Transparent 3D Printed Parts
Transparent 3D Printing works like magic. There are applications in 3D Printing that require clear display models. When manufacturing parts in Stereolithography(SLA) technology in clear material, the parts come out translucent (50-60% transparency). To increase their transparency, we need to lacquer coat them. Lacquer coating is a post-processing technique where translucent parts are made transparent (up to 90% transparency) by applying a coat of epoxy-like resin. Lacquering also gives the parts a glossy surface finish and makes them leak-proof. A lacquer coat is usually applied with the help of a brush. Thus, for a part to be lacquer coated, the part surface should be easily accessible to the user.
To understand how lacquering is done, let’s take an example of a bottle. A typical bottle has a narrow opening (mouth) and a closed end (base). When this bottle is fabricated as a whole in SLA, there will be support structures generated inside the part geometry. It becomes difficult and practically impossible to insert tools inside the narrow opening to remove the support structures. Also, if the part has to be made transparent, it becomes difficult to lacquer coat the inner regions of the bottle which are inaccessible by a human hand. Hence, we recommend that, for part geometries like the bottle that need to be lacquer coated, the part should be split in two or more sections. The sections can be manufactured separately and can later be assembled together to form a single geometry. For better part assembly and part adherence, the parts should have a good wall thickness. We recommend a wall thickness of at least 2 mm.
By manufacturing the bottle in multiple sections, one can easily access the inner regions of the part; clean the support structures, and apply the lacquer coat. After the parts are manufactured, they are polished (using a sandpaper) till a smooth surface finish is achieved. Post which lacquer is applied on one of the sides of the bottle and it is kept for drying. The part takes anywhere between 4-6 hrs to dry. Then the process is repeated by polishing the other side and lacquer coating it.
After the two parts are assembled, a parting line can be seen on the interface of the two parts. But this parting line mark is only visual and with proper post-processing it doesn’t indicate discontinuity. That is, if one were to touch the part at that point, they wouldn’t feel the mark. Thus it does not impede the functionality of the part.
Once the parts are lacquered, they cannot be painted again. Lacquering gives the parts a glossy surface finish, making it difficult for the paint to stick to it. A regular post-processing operation like lacquering usually adds additional 2-3 business days to the project timeline.
To highlight the distinction between a lacquered and a non-lacquered part, see the image below.
Lacquer coating can also be done on Selective Laser Sintering (SLS) parts. Since SLS is a powder based technology, the parts are slightly porous. Lacquering is done on SLS parts to make them leak-proof and not to make them transparent, since SLS parts come in a natural opaque color. Lacquering gives the SLS parts a glossy look and a smooth surface finish. Also, due to lacquering, the grainy surface of SLS parts cannot be felt.