An efficient numerical model for the evaluation of compression flow of high-viscosity adhesives

In bonding processes, the main influence for the resulting adhesive distribution after pressing is the adhesive used on the surfaces to be bonded, the adhesive's initial distribution pattern and the pressing process itself. Therein, a particular issue is the creation, and transport, of air bubbles during manufacturing that strongly influences the joint's strength. Numerical simulation of the flow in these processes is most commonly based on Computational Fluid Dynamics (CFD). In the general 3D case, these simulations are very complex, time-consuming and are therefore rarely performed. Particular challenges stem from the usually thin layer of adhesive, which in turn requires extremely fine meshes, thus increasing the already high modelling cost. From another scientific discipline, the theory of lubricated friction contacts, it is known that the flow in narrow gaps can be approximated with the Reynolds equation, which does not discretize the height direction, thus significantly reducing overall modelling costs. For frictional contacts, the aforementioned simplification is numerically very efficient with respect to computational effort and convergence, and results in solutions very close to 3D-CFD simulations. As an extension of the Reynolds equation, in recent years the research group at the TU Braunschweig has developed a model that takes into account not only the efficient calculation of the interaction between flow and pressure build-up but also the dynamics in gaps that are only partially filled with fluids. This so-called PFG (Partially Filled Gaps) model is also able to explicitly describe the movement of air inclusions. This paper discusses the potential of this approach as a tool for describing the adhesive flows during pressing. It demonstrates that the theory of lubricated friction contacts is an interesting concept for a wide range of pressing process simulations.