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5143 |
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Wednesday, March 22, 2017, Hall Ford 2:25 PM Additive Manufacturing I |
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Improvement of electric charge transportation in metal powders for increased process stability in electron beam melting |
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Stephan Janson* / Institute for Machine Tools and Industrial Management
Technical University of Munich, Germany Bernhard Loitlesberger / iwb TU München, Germany Michael F. Zäh/ iwb TU München, Germany |
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Powder spreading, also referred to as smoke, is a relevant error in metal powderbed-based additive manufacturing via electron beam melting. Electrostatic repulsion was identified as main reason for this effect. Due to the minimal contact area and insulating impurity layers most metal powders show large resistivity values. With the electron beam supplying an electric current, a high charge density occurs at the location of the beam impact. The negatively charged particles repel each other leading to a powder cloud around the impact area. The manufacturing process is influenced in a negative way due to the lack of powder in the affected area. Additionally, the beam is widened and weakened by the particle cloud, inhibiting a stable process. The whirled up powder also contaminates the process chamber, increasing the changeover time between build jobs. Several strategies exist to avoid this phenomenon and to allow a stable build-up process all of them having drawbacks in regard to productivity. These strategies are evaluated and alternative approaches are introduced. Last, the results of experiments investigating the effectiveness of these new approaches are presented. |