Guide to Transparent 3D Printing

Transparent materials like glass or acrylic are widely used in consumer products, industrial applications, healthcare, and more. However, traditional methods for prototyping or producing small batches of transparent parts can be expensive and inefficient. This raises the question: Can transparent parts be 3D printed? The answer is yes, with the right technology and materials.

Stereolithography (SLA) 3D printing can create transparent parts, and with certain post-processing steps, these parts can achieve optical clarity. Formlabs' latest resin 3D printers, the compact and ultra-fast Form 4 and the large-format Form 4L, elevate part clarity to a new level by utilizing Flexible Resin Tanks that reduce peel forces, resulting in clearer parts with smoother surfaces.

There are several types of materials that can be used to produce translucent and transparent 3D printed parts, including:

1. Clear Resin is a highly clear and colorless 3D printing resin, offering an optimal balance of print speed, high accuracy, transparency, robust mechanical properties, and an easy, reliable workflow. It is suitable for fluidics, mold making, optics, lighting, showcasing internal structures of parts, and all applications requiring translucency.
2. Elastic 50A Resin is a soft and flexible material with a translucent appearance. It is ideal for prototyping parts typically made from silicone.
3. Flexible 80A Resin is a soft-touch material that is stiffer than Elastic 50A and also translucent. It is suitable for simulating the flexibility of rubber or TPU.
4. BioMed Clear Resin is a transparent, strong, durable, and wear-resistant material for applications requiring biocompatibility, supporting long-term skin contact (over 30 days), respiratory gas pathway contact, and mucous membrane contact (over 30 hours), or short-term contact with bone, tissue, and dentin (under 24 hours).
5. BioMed Elastic 50A Resin is a soft, flexible, and transparent material for biocompatible applications requiring user comfort and long-term skin contact (over 30 days) or short-term mucous membrane contact (under 24 hours).
6. BioMed Flex 80A Resin is a rigid, flexible, and transparent material for biocompatible applications requiring durability and long-term skin contact (over 30 days) or short-term mucous membrane contact (under 24 hours).

In this guide, we will explore various finishing methods to create transparent 3D printed parts for a wide range of applications, from optics and light pipes to fluidics. The methods presented range from quick approaches for sufficient translucency to specialized techniques for achieving optical clarity.

Applications of Transparent 3D Printing

Clear and transparent 3D printed parts are suitable for creating transparent prototypes, showcasing internal cavities and details, making enclosures for LED lights, creating windows, or printing transparent anatomical models and medical devices.

Formlabs and our customers have used Clear Resin to create optically clear lenses for fully 3D printed cameras, tiles for the Fresnel lens installation in Times Square, light pipes, prisms, microfluidic devices, and many other applications.

Formlabs Applications Engineer Amos Dudley designed and 3D printed lenses for a fully 3D printed camera.

FAQ: Can acrylic be 3D printed?

Yes, but with considerations. Polymethylmethacrylate (PMMA), commonly known as Acrylic, is a transparent thermoplastic often used as a more durable alternative to glass. While acrylic can be 3D printed using Fused Deposition Modeling (FDM), it is not very user-friendly in practice due to the material's toxicity and tendency to warp easily. Furthermore, the printed parts will only be semi-translucent due to the lower resolution of FDM printers.

If you need to print parts with an acrylic-like appearance and true transparency, we recommend 3D printing with an SLA printer using Clear Resin and then post-processing the part to achieve full transparency using one of the methods mentioned in this article. Using Acrylic Spray is one method that helps to enhance the clarity of the part.

Post-Processing Methods for Clear 3D Printed Parts

We have tested several post-processing techniques for parts printed with Clear Resin. In this article, we will cover manual sanding, clear coating, and resin dipping. Each method requires a different level of effort, depending on the desired transparency and surface quality of your part.

Manual Sanding and Polishing

Applications: Manual sanding and polishing can yield good results for parts with simple geometries and minimal details, but it is less suitable for finishing complex models. It is also very challenging to achieve total optical transparency with this method.

You will need to sand with very fine grit sandpaper to make the part transparent through manual sanding. However, with enough time and care, parts can be sanded and polished to a clarity similar to a magnifying glass. Still, removing all layer lines through manual sanding alone is very challenging. You might still notice micro-scratches when holding the part at a shallow angle to the light.

Method: Use multiple grits of sandpaper, gradually increasing the grit level to smooth the surface. Then, polish the part with an acrylic cleaner and a microfiber cloth.

When sanded to approximately 3000 Grit, transparent 3D printed parts begin to become shiny and feel very smooth. When sanded to 12000 Grit, the part will have a reflective surface. We recommend using sandpaper and Micromesh pads with grits ranging from 400 to 12000 Grit, increasing by approximately 200 Grit at a time. Sand carefully, clean the part each time you change grit levels, and ensure all scratches from the previous step are removed before moving to a finer grit.

Our support website has a step-by-step illustrated guide for manual sanding, including an optional additional step for coating with Acrylic Spray.

Tip: If you only need semi-transparency, simply use mineral oil to create a uniform surface and help hide light-reflecting points on the part.

We have tested various methods for sanding and clarifying transparent 3D printed parts, from hand sanding and spray coating to resin dipping.

Spray Coating

Applications: Spray coating is a quick and easy way to increase part clarity with minimal loss of detail. This method is effective for all types of models, as it can cover complex details that might be difficult to reach with conventional sanding and polishing.

A clear coating alone can help conceal layer lines and protect the part from UV radiation, which might otherwise cause yellowing and unintended post-curing.

If you want a smooth, glass-like surface finish, manual sanding and polishing should be performed before coating. The more you sand the surface before coating, the clearer the part will be. This additional step is ideal for post-processing prototypes that need to look like fully transparent plastic, such as packaging, bottles, and microfluidics.

Method

There are several options for clear coating 3D printed parts, from affordable sprays to products requiring specialized facilities and equipment.

1. General Purpose Clear Coat Spray Paints: A variety of good quality and inexpensive sprays are available. We recommend using 2K Clear Coat.
2. Automotive Sprays: High-solids acrylic urethane clearcoats offer a very high gloss and are designed for air-drying or baking, but they require a spray gun and a dedicated spray area, as well as a base coat.

For spray coating, start with a clean, dry part that has been washed with Isopropyl Alcohol (IPA). Do not post-cure the part before spraying, as this can cause yellowing. Allow the part to air-dry completely, then apply 2–3 coats of clear coat in a dust-free environment.

Tip: For an additional cost, many auto body shops can perform the coating for you, using sprays like Lesonal Universal Clear. In many cases, these shops will use a mild solvent like Naptha to clean and prepare the part's surface before painting.

For the Window to the Heart installation in Times Square, the teams from Formlabs and Aranda/Lasch collaborated with an auto body shop to spray each tile with Lesonal Universal Clear.

Resin Coating

Applications: This method is best for cases requiring very high transparency and is only suitable for flat or nearly flat surfaces, such as lenses or windows for viewing the interior of parts.

Resin dipping results in a uniquely smooth surface with sharp and clear surface reflections.

This technique can also be used to create an even smoother surface for parts printed with other SLA materials, although it might slightly reduce some part details.

Method

Apply Clear Resin to the part using a syringe or by dipping the part as desired. The viscous resin will flow into and fill layer lines and scratches on the part, creating a perfectly smooth surface.

The resin layer should be as thin as possible but still cover all layer lines. If air bubbles appear, use a syringe to remove them. Then, fully post-cure the part using appropriate settings. Repeat the same process with the other side of the part, including both resin coating and post-curing.

Lenses after three stages of resin dipping. The finished lens is on the left.

Note: The resin dipping process will slightly alter the focal length of the lens. For the lenses of the fully 3D printed camera, Formlabs Applications Engineer Amos Dudley designed and printed a lens testing device.

Learn More About SLA 3D Printing

With the Form 4 MSLA 3D printer, you can create perfectly clear and transparent 3D printed parts at an affordable cost, with minimal post-processing.

Download our White Paper for a detailed overview of the SLA 3D printing ecosystem and a step-by-step 3D printing workflow.

To experience the quality and clarity of the parts yourself, request a free transparent 3D printed sample now.

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References

https://formlabs.com/global/blog/3d-printing-transparent-parts-techniques-for-finishing-clear-resin/