3D Printing Service ProvidersPost-Processing

From print to product: surface finishes for 3D printing

Finishing processes are integral to the 3D printing workflow

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While much of production work is done inside a 3D printer as a part is built up layer by layer, that’s not quite where the process ends. Post-processing is a vital step in 3D printing workflows, which takes printed components to finished products. That said, “post-processing” is not a specific process in itself, it’s a category that consists of multiple different treatments and techniques, which can be applied and combined to meet various aesthetic and functional requirements. 

As we’ll see in more detail in this article, there are numerous post-processing and surface finishing methods, including basic post-processing (such as support removal), surface smoothing treatments (both physical and chemical) and color treatments. Understanding the different processes at your disposal when 3D printing enables you to meet specifications and product requirements, whether your aim is to achieve a uniform surface finish, a specific aesthetic quality, or enhanced properties. Let’s dive in.

3D printed sample Xometry
Close-up of a MJF PA12 3D printed part vapour smoothed.

Basic post-processing for 3D printing

Basic post-processing typically refers to the initial steps involved once a 3D printed part has been removed from the build envelope and cleaned, including support removal and basic surface smoothing (in preparation for more thorough smoothing techniques).

Removal of support structures  

Many 3D printing processes, including fused deposition modeling (FDM), stereolithography (SLA), direct metal laser sintering (DMLS) and Carbon Digital Light Synthesis (DLS), require the use of support structures, which provide support for overhangs, bridges and delicate features. While useful in the printing process, these structures have to be removed before applying finishing techniques. 

Support removal can be achieved in a few different ways, but most common processes today involve manual work, such as cutting, to remove supports. In cases where water-soluble supports are used, support structures can be removed by submerging the printed object in water. There are also specialized solutions for automatic part removal, particularly for metal additive manufacturing, which use tools like CNC machines and robots to carefully cut away supports and maintain tolerances.

3D printed support removal
Visible support structures on 3D printed parts (Image: Formlabs)

Blasting

Another basic post-processing technique is blasting. This process involves spraying printed components with particles under high pressure. The impacts of the sprayed media against the surface of the print create a smoother, more even texture. 

Blasting is typically the first step in surface smoothing for 3D prints, as it is effective at removing material residues and creating a more uniform surface finish that is then ready for follow-up steps, like polishing, painting or dyeing. Notably, blasting does not result in a shiny or glossy finish.

Surface smoothing techniques for 3D printing

Besides basic blasting, there are other post-processing methods that can be used to give printed components enhanced smoothness as well as other surface characteristics, like a matte or glossy appearance. In some cases, finishing methods can be used to achieve smoothness for a variety of different build materials and printing processes. In other cases, however, surface smoothing treatments are only suitable for a specific type of material or print. Part geometry and print material are the two biggest considerations when choosing one of the following surface smoothing processes (all of which are available in Xometry’s Instant Quoting Engine.)

Bead blasting surface finishes
MJF Nylon PA12 3D prints comparison: as printed (left) vs. bead blasted (right)

Bead blasting

This post-processing technique is similar to basic media blasting in that it involves spraying particles at a print under high pressure. However there is an important difference: instead of using any type of particles (like sand), bead blasting uses spherical glass beads as media, which are blasted towards the print at a high velocity. 

The impact of the round glass beads on the print’s surface creates a much smoother and uniform finish. Besides the aesthetic function of bead blasting, the smoothing process can also improve a part’s mechanical strength without influencing the part’s dimensions. This is because of the spherical shape of the glass beads, which creates a very shallow impact on the part surface.

Media tumbling

Tumbling, also known as rumbling, is an effective post-processing solution for smaller components. This technique consists of placing 3D prints in a tumbler along with small chips made from ceramic, plastic or metal. The tumbler then rotates or vibrates, which causes the chips to rub against the printed parts to remove any surface irregularities and create a smooth finish. 

Tumbled surface finishes 3D printing
MJF Nylon PA12 3D printed parts comparison: as printed (left) vs. tumbled (right)

Media tumbling is more powerful than bead blasting and surface smoothness can be adjusted based on the tumbling media. For example, a more coarse surface texture can be created using lower grit media, while a smoother surface can be achieved using higher grit chips. Some of the most common large tumbling systems can process parts measuring 400 x 120 x 120 mm or 200 x 200 x 200 mm. In some cases, particularly for MJF or SLS parts, it is possible to polish components in a media tumbler.  

Vapor smoothing / Chemical vapor polishing

While the aforementioned smoothing techniques are all based on physical processes, vapor smoothing relies on a chemical reaction between the print material and vapor to create a smooth surface finish. Specifically, vapor smoothing consists of exposing a 3D print to a vaporized solvent (such as FA 326) inside a sealed processing chamber. The vapor adheres to the print’s surface and creates a controlled chemical melt, which levels any surface imperfections or peaks and valleys by redistributing the melted material. 

Vapor fused 3D printed surface finishes
MJF Nylon PA12 3D printed parts comparison: as printed (left) vs. black spray painted and vapor fused (right).

Vapor smoothing is also known for imparting a more polished, glossy surface finish. Typically, vapor smoothing is more expensive compared to physical smoothing processes, but can be preferred thanks to its superior smoothness and shiny finish. Vapor smoothing is compatible with most 3D printed polymer and elastomer materials.

Coloring processes for 3D printing

An optional post-processing step, coloring is a good way to enhance the aesthetic of a printed product. Despite the fact that there are different color options when it comes to 3D printing material (particularly FDM filaments), coloring as a post-process enables you to work with materials and printing processes that meet product specifications and achieve the right color match for a given product. Below are the two most common coloring methods for 3D printing.

Spray painting

Spray painting is a popular method that consists of applying a coat of paint to a 3D print using an aerosol spray applicator. By suspending a 3D print, paint can be sprayed evenly over the part, covering its entire surface. (Paint can also be applied selectively by using masking techniques.) This technique is common for both 3D prints and machined parts and is relatively low cost. However, it does have one significant drawback: because the paint is applied in a thin coating, if the printed part is scratched or wears out, the original print material color will become visible. The following coloring process solves this issue. 

Spray painted 3D print
SLS PA12 3D printed part with a black spray painting finish.

Dyeing

Unlike spray painting or brush painting, dyeing a 3D print penetrates below the surface. This has a couple of benefits. For one, if a 3D print wears or gets scratched, the vibrant color will endure. Dyeing also won’t peel, which paint can be known to do. Another big benefit of dyeing is that it doesn’t change the dimensional accuracy of a print: because the dye penetrates the surface of the build, it does not add any thickness and thus does not result in any loss of detail. The specific dyeing process does depend on the 3D printing process and material.

Dyed yellow 3D print sample Xometry
SLS PA12 3D printed part dyed in yellow.

Surface finishes for 3D printing at Xometry

Working with a production partner such as Xometry can open up access to all these finishing processes, enabling you to achieve professional 3D prints that meet both performance and aesthetic standards. For a full overview of Xometry’s surface finishing options and what they do, see the table below.

Surface finish

Suitable 3D printing technology

Advantages

Considerations

BlastingSLS• Gives smooth texture to  surface

• Makes surface paintable

• Low-cost

• Might lead to dimensional inaccuracy

• Does not give smooth finish

Bead BlastingSLS• Preservation of the part’s dimensions• Requires the use of extra materials
Chemical Vapour Polishing / Vapour smoothingMJF, SLS• Shiny finish• Lack of versatility
Media tumblingSLS• Good for small parts• Size limitations for large parts 

• Time-consuming

Spray paintingMJF• Cheap and rapid• Applies only on surface, inner color visible if surface is scratched
DyeingMJF (black), SLS (black, blue, green, red, yellow)• Dye penetrates into the part instead of only surface

• Very durable with superior aesthetics

• Costly compared to spray painting

Ultimately, post-processing is an essential part of the 3D printing workflow, from removing supports, to smoothing out part surfaces, to coloring prints for optimal aesthetic quality. Xometry offers end-to-end 3D printing services across the UK, Europe and America leveraging its vast fleet of 3D printing and post-processing systems as well as its team’s deep knowledge of AM production. The service also offers an Instant Quote Engine that allows you to accelerate prototyping and production jobs. Discover the endless 3D printing possibilities with Xometry here.

This article was published in collaboration with Xometry. 

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Tess Boissonneault

Tess Boissonneault is a Montreal-based content writer and editor with five years of experience covering the additive manufacturing world. She has a particular interest in amplifying the voices of women working within the industry and is an avid follower of the ever-evolving AM sector. Tess holds a master's degree in Media Studies from the University of Amsterdam.

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