The technique of solving the inverse heat conduction problem to determine the steady state welding conditions corresponding to observable or desired weld features is outlined. The objective function includes calculated and experimental values of the temperature related functions, constraints, and regularisation of unknown parameters. The algorithm used to determine the minimum of the objective function is presented. As an example, the temperature field and its corresponding grain structure have been calculated taking into consideration the latent heat and fluid flow in the laser welding of two aluminium alloys. The weld width and texture orientation have been used as the temperature related functions. The results of the simulations are directly compared with the experimental evidence.
A novel approach for the reconstruction of an equivalent volumetric heat source from a known weld pool shape is proposed. It is based on previously obtained weld pool geometries from a steady-state thermo-fluid dynamics simulation. Hereby, the weld pool dimensions are obtained under consideration of the most crucial physical phenomena, such as phase transformations, thermo-capillary convection, natural convection, and temperature-dependent material properties. The algorithm provides a time and calibration efficient way for the reproduction of the weld pool shape by local Lamé curves. By adjusting their parameters, the identification of the finite elements located within the weld pool is enabled. The heat input due to the equivalent heat source is assured by replacing the detected nodes' temperature by the melting temperature. The model offers variable parameters making it flexible and adaptable for a wide range of workpiece thicknesses and materials and allows for the investigation of transient thermal effects, e.g., the cooling stage of the workpiece. The calculation times remain acceptably short especially when compared to a fully coupled process simulation. The computational results are in good agreement with performed complete-penetration laser beam welding experiments.
Experiments were carried out to determine the properties of the welded joints in 8 mm thick high-strength steels produced by quenching and tempering and thermomechanical rolling with accelerated cooling (tensile strength 821-835 MPa). The dependence of the strength, elongation, hardness, impact energy and crack opening displacement on the heat input in the range 1.0 -0.7 kJ mm 21 was determined. The results show that the dependence of the strength of the welded joints decreases and that of the elongation increases. The heat input has only a slight effect on the impact energy and crack opening displacement in the heat-affected zone.
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