degradation during welding of high-performance thermoplastic composites to thermoset composites

“…6 is consistent with the fact that, during the welding process, heat is generated at a faster rate at the edges of the welding overlap [18]. The fact that the transverse internal edge of the overlap seemed less affected than the rest is attributed to a more effective heat transfer from that edge to the relatively colder adherend outside of the welding area through the unidirectional carbon fibres.…”

“…The combination of thermal damage and the mechanical vibration exerted in the adherends during welding causes the fibre bundles to detach along the longitudinal overlap edges. Furthermore, the higher stresses generated at the welding interface by the higher force and higher amplitude used to achieve the short heating time [18] combined with the thermal exposure are believed to cause the longitudinal cracks observed in Fig. 6 (right).…”

A comparative evaluation between flat and traditional energy directors for ultrasonic welding of CF/PPS thermoplastic composites

“…It must be noted that the power represented in that Figure, shown as a percentage of the total available power (3000 W), is the electrical power consumed by the piezoelectric converter to achieve constant-amplitude welding. As explained in [7], it is believed that only a relatively little fraction of this total power is effectively used for the welding process. However, the different events identified in the power curve can be linked to physical changes occurring in the welding stack, as shown in [2], since all of the other elements affected by the vibration during the welding process (booster, sonotrode, welding jig and anvil) can be considered 'inert' to the vibration relative to the welding stack.…”

A Numerical Analysis of the Temporal and Spatial Temperature Development during the Ultrasonic Spot Welding of Fibre-Reinforced Thermoplastics

“…If solved using these methods, then the model would require a very large number of sub-steps to cover the entire weld duration. This problem has been solved by Levy et al [11][12][13] through the implementation of the time-homogenisation method. The space-time homogenisation has been implemented by Boutin et al [14] to study the heat generation by mechanical work in structures subjected to a cyclic loading for long durations of time, such as in fatigue testing.…”