Finite element modeling and simulation of vacuum brazing processes with a focus on cycle-dependent component distortion

Abstract

For the production of high-strength connections by brazing, it is very important to control component distortion and the gap size that depends on it. In particular, nickel-based filler metals will form brittle phases at larger gaps which extraordinarily reduce the joint strength. Thus, a model using fi nite element analysis was developed in Ansys Workbench to calculate the cycle-dependent component deformation of brazing assemblies during the joining process. At first, this cpaper describes the most important aspects to consider when simulating thermal radiation in a vacuum furnace from a constructive point of view. Furthermore, a new model strategy is shown which keeps the calculation times moderate by a clever choice of supports and boundary conditions. It could be shown that the component deformation during heating can be easily kept in the elastic range and can be almost completely eliminated by using a geometry-dependent soaking time. In contrast, high cooling rates were shown to result in thermally induced stresses well above the elastic yield limit, causing signifi cant component deformation. With further cooling, the deformation decreases signifi cantly, but it depends on the initial stress, the geometry and the cooling rate if the deformation can be completely leveled out during the shrinkage of the component. In addition, it was shown that the distortion of the component is highly aff ected by the local position in the heating chamber. As a result of the analyses, the simulation results were used to design a fi xture for vertical positioning which signifi cantly reduced the distortion of the brazed component.