Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Build-up strategies for laser metal deposition in additive manufacturing
    ( 2018)
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Laser Metal Deposition (LMD) as a technology for additive manufacturing allows the production of large components outside of closed working chambers. Industrial applications require a stable process as well as a constant deposition of the filler material in order to ensure uniform volume growth and reproducible mechanical properties. This paper deals with the influence of travel path strategies on temperature profile and material deposition. Meandering and spiral hatching strategies are used in the center as well as in the edge of a specimen. The temperature is measured with thermocouples attatched to the backside of the specimen. The tests are carried out on the materials S235JR and 316L. The results show a strong dependence of the maximum temperatures on the travel path strategy and the welding position on the component.
  • Publication
    3D laser metal deposition: Process steps for additive manufacturing
    ( 2018)
    Graf, Benjamin
    ;
    Marko, Angelina
    ;
    Petrat, Torsten
    ;
    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 steps for LMD as additive manufacturing technology are 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 the high geometric flexibility needed for additive manufacturing, 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 analyzed based on design of experiments. In the second step, a 3D build-up strategy for cylindrical specimen with high dimensional accuracy is described. Process parameters, travel paths, and cooling periods between layers are adjusted. Tensile tests show that mechanical properties in the as-deposited condition are close to wrought material. As practical example, the fir-tree root profile of a turbine blade is manufactured. The feasibility of LMD as additive technology is evaluated based on this component.
  • Publication
    Build-up strategies for temperature control using laser metal deposition for additive manufacturing
    ( 2018)
    Petrat, Torsten
    ;
    Winterkorn, René
    ;
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    The track geometry created with laser metal deposition (LMD) is influenced by various parameters. In this case, the laser power has an influence on the width of the track because of an increasing energy input. A larger melt pool is caused by a rising temperature. In the case of a longer welding process, there is also a rise in temperature, resulting in a change of the track geometry. This paper deals with the temperature profiles of different zigzag strategies and spiral strategies for additive manufacturing. A two-color pyrometer is used for temperature measurement on the component surface near the melt pool. Thermocouples measure the temperatures in deeper regions of a component. The welds are located in the center and in the edge area on a test part to investigate the temperature evolution under different boundary conditions. The experiments are carried out on substrates made from mild steel 1.0038 and with the filler material 316L. The investigations show an influence on the temperature evolution by the travel path strategy as well as the position on the part. This shows the necessity for the development and selection of build-up strategies for different part geometries in additive manufacturing by LMD.
  • 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
    Temperature generation of different travel path strategies to build layers using Laser Metal Deposition
    ( 2017)
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Winterkorn, René
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Laser Metal Deposition offers the chance to build near net shape parts. The temperature evolution within the process has an influence on track and layer geometries. There are special travel path strategies required to produce near net shape components and reduce shape deviation resulting of error propagation. This paper deals with the temperature progression of individual layers and the maximum heating of deeper substrate regions. Spiral and zig-zag strategies are examined. The investigations are carried out using S235JR as substrate and 316L as powder material. The influence of different strategies on temperature evolution is discussed. The results from the experiments show that various production strategies are associated with different temperature fields. Furthermore, the extent of the temperature variations of layer strategies and layer position are strongly dependent on the production direction. These results demonstrate the importance of developing suitable build-up strategies for parts of complex shape to ensure a stable process with constant temperature as well as even layers.
  • Publication
    Combined laser additive manufacturing for complex turbine blades
    ( 2016)
    Graf, Benjamin
    ;
    Gook, Sergej
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Laser beam processes are increasingly used in the field of additive manufacturing. Prominent methods are either powderbed-based like Laser Metal Fusion (LMF), or utilizing a powder nozzle like Laser Metal Deposition (LMD). While LMF allows the manufacturing of complex structures, build rate, part volumes and material flexibility are limited. In contrast, LMD is able to operate with high deposition rates on existing parts, and materials can be changed easily during the process. However LMD shape complexity is limited. Utilizing their respective strengths, a combination of these two additive technologies has the potential to produce complex parts with high deposition rates and increased material flexibility. In this paper, combined manufacturing with additive technologies LMF and LMD is described. Its benefit for industry with emphasis on turbomachinery is shown. As reality test for the innovation, an industrial turbine blade is manufactured.
  • Publication
    Combined laser additive manufacturing with powderbed and powder nozzle for turbine parts
    ( 2016)
    Graf, Benjamin
    ;
    Schuch, Michael
    ;
    Petrat, Torsten
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Metal additive manufacturing is often based on laser beam processes like Laser Metal Fusion (LMF) or Laser Metal Deposition (LMD). The LMF process is in particular suitable for very complex geometries. However build rate, part volume and material flexibility are limited in LMF. In contrast, LMD achieves higher deposition rates, less restricted part sizes and the possibility to change the material composition during the build-up process. On the other hand, due to the lower spatial precision of the material deposition process, the complexity of geometries is limited. Therefore, combined manufacturing with both LMF and LMD has the potential to utilize the respective advantages of both technologies. In this paper, combined additive manufacturing with LMF and LMD is described for Ti-6Al-4V and Inconel 718. First, lattice structures with different wall thickness and void sizes are built with LMF. The influence of LMD material deposition on these LMF-structures is examined regarding metallurgical impact and distortion. Cross-sections, x-ray computer tomography and 3D-scanning results are shown. For the titanium alloy specimen, oxygen and Nitrogen content in the deposited material are analysed to evaluate the LMD shielding gas atmosphere. The results are used to develop guidelines for a LMD build-up strategy on LMF substrates. With these findings, a gas turbine burner is manufactured as reality test for the combined approach.
  • Publication
    Laser metal deposition as repair technology for a gas turbine burner made of Inconel 718
    ( 2016)
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Maintenance, repair and overhaul of components are of increasing interest for parts of high complexity and expensive manufacturing costs. In this paper a production process for laser metal deposition is presented, and used to repair a gas turbine burner of Inconel 718. Different parameters for defined track geometries were determined to attain a near net shape deposition with consistent build-up rate for changing wall thicknesses over the manufacturing process. Spot diameter, powder feed rate, welding velocity and laser power were changed as main parameters for a different track size. An optimal overlap rate for a constant layer height was used to calculate the best track size for a fitting layer width similar to the part dimension. Deviations in width and height over the whole build-up process were detected and customized build-up strategies for the 3D sequences were designed. The results show the possibility of a near net shape repair by using different track geometries with laser metal deposition.
  • Publication
    Strategien zur Erreichung eines konstanten Volumenaufbaus bei der additiven Fertigung mittels Laser-Pulver-Auftragschweißen
    ( 2016)
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Der Einsatz von Hochleistungswerkstoffen verlangt nach einer hohen Endformnähe der zu fertigenden Bauteile, um den Aufwand und somit die Kosten für Materialeinsatz und Nachbearbeitung möglichst gering zu halten. Der additive Einsatz in Form des Laser-Pulver-Auftragschweißens bietet hierfür durch den gezielten Materialauftrag ein hohes Potential. Herausforderungen bestehen in Bereichen der Vorhersagbarkeit und der Reproduzierbarkeit des Materialauftrages, sowie der Fertigungszeit. Unterschiedliche Einflüsse bei der Schichterzeugung führen dabei zu Abweichungen von der Soll-Geometrie. Die vorliegenden Untersuchungen behandeln den Einfluss von Spurgeometrie, Spurüberlappung, Verfahrweg und Aufbaureihenfolge auf die entstehende Bauteilform. Die Teilung einer Lage in Rand- und Kernbereich ermöglicht einen konturangepassten Verfahrweg und eine Erhöhung der Endformnähe innerhalb einer Ebene. Die Verwendung unterschiedlicher Spurgrößen bei der Bauteilerzeugung verdeutlicht die Möglichkeiten einer hohen Auftragsrate bei gleichzeitig hoher Formgenauigkeit. Bereits kleine Unterschiede beim Materialauftrag zwischen Kern- und Randbereichen, Start- und Endpunkten sowie in Bereichen des Richtungswechsels führen aufgrund von Fehlerfortpflanzung nach mehreren Lagen zu Abweichungen in der Aufbaurichtung. Kompensierungen mittels angepasster Baustrategien werden aufgezeigt und diskutiert. Die Nickelbasislegierung Inconel 718, die Titanlegierung Ti-6Al-4V sowie der austenitische Stahl 316L sind Bestandteil der vorliegenden Untersuchungen. Die gewonnenen Erkenntnisse verdeutlichen das Potenzial einer angepassten Aufbaustrategie zur reproduzierbaren Erzeugung von Bauteilen am Beispiel unterschiedlicher Körpergeometrien.
  • Publication
    Build-up strategies for generating components of cylindrical shape with laser metal deposition
    ( 2015)
    Petrat, Torsten
    ;
    Graf, Benjamin
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Laser Metal Deposition (LMD) as additive manufacturing process offers the potential to produce near net shape components. This reduces the amount of material and post-processing. The components are composed of individual layers. Already small irregularities within a layer can add up over multiple layers and lead to error propagation. This paper deals with the issue of build-up strategies to minimize irregularities and prevent error propagation. Different travel paths and the influence of a changing starting point regarding to error propagation are discussed. Different deposition rates between core and peripheral area are detected and successfully compensated by adjusting the buildup sequence. Stainless steel and titanium alloy Ti-6Al-4V are used in the experiments. The results are intended to illustrate the potential of an adjusted build-up strategy and provide basic information on the way to an automated deposition process. This paper is of interest for engineers in industry or science using LMD as additive manufacturing process.