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Laser micro fabrication of fiber reinforced plastics

Presentation held at 9. Internationales Lasersymposium und Internationalen Fügetechnischen Symposium "Tailored Joining" 2016, Dresden, 22.-24.2.2016
: Franke, Volker; Schilling, Niels; Krupop, Benjamin

2016, 20 pp.
Internationales Lasersymposium <9, 2016, Dresden>
Internationales Fügetechnisches Symposium "Tailored Joining" <2016, Dresden>
Fraunhofer IWS ()
Anfrage beim Institut / Available on request from the institute

Fiber reinforced plastics offer great potentials for lightweight construction in a wide range of applications due to their high specific strength. For high volume applications fiber reinforced compounds with thermoplastic matrix are promising due to the usability of injection molding for production. This process offers the potential of short production cycles for manufacturing [1]. Additionally it facilitates the fabrication of hybrid structures as a combination of long fiber reinforced components with additional structures made of unreinforced or short fiber reinforced structures. Tailored laser processes present a solution to increase the strength of the interface between both sub-structures. Results of laser processing fiber reinforced thermoplastics with different laser sources are presented. Aim of the study is to determine the process windows for a selective ablation of polymer matrix as well as a homogenous ablation of both matrix and fibers. Goal of selective ablation is to bare the load carrying fibers at the surface without damaging them for a subsequent injection molding process. Laser sources with different wavelengths (10.6 μm, 1064 nm, 532 nm, 355 nm) and pulse durations (μs, ns and ps) are compared regarding the ablation behavior of natural and black colored glass fiber reinforced polypropylene (PP). Depending on the material properties the ablation behavior of the composite can be switched from selective ablation of the polymer matrix to a homogenous ablation of the complete material by varying pulse duration, laser fluence and wavelength. Ablation thresholds have been identified for the different laser beam sources and different material properties. The far infrared radiation of the CO2-Laser is strongly absorbed by both – polymer matrix and reinforcing glass fibers. Therefore predominantly homogeneous ablation of the whole composite material takes place. In this setup the ablation process is almost independent from the content of carbon black within the PP. Best results regarding selective matrix ablation were achieved for pigmented polymer with ns lasers and 1064 nm wavelength. At this parameter combination a wide process window can be utilized without damaging the reinforcing fibers. These results are not transferable to unpigmented composites where only insufficient absorption of the infrared laser radiation is reached within the polymer. Utilizing UV radiation with ns pulse durations facilitates a process to selectively bare the fibers close to the composite surface but thermal and absorption behavior is limiting the process window. With ultrashort pulsed lasers selective matrix removal as well as homogeneous composite ablation has been demonstrated. Microscopic damage within the glass fibers is limiting the process window for selective ablation and needs further investigation. Tests of the tensile strength of joined composite samples show a significant increase of the bond strength of samples with exposed fibers compared to untreated composites.