Ultrasonic Welding. Simulation of the Flow at the Interface

The recent development of thermoplastic matrix composite materials was followed by new assembling process. The present work focuses on ultrasonic welding of structural composite aeronautical part. In this process, triangular bulges (energy directors) are molded on the border of one of the plane to be welded. The process then consists in applying an ultrasonic (20 KHz) sinusoidal compression stress between the two plates. The strain concentrates in the energy directors that melt because of the viscous dissipation. The triangles then progressively flow on the whole interface and perform welding. In order to study the influence of the process parameters on the quality of the welding, we propose a modeling and a simulation of the process. We focus on the flow of polymer at the welding interface. The modeling consists in two mechanical problems and one thermal problem. A multiphysic simulation code was developed for solving theses three problems. The evolution of the interface is simulated using a level-set in an eulerian framework. The first 2D simulations show that voids are trapped at the interface. This is confirmed with tests. The numerical tool is then used to investigate the influence of the process parameter on the quality of the adhesion. Dynamic welding, where the tool is advancing, is an extension of the process that limits voids at the interface. The simulation of the induced 3D flow is under investigation. It should allow to explain the better quality of the welding.