Material-specific interface design with pulsed laser structuring for increased joint strength in functionalized thermoplastic fiber composite hollow profile structures
Topic(s) : Special Sessions
Co-authors​ :
Daniel WOHLFAHRT (GERMANY), Alexander LIEBSCH (GERMANY), Thomas KUNTZE (GERMANY)Abstract :
Lightweight vehicle structures are a key factor on the road to resource-saving mobility. Against the backdrop of current climatic and political developments, ecological and social aspects are playing an increasingly important role alongside technical and economic criteria. Load-bearing structures in the form of the FuPro construction method (Fig. 1), a fiber composite construction method (FRP) made of thermoplastic composites (TPC) hollow profiles, organic sheets and injection molding, enable cost-effective, lightweight and environmentally friendly components. The recyclability of the new materials and vehicle structures also shows great potential for improving environmental compatibility. The use of simple thermoplastic fiber composites (FRP) as a recyclable monomaterial solution suitable for large-scale production, for example from glass fiber-polypropylene composites, is predestined for this.
There are design and production-related interfaces between the individual semi-finished products. These should have durable and high joint strengths. To achieve this, the joints are pre-treated. By using pulsed laser struturing, pre-treatment can be carried out without material contamination and without the use of adhesion promoters. This also enables the material-selective processing of temperature-sensitive FRP, as the non-contact processing avoids any mechanical stress and thermal damage can be ruled out.
Corresponding laser pulse processes are being developed and optimized for implementation. Extensive laser structuring studies with varying laser pulse powers (Fig. 2), different structural patterns and microscopic evaluations provide an in-depth understanding of the interface pre-treatment. In this way, targeted fiber exposures or surface adjustments are realized and made available for further processing. Two interface variants are being investigated. One is the injection molding/overmolding of TPC hollow profile elements and the other is the pressing of melted TPC shaped sheet form elements onto the TPC hollow profile elements. During injection molding, parameters such as the injection speed and the melt temperature are varied. During press-fitting, not only the laser structure but also the penetration depth and the temperature of the melted TPC molded sheet are changed. The basis for the extensive series of tests on these compounds is the base material glass fiber polypropylene. The joint strength is determined using individual overlap shear tests and compared with the parameter variations in order to evaluate the joint potential. The optimum production parameters are also specified. Even in the first test variants, the joint strength was increased by more than 600% compared to the untreated joint.
There are design and production-related interfaces between the individual semi-finished products. These should have durable and high joint strengths. To achieve this, the joints are pre-treated. By using pulsed laser struturing, pre-treatment can be carried out without material contamination and without the use of adhesion promoters. This also enables the material-selective processing of temperature-sensitive FRP, as the non-contact processing avoids any mechanical stress and thermal damage can be ruled out.
Corresponding laser pulse processes are being developed and optimized for implementation. Extensive laser structuring studies with varying laser pulse powers (Fig. 2), different structural patterns and microscopic evaluations provide an in-depth understanding of the interface pre-treatment. In this way, targeted fiber exposures or surface adjustments are realized and made available for further processing. Two interface variants are being investigated. One is the injection molding/overmolding of TPC hollow profile elements and the other is the pressing of melted TPC shaped sheet form elements onto the TPC hollow profile elements. During injection molding, parameters such as the injection speed and the melt temperature are varied. During press-fitting, not only the laser structure but also the penetration depth and the temperature of the melted TPC molded sheet are changed. The basis for the extensive series of tests on these compounds is the base material glass fiber polypropylene. The joint strength is determined using individual overlap shear tests and compared with the parameter variations in order to evaluate the joint potential. The optimum production parameters are also specified. Even in the first test variants, the joint strength was increased by more than 600% compared to the untreated joint.