Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Heat treatment of SLM-LMD hybrid components
    ( 2019)
    Uhlmann, Eckart
    ;
    Düchting, Jan
    ;
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Additive manufacturing is no longer just used for the production of prototypes but already found its way into the industrial production. However, the fabrication of massive metallic parts with high geometrical complexity is still too time-consuming to be economically viable. The combination of the powder bed-based selective laser melting process (SLM), known for its geometrical freedom and accuracy, and the nozzle-based laser metal deposition process (LMD), known for its high build-up rates, has great potential to reduce the process duration. For the industrial application of the SLM-LMD hybrid process chain it is necessary to investigate the interaction of the processes and its effect on the material properties to guarantee part quality and prevent component failure. Therefore, hybrid components are manufactured and examined before and after the heat treatment regarding the microstructure and the hardness in the SLM-LMD transition zone. The experiments are conducted using the nickel-based alloy Inconel 718.
  • Publication
    Microstructure of Inconel 718 parts with constant mass energy input manufactured with direct energy deposition
    ( 2019)
    Petrat, Torsten
    ;
    Brunner-Schwer, Christian
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    The laser-based direct energy deposition (DED) as a technology for additive manufacturing allows the production of near net shape components. Industrial applications require a stable process to ensure reproducible quality. Instabilities in the manufacturing process can lead to faulty components which do not meet the required properties. The DED process is adjusted by various parameters such as laser power, velocity, powder mass flow and spot diameter, which interact with each other. A frequently used comparative parameter in welding is the energy per unit length and is calculated from the laser power and the velocity in laser welding. The powder per unit length comparative parameter in the DED process has also be considered, because this filler material absorbs energy in addition to the base material. This paper deals with the influence of mass energy as a comparative parameter for determining the properties of additively manufactured parts. The same energy per unit length of 60 J/mm as well as the same powder per unit length of 7.2 mg/mm can be adjusted with different parameter sets. The energy per unit length and the powder per unit length determine the mass energy. The laser power is varied within the experiments between 400 W and 900 W. Energy per unit length and powder per unit length are kept constant by adjusting velocity and powder mass flow. Using the example of Inconel 718, experiments are carried out with the determined parameter sets. In a first step, individual tracks are produced and analyzed by means of micro section. The geometry of the tracks shows differences in height and width. In addition, the increasing laser power leads to a higher dilution of the base material. To determine the suitability of the parameters for additive manufacturing use, the individual tracks are used to build up parts with a square base area of 20×20 mm². An investigation by Archimedean principle shows a higher porosity with lower laser power. By further analysis of the micro sections, at low laser power, connection errors occur between the tracks. The results show that laser power, velocity and powder mass flow must be considered in particular, because a constant mass energy can lead to different geometric as well as microscopic properties.
  • Publication
    Assessing the predictive capability of numerical additive manufacturing simulations via in-situ distortion measurements on a LMD component during build-up
    ( 2018)
    Biegler, Max
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Due to rapid, localized heating and cooling, distortions accumulate in additive manufactured laser metal deposition (LMD) components, leading to a loss of dimensional accuracy or even cracking. Numerical welding simulations allow the prediction of these deviations and their optimization before conducting experiments. To assess the viability of the simulation tool for the use in a predictive manner, comprehensive validations with experimental results on the newly-built part need to be conducted. In this contribution, a predictive, mechanical simulation of a thin-walled, curved LMD geometry is shown for a 30-layer sample of 1.4404 stainless steel. The part distortions are determined experimentally via an in-situ digital image correlation measurement using the GOM Aramis system and compared with the simulation results. With this benchmark, the performance of a numerical welding simulation in additive manufacturing is discussed in terms of result accuracy and usability.
  • Publication
    Embedding electronics into additive manufactured components using laser metal deposition and selective laser melting
    ( 2018)
    Petrat, Torsten
    ;
    Kersting, Robert
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    The paper deals with the integration of a light emitting diode (LED) into an additive manufactured metal component. Selective laser melting (SLM) and laser metal deposition (LMD) are used. The material used is the chrome-nickel steel 316L. The basic component is manufactured by means of SLM and consists of a solid body and an area with grid structure. The solid body includes a duct in the shape of a groove with a recess for the positioning of the power cable. The LED is embedded in the grid structure via an inlet from the solid body. In further processing, the groove is filled with LMD. Two strategies with different parameter combinations were investigated. It shows that a high energy input near the power cable leads to its destruction. By using multiple parameter combinations during the manufacturing process, this destruction can be prevented. There was a comparison of both strategies with regard to the necessary number of tracks and duration of welding time.
  • Publication
    Laser-plasma-cladding as a hybrid metal deposition-technology applying a SLM-produced copper plasma nozzle
    ( 2018)
    Brunner-Schwer, Christian
    ;
    Kersting, Robert
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Laser-Metal-Deposition (LMD) and Plasma-Transferred-Arc (PTA) are well known technologies which can be used for cladding purposes. The prime objective in combining LMD and PTA as a Hybrid Metal Deposition-Technology (HMD) is to achieve high deposition rates at low thermal impact. Possible applications are coatings for wear protection or repair welding for components made of steel. The two energy sources (laser and plasma arc) build a joint process zone and are configurated to constitute a stable process at laser powers between 0.4-1 kW (defocused) and plasma currents between 75-200 A. Stainless steel 316L serves as filler material. For this HMD process, a plasma Cu-nozzle is designed and produced by powder bed based Selective Laser Melting. The potential of the HMD technology is investigated and discussed considering existing processes. This paper demonstrates how the interaction of the two energy sources effects the following application-relevant properties: deposition rate, powder efficiency and energy input.
  • Publication
    3D laser metal deposition in an additive manufacturing process chain
    ( 2017)
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Laser metal deposition (LMD) is an established technology for two-dimensional surface coatings. It offers high deposition rates, high material flexibility and the possibility to deposit material on existing components. Due to these features, LMD has been increasingly applied for additive manufacturing of 3D structures in recent years. Compared to previous coating applications, additive manufacturing of 3D structures leads to new challenges regarding LMD process knowledge. In this paper, the process chain for LMD as additive manufacturing technology is described. The experiments are conducted using titanium alloy Ti-6Al-4V and Inconel 718. Only the LMD nozzle is used to create a shielding gas atmosphere. This ensures high geometric flexibility, although issues with the restricted size and quality of the shielding gas atmosphere arise. In the first step, the influence of process parameters on the geometric dimensions of single weld beads is analysed based on design of experiments and statistical evaluation. The results allow adjusting the weld bead dimensions for the specific component geometry. In the second step, features of a 3D build-up strategy for high dimensional accuracy are discussed. For this purpose, cylindrical specimens consisting of more than 200 layers are built. Welding of multiple layers on top of each other leads to heat accumulation. Consequently, the molten pool is increased and weld bead height and width are changed. Furthermore, cooling times are prolonged. The build-up strategy has to be adjusted to deal with these issues. Process parameters, travel paths and cooling breaks between layers are varied. Temperatures during the deposition process are measured with pyrometer and thermography. The specimens are analysed with metallurgic cross sections, x-ray and tensile test. Tensile tests show that mechanical properties in the as-deposited condition are close to wrought material. The results are used to design guidelines for a LMD build-up strategy for complex components. As reality test, parts of a gas turbine burner and a turbine blade are manufactured according to these build-up strategies. Build-up rate, net-shape and microstructure of these demonstrative components are evaluated. This paper is relevant for industrial or scientific users of LMD, who are interested in the feasibility of this technology for additive manufacturing.
  • Publication
    Laser-Pulver-Auftragschweißen zum additiven Aufbau komplexer Formen
    ( 2015)
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Das Laser-Pulver-Auftragschweißen als additives Fertigungsverfahren ermöglicht einen endformnahen Aufbau von Bauteilen. Ein Zielkonflikt besteht zwischen der Forderung nach hoher Aufbaurate und hoher Endformnähe, welcher von der Schweißraupengröße wesentlich beeinflusst wird. In dieser Veröffentlichung wird das Laser-Pulver-Auftragschweißen eingesetzt, um komplexe Formen additiv aufzubauen. Am Beispiel eines Tannenbaumprofiles werden unterschiedliche Einflussfaktoren dargestellt. Dazu gehören die Raupengeometrie, die Überlappung einzelner Raupen, die Verwendung unterschiedlicher Aufbaustrategien und die Teilung des Gesamtkörpers in Teilkörper. Der Zielkonflikt wird durch die Herstellung von Probekörpern mit unterschiedlichen Steigungswinkeln an den Seitenflächen verdeutlicht. Die Ergebnisse zeigen eine verbesserte Endformnähe in Bereichen flacher Steigung beim Einsatz kleiner Schweißraupen. Im Vergleich dazu erlauben die Schweißparameter der großen Raupen eine 5-fach höhere Aufbaurate. Bei einer Raupenüberlappung kleiner und großer Raupengeometrien innerhalb einer Lage treten Anbindungsfehler auf. Strategien zur Behebung dieses Fehlers durch Anpassung der Schweißreihenfolge werden in dieser Veröffentlichung aufgezeigt. Diese Erfahrungen werden genutzt, um einen Gesamtkörper aus Teilkörpern unterschiedlicher Raupengeometrien zu fertigen.