Date

2022-4-25

Author

Kahraman, Ece

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Powder bed additive manufacturing methods use the powder form of the material of the part to be produced as raw material. The quality of the production is highly dependent on the properties of the powder used in the first place. Consistently using new unused powder for each new additive manufacturing is costly and removes the advantage of additive manufacturing, i.e. low amount of waste material. In powder bed additive manufacturing methods, powders are laid layer by layer and melted by laser or electron beam to form the final piece. Since the areas determined according to the CAD data of the part in each layer are scanned and melted, the surrounding powders remain unmelted and at the end of the production, the part is cleaned from the remaining powders. Bringing these remained powders back into another production is cost-effective. However, it is important not to compromise on the quality of the parts. Therefore, it is necessary to investigate the effects of reusing metal powders on additive manufacturing parts. In this thesis, the effects of powder reuse on the properties of selective laser melted 17-4 PH stainless steel were investigated. Using the same powder, 10 successive productions were carried out. In the productions, it is aimed to increase the thermal history of the powders as much as possible by producing geometries in a way that the powders will be most affected by the laser. Samples were taken from the powders in accordance with the standards before the first production and after the last production. These samples were subjected to various tests such as shape analysis, dimensional analysis and chemical composition analysis. In addition, block parts and tensile test specimens were produced in order to examine the part properties in certain productions. As a result of reuse of the powders 10 times, no change was observed in the powder shapes, bulk densities, particle size distribution and mechanical properties of the obtained parts. However, the tapped density value of the reused powder increased by 7.7% compared to the unused powder. In addition, it was determined that the oxygen ratio increased by 16% and the nitrogen ratio increased by 17% in reused powders. It is evaluated that with the further increase of the reuse cycle of the powder, the powders will become more contaminated and the raw material will go out of specification.

Subject Keywords

Additive Manufacturing, Powder Characterization, Metal Powder Reuse, Selective Laser Melting

URI

https://hdl.handle.net/11511/97322

Collections

Graduate School of Natural and Applied Sciences, Thesis