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

Abstract

Vacuum brazing is a black box process, so component distortion that occurs during the heat treatment is difficult to prove experimentally. Thus, a novel FE-model was developed in ANSYS Workbench to calculate the time and location resolved component deformation of AISI 316L/B-Ni2 brazing assemblies. In this regard, a new method of radiation and contact modeling was developed that enabled a significant reduction of the calculation times and solved the convergence issue for simulating the distortion of large-scale, thin components. The results showed 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 to this, high cooling rates were found to result in thermally induced stresses well above the elastic yield limit, causing significant component deformation. With further cooling, the deformation decreases significantly, but it depends on the initial stress state, the geometry, and the cooling rate whether the deformation can be completely leveled out during the shrinkage of the component. Thus, the initially high cooling rates were identified to be responsible for the final distortion. Furthermore, this was highly affected by the local position in the heating chamber. The simulation results were used to design a fixture for vertical positioning, which reduced the max. temperature difference in the brazing assembly from 141 to 79 °C, the max. interim distortion from 275 to 31 µm, and the final distortion from 14 to 8 µm.