Temperature and Displacement Fields Measurements to Assist the Numerical Simulation of the Welding-Brazing Process of Thin Automotive Parts

Abstract

Car manufacturers use many different mechanical or thermo-mechanical processes to assemble thin metal sheets. Each of these processes may induce –more or less localizedundesirable deformations of the assembled sheets. The numerical simulation of these deformations via the use of predictive thermo-mechanical finite element analyses may help and reduce development time and cost. To validate such complex non-linear numerical simulations by comparison of the numerical results with experimental evidence, it is necessary to develop well-controlled and highly instrumented tests. Welding-brazing is one the various assembly processes involving a heat source used by car manufacturers to assemble thin –typically 0.7 to 1mm thick- metal sheets. Predictive heat transfer simulations of this process require accurate modelling of both the heat source and the boundary conditions imposed onto the assembled sheets –including the contact between the sheets. Using ABAQUS general-purpose finite element code for this study, the welding-brazing heat source is modelled as the combination of a 3D volumetric source corresponding to the welding-brazing joint, and a 2D surface source corresponding to the heat flux emitted by the laser beam onto the sheets in the vicinity of the joint. Besides, the contact between the sheets is modelled by a thermal resistance depending on the pressure between the sheets when they are in contact, or the distance between them when they are apart. Identification of heat source and contact models is derived from the results of weldingbrazing tests instrumented with thermocouples and infrared cameras. Micrographic observations in the vicinity of the welding-brazing joint are used to (partially) validate the numerical predictions of the Heat Affected Zone (HAZ). After validation of this heat transfer numerical analysis, the thermo-mechanical analysis of the process will be validated by comparison of the predicted displacement fields with the results of 3D Digital Image Correlation (stereo-correlation) measurements made during the welding-brazing tests.