University of Twente Student Theses


3D Printing : depowdering techniques

Siddiqui, M.Z. (2017) 3D Printing : depowdering techniques.

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Abstract:Additive manufacturing is a technology that has broken conventional manufacturing barriers. Simple to complex structures such as a screw or a mechanical turbine, can be simply drafted in CAD and ultimately be "printed" for functional use. The freedom to print any complex shape favors additive manufacturing over conventional methods of manufacturing. Current additive manufacturing allows the possibilities for: Organ printing, electronics, food, metal, ceramics and plastics printing. In the Selective Laser Melting (SLM), the structure is built or printed through spherical particles of powder that typically lie in the micron-sized range. The laser sinters (melts) the powder together to form a final shape. Naturally, not all the powder is used to print the structure, but instead used as a base or support for the next successive layer during the printing process. Thus, once the printing process is complete, the powder present within the structure becomes part of the internal structure. These small particles can clog small precise orifices, channels' and any opening within the structure. This would defeat the purpose, for instance, the functionality of a printed heat exchanger which has loose internal powder, in terms of fluid flow and heat exchange. Therefore, there is a need to have a completely powder-free internal structure, from the manufacturing perspective and the clientele requirement. The main aim of this report is to determine how to efficiently remove excess powder from a 3D printed structure. To do this, experiments are first conducted to see if the loose powder would completely flow out of a structure at different orientations. The results of the experiments are then compared with the Simulation model developed by Maurice Limpens. The experiment was not able to depowder the structure completely whereas in the simulation the structure completely depowders. The main differences (namely interlocking, frictional forces and free flow of the powder) between experimental and simulated results are due to the fact that the latter assumes an ideal behavior of powder flow. Since the initial goal of depowdering was not successfully met with previous experiments, current available techniques for complete cleaning are then investigated. These techniques are (but not limited to): Laser Shockwaves Cleaning, Ultrasound, Gravity and Vibrations, and Electromagnetism. Ultrasound was chosen as the mode for cleaning, since among all the available techniques ultrasound shows promising evidence of cleaning. The results from the cleaning experiment does in fact prove complete cleaning of the structure. Ultrasounds may require long cleaning hours (more than 24 hours) before the structure is completely clean. Different cleaning combinations and sequences (for instance, extreme manual tapping and shaking of the structure followed by water flushing ultimately placed under ultrasounds) drastically reduce the time required under ultrasounds. Within the scope of this report, the depowdering of 3D printed metals is prioritized. Furthermore experiments should be conducted with various geometries and different material structures in order to obtain improved results for better agreement between simulated and experimental results. The simulation can incorporate the real flow behavior of powder (effects of interlocking and friction) while experiments can be improved by adding excitation effects to see how it influences the powder flow. With regards to complete cleaning, other cleaning techniques can be investigated to see how they compare with ultrasounds. Additional understanding on how each respective structure (build geometry, type of metal, shapes) behave under the influence of ultrasound waves is needed. Last but not the least, freshly 3D printed structures should be used to obtain excellent depowdering results for real life practical applications.
Item Type:Internship Report (Master)
TNO-Netherlands Organisation for Applied Research, the Netherlands
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Keywords:3D printing, selective laser melting, depowdering techniques, cleaning, ultrasonic cleaning, metal printing, additive manufacturing
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