Laser-based Additive Manufacturing of Metal Parts from Powder in Microgravity

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During any deep space mission (e.g. flying to Mars), spare parts are needed to keep the spacecraft operational. Instead of manufacturing spare parts on Earth and bringing them along, parts can be produced during the mission by additive manufacturing (AM). By utilizing AM, the total mass of the mission is greatly reduced and its safety is increased, since it is possible to react to component failure more flexibly.Multiple AM processes have been researched that work in microgravity. However, no AM process that works in microgravity has been researched that is capable of simultaneously being able to produce net shapes solely by AM, repairing surfaces, and producing different alloys. Laser Metal Deposition (LMD) is capable of achieving these goals. During the LMD process, a laser beam creates a melting pool on the work piece. Simultaneously, a fluidized metal powder is injected into the melting pool. When the laser beam traverses the work piece, the melting pool solidifies thus creating an elevated structure on the work piece.The research goal is to develop and characterize the LMD process in microgravity. The characterization of the LMD process is achieved by analyzing the manufactured specimens. The following attributes of the specimens are analyzed: geometry, metallography, hardness and uniaxial tensile strength. The major process parameters that are varied during the LMD process are the beam power, the powder attributes, and the feed rate.To achieve the research goal two primary objects have to be accomplished: the powder feeding and the laser-based creation of the melting pool must work in microgravity. For both primary objects fundamental research under microgravity conditions is necessary. Microgravity is achieved by the Einstein-Elevator - a novel drop tower that has a much higher repetition rate than conventional conveyors and thus allows testing a higher number of specimens.Within the research project, two powder feeder prototypes are built and tested in the Einstein-Elevator: a discontinuous and a continuous one. The development of the prototypes is aided by performing numerical CFD and DEM simulations to analyze the gas and particle behavior under microgravity.Laser based melting of metals in microgravity is researched by integrating a laser into the Einstein-Elevator. To operate this laser in the Einstein-Elevator, a process chamber is required that provides an inert gas atmosphere. Furthermore, a portable energy source and a heat exchanger is integrated into the Einstein-Elevator.