07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8
Browse
16 results
Search Results
Item Open Access Local laser heat treatment of AlSi10Mg as-built parts produced by Laser Powder Bed Fusion(2024) Kramer, Steffen; Jarwitz, Michael; Schulze, Volker; Zanger, FrederikToday, complex structural components for lightweight applications are frequently manufactured by laser powder bed fusion (PBF-LB), often using aluminum alloys such as AlSi10Mg. However, the application of cyclic load cases can be challenging as PBF-LB produced AlSi10Mg parts typically have low ductility and corresponding brittle failure behavior in the as-built condition. Therefore, this paper presents investigations on the feasibility of a laser heat treatment of PBF-LB produced AlSi10Mg parts to locally increase the ductility and decrease the hardness in critical areas. Potential heat treatment process parameters were derived theoretically based on the temperature fields in the material calculated assuming three-dimensional heat conduction and a moving heat source. PBF-LB produced specimens were then laser heat treated at varying laser power and scan speed. Hardness measurements on metallographic cross sections showed hardness reductions of over 35 % without inducing hydrogen pore growth.Item Open Access Influence of geometry variations during pyrometric temperature measurement in laser material processing(2024) Traunecker, David; Jarwitz, Michael; Michalowski, AndreasItem Open Access Stream finishing of additively manufactured AlSi10Mg PBF-LB parts: influence on surface quality and fatigue behaviour(2024) Wexel, Helena; Kramer, Steffen; Schubert, Johannes; Schulze, Volker; Zanger, FrederikItem Open Access Comparison of in-process laser drying with furnace and vacuum drying to reduce moisture of AlSi10Mg powder processed in Laser Powder Bed Fusion(2024) Lubkowitz, Victor; Fayner, Leonie; Kramer, Steffen; Schulze, Volker; Zanger, FrederikIn most powder bed-based laser melting systems (PBF-LB), metal powders must be handled without inertization but in an air atmosphere for a short time, increasing the AlSi10Mg powder moisture and reducing the achievable component density. Consequently, different drying methods were investigated. Drying in a furnace with an inert atmosphere, using a vacuum to evaporate the water at low temperatures, and vaporizing moisture layerwise from the spreaded powder with a defocused, low-power laser beam as a further process step of the PBF-LB process. Therefore, four different moisturized powders, which were dried with different settings for the drying methods, are analyzed. All drying methods reduce the moisture content of the powder, with in-process drying being the most effective. Due to the oxide layer growth around the particles during furnace and vacuum drying, the achievable sample density after drying is worse. In-process drying with low energy density is the best option to reach a reduction of hydrogen pores and an increase of density.Item Open Access Different coupling mechanisms for a novel modular plate in acetabular fractures : a comparison using a laparoscopic model(2024) Menger, Maximilian M.; Herath, Steven C.; Ellmerer, Andreas E.; Trulson, Alexander; Hoßfeld, Max; Leis, Artur; Ollig, Annika; Histing, Tina; Küper, Markus A.; Audretsch, Christof K.Introduction: Acetabular fractures are among the most challenging injuries in traumatology. The complex anatomy usually requires extensive surgical approaches baring the risk for iatrogenic damage to surrounding neurovascular structures. As a viable alternative, minimally invasive endoscopic techniques have emerged during the recent years. This paper reports on the feasibility of different coupling mechanisms for a novel suprapectineal plate especially designed for minimally invasive acetabular surgery. Methods: A total number of 34 participants contributed to the present study, who differed in their arthroscopic and surgical experience. A laparoscopic model was used to compare four different coupling mechanisms by the number of failed attempts, the time required for plate fixation, the influence of surgical experience as well as the learning success for each individual coupling mechanism. Moreover, the feasibility of each mechanism was evaluated by a questionnaire. Results: The results demonstrate that plates employing grooved and pressure-sliding coupling mechanisms exhibit fewer failed attempts and reduce trial times, especially in contrast to sole sliding mechanisms. Furthermore, our study revealed that proficiency in endoscopic procedures significantly influenced the outcome. Notably, the subjective evaluation of the participants show that the pressure base and pressure-slide base plate designs are the most supportive and feasible designs. Conclusions: In summary, the present study evaluates for the first-time different plate and coupling designs for minimal-invasive surgery, indicating a superior feasibility for plates with a grooved and pressure-sliding mechanism.Item Open Access Self-shielding of X-ray emission from ultrafast laser processing due to geometrical changes of the interaction zone(2024) Holland, Julian; Hagenlocher, Christian; Weber, Rudolf; Graf, ThomasMaterials processing with ultrashort laser pulses is one of the most important approaches when it comes to machining with very high accuracy. High pulse repetition rates and high average laser power can be used to attain high productivity. By tightly focusing the laser beam, the irradiances on the workpiece can exceed 1013 W/cm2, and thus cause usually unwanted X-ray emission. Pulsed laser processing of micro holes exhibits two typical features: a gradual increase in the irradiated surface within the hole and, with this, a decrease in the local irradiance. This and the shielding by the surrounding material diminishes the amount of ionizing radiation emitted from the process; therefore, both effects lead to a reduction in the potential X-ray exposure of an operator or any nearby person. The present study was performed to quantify this self-shielding of the X-ray emission from laser-drilled micro holes. Percussion drilling in standard air atmosphere was investigated using a laser with a wavelength of 800 nm a pulse duration of 1 ps, a repetition rate of 1 kHz, and with irradiances of up to 1.1·1014 W/cm. The X-ray emission was measured by means of a spectrometer. In addition to the experimental results, we present a model to predict the expected X-ray emission at different angles to the surface. These calculations are based on raytracing simulations to obtain the local irradiance, from which the local X-ray emission inside the holes can be calculated. It was found that the X-ray exposure measured in the surroundings strongly depends on the geometry of the hole and the measuring direction, as predicted by the theoretical model.Item Open Access Application of output constraints to a physics-informed hybrid model for the prediction of the threshold of deep-penetration laser welding(2024) Jarwitz, Michael; Michalowski, AndreasPhysics-informed hybrid models, the combination of physics and machine learning, have already shown considerable benefits for quantitative predictions of process constraints, such as the threshold of deep-penetration laser welding. However, despite the improved prediction accuracy and extrapolation capability of such models, there can still be cases where the predictions of the model, including the confidence region, result in values that are not consistent with physical boundary conditions. Therefore, this paper presents the application of additional output constraints to a physics-informed hybrid model to further improve the compliance of the model with physics. Gaussian processes are used for the machine learning model and output warping is used to incorporate the output constraints directly into the model. The approach is demonstrated at the example of a hybrid model for the prediction of the threshold of deep-penetration laser welding.Item Open Access Application of a physics-informed hybrid model with additional output constraints for the prediction of the threshold of deep-penetration laser welding(2025) Jarwitz, Michael; Michalowski, AndreasThe quantitative prediction of process constraints, such as the threshold of deep-penetration laser welding, plays a crucial role for the fast and reliable development of robust process windows for laser manufacturing processes. A physics-informed hybrid model with additional output constraints for the prediction of the threshold of deep-penetration laser welding is presented. A “residual model” approach is used, where a machine learning model, employing Gaussian processes, is used to model and compensate for the deviations between experiments and a physical model, and output warping is used to incorporate additional output constraints into the model. The main benefits that result from applying such a model are found to be (1) an increased prediction accuracy compared to only using the physical model, leading to a reduction of the mean relative error of about 76%; (2) a reduction of the number of required training data compared to only using a black-box machine learning model; (3) an increased prediction accuracy compared to only using a black-box machine learning model; (4) and an increased compliance with physical boundary conditions by applying the additional output constraints.Item Open Access Supercritical melt flow in high-speed laser welding and its interdependence with the geometry of the keyhole and the melt pool(2024) Reinheimer, Eveline N.; Berger, Peter; Hagenlocher, Christian; Weber, Rudolf; Graf, ThomasThe advent of undercuts and humping limits the applicable speed of deep-penetration laser welding. Recent findings additionally show that a significant change of the keyhole’s shape is associated with the occurrence of undercuts. Considering that undercuts and humping are melt flow–induced defects, this leads to the question of how the geometry of the keyhole and the melt pool influence the melt flow and vice versa. In this work, the Froude number was used to characterize the melt flow around a keyhole. X-ray images of the keyhole and cross-sections of the weld were therefore used to determine the geometrical boundaries of the melt flow, to estimate the average melt velocity around the keyhole, and finally determine its Froude number. The flow around a cylindrically shaped keyhole was found to always be subcritical, whereas supercritical melt flow was observed around the elongated keyholes that are formed at higher welding speed. The findings may be interpreted in the sense that the elongation of the keyhole is a consequence of a supercritical stream of the melt flowing underneath and around the keyhole. This perception is consistent with the long-known experience that humping may be avoided by reducing the flow speed of the melt by widening the melt pool surrounding the keyhole (e.g., by means of beam shaping) and suggest a new explanation for the elongation of the keyhole at increased welding speed.Item Open Access The change of the absorptance at the transition from partial- to full-penetration laser welding(2024) Wagner, Jonas; Hagenlocher, Christian; Weber, Rudolf; Graf, ThomasFull-penetration laser welding processes are necessarily associated with significant changes of the geometrical properties of the keyhole at the beginning of the process when the keyhole expands all the way through the workpiece and finally pierces the bottom of the sheet. The impact that this transition has on the absorptance was investigated by means of X-ray imaging to determine the geometry of the keyhole and subsequent raytracing to calculate the distribution of the absorbed irradiance. The results show a significant drop of the overall absorptance when the bottom of the capillary opens through the rear side of the workpiece which in practice is noticed by an unstable behavior of the keyhole. Since the drop of the absorptance is less pronounced for smaller diameters of the keyhole, one may recommend the application of laser beams with small diameters at least during the initial phase until the keyhole is fully developed and reliably reaches through the bottom surface of the welded sheet.