Beyond 3D printing - multi-axis CNC machining of TPMS geometries for sustainable water generation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-09-01 |
| Journal | The International Journal of Advanced Manufacturing Technology |
| Authors | Md Shafikul Islam, Fatema Tuz Zohra, Bahram Asiabanpour |
| Institutions | Texas State University |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Value Proposition: This research validates multi-axis CNC machining (Subtractive Manufacturing, SM) as a scalable and cost-effective alternative to Additive Manufacturing (AM) for fabricating Triply Periodic Minimal Surface (TPMS) geometries, specifically targeting enhanced condensation efficiency in Atmospheric Water Generation (AWG) systems.
- Feasibility Demonstrated: Successful fabrication of single-layer Schwarz and Neovius TPMS geometries on Aluminum 6061-T6 blocks was achieved using 5-axis CNC machining, confirming acceptable dimensional accuracy and surface finish.
- Economic Scalability: For medium- to high-volume production (200 units), SM reduces the per-part cost of Schwarz TPMS blocks by up to 75% compared to Direct Metal Laser Sintering (DMLS)-based AM.
- Material Selection: Aluminum 6061-T6 was chosen for its optimal balance of high thermal conductivity (150-230 W/mK), excellent machinability, and natural corrosion resistance, crucial for long-term AWG durability.
- Manufacturing Limitations: Highly complex TPMS topologies (Lidinoid, Split-P, Diamond unit cell) proved infeasible for current SM techniques due to severe tool accessibility issues, frequent tool collisions, and the inability to reach deep internal grooves.
- Methodology: The study employed advanced CAM simulation (Mastercam) and hybrid toolpath strategies (flowline, pocketing) to navigate complex curvatures, addressing challenges related to tool interference and surface fidelity.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material (Condenser) | Aluminum 6061-T6 | N/A | Selected for AWG components |
| Thermal Conductivity (Al 6061) | 150-230 | W/mK | Essential for rapid heat transfer in condensation |
| Machining Process | 5-axis CNC Milling | N/A | Subtractive Manufacturing (SM) method |
| TPMS Geometry Type | Schwarz, Neovius | N/A | Successfully fabricated single-layer structures |
| TPMS Block Dimensions (Tested) | 40 x 30 x 30 | mm | Single-layer cross-section size |
| Finishing Tool Diameter | 1/16, 1/32 | inch | Flat end mills used for intricate pocket features |
| Gyroid Unit Cell Thicknesses | 6.35, 1.5875 | mm | Variations tested for manufacturability |
| Cost Reduction (SM vs. AM) | Up to 75 | % | Cost savings for Schwarz blocks at 200 units volume |
| High Volume Unit Cost (SM) | 7.63 | USD | Cost per single Schwarz layer (Company A, 200 units) |
| High Volume Unit Cost (AM) | 211.15 | USD | Cost per full Schwarz block (Company B, 200 units, DMLS AlSiMg) |
| Infeasible Geometries | Lidinoid, Split-P | N/A | Exceeded current subtractive manufacturing capabilities |
Key Methodologies
Section titled âKey Methodologiesâ-
Geometry Selection and Optimization:
- Six common TPMS topologies (Gyroid, Schwarz, Diamond, Lidinoid, Neovius, Split-P) were selected for their high surface-to-volume ratios, crucial for AWG efficiency.
- Models were generated and optimized using nTop software, leveraging its advanced computational tools for complex geometry handling.
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Manufacturing Strategy Development:
- Two distinct CNC machining strategies were developed and evaluated:
- Unit Cell-Based Fabrication: Machining the fundamental repeating element (e.g., Diamond unit cell) for subsequent assembly.
- Layer-by-Layer Fabrication: Extracting and machining a single cross-sectional layer of the full structure (e.g., Schwarz single layer). The single-layer approach proved more successful for complex geometries.
- Two distinct CNC machining strategies were developed and evaluated:
-
CAD/CAM Implementation:
- Mastercam was used for Computer-Aided Manufacturing (CAM) simulation and toolpath generation.
- The virtual setup precisely replicated the physical environment (Aluminum block in a V562 self-centering CNC vise) to predict tool collisions and spatial constraints.
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Toolpath Optimization and Tooling:
- Advanced 5-axis flow operations, surface flowline, and pocketing were combined to follow intricate curvatures and remove material efficiently.
- Small-diameter flat end mills (down to 1/32-in.) were employed to achieve fine detailing and navigate restricted internal features.
- Cutting parameters (feed rate, plunge rate, spindle speed) and tool orientation were meticulously optimized to minimize tool deflection and ensure dimensional accuracy.
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Feasibility and Validation:
- Initial tests for highly complex structures (Gyroid) were conducted on wax blocks to assess feasibility and mitigate the risk of tool breakage before committing to the rigid Aluminum 6061-T6 substrate.
- Successful fabrication was achieved for Schwarz and Neovius single layers on aluminum, validating the SM approach for these specific TPMS types.
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Economic Analysis:
- Cost quotations were obtained from leading AM (DMLS AlSiMg) and SM (CNC Al 6061-T6) vendors for 1, 100, and 200 units of the Schwarz geometry to quantify scalability and economic viability.
Commercial Applications
Section titled âCommercial Applicationsâ- Sustainable Water Resource Engineering: Direct application in next-generation AWG systems, providing high-efficiency, scalable, and durable metallic condensers for freshwater extraction in arid or resource-limited regions.
- High-Performance Heat Exchangers: Fabrication of complex TPMS structures for use in compact, high-efficiency heat transfer applications, including liquid-cooled IGBT modules, micro gas turbines, and general thermal management systems.
- Advanced Manufacturing and Prototyping: Offers a proven, cost-competitive manufacturing route for metallic lattice structures in medium-to-high volumes, traditionally dominated by expensive AM processes.
- Aerospace and Automotive Cooling Systems: Production of lightweight, high-surface-area components (using Al 6061-T6) where structural integrity and efficient heat dissipation are critical, such as in engine cooling or battery thermal management.
- Biomimetic and Porous Media Design: Provides a method for creating highly controlled, periodic porous structures for filtration, catalysis, or biomedical scaffolds where precise surface finish and material flexibility are required.
View Original Abstract
Abstract `Atmospheric water generation (AWG) offers a sustainable solution to global freshwater scarcity by extracting moisture from the air. Transitioning from flat 2D plates to three-dimensional triply periodic minimal surface (TPMS) geometries substantially increases available surface area and, in turn, the potential water generation rate. This shift enhances condensation efficiency, as 3D structures expose more surface within the same volume, maximizing contact with humid air. While additive manufacturing (AM) enables the creation of these intricate TPMS structures, AM processes are often constrained by limited material selection, suboptimal surface roughness, and high unit costs that hinder economical scalability. To address these limitations, this study explores whether subtractive manufacturing can serve as a viable and scalable alternative for producing TPMS geometries with greater material flexibility and improved surface finish. To overcome these challenges, this study investigates the feasibility of employing multi-axis subtractive manufacturingâspecifically computer numerical control (CNC) machiningâto fabricate a range of common TPMS topologies (Gyroid, Schwarz, Diamond, Lidinoid, Neovius, and Split-P). Aluminum 6061-T6 is used for its thermal conductivity, machinability, and corrosion resistance. Two machining strategies, unit-cell and layer-by-layer approaches, are developed using CAD preprocessing and toolpath optimization to address issues of tool accessibility, collision avoidance, and surface fidelity. Experimental results demonstrate successful fabrication of Schwarz and Neovius single-layer structures with acceptable dimensional accuracy and surface finish, while more complex geometries encountered limitations due to tool reach and excessive machining time. A detailed cost comparison reveals that, for medium to high production volumes, subtractive methods can reduce per-part cost by up to 75% compared to direct metal laser sintering (DMLS)-based AM, making CNC machining a compelling alternative for scalable deployment of TPMS-enhanced AWG components. Finally, the paper outlines the key technical hurdlesâsuch as fixture design and cutter selectionâthat must be addressed to broaden the applicability of subtractive manufacturing for future AWG system development. Graphical Abstract