Innovative Material Processing
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In line with the energy transition, it is desirable to replace fossil fuels in the curing process of industrial powder coatings. Infrared heating is the considered method here. Near Infra Red-emitter arrangement in the reflective heating chamber, their geometry and the dwell time of the components are crucial for a successful and efficient process. Process optimization has to consider the optical parameter variation of the powder coating during the procedure. Measurements in the NAPUBEST (“Nachhaltige Pulverbeschichtungs-
Technologie”: sustainable powder coating technology) prototype are compared with optical simulations of the setup to get the simulation parameters in agreement with reality and to provide a foundation for the layout of industrial processes.
Infrared illumination powered by renewable energy sources can replace conventional heating based on fossil fuels. The use of infrared radiation as a heat source for industrial powder coating systems also provides a very fast and direct heating of the coating materials. Nevertheless, the difficulty of an evenly distributed illumination for industrial products with different shapes prevented this technology from a widespread use so far. Innovative approaches need to be adapted for the intended use of infrared heating in industrial powder coating processes. The prototype infrared furnace in our laboratory with highly reflective walls and a special octagonal design facilitates a largely homogeneous illumination even of geometrically complex products. An infrared camera visualizes temperature profiles of white and black coating samples during the heating process. The subsequent comparison of the experimental results with corresponding simulations will deliver the basis for the layout of future industrial facilities.
We report on a study of the mechanical properties of hybrid-additive manufactured Inconel 718 double-periodic lattice structures. For this, a hybrid approach, combining Laser Powder Bed Fusion (PBF-LB/M) and in-situ high-speed milling, is employed. Within this technique, the PBF-LB/M process is interrupted after several layers, as the milling process starts, enabling a machining of inlaying structures.
We report on the effect of hot isostatic pressing combined with solution and ageing treatment in different sequences on the mechanical properties of Inconel 718 specimens, which in turn have been fabricated by a hybrid additive manufacturing approach. The latter combines conventional laser powder bed fusion and in-situ high speed milling, yielding superior surface quality as being quantified by Ra about 1 μm. In a comparative study between hybrid additively manufactured parts and those built without milling, we find that, in general, any combination of heat treatment leads to a higher ultimate tensile strength and an improved endurance limit, while, however, hot isostatic pressing affects these figures of merit most. In addition, metallographic analysis reveals increased density and hardness for hot isostatic pressed parts due to precipitation hardening. These improvements of the mechanical properties are found to be even more pronounced when the printed parts are manufactured by the hybrid additive approach, i.e., for parts with improved surface conditions.
We report on the optimization of tensile properties and fatigue behaviour of Laser Powder Bed Fusion (PBF-LB/M)-built IN718 components employing an innovative hybrid additive-subtractive technology and various heat treatments. The hybrid approach comprises PBF-LB/M with in situ high-speed milling. Double Ageing, solution and ageing treatment, as well as Hot Isostatic Pressing are used to improve ultimate tensile strength and endurance limit. As a result, the advantages of the hybrid-machined components are clearly demonstrated by their improved mechanical properties. These enhanced properties are associated to changes in microstructure, which are identified as precipitations of IN718. Furthermore, crack initiation and crack growth for high cycle numbers as well as sudden fractures are determined.
A study of the mechanical properties of hybrid additive manufactured IN718 components is presented, optimising mechanical properties due to an in-situ high-speed milling and different heat treatment processes. At first, the impact of different heat treatment processes is investigated, as the changes in microstructure during the process lead to different mechanical properties. Static and dynamic mechanical load behaviour is tested, quantifying microstructural changes by means of the Ultimate Tensile Strength (UTS) and the endurance limit. Furthermore, sole PBF-LB/M- and hybrid built components are compared, investigating the effect of a surface finish on the static and dynamic load behaviour, as superficial cracks and melting errors diminish the UTS and the endurance limit of PBF-LB/M-built components. Within these experiments, a change of fatigue behaviour for the heat-treatedstates can be observed, compared to the as-built state of the PBF-LB/M, as the development of different phases during heat treatment leads to an improvement of the endurance limit for, e.g., solution and ageing treated components. Additionally, the improvement of the surface quality to Ra = 2 µm leads to a significant increase of the dynamic mechanical load behaviour of hybrid-built components, as superficial cracks and surface defects are reduced.
We report on a comprehensive study of tensile strength and fatigue behaviour depending on process parameters and ambient temperature. For this, Polyamide-12 components are fabricated using Selective Laser Sintering. Firstly, different process parameters like, e.g, scan-speed, laser power, and applied energy density are varied. Secondly, the ambient temperature during testing is varied, evaluating the impact of decreased, respectively increased test temperatures on the characteristics of the Polyamide-12 components. For all components, the static and dynamic mechanical load behaviour is investigated, quantifying the changes in the Ultimate Tensile Strength (UTS) and the endurance limit. As the applied energy density transpires as a decisive parameter, a variation leads to significant changes in UTS and endurance limit, whereas an adjustment of scan-speed and laser power at a constant energy density do not affect the mechanical properties. Finally, the ambient temperature during testing is evaluated, demonstrating different ambient application conditions. The impact of an active cooling of the component as well as increased temperatures on the mechanical behaviour is tested, providing fundamental findings on the operating life of Polyamide-12 components.
Microstructural Fracture Behaviour of PBF-LB/M Inconel 718 Components within different HIP Processes
(2025)
We report on a study of different hot isostatic pressing (HIP) cycles, improving the mechanical properties of additively manufactured Inconel 718 components. For this, PBF-LB/M built components are post-processed by different HIP sequences, as gas pressure and processing time are varied, leading to differences in microstructure and material characteristics. Static and dynamic mechanical testing are performed, evaluating the changes in mechanical properties with particular focus on the ultimate tensile strength and endurance limit. Furthermore, metallographic analysis is employed to investigate the achieved density and microhardness. Microstructural analysis, showing the grain boundaries, is used to identify generated phases and precipitations of the material matrix. Moreover, the fracture behaviour is classified by grain deformation during mechanical testing. As the HIP leads to microstructural changes of Inconel 718 components, mechanical properties can be improved significantly, enhancing the ultimate tensile strength and simultaneously the endurance limit.
As lattice structures in various designs are used in additive manufacturing for lightweight components, the mechanical characterisation and fracture behaviour is of upmost importance for their industrial application. In this study, the fatigue behaviour of Inconel 718 lattice structures is evaluated, comparing sole PBF-LB/M to a hybrid additive manufacturing process combining PBF-LB/M with in-situ high-speed milling. At first, the static and dynamic mechanical load behaviour of different packing densities is analysed, determining the compressive strength and the endurance limit. Secondly, hybrid additive manufactured components are compared to PBF-LB/M built parts with respect to these mechanical properties, revealing improved compressive properties and modified regimes of fatigue. In addition, differences in fracture behaviour are qualified by fractographic and surface analysis. Overall, it can be summarized that the mechanical load characteristics, especially the fatigue behaviour, are improved for hybrid additively manufactured components with a superior surface quality of Ra < 1 µm.
As the correlation between design rules and process limitations is of the upmost importance for the full exploitation of any manufacturing technology, we report a design guide for hybrid-additive manufacturing of Inconel 718. Basic limitations need to be evaluated for this particular hybrid approach that combines laser powder bed fusion (PBF-LB/M) and in situ high-speed milling. Fundamental geometric limitations are examined with regard to the minimum feasible wall thickness, cylinders, overhanging structures, and chamfers. Furthermore, geometrical restrictions due to the integrated three-axis milling process with respect to inclinations, inner angles, notches, and boreholes are investigated. From these findings, we derive design guidelines for a reliable build process using this hybrid manufacturing. Additionally, a design guideline for the hybrid-additive manufacturing approach is presented, depicting a step-to-step guide for the adjustment of constructions. To demonstrate this, a powder nozzle for a direct energy deposition (DED-LB/M) process is redesigned following the previously defined guidelines. This redesign encompasses analysis of the existing component and identification of problematic areas such as flat angles, leading to a new construction that is suitable for a hybrid-additive manufacturing approach.