@article{SchkutowScholleFuhrbergetal.2020, author = {Schkutow, Andreas and Scholle, Karsten and Fuhrberg, Peter and Frick, Thomas}, title = {Scanning techniques for optimized damage tolerance in quasi-simultaneous laser transmission welding of plastics}, series = {Procedia CIRP}, volume = {94}, journal = {Procedia CIRP}, publisher = {Elsevier BV}, issn = {2212-8271}, doi = {10.1016/j.procir.2020.09.120}, pages = {697 -- 701}, year = {2020}, abstract = {Fiber lasers are increasingly replacing the commonly used diode lasers in laser transmission welding of plastics for challenging applications due to their superior beam quality and the ability to use long working distances and small spot sizes. At the same time, these smaller spot sizes increase the risk of thermal degradation. In this work, we investigate different scanning strategies that allow controlling the weld seam widths. These strategies are characterized regarding the demands on the performance of the scanner system, the risk of thermal degradation and the mechanical properties of the resulting welds.}, language = {en} } @inproceedings{SchkutowFrickLamrinietal.2019, author = {Schkutow, Andreas and Frick, Thomas and Lamrini, Samir and Scholle, Karsten and Fuhrberg, Peter}, title = {Residual stresses and crack formation in laser welding of amorphous polymers}, series = {Lasers in Manufacturing Conference 2019}, booktitle = {Lasers in Manufacturing Conference 2019}, pages = {9}, year = {2019}, abstract = {Residual stresses in welded parts can limit the mechanical performance and reliability of the components. In polymers, especially in amorphous thermoplastics, tensile residual stresses in the presence of certain media can lead to environmental stress cracking, which can result in catastrophic failure of the connection. In this work the mechanisms of stress generation in welding of plastics is compared to metallic materials and methods for evaluating residual stresses are discussed in terms of suitability to polymer materials. The application of solvents in liquid and vapor phase is shown to be a useful tool for intentionally inducing stress cracking in laser-welded parts to evaluate and compare residual stress levels and orientations in the weld zones. Appropriate process parameters are examined for reducing welding stresses.}, language = {en} } @inproceedings{SchkutowFrickScholleetal.2019, author = {Schkutow, Andreas and Frick, Thomas and Scholle, Karsten and Lamrini, Samir and Fuhrberg, Peter}, title = {Experimental characterization of spectral scattering properties of polymers for laser welding applications}, series = {Proceedings of LAMP2019}, booktitle = {Proceedings of LAMP2019}, publisher = {Japan Laser Processing Society (JLPS)}, year = {2019}, abstract = {Laser transmission welding of polymers is a widely used joining technique for automotive components, consumer products, medical applications and others. The process is strongly dependent on the transmission properties of one of the joining partners to ensure a suitable laser intensity distribution in the joining zone between the two components. Scattering at crystalline structures, additives or reinforcements in composites as well as the absorptivity of the matrix can compromise the transmitted beam profile [1, 2, 3]. Successful welding of these materials is therefore often limited to thin parts. This work describes methods for measuring the spectral absorption, transmission and scattering properties to assess the weldability of scattering materials. Since many of these materials show anisotropic properties due to the manufacturing processes and the fiber orientation, the transmission properties are influenced by the polarization state of the laser beam. An experimental setup shown in Fig. 1, using a commercially available Spectrophotometer with integrating sphere, is used to measure direct transmission, forward and backward directed scattering and the reflection of linearly polarized light after interaction with amorphous and semicrystalline polymers as well as particle and fiber reinforced thermoplastic composites. The spectral measurements reveal that compared to commonly used lasers emitting at about 1.0 μm the application of laser wavelengths in the range of 1.3 to 2.0 μm can lead to increased transmission and reduced scattering losses within the materials. Variation of the polarization adds an additional degree of freedom to influence the transmission properties, especially in highly anisotropic materials or composites. For validation of the spectrometric results welding experiments using a conventional diode laser beam source and a unpolarised and a linearly polarized 2.0-μm single-mode Tm-fiber [4] were carried out. Additionally the resulting laser beam profiles after transmission through different amorphous and semicrystalline polymeric materials were measured using a scanning slit beam profiler. Using a suitable laser wavelength and adjusted polarization successful welding was achieved for highly scattering materials that could not be welded using a conventional diode laser beam source. [1] X. F. Xu, A. Parkinson, P. J. Bates and G. Zak, Effect of part thickness, glass fiber and crystallinity on light scattering during laser transmission welding of thermoplastics, Optics \& Laser Technology 75, pp. 123-131, 2015. [2] V. Mamuschkin, A. Roesner, M. Aden, Laser Transmission Welding of White Thermoplastics with Adapted Wavelengths, Physics Procedia, 41, p. 172-179, (2013). [3] T. Frick and A. Schkutow, Laser transmission welding of polymers-Irradiation strategies for strongly scattering materials. Procedia CIRP, 74, p. 538-543, (2018). [4] K. Scholle, M. Sch{\"a}fer, S. Lamrini, M. Wysmolek, M. Steinke, J. Neumann, P. Fuhrberg, All-fiber linearly polarized high power 2-μm single mode Tm-fiber laser for plastic processing and Ho-laser pumping applications, Proc. SPIE 10512, Fiber Lasers XV: Technology and Systems, 105120O, (2018).}, language = {en} }