Additive manufacturing capabilities for heat switch technology: Key challenges knowledge gaps
Creators: name:  J. MASEK 
name:   F. LOFFELMANN 
name:   R. POPELA 
name:   P. KUBIK 
name:   F. SEBEK 
name:   D. KOUTNY 
name:   M. MALY 
name:   L. PANTELEJEV 
name:   L. PAMBAGUIAN 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: STRUCTURES
MATERIALS
ADDIDITVE MANUFACTURING

description: Additive manufacturing of metals, as a growing market, has a lot to offer in terms of design-manufacturing capabilities and sustainability [1]. Therefore, it attracts key players in the space industry and entrepreneurs to reach better performance of parts at a lower mass. One of the game-changing applications is thermal hardware. The paper is to provide an overview of the key challenges and knowledge gaps in additive manufacturing applied to two parts of the novel heat switch technology. In addition, to provide a context of modern trends in additive for further evolution of parts. Baseplate part represents of paraffin pressure container. The component (O32 mm and 17.6 mm in height) of mass roughly 30 g shall withstand an internal pressure of up to 16 MPa, while the deformations reach 0.02 mm. The flatness of the plate is essential to provide a contact interface for efficient heat transfer. Structural reinforcement encourages couple of design solutions, such as topology, parametric or multi-material optimization. The aim was to reach the best mass-to-stiffness ratio and to demonstrate the capabilities of conventional SW tools. Multi-material optimization led to significant improvements, but did not meet design requirements [2]. Therefore three competitive designs were selected, two geometry concepts are based on topology optimization (min. wall thickness 0.3 and 2.0 mm) and one geometry is based on parametric optimization of reinforcing ribs. The key challenge was to eliminate internal support structures within a bioinspired design for successful manufacturing. The second part, Flexible structure, represents the path of heat transfer. The component (O56 mm and 24 mm in height) of mass roughly 70 g has a two-position on/off mode allowing a vertical movement of 1.7 mm and a thermal conductivity 1.5 W/K. A flexible single-structure proved to be not feasible using currently available materials. A two-part mechanism with 5 contact levels was selected. The design based on stems and branches in a \"tree shape\" with variable thickness is to meet the requirements. The key manufacturing challenge was to ensure that all 190 surfaces are in contact at the same time for efficient heat transfer. The accuracy of surface treatment should be less than 0.016 mm in parallelism and a roughness Ra 3.2 m. Only three unconventional technologies are applicable - (Wire) Electrical Discharge Machining (WEDM/EDM) and Electro-Chemical Machining (ECM). Design, surface treatment and manufacturability together form a matrix of feasibility. Elements of concurrent design and manufacturing engineering were implemented to save time over the development cycle [3]. Additive production of both technology demonstrators was performed on a SLM 280HL machine using a 400 W ytterbium-fiber laser and a layer thickness of 50 m. AlSi10Mg powder was chosen over other materials due to its thermo-mechanical specific properties after artificial ageing. Inspections by mCT and optical 3D scanning showed that most deviations are within 0.20 mm. No crack was observed, only a few internal pores due to insufficient powder fusion. The parts will be verified by static-load tests and thermal-vacuum tests in the range of -30 C to 60 C and vacuum levels up to 10-3 Pa. At the conclusion, we briefly review the knowledge gaps in the current state-of-the-art, such as software challenges with additive constraints, multi-material and multi-disciplinary optimization [4] or lack of material data on surface treatment, stress-corrosion cracking, material obsolescence and cold welding. Furthermore, issues related to the qualification of parts as the effect of defects and the manufacturing in-process control to mitigate cracks and porosity. All were also identified as major issues in our research. The presented outputs represent a successful demonstration of the capabilities, maturity and applicability of additive design manufacturing. However, there are several future steps on the way to full qualification. It is estimated that the readiness of both additive parts was increased from TRL 2 to 3-4 within the project, under the supervision of ESA.