Oliver Kreis:

Integrated manufacturing -

Process integration by hydroforming, cutting and laser beam welding in one single tool and its tele- and multimedia presentation



The integration of processes and the combination of innovative manufacturing technologies offer a large variety of possibilities to shorten process chains while maintaining or even enhancing the complexity and quality of technical products. The reduction of processes allows the realization of cost saving potentials.

Therefore, this thesis presents a methodology for the modeling of processes and process chains and shows exemplarily the development of a shortened process chain for the manufacturing of sheet light weight parts, that integrates the processes preforming by hydroforming, mechanical shear cutting, joining by laser beam welding and hydrocalibrating in one single tool. The main objectives of the examinations are the systematic analysis of the integration of the laser beam welding process in a hydroforming tool, the optimization of the welding process and the deduction of generally admitted knowledge.

Based on a system-theoretical modeling, a modeling of the input and output factors is developed. The modeling of the system design shows the kinematics and the necessary velocities and accelerations of the welding robot axes. The integrated joining process is optimized in several steps. A systematic experimental analysis of the relevant input and output parameters leads to a deepened understanding of the joining process. The conducted experiments prove the general suitability of the laser beam welding process for the integration in a hydroforming tool and the technical feasibility of the examined process integration.

Maximum tensile force, pore volume, impermeability and forming capability are general significant quality criteria of a weld seam that is contaminated with hydroforming media and lubricants. By using optimized process guiding strategies, the flange can be joined with a good welding quality. Feed speed and laser power are the most significant input parameters of the welding process. The feed speed of the tool center point has to be as constant as possible. If the feed speed is too high, the maximum tensile force of the weld is too low. At low feed speeds, the higher dynamics and mixing of the keyhole in the melt leads to a strong disposal of contaminations in the keyhole and in the melt, resulting in a strong increase of the pore volume. Generally, a high laser power improves the evaporation and outgassing of the contaminations. Lubricants with a high viscosity guarantee a good hydroforming process. Occasionally, they don't evaporate without residues in the welding process, casually resulting in leakages in the weld. By using a specific lubricant with a low viscosity, the impermeability of the weld can be secured even in the critical area of the weld overlap. The weld can be formed without failure, allowing a draw-in of the flange in the final hydroforming process (hydrocalibrating). A process window summarizes the conducted welding experiments.

In an interdisciplinary approach, the essential results of the work are additionally presented in a scientific-based tele- and multimedia presentation that enables a knowledge transfer anywhere at any time with a high clearness, flexibility and learning efficiency.