Use the following finishing methods to create transparent 3D printed parts for a variety of applications, from optics to light pipes to fluidics. Methods range from quick solutions for adequate transparency, to niche techniques for creating optically clear parts.
The Formlabs Clear Resin is perfect for showing housing LEDs, inner details, or creating windows. Formlabs and their customers have used Clear Resin to produce a completely optically clear lens for a fully 3D printed camera, tiles for a Fresnel lens installation in Times Square, millifluidic devices and more.
Formlabs applications engineer Amos Dudley designed and 3D printed a lens for a fully 3D printed camera.
Formlabs have tested several techniques for post-processing parts printed in Clear Resin. Cover manual sanding, clear coating and resin dipping will be covered in this post. Each finishing option requires varying levels of effort, depending on the degree of transparency and surface finish your part needs.
Applications: For simple shapes with few details, manual sanding and polishing can be effective. However, they are less suited to finishing complex models. It is extremely difficult to reach total optical transparency with this technique.
You’ll have to sand to extremely fine grits to manually finish a transparent part, but with some effort, sanding and polishing parts to be as clear as a magnifying glass is possible. However, it is very challenging to completely eliminate all layer lines via manual finishing – micro scratches may be noticeable when holding the part at a shallow angle to the light.
Instructions: To smooth you surface - use a range of incremental sandpaper grits then polish the part with acrylic cleaner and a microfiber cloth.
At around 3000 grit, stereolithography (SLA) printed parts become glossy and very smooth to the touch and by 12000 grit, they achieve reflectiveness. Try using a range of sandpaper and micromesh pads with grits from 400 to 12000, in increments of 200, slowly and carefully clean the lens between grit levels and eliminate scratches from the previous level before moving on to the next.
Formlabs support site offers a simple visual step-by-step guide for manual sanding, including an optional finish with acrylic spray.
Note: If semi-transparency is only needed, mineral oil can be used to create an even finish and hide any light spots on your part.
Formlabs have tested a variety of methods of polishing clear 3D prints, from hand sanding and spray coating to resin dipping.
Applications: Spray coating is a simple and a fast way to improve the clarity of parts without much reduction in detail. This technique is effective for all kinds of models, as it’s able to coat intricate details that may be hard to reach with normal sanding and polishing.
Clear coating itself helps to disguise layer lines and acts as UV protection. UV exposure can cause yellowing and unintended post-curing. If you’re looking for a smooth, glass-like surface finish, perform the manual sanding and polishing technique before coating. The more sanding done before the clear coating, the clarity improves. This extra step is great for post-processing prototypes that look like fully transparent plastic, for example; packaging, bottles and microfluidics.
Instructions: There are numerous options for clear coating, from low-cost sprays to products that require a dedicated room and tools.
Automotive sprays: Products similar to Lesonal Universal Clear, a high-solids acrylic urethane clear coat, offer very high gloss and are designed for air-dry baking conditions, but need a spray gun and space for spraying. Lesonal Universal Clear and similar sprays require a base coat.
For spray coating, start with a clean, dry part already washed in isopropyl alcohol (IPA). Do not post-cure the part ahead of spraying, as this can cause yellowing. Let the part air dry. Once it’s completely dry, apply two to three spray coats in a dust-free environment.
Note: For a fee, auto body shops may do the coating for you with a spray like Lesonal Universal Clear. In most cases, these shops will use a light solvent, like naptha to clean and prepare the part’s surface prior to painting.
For an installation in Times Square, Window to the Heart, the Formlabs and Aranda/Lasch teams worked with an auto body shop to spray coat each tile in Lesonal Universal Clear.
Applications: This method is best for when you need very transparent parts, and only works on flat or near-flat surfaces, such as a lens or a window into the interior of a part.
Resin dipping results in parts that are extremely smooth, with clear and sharp surface reflections.
Note: This technique can be used to create an even smoother finish for parts printed in other SLA materials, although it can reduce detail.
Instructions: Apply Clear Resin to the part with drops from a syringe, or by dipping the part as desired. The viscous resin will fill layers and scratches on the part, forming a completely smooth surface.
The layer of resin should be as thin as possible, while still eliminating layer lines. Pull off any bubbles with a syringe. Completely post-cure the part using the appropriate settings and then repeat the process for the other side, both dipping and post-curing.
Three stages of resin-dipped lenses, with the final lens on the left
Note: The dipping process alters focal length slightly for lenses. For the Formlabs 3D printed camera lens, Formlabs applications engineer Amos Dudley designed and printed a lens testing device.