[3D Printing] Waterproof 3D Printing Guide: Comparing FDM, SLA, and SLS Technologies

Waterproof 3D Print Testing in FDM, SLA, and SLS

Formlabs collaborated with the University of Rhode Island Underwater Robotics and Imaging Laboratory (URIL) to produce multi-part enclosures using Fused Deposition Modeling (FDM), Stereolithography (SLA), and Selective Laser Sintering (SLS), and tested them in an underwater simulated pressure chamber.

The research focused on the watertightness of multi-part enclosures, and the test data includes pressure resistance results, O-ring recommendations, and enclosure design principles. As a result, it was demonstrated that by adopting appropriate manufacturing techniques, materials, and sealing designs, watertight enclosures required for high-pressure environments can be produced through a simpler and more cost-effective process.

Therefore, even if a material itself has excellent water resistance, leakage can occur from seams in multi-part configurations. Conversely, by utilizing precise tolerances, threaded structures, interlocking designs, gaskets, and O-rings, the watertightness of the entire assembly can be effectively improved.

Applications and Fields of Watertight 3D Printed Parts

Watertight parts are utilized in ships and outboard motors, deep-sea robots, underwater photography, sampling equipment, and sensor housings. Furthermore, they are widely used in automotive, chemical research, architecture, and infrastructure requiring fluid transport and containment.

The installation environments for ecological, geological, and climate research are constantly changing, so off-the-shelf standard equipment may not always be suitable. 3D printing allows for rapid production of custom research tools tailored to sensors, connection ports, mounting positions, and operating environments.

NOAA 3D Prints Waterproof Parts for Coral Research

To study coral reef decline, the National Oceanic and Atmospheric Administration (NOAA) Atlantic Oceanographic and Meteorological Laboratory (AOML) and partner organizations are investigating wild corals and reproducing specific conditions in controlled environments to analyze coral responses to rising water temperatures and climate change.

AOML utilizes Formlabs SLA and Fuse series SLS machines to produce highly durable sampler housings, experimental sensor fixtures, and custom aquarium components. Diverse material options enable researchers to rapidly design, iterate, and deploy waterproof 3D printed parts, improving the standardization, accuracy, and comparability of experiments.

"We reduced the cost of the initial sampler design from $1,000 to $220. This allows us to deploy five samplers now with the budget we previously had for only one."

Nate Formel, AOML Researcher

Why Conventional Underwater and Watertight Components Are Difficult to Customize

Conventional watertight components are typically made from metal, injection-molded plastics, or rubber. While unit costs can be reduced in mass production, attempting to modify connectors, jigs, or housings for specific research or equipment needs incurs huge mold and development costs and long lead times.

Multi-part enclosures are usually sealed by screws, interlocking structures, O-rings, and gaskets. O-ring compression, inner diameter, cross-sectional diameter, material, and operating pressure all directly affect the sealing effectiveness, making it extremely time-consuming to select and evaluate the optimal standard for custom enclosures.

Comparing Waterproof 3D Printing Technologies: FDM, SLA, and SLS

Underwater robots and mechanical components have unique functions, and the required size, pressure, material, and sealing methods vary from project to project. When selecting a 3D printing technology, it is necessary to comprehensively evaluate surface porosity, tolerance, inter-layer bonding strength, material properties, post-processing, and anticipated operating pressure.

FDM

While cost-effective, the minute gaps between layers can lead to water absorption or leakage, often necessitating adjustments to printing settings or post-processing such as coating.

SLA

With smooth surfaces, extremely low porosity, and high dimensional accuracy, it is ideal for producing threaded joints, precision sealing surfaces, and pressure-resistant watertight enclosures.

SLS

Suitable for producing highly durable parts with significant geometric freedom. Excellent watertightness can be achieved by combining appropriate tolerance design, material selection, and seal design.

Fused Deposition Modeling (FDM)

FDM extrudes molten thermoplastic material through a nozzle, building parts layer by layer. Parts often exhibit anisotropy, meaning their mechanical properties vary depending on the direction of applied force. Additionally, minute gaps between layers pose a risk of water penetration.

Untreated, sealed FDM parts do not always reliably form pressure seals. In high-pressure environments, enclosures may rupture along layer lines or implode. The following measures are effective in improving the watertightness of FDM parts:

• Thoroughly reduce unnecessary gaps, connection ports, and openings.
• Increase wall thickness and shell count, and optimize extrusion multiplier and layer height.
• Select appropriate materials such as PETG or polypropylene (PP).
• Seal surfaces by sanding, vapor smoothing, resin coating, or other coatings.
• Perform immersion tests and hydrostatic verification under anticipated actual operating pressures.

While these methods improve the watertightness of parts, they do not directly guarantee suitability for high-pressure underwater environments.

Stereolithography (SLA)

SLA uses a light source to cure liquid resin layer by layer, cross-linking polymer chains within and between adjacent layers. This process creates smooth surfaces with minimal visible layer lines and extremely low porosity, resulting in high dimensional tolerances suitable for precision assembly.

Multi-part SLA enclosures can be precisely joined with threaded structures and interlocking designs, and air gaps can be eliminated by combining them with O-rings, sealants, and gaskets. Various test studies have demonstrated that housings with appropriate SLA materials and designs can withstand high water pressure, but the actual durability values must be individually verified based on materials, wall thickness, geometry, printing conditions, and actual durability values.

Selective Laser Sintering (SLS)

SLS sinters cross-sections on a powder bed with a laser, and then repeatedly forms layers by adding new powder. SLS parts offer excellent design freedom and durability, and if dimensional tolerances, surface treatment, and sealing structures are appropriate, watertight enclosures with high performance can be produced.

Design Techniques for 3D Printed Waterproof Enclosures

The watertight performance of an enclosure is determined by the material, body structure, and assembly design. While SLA and SLS can create mating structures with very tight tolerances, integrating independent sealing mechanisms such as O-rings is strongly recommended for high-pressure environments.

1. Reduce parting lines: Keep parting lines to the minimum necessary for maintenance and assembly, reducing the number of parts and potential leakage paths.
2. Control wall thickness and corner geometry: Avoid excessively thin walls or significant stress concentrations, and add fillets (rounded edges) to enhance pressure resistance.
3. Design stable sealing surfaces: Maintain dimensional consistency for O-ring grooves, end caps, and housing mating surfaces, and finish surfaces smoothly.
4. Select materials appropriate for the operating environment: Evaluate the effects of water pressure, temperature, chemicals, UV light, and prolonged underwater immersion.
5. Conduct testing in the actual environment: "Waterproof" and "pressure-resistant" are not the same. Always verify under anticipated operating conditions and with a safety factor.

URIL Deep-Sea Enclosure Design

URIL is working to lower hardware barriers in deep-sea research. By adopting SLA machines like the Form 3+ and the large-format Form 3L, the research team can self-produce high-precision deep-sea exploration tools and share open-source designs with research communities that previously lacked resources for underwater data collection.

Key research achievements include the DEEPi deep-sea imaging and control system, passive vibration isolation technology for offshore mobile vessels, and biomimetic (bio-inspired) pressure-resistant enclosures based on the shell geometry of nautilus.

Biomimetic Pressure-Resistant Enclosures

The research team used scanning and digital reconstruction techniques to analyze how the nautilus shell maintains its structure in the high-pressure deep-sea environment. They compared conventional pressure-resistant structures like spheres and cylinders with complex biomimetic shapes, exploring their potential as housings for deep-sea robots.

Selecting O-Rings for 3D Printed Waterproof Housings

URIL evaluated face-seal and bore-seal type O-rings and recommends the "face-seal" method for housing design. After determining the inner and outer diameters of the housing, selecting a size that matches the inner diameter ensures that the O-ring fits snugly between the end cap and the body mating surface.

In a series of experimental results, "dash 100 series" O-rings with a cross-sectional diameter of approximately ⅛ inch (0.139 inches / approximately 3.53mm) showed extremely high sealing reliability for SLA printed parts. In actual designs, please select the optimal standard based on O-ring material, compression rate, groove dimensions, operating temperature, and pressure conditions.

Conclusion on Selecting Waterproof 3D Printing Technology

Whether a waterproof enclosure functions reliably is not solely determined by the choice of printing technology. Material used, wall thickness, geometry, printing orientation, post-curing, surface treatment, O-ring design, and final assembly quality all directly influence watertight performance and pressure resistance.