Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Characterization of Ti-6Al-4V Fabricated by Multilayer Laser Powder-Based Directed Energy Deposition
    ( 2022)
    Ávila Calderón, Luis Alexander
    ;
    Graf, Benjamin
    ;
    Rehmer, Birgit
    ;
    Petrat, Torsten
    ;
    Skrotzki, Birgit
    ;
    Rethmeier, Michael
    Laser powder-based directed energy deposition (DED-L) is increasingly being used in additive manufacturing (AM). As AM technology, DED-L must consider specific challenges. It must achieve uniform volume growth over hundreds of layers and avoid heat buildup of the deposited material. Herein, Ti-6Al-4V is fabricated using an approach that addresses these challenges and is relevant in terms of transferability to DED-L applications in AM. The assessment of the obtained properties and the discussion of their relationship to the process conditions and resulting microstructure are presented. The quality of the manufacturing process is proven in terms of the reproducibility of properties between individual blanks and with respect to the building height. The characterization demonstrates that excellent mechanical properties are achieved at room temperature and at 400 C.
  • Publication
    Influence of electron beam welding parameters on the weld seam geometry of Inconel 718 at low feed rates
    ( 2020)
    Raute, Julius
    ;
    Jokisch, Torsten
    ;
    Marko, Angelina
    ;
    Biegler, Max
    ;
    Rethmeier, Michael
    Ni-based superalloys are well established in various industrial applications, because of their excellent mechanical properties and corrosion resistance at high temperatures. Despite the high development stage and a common industrial use of these alloys, hot cracking remains a major challenge limiting the weldability of the materials. As commonly known, the hot cracking susceptibility during welding increases with the amount of precipitation phases. Hence, a large amount of highstrength Ni-Alloys is rated as non-weldable. A new approach based on electron beam welding at low feed rates shows great potential for reducing the hot cracking tendency of precipitation-hardened alloys. However, geometry and properties of the weld seam differ significantly in comparison to the common process range for practical uses. The aim of this study is to investigate the influence of welding parameters on the seam geometry at low feed rates between 1 mm/s and 10 mm/s. For this purpose, 25 bead on plate welds on a 12 mm thick sheet made of Inconel 718 are carried out. First, the relevant parameters are identified by performing a screening. Then the effects discovered are further studied by using a central composite design. The results show a significant difference between the analyzed weld seam geometry in comparison to the well-known appearance of electron beam welded seams.
  • Publication
    Hybrid laser arc welding of thick high-strength pipeline steels of grade X120 with adapted heat input
    ( 2020)
    Üstündag, Ömer
    ;
    Gook, Sergej
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    The influence of heat input and welding speed on the microstructure and mechanical properties of single-pass hybrid laser arc welded 20 mm thick plates of high-strength pipeline steel X120 were presented. The heat input was varied in the range of 1.4 kJ mm-1 to 2.9 kJ mm-1, while the welding speed was changed between 0.5 m min-1 and 1.5 m min-1. A novel technique of bath support based on external oscillating electromagnetic field was used to compensate the hydrostatic pressure at low welding velocities. A major advantage of this technology is, that the welding speed and thus the cooling time t8/5 can be variated in a wide parameter window without issues regarding the weld root quality. The recommended welding thermal cycles for the pipeline steel X120 can be met by that way. All tested Charpy-V specimens meet the requirements of API 5 L regarding the impact energy. For higher heat inputs the average impact energy was 144 ± 37 J at a testing temperature of -40 °C. High heat input above 1.6 kJ mm-1 leads to softening in the weld metal and heat-affected-zone resulting in loss of strength. The minimum tensile strength of 915 MPa could be achieved at heat inputs between 1.4 kJ mm-1 and 1.6 kJ mm-1.
  • Publication
    Porosity of LMD manufactured parts analyzed by Archmimedes method and CT
    ( 2018)
    Marko, Angelina
    ;
    Raute, Julius
    ;
    Linaschke, Dorit
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Pores in additive manufactured metal parts occur due to different reasons and affect the part quality negatively. Few investigations on the origins of porosity are available, especially for Ni-based super alloys. This paper presents a new study to examine the influence of common processing parameters on the formation of pores in parts built by laser metal deposition using Inconel 718 powder. Further, a comparison between the computed tomography (CT) and the Archimedes method was made. The investigation shows that CT is able to identify different kinds of pores and to give further information about their distribution. The identification of some pores as well as their shape can be dependent on the parameter setting of the analysis tool. Due to limited measurement resolution, CT is not able to identify correctly pores with diameters smaller than 0.1 mm, which leads to a false decrease in overall porosity. The applied Archimedes method is unable to differentiate between gas porosity and other kinds of holes like internal cracks or lack of fusion, but it delivered a proper value for overall porosity. The method was able to provide suitable data for the statistical evaluation with design of experiments, which revealed significant parameters on the formation of pores in LMD.
  • Publication
    Statistische Analyse der Schweißraupengeometrie von Ti6Al4V beim Laserbeschichten
    ( 2017)
    Marko, Angelina
    ;
    Graf, Benjamin
    ;
    Rethmeier, Michael
    Die Bedeutung des Laser-Pulver-Auftragsschweiß-Prozesses hat in den letzten Jahren enorm zugenommen, da er vielfältig eingesetzt werden kann. Ein Beispiel hierfür ist die Reparatur von Turbinenschaufeln. Um eine hohe Qualität und Zuverlässigkeit hierbei zu gewährleisten, ist eine Anpassung der Schweißraupengeometrie an die jeweilige Reparaturaufgabe notwendig. Die Schweißraupengeometrie beeinflusst die metallurgische Verbindung und den Grad der Aufmischung sowie eventuelle Anbindungsfehler. Aus diesem Grund ist es wichtig, die Effekte der unterschiedlichen Parameter auf die Spurgeometrie zu kennen. Ein bewährtes Werkzeug hierfür ist die statistische Versuchsplanung (DoE). Hierbei kann der Nutzer jedoch zwischen einer Vielzahl von Versuchsplänen wählen. Es wird davon ausgegangen, dass bei größeren Versuchsräumen ein höherer Informationsgewinn erfolgt. Aus diesem Grund wird in dieser Arbeit ein vollfaktorieller Versuchsplan, der in fünf Stufen variiert wird, mit einem zentral zusammengesetzten Versuchsplan (CCD) verglichen. Außerdem werden Grenzen des Prozesses aufgezeigt und der Versuchsraum entsprechend durch Eingrenzungen angepasst. Die Ergbnisse zeigen, dass sowohl der vollfaktorielle Versuchsplan als auch der zentral zusammengesetzte Versuchsplan die wichtigsten Effekte aufzeigt. Lediglich die Effektstärke kann durch den CCD-Versuchsplan nicht eindeutig bestimmt werden. Für den industriellen Einsatz wird daher unter Berücksichtigung der Kosteneffizienz der Einsatz eines CCD-Versuchsplanes empfohlen.