Guide to 3D Printed Masking Tools For Painting, Coating, and More

Masking, or the strategic covering of certain areas during a processing step such as painting, media blasting, or metalizing, is traditionally a labor-intensive step in manufacturing processes with a low margin for error. 3D printing presents a cost-effective means of creating customized masking parts that can fit complex geometries and be used repeatedly, reducing the need for hours of manual labor during post-production workflows. 

Both stereolithography (SLA) and selective laser sintering (SLS) 3D printing technologies can be used in the manufacturing of masking tools, and each presents unique advantages. In this guide, we will outline the considerations to take when creating masks, how to evaluate which 3D printing technology is right for your workflow, and provide examples of customers successfully finishing their parts with the help of 3D printed masks.

Masking is the strategic covering of certain areas on a part that need to remain free of any coating, painting, metallizing, or other surface finishing processes. Those areas may need to remain untouched for various reasons — because they will become an attachment area for an assembly, for electrical conductivity reasons, or because they might need to be coated in some other material or color, among others. Masks are therefore manufacturing aids that can be customized and made to correspond to each final part, or created once and used as each part goes through the finishing process individually. 

Coating, painting, or metallizing processes can vastly improve both the functionality and appearance of parts used in any industry, but these processes often involve extra steps, one of which is masking. Masking is the strategic covering of certain areas on a part that need to remain free of any coating. That area may need to remain untouched for multiple reasons — because it will become an attachment area for an assembly, for electrical conductivity reasons, or because it might need to be coated in some other material or color, among others.

Traditional masking workflows include manually measuring and cutting masking tape, machining metal or plastic masks, or sometimes coating an entire part and then machining or scraping away the coating from the designated area. Taping workflows, though they use cheap materials, are extremely labor-intensive, and can add minutes of labor time per part on a production line. Machined masks can be repeatedly used but are expensive to manufacture, and the machining process confers some geometric limitations.

Masks are an ideal application for 3D printing — they are often needed in low-volume production quantities and with very specific geometries to ensure they only cover certain areas at the center, on the edges, or in a specific pattern across a larger part. There are many types of coatings that are compatible with 3D printed masks including Cerakote, airbrushing, spray paint, low-temperature and UV powder coating, vacuum metallization, and even subtractive processes like media blasting, where the mask covers a designated area to preserve the coating or surface finish it already has. 3D printed masks can be produced with less labor, offer more repeatability, and simplify many complex masking jobs. The technology can also be used to prototype and test a mask design before moving to machined metal masking if absolutely necessary for temperature tolerances.

There are a few factors to consider when selecting a material option for producing masks. These factors are mechanical and chemical requirements, part fit, and production requirements.

• Temperature: The largest limiting factor for 3D printed masking is temperature. Some coatings, such as powder coatings, cure at temperatures above 238° C. To select the most appropriate 3D printing material for an application, consult the Technical Data Sheet to find the heat deflection point before using it in a coating process. For many lower-temperature powder coating processes, High Temp Resin can withstand up to 238° C.

• Abrasiveness: Some finishing processes, like media blasting or vibratory tumbling, are subtractive, so the use of masking tools is to keep the coating of certain surfaces protected, rather than bare. These processes are more abrasive, and the masks need to be made from materials that can withstand the forces of the media used, like ceramic pellets or walnut shells. For these instances, use a harder material such as Rigid 10K Resin for SLA parts or Nylon 12 GF Powder for SLS parts.

• Solution Use: Many coatings require solutions, both basic and acidic. If an acidic or basic solution is part of the processing workflow, make sure to compare the TDS with the chemical requirements. Some Formlabs SLA resins perform better than others when submerged in different solutions. If an acidic solution is a part of your workflow, consider using Tough 1500 Resin or Rigid 10K Resin. The full set of Formlabs materials’ TDS can be found on our website.

• Part Fitment: Both Formlabs SLA and SLS materials offer a range of compliance and stiffness. Creating masks traditionally limits options for trying out new materials, because machining or molding parts is cost-prohibitive for one-off test runs. Having a 3D printer expands material possibilities for masks — you can try multiple materials at a very low cost per part.
  
  For Formlabs SLA, press-on fitment can be easily achieved with a material like Tough 1000 Resin. For SLS printers, Nylon 11 Powder is a good option for parts that have to flex very slightly and be used repeatedly. For masks that require a higher flexural modulus, Rigid 10K Resin or Nylon 12 Powder are excellent options. The accessibility of the Formlabs SLA and SLS platforms enables businesses to try multiple materials and find the one that best suits their particular workflow. Then, when the end part changes and a new modulus is required, businesses can switch masking materials again, without having sunk thousands of dollars into tooling.

• Production Requirements: Some masking applications require only one or two masks, while others need to match the volume of masks to the volume of parts. Formlabs’ SLA printers, both Form 3+ and Form 3L, are great choices for low volumes of masks, such as subtractive processes that can only be done a few at a time. The Fuse 1+ 30W SLS printer is better suited for higher volumes of masks given its ability to vertically stack multiple parts within the same build. For applications such as automated painting or Cerakoting with a Cerakote robot, where tens or hundreds of parts can be finished at once, printing masks at a higher volume on an SLS 3D printer is a better option.

NIC Industries, the manufacturer of Cerakote, has been coating 3D printed parts and using 3D printed masks for a long time, and find them especially useful when deploying their robotic Cerakoting machine for high volume production. 

For a batch production run of sample parts, they worked with Formlabs to produce 1,000 units, using SLS 3D printed masks to quickly and efficiently mask certain surfaces. Masks were printed using Nylon 12 Powder on the Fuse 1+ 30W SLS printer, and served to cover the inside of the two-part final product assembly to prevent overspraying and ensure clean delineation between colors. The masks also serve to fixture the part to the robotic applicator assembly, allowing for high throughput, and consistent coating.

^{SLS 3D printed mask and fixture (left), 3D printed masks fixtured to allow for robotic coating (center), and two-piece SLS 3D printed sample part, finished with Cerakote H-Series (right).}

On another part, NIC industries needed to post-process this bow riser, but protect the inner channel of a screw thread during the coating phase before final assembly. Prior to having Cerakote applied, NIC Industries designed and 3D printed a mask to protect interior surfaces of this bow riser. They designed a plug-style mask that fits into the screw thread and prevents any coating material from entering the cavity to ensure a smooth threading in the final assembly. The plugs can be easily removed, flex slightly to pop in and out of the cavity, and are durable enough to be used for hundreds of coating applications. 

Productive Plastics is an industrial thermoformer that uses Fuse Series SLS printers for a variety of manufacturing aids on the factory floor. During the painting process, they use tape to cover a critical copperized surface and protect it from paint. They needed to cut the rest of the tape away, tracing the outside of the copper surface, which took several minutes to do accurately.

With a 3D printed mask that perfectly fits over the copperized surface, they can quickly stencil around the mask and remove the unnecessary tape, without worrying about damaging the copper.

The following example of a 3D printed mask for a small pump housing demonstrates the costeffectiveness of 3D printed masking parts, on both SLS and SLA printers. The pump housing (grey) requires masking on the interior surfaces prior to coating. The interior surface is masked with a Nylon 12 Powder part (black) printed on the Fuse 1+ 30W SLS printer. This part has features that enable easy alignment as well as fixturing and protects the interior of the pump while the outside is coated. SLS printing was a good choice for this component due to the lack of supports required for the complex alignment pins and fixturing features. The top-facing circular feature is masked with a cap printed in Durable Resin (white) on the Form 3+. Durable was a good choice for this component as it could be printed flat on the build platform and the compliance of durable allows it to press fit into the outlet hole of the pump housing ensuring a snug fit.