The aeronautic industry has to face the demand of cost reduction by its customers. These costs are divided into acquisition and operating costs. Both can be reduced by optimization and automation of production steps and by using highly integrated light weight structures. Within the EU-founded FP 6 project ECOSHAPE a laser beam forming (LBF) process for the laser beam bending of complex fuselage aluminum panels has been developed. The aim was to build up the fundamental know-how for an industrial manufacturing process performing most production steps in flat condition due to a minimum of machining costs, technological complexity and a maximum of robustness and reliability. To facilitate the cost intensive qualification of the LBF-process the metallurgical behavior of the aluminum alloys is investigated as well as the influences of the single structural elements of the fuselage panels like stingers and pockets on the forming result. For the industrial upgrade the process is integrated into a discrete control loop using the geometry of the panel as control variable.
The aim of this contribution is to study the influence of the laser beam on the structural properties of sheet metals during welding by considering particular process effects. The interaction between process parameters, such as the exact positioning of the laser focus and the weld gap between sheets, affects the stability of the laser beam welding process and thus the quality of weld seams. Furthermore, additional interaction of the welding process with manufacturing tolerances and structural properties, i.e., material thinning and residual stresses after forming, influence the behavior of structures. Heat effects during and after the laser beam welding process produce residual stresses as well as phase transformation, in the case of steel alloys, in the weld seam and the heat affected zone. For this reason distortion of the whole welded structure is caused. Depending, next to the laser beam parameters, on the type of welded joint, on the structure geometry and on the clamping conditions, the residual stresses and the distortion of structures may vary. In order to examine the process design variation, three different types of welded joints were considered. A lap and a fillet seam as well as a heat conduction bead-on-plate seam on a formed sheet of steel were produced and the distortion was measured. Finally, the results are compared with the finite element analysis.
During the joining process of complex body components in the automobile industry, dimensional accuracy is essential. In order to predict the behavior and to improve the geometrical quality of joined sheet metal parts during the welding and cooling process, a simulation method by means of finite elements is applied. This should be done in the early stage of the product’s life cycle to reduce process adjustments, which are time and money consuming. In recent years the simulation of welding was basically feasible by models consisting of volume elements. This way the metallurgical phase transformation, which is responsible for the behavior of the treated parts during the cooling process, can be established for a specific material. The use of volumes has a negative influence on the calculation time and it is not applicable for sheet metals. Especially, if effects from previous forming processes are to be considered. Additionally, the application of shells can meet the requirements of an analysis of the effects of welding when the metallurgical material properties are taken into account. In this paper an example of a sheet metal (DC04, former St 14) will be examined with the aid of a finite element analysis. Firstly, a transient temperature field is calculated in a thermal simulation by applying a certain method. In this calculation only the thermal properties of the material are used. Secondly, the transient temperature field is used as the initial load for the thermo-mechanical analysis. The distortion and the residual stresses of the work piece can be calculated using thermo-mechanical properties and material phase transformations.
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