Beyond 3D printing - multi-axis CNC machining of TPMS geometries for sustainable water generation

At a Glance

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

Technical Documentation & Analysis: TPMS Geometries for Advanced AWG Systems

Executive Summary

Application Validation: Multi-axis CNC machining (Subtractive Manufacturing, SM) is confirmed as a viable and highly scalable alternative to Additive Manufacturing (AM) for fabricating Triply Periodic Minimal Surface (TPMS) geometries used in Atmospheric Water Generation (AWG) systems.
Geometric Success: Successful single-layer fabrication was achieved for Schwarz and Neovius TPMS structures in Aluminum 6061-T6, demonstrating acceptable dimensional accuracy and surface finish.
Economic Advantage: SM offers significant cost reduction, lowering the per-part cost by up to 75% compared to Direct Metal Laser Sintering (DMLS) for medium-to-high volume production runs.
Performance Gap: The study highlights that maximizing AWG efficiency requires materials with superior thermal properties and surface finish, as Aluminum 6061-T6 (150-230 W/m.K) is limited by comparison.
6CCVD Value Proposition: CVD Diamond (SCD/PCD) offers thermal conductivity up to 10 times greater than Al 6061-T6, coupled with superior surface quality (Ra < 1nm) and chemical inertness, making it the ideal material for next-generation, high-efficiency AWG condensers.
Manufacturing Solution: 6CCVD provides custom, large-area PCD and SCD substrates, along with specialized metalization services, to overcome the material and integration challenges identified in the research.

Technical Specifications

The following data points summarize the key parameters and outcomes of the TPMS fabrication study, highlighting the performance context for material selection.

Parameter	Value	Unit	Context
Target Application	AWG Condensation	N/A	Enhanced by high surface-to-volume ratio TPMS
Fabrication Method Studied	Multi-axis CNC Machining	5-axis	Subtractive Manufacturing (SM)
Material Tested	Aluminum 6061-T6	N/A	Selected for machinability and corrosion resistance
Thermal Conductivity (Al 6061-T6)	150-230	W/m.K	Baseline performance for heat transfer
Thermal Conductivity (6CCVD SCD)	Up to 2000	W/m.K	10x improvement for condensation efficiency
Successful Geometries (SM)	Schwarz, Neovius	Single-layer	Demonstrated feasibility on Al 6061-T6
Unsuccessful Geometries (SM)	Lidinoid, Split-P	Unit cell/Single-layer	Limited by tool reach and complexity
Cost Reduction (SM vs. AM)	Up to 75	%	Cost savings for high-volume Schwarz blocks
Surface Finish Requirement (SCD)	Ra < 1	nm	6CCVD standard for optimal droplet shedding

Key Methodologies

The research focused on validating the feasibility of multi-axis CNC machining for complex TPMS structures, employing rigorous design and simulation protocols.

Geometry Generation: TPMS structures (Gyroid, Schwarz, Diamond, Lidinoid, Split-P, Neovius) were initially designed and optimized using the nTop platform, leveraging its advanced computational tools for high surface-to-volume ratio geometries.
Material Preparation: Aluminum 6061-T6 blocks (e.g., 40 mm x 30 mm x 30 mm) were secured in a V562 self-centering CNC vise for machining trials.
Machining Strategy Development: Two primary subtractive strategies were developed and evaluated: Unit Cell-based fabrication (for fundamental repeating elements) and Single-Layer machining (for cross-sectional slices).
Toolpath Optimization: Mastercam was utilized for 5-axis CNC toolpath generation. This involved advanced motion control, collision detection, and hybrid approaches combining surface flowline and pocketing operations.
Tooling Selection: A variety of small-diameter flat and ball end mills (down to 1/32-in.) were employed to navigate intricate internal features, necessitating careful optimization of feed rate, plunge rate, and spindle speed to minimize tool deflection and wear.
Validation: Machining outcomes were assessed based on dimensional accuracy, surface finish, and feasibility (tool accessibility, collision avoidance). Successful results were achieved for Schwarz and Neovius single layers on aluminum.

6CCVD Solutions & Capabilities

This research confirms the economic viability of scaling complex geometries via subtractive methods, but the material choice (Al 6061-T6) limits ultimate AWG performance. 6CCVD specializes in MPCVD diamond, offering the necessary material and fabrication solutions to achieve maximum thermal efficiency and durability in next-generation AWG systems.

Applicable Materials

To replicate and significantly extend this research, 6CCVD recommends the following materials, leveraging diamond’s superior properties for heat transfer and surface quality:

Thermal Grade Single Crystal Diamond (SCD): Required for maximum heat transfer efficiency. With thermal conductivity up to 2000 W/m.K, SCD dramatically outperforms Al 6061-T6, ensuring rapid heat dissipation from the cold side of the Peltier module and maximizing condensation rates.
Optical Grade Polycrystalline Diamond (PCD): Ideal for large-scale, cost-effective TPMS substrates. 6CCVD can supply PCD plates up to 125 mm in diameter, addressing the scalability requirements identified in the cost analysis.
Boron-Doped Diamond (BDD): If the AWG design requires integrated electrochemical sensing or heating elements, BDD offers a robust, conductive platform compatible with the TPMS geometry.

Customization Potential

The paper highlighted challenges related to integrating the TPMS structures with the Thermoelectric Cooling (TEC) system, requiring precise dimensions and robust interfaces. 6CCVD directly addresses these integration needs:

Research Requirement	6CCVD Customization Service	Benefit to AWG Engineers
Custom Dimensions (Paper used 40x30mm blocks)	Custom plates and wafers up to 125 mm (PCD) and 10 mm thick (Substrates).	Enables fabrication of full-size AWG condenser blocks, moving beyond single-layer prototypes.
TEC Interfacing (Requires robust electrical/thermal contact)	In-house Metalization Services (Au, Pt, Pd, Ti, W, Cu).	Provides robust, low-resistance contacts for seamless integration with Peltier modules and heat sinks.
Surface Finish (SM challenge: scalloping, Ra > 5nm)	Precision Polishing (Ra < 1nm for SCD; Ra < 5nm for PCD).	Ensures ultra-smooth surfaces, critical for promoting dropwise condensation and efficient droplet shedding, maximizing AWG output.
Complex Geometry Fabrication	Advanced Laser Cutting & Etching	While the paper focused on CNC, 6CCVD can utilize advanced diamond processing techniques to create highly precise micro-features and complex TPMS structures directly into the diamond substrate.

Engineering Support

6CCVD’s in-house PhD team specializes in optimizing CVD diamond properties for extreme applications. We can assist researchers and engineers with material selection for similar AWG and Heat Exchanger projects, focusing on:

Determining the optimal diamond grade (SCD vs. PCD) based on required thermal conductivity and size constraints.
Designing metalization stacks to ensure long-term reliability and thermal stability in humid environments.
Consulting on surface topography and polishing specifications to maximize condensation efficiency and droplet dynamics.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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 manufacturing—specifically computer numerical control (CNC) machining—to 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 hurdles—such as fixture design and cutter selection—that must be addressed to broaden the applicability of subtractive manufacturing for future AWG system development. Graphical Abstract

Tech Support

Original Source

DOI: https://doi.org/10.1007/s00170-025-16430-w