Interactions in laser joining of metals to polymers
Materials in Sintering Processes and Generative Manufacturing Processes
Mechanical Properties of Metallic Materials and their Microstructural Origins
Final Report Abstract
Metal-plastics-joints continue to gain in importance. While plastics are characterised by low density, a low price per volume and almost free shaping, metals can be subjected to high loads due to their mechanical properties. This means that both rigid and lightweight components can be designed. Due to the different melting temperature ranges and the lack of chemical compatibility between plastic and metal, welding as a joining process based on material bond-ing is not suitable for joining metal-plastics-hybrids. A promising joining technology is joining from plastics to steel by laser radiation. A bond is realised by wetting the steel with the molten plastic, while the steel remains in a solid state. The exact adhesion mechanisms and composite properties are still the subject of research. The aim of this research project is to provide a fundamental understanding of the prevailing adhesion mechanisms and composite properties. In addition, an in-depth understanding of the damage behaviour of laser-joined plastic-metal composites that have undergone physical/chemical surface treatment will be obtained. To answer the research questions, on the one hand, the surfaces of the hybrid components were treated and coated with different methods prior to thermal joining. On the other hand, joining tests were carried out with an additional metallic intermediate layer in the form of a foil. In both cases, the influence on the joint strength were analysed. Besides the experimental tests, the joining processes were simulated thermally and thermomechanically. In addition to determining the temperature development in the joining zone, the induced residual stresses and the resulting bond strengths were calculated and validated with the corresponding results from the practical tests. It became apparent that sufficient mechanical interlocking is necessary for laser joining of non-polar plastics to steel, as otherwise no bond can be achieved. It has also been observed that low-pressure plasma treatment led to a reduction in the strength of both PA6.6 and PP. This is due to the fact that over-treatment with plasma leads to molecular degradation of the plastic. The tensile shear strength of the composites is primarily dependent on the thermal conductivity in the interface area. The higher the thermal conductivity of the applied metallic interlayer, the lower the tensile shear strength. The material applied in the joining zone also had an influence on the corrosion resistance of the composites. After alternating tests, interlayers made of corrosion-resistant materials such as titanium in combination with non-hydrophilic plastics such as PP showed higher strength compared to uncoated samples. Furthermore, a thermal and thermomechanical simulation model has been developed as part of the project. Both the tem-peratures and the strengths determined from the residual stresses could be calculated and, in some cases, gave results close to the process. However, there is still potential to improve the model by simulating the melt flow of the plastic in the future and taking into account the laser distribution.
Publications
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Entwicklung eines thermischen Simulationsmodells für das Laserdurchstrahlfügen von PA-6.6 mit CrNi-Stahl, Joining plastics. 3, S. 170–176.
Hopmann, C.; Knupe-Wolfgang, P.; Bölle, S.; van der Straeten, K. & Timmer, C.
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Influence of different surface metallizations on the lap shear strength of laser hybrid metal-plastic joints, MCIC 2022, Chemnitz
Timmer, Christian
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Influence of Metallic Interlayers on the Lap Shear Strength of Laser Joined Plastic and Metal Hybrids. MDPI AG.
Tillmann, Wolfgang; Wojarski, Lukas; Hopmann, Christian; Fatherazi, Patricia & Timmer, Christian
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The Influence of Low-Pressure Plasma Treatments on the Lap Shear Strength of Laser-Joined AISI 304 Hybrids with Polypropylene and Polyamide 6.6. Applied Sciences, 13(24), 13275.
Tillmann, Wolfgang; Wojarski, Lukas; Hopmann, Christian; Fatherazi, Patricia & Timmer, Christian
