توسعه یک مدل سه بعدی شبیه سازی عددی محلی برای لیزر شکل دهنده در فرایند اجزای آلومینیوم

The laser beam forming (LBF) process uses the energy of relatively high-powered lasers to cause permanent deformations of components, through the local introduction of thermal stresses. LBF of aluminium material is a process, complex and sensitive, due to the complicated physical phenomena taking place during laser processing. Therefore, definition of optimal process parameters, such as laser power and processing velocity, which will result to desired bending patterns, as well as investigation of forming limits of various components require significant experimental effort. Herein, numerical simulation of LBF process is used to provide partial solution to the problem, by developing a local Finite Element simulation model, capable to predict temperature fields and deformation shapes of laser beam-treated aluminium specimens. The numerical algorithm is based on a non-linear three-dimensional transient thermal–structural analysis, temperature-dependent thermal and mechanical material properties and a laser beam heat flux model. The developed model is validated through the comparison of numerically predicted distribution of temperatures and bending angles to corresponding experimental data of single and multiple laser beam passes. The validated model is then used to define optimal process parameters for the laser forming process of aluminium panels.

Laser forming recently emerged as a new shaping technique that offers excellent reproducibility, low manufacturing time and cost, as well as, relatively low thermal influence on the material mechanical properties. For those reasons, laser forming is a promising technique with several potential applications in the automobile, shipbuilding and in particular aerospace industry, where the demand to form integrally stiffened structures is high. In comparison to conventional forming technologies, LBF provides the potential for many technological advantages, especially in cases of forming complex or semi-assembled structures of various thicknesses and material types, as well as in rapid prototyping applications. Although the traditional application of laser forming has been to various steel materials, laser forming process of certain types of aluminium alloys has been recently the object of considerable attention in the aerospace industry. However, the low thickness of formed parts, the elevated laser beam light reflection and the high heat conduction of aluminium alloys are some of the main reasons, which make the use of laser forming process more difficult and complex, as compared to its application to steel forming. During laser forming, the irradiated material is formed under the action of local plastic strains induced by laser heating of the material, instead of the action of mechanical forces and moments applied by the common sheet bending techniques. The local nature of laser irradiation yields high temperature gradients between the irradiated surface and the neighboring material. The high temperature gradients, force the material to expand non-uniformly, which results in irregular thermal expansion between the target and lower surface. As a result the specimen initially bends negatively, as viewed from the laser beam. The non-uniform expansion of the material leads to non-uniform thermal stresses, which result to plastic deformation at locations where thermal stresses exceed the material's yield point. During cooling, the upper material layers shrink more than the bottom, resulting in permanent specimen bending towards the laser beam.

A three-dimensional Finite Element model capable of simulating single and multi-pass laser beam forming process, as well as, predicting temperature distributions and bending shape of LBF aluminium components has been presented. All the major physical phenomena of the heating and cooling stages of the LBF process are simulated through a non-linear thermal–structural analysis. The developed model considers temperature-dependent thermal and mechanical material properties and a Gaussian moving heat flux source applied on the specimen external surface. The model is capable of predicting temperature distributions and final bending angles in good agreement to experimental data. The simulation algorithm is applied in the definition of optimum forming parameters for 6013-T4 and 2024-T351 components. It is shown that increasing laser power or decreasing forming speed leads to higher bending angles, as well as that increasing plate thickness results in lower achieved bending angles.