Metal Additive Manufacturing of Space Components @ DLR

Abstract

Additive manufacturing (AM) offers enormous potential for the production of complex geometries, especially for components required in small quantities such as typically found in space applications. However, in order to exploit the strengths of AM, it is crucial to consider each step in the development and manufacturing chain. This will be illustrated on different use-cases studied at the German Aerospace Center (DLR) - Institute of Materials Research in cooperation with other DLR institutes. In the case of a Ti-6Al-4V shrouded turbopump impeller with a conventional design, one particular focus was on developing the build strategy (process parameters, optimization of support structures) since residual stresses and consequently distortion proved to be major challenges. Moreover, heat treatments and surface finishing steps were applied. The component was successfully validated in a spin test. Other typical components investigated are structural part for aeronautic purposes such as, e.g., a satellite thruster brackets consisting typically of aluminum alloys. Key to these parts is usually a suitable design and topology optimization that already considers factors that govern the economic viability: Build rates, material costs, and printability. Thus, the build orientation and geometry can be optimized simultaneously to minimize the amount of supports that need to be removed later. Furthermore, a tool was developed that allows to segment components according to their load distribution. The productivity can be increased when appropriate parameter sets are selected: Only the highly stressed areas need to be processed with a low build rate to achieve the best material quality, while the rest of the component can be built much faster, potentially even with different layer thicknesses. Another possible use of AM is in the production of combustion chamber liners, potentially allowing cost and time savings but, more importantly, highly complex and novel cooling designs. In preliminary studies, a process window of CuCr1Zr was first determined and effects such as overheating were investigated. As a supplement, the SLM 280HL in situ melt pool monitoring system, consisting of two photodiodes, was used for evaluation of the printing process. The experience gained was subsequently used to manufacture various combustion chamber designs, some of which incorporate novel cooling geometries.