Proof of principle of a paste-based quality control method for roughness evaluation in inner channels of additively manufactured parts

Betreuer/in:            Dirk Herzog           
Dekanat/Institut:   Institut für Industrialisierung Smarter Werkstoffe, M-27           


Additive manufacturing (AM) offers great potential for the simple and direct production of complex and functional components made of polymers and metals. Among the different AM processes, Laser Powder Bed Fusion (PBF-LB/M) is the most widely used process for rapid manufacturing of metal parts, as it is able to fulfill requirements of serial production even in heavily regulated industries such as medical and aerospace while possessing an acceptable productivity at the same time.

One feature that is frequently used in the design of AM parts are hollow inner structures, e.g. cooling channels in turbine blades, conformal cooling of tools, or flow channels in heat exchangers. The geometric design freedom allows for very complex designs of such channels following e.g. the outer contour, highly adding to the functionality of the part (e.g. more efficient cooling). However, the complexity also poses a challenge in the post-processing and quality control of these channels. The roughness of as-build parts from PBF-LB/M is often not sufficient, making post-processing a necessity to achieve the desired surface roughness. A high surface roughness in inner channels may negatively impact the functionality and lead to reduced flow rates due to high friction, turbulences, and pressure loss in the system. While outside surfaces can be treated by various processes, such as grinding, polishing, etc., complex inner structures are hardly accessible. In order to reduce the surface roughness, specific processes such as electropolishing, vibratory grinding or abrasive flow machining have been successfully applied. It is however still a challenge to assess the remaining surface roughness after post-processing, as part of a quality control.

This student thesis shall therefore evaluate a new method, based on a functional paste, which is pressed through the inner channels and reacts according to the channel wall roughness. The thesis will include research on the formulation of the paste, the design and manufacture of representative test specimens with defined roughness values, establish an experimental set-up for the testing, and will result in a proof-of-principle for the approach as the overall objective.

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