ASSEMBLY
The assembly, filling, and sealing phase transforms the separate main and closing parts into a fully functional, hermetically sealed sandwich deck plate containing 16 active triangular heatpipe segments per 30×30 mm cell. This critical sequence—evacuation, precise fluid charging (30-60% fill), mating of complementary wick structures, and leak-proof joining—occurs while parts remain physically separate to enable internal access to the 2 mm vapor channels and gyroid wick regions. The process eliminates discrete plugs, external tubes, or secondary fluid ports, achieving unprecedented integration density for avionics thermal management.
Pre-Assembly Preparation and Inspection
Before assembly begins, both the main part and the closing part undergo extensive inspection to ensure that every internal feature has been manufactured according to design specifications. The main part is inspected using computed tomography (CT) scanning to verify the integrity of the 0.3 mm triangular compartment walls, the continuity of the 0.2 mm gyroid wick ligaments, and the openness of all 2 mm vapor channels distributed across the deck plate. For a 150 × 150 mm deck plate, nearly 250 individual channels are examined to ensure there are no blockages caused by residual powder or manufacturing defects. Helium leak testing is also performed to verify that each vapor channel remains completely open after additive manufacturing, while surface profilometry confirms that the mating surfaces maintain a flatness below 50 μm RMS, ensuring excellent contact during assembly.
The closing part is inspected separately using high-resolution optical scanning to confirm that its wick projections match the dimensions of the corresponding cavities within a tolerance of ±25 μm. Scanning Electron Microscopy (SEM) is employed to verify the morphology of the gyroid ligaments, ensuring that the capillary structures remain intact and capable of transporting the working fluid effectively. Alignment pins or machined registration features incorporated into the lattice frame provide positional accuracy better than 100 μm during assembly. Prior to joining, both components are cleaned in a Class 100 cleanroom using an ultrasonic isopropyl alcohol bath followed by plasma cleaning, removing oxides, hydrocarbons, and microscopic contaminants from the aluminum surfaces to achieve high-quality hermetic bonding.
Evacuation Procedure
After inspection, the main component is transferred into a high-vacuum chamber where it is secured using specialized fixtures that expose all vapor channel openings. A custom-designed manifold seals against the lattice frame and provides simultaneous access to every 2 mm channel, enabling complete evacuation of internal cavities. Maintaining vacuum integrity during this stage is critical because any residual gas or moisture trapped within the channels would significantly reduce the thermal performance of the finished heat pipe. The chamber initially operates below 10⁻⁵ mbar, ensuring that the internal environment approaches aerospace-quality vacuum conditions before working fluid charging begins.
The evacuation process is carried out in multiple stages to maximize removal of contaminants. A rough vacuum of approximately 10⁻² mbar removes trapped air and verifies channel connectivity through pressure rise testing. Turbo molecular pumps subsequently reduce the pressure to around 10⁻⁶ mbar while the component undergoes a bake-out at approximately 120°C for two hours, desorbing moisture from the porous gyroid wick. Finally, ion pumps establish an ultra-high vacuum below 10⁻⁷ mbar suitable for spacecraft applications, while a residual gas analyzer confirms that oxygen and water vapor concentrations fall below 1%. During the final stage, the lattice core is maintained near 80°C to remove any remaining bound moisture within the 0.2 mm wick ligaments and to verify wick permeability through controlled pressure recovery measurements.
Working Fluid Charging
Once the internal cavities have been completely evacuated, the working fluid is introduced into the heat pipe network under controlled vacuum conditions. Acetone is selected as the working fluid because it is chemically compatible with aluminum, exhibits excellent capillary wetting characteristics, and performs efficiently within the expected operating temperature range of approximately 40–80°C encountered in spacecraft avionics. In addition, acetone possesses relatively low surface tension and high latent heat of vaporization, allowing efficient transport of thermal energy through repeated evaporation and condensation cycles. Before filling, the acetone undergoes triple distillation and repeated freeze–pump–thaw degassing to eliminate dissolved gases that could otherwise reduce heat pipe efficiency.
The charging process is carefully controlled using a precision leak valve that introduces acetone vapor into the evacuated channels. The partial pressure is regulated to obtain a liquid fill ratio of approximately 30–60% of the total internal channel volume, which corresponds to the calculated volume of the interconnected channel network. As the vapor enters the structure, capillary forces naturally draw the liquid into the porous gyroid wick, ensuring uniform saturation throughout the lattice. Real-time monitoring using precision weighing systems and embedded temperature sensors verifies consistent fluid distribution across all heat pipe segments. Once the desired fill level is achieved, the chamber is isolated and the internal pressure is allowed to stabilize at the vapor pressure of acetone. Ultrasonic inspection confirms complete wick wetting without dry regions, after which temporary vacuum-rated caps are installed on the projection tips to prevent evaporation before final assembly.
Precision Mating Assembly
Following fluid charging, the main and closing components are brought together using a precision alignment system specifically designed for micron-level positioning. A custom kinematic fixture equipped with six-axis micrometer adjustments provides translational accuracy of approximately ±10 μm and angular accuracy of about ±5 arcseconds. Machine vision cameras identify fiducial markers machined onto both components and continuously monitor alignment during assembly, ensuring that every wick projection enters its corresponding triangular compartment without interference. Such precision is essential because even small misalignments could damage the delicate gyroid wick or obstruct the internal vapor channels.
The closing component is lowered vertically at an extremely slow speed of approximately 0.1 mm/s, allowing the complementary gyroid wick structures to interpenetrate gradually without deformation. As the projections enter the triangular compartments, nearly 80% surface contact is established between the two wick structures, forming a continuous three-dimensional capillary network throughout the deck plate. Simultaneously, the ends of the 2 mm vapor channels become completely sealed through geometric engagement, eliminating the need for separate plugs or adhesives. A uniform compressive force between 50 and 100 N ensures complete seating of the mating surfaces, while acoustic emission sensors detect any abnormal contact that might indicate interference. Temporary perimeter clamps maintain precise alignment and preserve the internal vacuum until permanent hermetic joining is completed.
Hermetic Joining Process
After successful mating, the assembled deck plate undergoes permanent hermetic sealing using high-precision laser welding. A fiber laser operating at approximately 1070 nm with an output power between 1 and 2 kW is used together with a focused beam diameter of 50–100 μm and a wobble scanning pattern that distributes heat uniformly around the joint. Welding parameters are selected to produce keyhole-mode penetration through the full 5 mm thickness of the mating interface while minimizing thermal distortion. Argon shielding gas containing less than 50 ppm oxygen protects the molten aluminum from oxidation throughout the process, ensuring high-quality aerospace-grade welds.
The welding sequence begins with multiple continuous perimeter welds around the 150 × 150 mm deck frame, followed by internal welds along major truss members to increase structural rigidity. Additional spot welds are applied at each lattice junction to reinforce local sealing and improve mechanical reliability. As an alternative manufacturing method, aluminum-silicon brazing using 4047 filler alloy may be employed for narrow gaps requiring capillary filling at temperatures between approximately 520 and 580°C. Immediately after joining, helium mass spectrometer leak testing is performed with a sensitivity of approximately 10⁻⁸ mbar·L/s. Each heat pipe segment is individually pressurized and inspected to verify complete hermetic sealing, ensuring long-term containment of the working fluid throughout the spacecraft mission.
Post-Assembly Validation
After permanent sealing, the completed deck plate undergoes a comprehensive qualification program to verify its structural integrity, thermal performance, and long-term operational reliability. Thermal cycling between approximately −40°C and +80°C is performed for multiple cycles to evaluate the stability of the aluminum structure, the gyroid wick, and the acetone working fluid under repeated expansion and contraction. Proof pressure testing using helium at approximately 2 bar verifies that the welded enclosure maintains its mechanical strength and leak-tightness without deformation or rupture. These tests demonstrate that the integrated heat pipe array can safely withstand expected spacecraft environmental conditions.
Functional thermal testing is then conducted by applying a uniform heat input of approximately 100 W while infrared thermography records the temperature distribution across the deck plate. The measured temperature gradients are compared with numerical predictions to verify effective heat spreading and confirm that all heat pipe segments remain operational. Finally, vibration and mechanical qualification tests covering frequencies from approximately 20 to 2000 Hz simulate launch conditions and microgravity operation, ensuring that the working fluid remains properly contained within the wick structure under dynamic loading. Successful completion of these validation procedures demonstrates that the integrated aluminum deck plate is flight-ready, capable of dissipating approximately 100–200 W of avionics heat within a compact 45 mm structural thickness while eliminating the need for external thermal management hardware.