Laserbasiertes Fügen von Kunststoff-Metall-Hybridverbindungen mittels selbstorganisierter Mikrostrukturen

  • Laser-based joining of plastic-metal hybrid joints by means of self-organizing microstructures

van der Straeten, Kira Martina; Poprawe, Reinhart (Thesis advisor); Hopmann, Christian (Thesis advisor)

1. Auflage. - Aachen : Apprimus Verlag (2021)
Book, Dissertation / PhD Thesis

In: Ergebnisse aus der Lasertechnik
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

For the implementation of innovative lightweight concepts, the combination of dissimilar materials and the joining processes necessary for the production of hybrid components play an important role. A promising approach for joining plastics and metals is the two-stage process chain of laser-based joining of hybrid compounds, which enables the joining of thermoplastics and metals without the use of additives. In the first process step, the metal surface is laser structured in order to create cavities with undercut geometry into the material and to increase the surface area. In the subsequent joining process, energy in the form of laser radiation is then introduced into the joining zone, absorbed on the metal surface and converted into heat. Through thermal contact with the metal surface, the thermoplastic material is plasticized and pressed into the structures of the metal surface by applying an external joining force. Once the plastic has solidified, a firm and durable bond is created between the two materials. Within the scope of this work, a novel structuring approach was developed to join steel (X5CrNi18-10, 1.4301) and thermoplastics (PA and PP) with high bond strength and long-term stability. During ablation with ultrashort pulsed laser radiation spongy, self-organizing microstructures can be formed on metal surfaces, which are superimposed with nanostructures. Initially, the factors influencing the formation of these so-called cone-like protrusions (CLP) were investigated and the resulting surface structures were characterized in terms of structural geometry, surface enlargement and wetting properties. Starting from the process fundamentals of the laser microstructuring and joining process, the knowledge gained from the surface characterization is used to investigate the influence of the structural properties on the joint strength and the adhesion mechanisms in the hybrid compound. Due to the fully microstructured surface with high surface enlargement and undercuts, very high composite strengths are achieved, which cannot currently be achieved with other surface pretreatments. Especially in combination with non-polar plastics such as polypropylene, without modification of the surface topography, no adhesion with steel surfaces can be achieved, as these do not form polar bonds or specific adhesion. In hybrid joints, mechanical adhesion is the predominant adhesion mechanism and specific adhesion only occurs in combination with polar plastics (PA). Overall, the bond strength of the hybrid connection is strongly dependent on the load direction. Very high forces up to 50 Mpa can be transmitted under shear load. In addition, the joint has very good properties with regard to fatigue strength, long-term stability and media tightness. Finally, the joining technology was demonstrated and evaluated in an application case study.

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