@inproceedings{AmendLaumerRothetal., author = {Amend, Philipp and Laumer, Tobias and Roth, Stephan and Baat, Florian and Schmidt, Michael}, title = {Investigations on Laser-based Hot-melt Bonding of Additive Manufactured Plastic Parts to Metal Sheets for Strong and Tight Multi-material Joints}, series = {Laser in Manufacturing (LIM 2017), Munich, Germany}, booktitle = {Laser in Manufacturing (LIM 2017), Munich, Germany}, abstract = {In this paper, first results regarding the realization of laser-based hot-melt bonding of additive manufactured plastics parts to metal sheets for strong and tight multi-material joints are presented. Compared to earlier investigations, in which nearly solely extruded plastic materials were applied, the use of additive manufactured plastics complements the research field with a promising approach. Besides the typical advantages of multi-material joints regarding weight reduction and high strengths, such parts can meet the needs of constructional freedom and the avoiding of tool costs. Materials used for this paper are aluminum (AlMg3), stainless steel (1.4301) and polyamide 12 (PA12). The performed experiments resulting in multi-material joints between metal and polyamide. The realized specimens undergo a tensile shear test and a tightness test, in which the characteristics of the joints are determined.}, language = {en} } @article{Laumer, author = {Laumer, Tobias}, title = {Realization of Multi-material Polymer Parts by Simultaneous Laser Beam Melting}, series = {Journal of Laser Micro/Nanoengineering (JLMN)}, volume = {10}, journal = {Journal of Laser Micro/Nanoengineering (JLMN)}, number = {2}, publisher = {Japan Laser Processing Society}, doi = {10.2961/jlmn.2015.02.0006}, pages = {140 -- 147}, abstract = {In this paper, first results regarding the realization of multi-material parts by Simultaneous Laser Beam Melting (SLBM) of polymers are presented. This new approach allows the layerwise generation of parts consisting of different polymer materials within one building process. Besides the typical advantages of additive manufacturing technologies, such parts can fulfill different product requirements concomitant and therefore could enlarge the overall field of application. The powder materials used for this paper are polyethylene (PE) and a polyamide based thermoplastic elastomer (TPE). After depositing the powder materials next to each other, infrared-emitters heat the lower melting polymer and a CO2 laser provides the preheating temperature of the higher melting polymer. In the last step, a thulium fibre laser melts the two preheated powders simultaneously.The realized specimens are characterized by cross sections and their tensile strengths are determined. Additionally, the new approach of the simultaneous energy irradiation is investigated using a Finite Element Analysis in order to gain a more profound process understanding. In that sense, the influence of the size of the exposure area on the reachable maximum temperatures inside that area was analyzed by the simulation and compared to experimental studies.}, language = {en} } @inproceedings{LaumerKargSchmidt, author = {Laumer, Tobias and Karg, Michael Cornelius Hermann and Schmidt, Michael}, title = {Additive Manufacturing of Gradient and Multimaterial Components}, series = {International Conference on Competitive Manufacturing COMA, 2013, Stellenbosch}, booktitle = {International Conference on Competitive Manufacturing COMA, 2013, Stellenbosch}, abstract = {In the paper first results regarding the realisation of gradient and multi-material parts manufactured by Laser Beam Melting in powder bed of metals and polymers are published. Gradient properties of additively manufactured metal parts can be achieved by varying the composition of alloying components in the powder and adapting process strategies. As an alternative to atomizing pre-alloyed materials, mixtures of different powders are investigated. For realizing multi-material-parts from polymers, at first relevant material properties concerning compatibility have to be analysed. Therefore the paper shows the main requirements for compatibility between different materials and also first results regarding the compatibility of polymer powders and possible combinations for the manufacturing of multi-material components by laser beam melting of polymers.}, language = {en} } @inproceedings{LaumerKargSchmidt, author = {Laumer, Tobias and Karg, Michael Cornelius Hermann and Schmidt, Michael}, title = {Neue Prozessstrategien zur Herstellung von Multi-Material-Bauteilen mit Hilfe des Laserstrahlschmelzens}, series = {Industriekolloquium des SFB 814, 2, 2013, N{\"u}rnberg}, booktitle = {Industriekolloquium des SFB 814, 2, 2013, N{\"u}rnberg}, publisher = {Universit{\"a}t Erlangen-N{\"u}rnberg, Lehrstuhl f{\"u}r Kunststofftechnik}, isbn = {978-3-931864-59-0}, language = {de} } @article{LaumerWudyDrexleretal., author = {Laumer, Tobias and Wudy, Katrin and Drexler, Maximilian and Amend, Philipp and Roth, Stephan and Drummer, Dietmar and Schmidt, Michael}, title = {Fundamental investigation of laser beam melting of polymers for additive manufacture}, series = {Journal of Laser Applications}, volume = {26}, journal = {Journal of Laser Applications}, number = {4}, publisher = {AIP Publishing}, issn = {1938-1387}, doi = {10.2351/1.4892848}, abstract = {By selective laser sintering (SLS), polymer powders are molten layer by layer to build conventional prototypes or parts in small series with geometrical freedom that cannot be achieved by other manufacturing technologies. The SLS process is mainly defined by the beam-matter interaction between powder material, laser radiation and different material characteristics by itself. However the determination of these different material characteristics is problematic because powder material imposes certain requirements that cannot sufficiently be provided by conventional measurement methods. Hence new fundamental investigation methods to determine the optical and thermal material characteristics like the thermal diffusivity, thermal conductivity, or the influence of different heating rates on the melting behavior are presented in this paper. The different analysis methods altogether improve the process of understanding to allow recommendations for the future process controlling.}, language = {en} } @article{KuettnerRathsFischeretal., author = {Kuettner, Andreas and Raths, Max and Fischer, Samuel and Laumer, Tobias}, title = {Heat staking of polymer parts generated by fused layer modeling}, series = {The International Journal of Advanced Manufacturing Technology}, volume = {128}, journal = {The International Journal of Advanced Manufacturing Technology}, publisher = {Springer Nature}, doi = {10.1007/s00170-023-11850-y}, pages = {547 -- 562}, abstract = {Heat staking is a joining technology by which thermoplastic pins are formed by force and temperature to create a form- and force-fitting connection between components. This paper examines the characteristics of 3D printed pins in comparison to conventionally turned pins for heat staking applications. The 3D printed pins are created using fused layer modeling, with variations in horizontal and vertical building directions, as well as different layer thicknesses. The study investigates the impact of significant factors on the heat staking process, including the forming force and temperature. Tensile tests, micrographs, and micro-CT measurements were conducted to determine the properties of the heat-staked joints. Additionally, a stage plan was developed to enhance the understanding of the forming process of both printed and conventionally turned materials. The findings suggest that, under specific process parameters, 3D printed pins exhibit comparable strength to conventionally manufactured pins. The research also demonstrates that the anisotropy resulting from the layer-by-layer construction of the pins significantly influences the strength of the connection. Furthermore, the study reveals that 3D printed pins exhibit good forming accuracy during the heat staking process, and the cavities formed during printing can be substantially reduced.}, language = {en} } @article{RathsBauerKuettneretal., author = {Raths, Max and Bauer, Lukas and Kuettner, Andreas and Fischer, Samuel and Laumer, Tobias}, title = {Gradual error detection technique for non-destructive assessment of density and tensile strength in fused filament fabrication processes}, series = {The International Journal of Advanced Manufacturing Technology}, journal = {The International Journal of Advanced Manufacturing Technology}, number = {131}, publisher = {Springer}, address = {London}, issn = {1433-3015}, doi = {10.1007/s00170-024-13280-w}, pages = {4149 -- 4163}, abstract = {Fused filament fabrication (FFF) is a widely used additive manufacturing process for producing functional components and prototypes. The FFF process involves depositing melted material layer-by-layer to build up 3D physical parts. The quality of the final product depends on several factors, including the component density and tensile strength, which are typically determined through destructive testing methods. X-ray microtomography (XCT) can be used to investigate the pore sizes and distribution. These approaches are time-consuming, costly, and wasteful, making it unsuitable for high-volume manufacturing. In this paper, a new method for non-destructive determination of component density and estimation of the tensile strength in FFF processes is proposed. This method involves the use of gradual error detection by sensors and convolutional neural networks. To validate this approach, a series of experiments has been conducted. Component density and tensile strength of the printed specimens with varying extrusion factor were measured using traditional destructive testing methods and XCT. The cumulative error detection method was used to predict the same properties without destroying the specimens. The predicted values were then compared with the measured values, and it was observed that the method accurately predicted the component density and tensile strength of the tested parts. This approach has several advantages over traditional destructive testing methods. The method is faster, cheaper, and more environmentally friendly since it does not require the destruction of the product. Moreover, it facilitates the testing of each individual part instead of assuming the same properties for components from one series. Additionally, it can provide real-time feedback on the quality of the product during the manufacturing process, allowing for adjustments to be made as needed. The advancement of this approach points toward a future trend in non-destructive testing methodologies, potentially revolutionizing quality assurance processes not only for consumer goods but various industries such as electronics or automotive industry. Moreover, its broader applications extend beyond FFF to encompass other additive manufacturing techniques such as selective laser sintering (SLS), or electron beam melting (EBM). A comparison between the old destructive testing methods and this innovative non-destructive approach underscores the possible fundamental change toward more efficient and sustainable manufacturing practices. This approach has the potential to significantly reduce the time and cost associated with traditional destructive testing methods while ensuring the quality of FFF-manufactured products.}, language = {en} } @inproceedings{LaumerStichelAmendetal., author = {Laumer, Tobias and Stichel, Thomas and Amend, Philipp and Schmidt, Michael and Gachot, A.}, title = {Simultaneous Energy Deposition for Laser Beam Melting of Polymers}, series = {Proceedings of the Polymer Processing Society 29th Annual Meeting, N{\"u}rnberg, 2013}, booktitle = {Proceedings of the Polymer Processing Society 29th Annual Meeting, N{\"u}rnberg, 2013}, publisher = {American Institute of Physics}, address = {New York}, language = {en} } @article{StichelFrickLaumeretal., author = {Stichel, Thomas and Frick, Thomas and Laumer, Tobias and Tenner, Felix and Hausotte, Tino and Merklein, Marion and Schmidt, Michael}, title = {A Round Robin study for Selective Laser Sintering of polyamide 12: Microstructural origin of the mechanical properties}, series = {Optics \& Laser Technology}, volume = {89}, journal = {Optics \& Laser Technology}, publisher = {Elsevier}, doi = {10.1016/j.optlastec.2016.09.042}, pages = {31 -- 40}, abstract = {The mechanical and microstructural investigation of polymer parts (polyamide 12) fabricated by Selective Laser Sintering as part of a Round Robin initiative is presented. The paper focuses on the microstructural analysis of the Round Robin samples and their evaluation regarding their effect on mechanical properties with respect to each other. Therefore optical microscopy on microtomed samples, X-ray computed tomography and Differential Scanning Calorimetry is used to determine the morphology of residual particle cores and of internal pores.}, language = {en} } @article{LaunhardtWoerzLodereretal., author = {Launhardt, M. and W{\"o}rz, A. and Loderer, A. and Laumer, Tobias and Drummer, Dietmar and Hausotte, Tino and Schmidt, Michael}, title = {Detecting surface roughness on SLS parts with various measuring techniques}, series = {Polymer Testing}, volume = {53}, journal = {Polymer Testing}, publisher = {Elsevier}, address = {Amsterdam}, isbn = {0142-9418}, issn = {1873-2348}, doi = {10.1016/j.polymertesting.2016.05.022}, pages = {217 -- 226}, abstract = {Selective Laser Sintering (SLS) is an additive manufacturing technique whereby a laser melts polymer powder layer by layer to generate three-dimensional parts. It enables the fabrication of parts with high degrees of complexity, nearly no geometrical restrictions, and without the necessity of a tool or a mold. Due to the orientation in the building space, the processing parameters, and the powder properties, the resulting parts possess an increased surface roughness. In comparison to other manufacturing techniques, e.g. injection molding, the surface roughness of SLS parts results from partially melted powder particles on the surface layer. The actual surface roughness must thus be characterized with respect to the part's eventual application. At the moment, there is no knowledge regarding which measuring technique is most suitable for detecting and quantifying SLS parts' surface roughness. The scope of this paper is to compare tactile profile measurement methods, as established in industry, to optical measurement techniques such as Focus Variation, Fringe Projection Technique (FPT), and Confocal Laser Scanning Microscope (CLSM). The advantages and disadvantages of each method are presented and, additionally, the effect of tactile measurement on a part's surface is investigated.}, language = {en} } @article{HupfeldLaumerSticheletal., author = {Hupfeld, T. and Laumer, Tobias and Stichel, T. and Schuffenhauer, T. and Heberle, J. and Schmidt, Michael and Barcikowski, S. and G{\"o}kce, B.}, title = {A new approach to coat PA12 powders with laser-generated nanoparticles for selective laser sintering}, series = {Procedia CIRP}, volume = {74}, journal = {Procedia CIRP}, publisher = {Elsevier}, doi = {10.1016/j.procir.2018.08.103}, pages = {244 -- 248}, abstract = {The modification of selective laser sintering (SLS) powder materials by nanoadditives offers the possibility to adapt the powder properties to the laser sintering process or the resulting part properties. To avoid agglomeration of the nanofiller, a new approach in which surfactant-free laser-generated colloidal nanoparticles are adsorbed onto the polymer surface directly in an aqueous solution is demonstrated. Based on this novel approach, polyamide 12 (PA12) powders are decorated with metal and oxide nanoparticles and processed via SLS. Electron microscopy and confocal laser scanning imaging are utilized to analyze the dispersion of the filler.}, language = {en} } @article{LaumerStichelNagulinetal., author = {Laumer, Tobias and Stichel, T. and Nagulin, K. and Schmidt, Michael}, title = {Optical analysis of polymer powder materials for Selective Laser Sintering}, series = {Polymer Testing}, volume = {56}, journal = {Polymer Testing}, publisher = {Elsevier Science}, address = {Amsterdam [u.a.]}, issn = {1873-2348}, doi = {10.1016/j.polymertesting.2016.10.010}, pages = {207 -- 213}, abstract = {This study increases the basic understanding of optical material properties of polymer powders used in selective laser sintering (SLS). Therefore, different polymer powder materials were analyzed regarding their optical material properties with an integration spheres measurement setup. By the measurements a direct connection between the absorption behavior of the solid material and the overall optical material characteristics of the same material in powdery form could be shown. The results were used to develop an advanced explanation model for the optical material properties of powders. At present, existing explanation models only consider the occurring of multiple reflections in the gaps between the particles to explain the overall optical material properties of powder materials. Thus, by also considering the absorption behavior of the single particles, the basic understanding of the beam-matter interaction and their effect on the optical material properties of powder materials can be expanded.}, language = {en} } @article{StichelRathsLaumeretal., author = {Stichel, T. and Raths, Max and Laumer, Tobias and Roth, Stephan}, title = {Multi-Material Deposition of Polymer Powders with Vibrating Nozzles for a New Approach of Laser Sintering}, series = {Journal of Laser Micro/Nanoengineering (JLMN)}, volume = {13}, journal = {Journal of Laser Micro/Nanoengineering (JLMN)}, number = {2}, publisher = {JLPS-Japan Laser Processing Society}, doi = {10.2961/jlmn.2018.02.0002}, pages = {55 -- 62}, abstract = {Conventional Selective Laser Sintering of polymers is restricted to the processing of single materials. The fabrication of components consisting of different material regions is a challenge which cannot be realized by standard coating devices basing on blades or rollers. Thus, advanced coating and deposition techniques are needed which enable the precise and reliable control over very small powder quantities in order to prepare arbitrary powder patterns with high accuracy and repeatability. In this report, the delivery of polymer powder by vibrating nozzles inside laser sintering machines is investigated. Therefore, a steel nozzle attached to a piezo actuator is integrated into a machine, whereas the nozzle itself features internal channels which allow the precise control over the powder temperature using heat transfer oil. The setup is used to study the influence of different system configurations on the powder deposition characteristics as resolution and layer surface roughness. The results show that temperature influences the mass flow depending on the material used and that a precise deposition of powder pattern with microscale resolution is possible with optimized parameters. Finally, the multimaterial powder pattern is fused by a new illumination strategy of laser sintering which is called Simultaneous Intensity-Selective Laser Sintering in order to demonstrate the potential of this new approach.}, language = {en} } @inproceedings{LaumerStichelSachsetal., author = {Laumer, Tobias and Stichel, T. and Sachs, Marius and Amend, Philipp and Schmidt, Michael}, title = {Qualification and modification of new polymer powders for laser beam melting using Ulbricht spheres}, series = {High value manufacturing : Advanced research in virtual and rapid prototyping ; Proceedings of the 6th International Conference on Advanced Research and Rapid Prototyping, Leiraia, Portugal, 1-5 October, 2013}, booktitle = {High value manufacturing : Advanced research in virtual and rapid prototyping ; Proceedings of the 6th International Conference on Advanced Research and Rapid Prototyping, Leiraia, Portugal, 1-5 October, 2013}, editor = {B{\´a}rtolo, Paulo}, publisher = {CRC Press}, address = {Boca Raton}, isbn = {978-1-138-00137-4}, pages = {255 -- 260}, abstract = {The restricted amount of available materials for Laser Beam Melting (LBM) of polymers is one of the main limitations for expanding the technology. Current qualification methods deal with problems like inadequate powder flowability or high part porosities among others but do not offer a detailed analysis of the important beam-matter-interaction between powder particles and electro-magnetic laser radiation. In this paper, polyethylene powder is qualified for the LBM process and specifically analyzed regarding the optical material properties of the powder for a wavelength of 10.6 μm. By admixing graphite as absorption intensifier the change of the optical material properties and the thereby connected processing parameters are analyzed. Furthermore an explanation approach is given to explain the relation between different transmittances of different powder particles and the optical material properties of the polymer powders.}, language = {en} } @article{KuettnerFischerLaumer, author = {Kuettner, Andreas and Fischer, Samuel and Laumer, Tobias}, title = {Mechanical and structural characterization of heat-staked parts realized by selective laser sintering of polyamide 12}, series = {The International Journal of Advanced Manufacturing Technology}, journal = {The International Journal of Advanced Manufacturing Technology}, publisher = {Springer}, doi = {10.1007/s00170-025-17319-4}, pages = {20}, abstract = {Heat staking is a joining process in which thermoplastic pins are formed by heat and pressure in a form-fitting and insoluble way. This study evaluates the mechanical performance and microstructure of selective laser sintered (SLS) polyamide 12 (PA 12) components before and after heat staking, compared with conventionally turned reference specimens. The components were characterized using tensile tests, micrographs, microscopy, and micro-CT measurements. For the tests, the forces and temperatures during heat staking were varied to determine the best process parameters. Tensile tests revealed that SLS joints achieved strengths of up to 33.6 MPa, approaching the 39.9 MPa of the turned references. Microstructural analysis showed a marked reduction in porosity due to heat staking. Porosity decreased from 3.9\% to 1.56\% at a staking force of 300 N and from 4.29\% to 0.81\% at 1000 N, highlighting the beneficial effect of increased force. These results demonstrate that heat staking parameters significantly influence local densification and mechanical performance, and that, under suitable conditions, SLS components can achieve joint strengths comparable to conventionally manufactured parts. The study shows that the heat staking process parameters have a significant influence on the local microstructure and thus on the mechanical performance and provides a basis for optimizing SLS components for new heat staking applications.}, language = {en} }