AMS Spring 2023

5 Professional Finishing Options for FDM Parts

6K SmarTech

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Despite the advances of other technologies, Fused Deposition Modeling (FDM) remains the go-to 3D printing process for prototypes and simple plastic parts. It’s fast, it’s cheap, and there are thousands of filament options to account for projects of all kinds. When people talk about 3D printing, they’re often talking about FDM.

But there are limitations to extrusion-based printing technologies. While FDM is a highly effective and versatile process, it has often lagged behind comparable technologies — Stereolithography, SLS, etc. — in terms of surface finish. Layer lines can be severe, and FDM parts aren’t always usable when taken straight from the print bed.

Fortunately, FDM parts don’t have to remain in their as-printed form. There are several professional post-processing techniques that can be used to remove layer lines, improve the overall surface finish of a part, or even add color and other aesthetic features.

3ERP, a global rapid prototyping company that specializes in on-demand 3D printed parts, recommends the following five finishing options, all of which can turn ordinary FDM parts into high-quality components.

Sanding

It might not sound complicated, but sanding is one of the most important techniques for achieving a professional finish on FDM printed parts.

Using textured sandpaper, it is possible to smooth the surface of a part in a way that clears imperfections (such as support marks) and removes visible layer lines. It is a manual process, however, which means care must be taken to apply the sandpaper evenly across the part.

Sanding 3D printed parts generally involves using sandpapers of varying grit levels. This means starting with a coarse sandpaper (100 grit or higher) that will remove large bumps and blemishes and gradually moving up to a very fine sandpaper (up to 5,000) to achieve a polished finish.

Although sanding is difficult when dealing with finer details or thin walls, it is highly effective for improving part smoothness and is a great way to prepare parts for coating or painting.

Bead blasting

While sanding is widely used for improving the smoothness of FDM parts, the process of bead blasting may offer a more comprehensive solution, especially for complex parts with hard-to-reach areas.

The bead blasting process involves firing an abrasive substance at the plastic part in a controlled manner, rather than rubbing it manually with sandpaper. It is much faster than sanding, and is also adjustable in terms of pressure and bead hardness.

The abrasive substance is blasted at the FDM part with a motion similar to spray painting, allowing for an even coating across the part.

Polishing

Polishing is an important finishing procedure for aesthetic parts, and follows naturally from sanding: once a part has been sanded with a very fine grit, it is ready for polishing if necessary.

While sanding is used to improve the smoothness of an FDM part, polishing takes things further by giving the plastic a shiny or mirror-like appearance. This may be necessary for aesthetic parts such as models, or for functional parts that require minimal friction.

During the polishing process, a cloth or buffing wheel is used to consistently apply polish to the surface of the part, giving the plastic a durable shine. Although it can take some time, the polishing process effectively transforms FDM parts, giving them the appearance of injection molded components.

Painting

There is a huge variety of materials available for FDM 3D printing, from standard PLA and ABS to more specialist engineering composites designed for functional applications. Many of these materials are available in a range of colors.

Nonetheless, FDM parts often require a coat of paint after the 3D printing stage. This might be because the filament is unavailable in a specific shade, or because a part requires different colors in different sections.

At 3ERP, we offer a variety of painting options, including matte, satin, high-gloss, textured and soft-touch coatings. Shades can be color-matched for branding purposes, while priming (before) and polishing (after) is also provided.

Painting should be considered for any parts used in consumer products, with the only potential pitfall being a slight adjustment to dimensions. (Mechanical parts with exceptionally high tolerances may be better left unpainted.)

Metal coating

A dramatic rise in metal additive manufacturing technologies has made 3D printed metal parts more accessible to companies of all sizes. However, thin metal coatings can also be added to plastic parts made with FDM — a cheaper option when a metallic appearance is the main requirement.

There are several options for adding a metal coating to FDM parts, many of which are difficult or impossible to achieve without professional equipment. These include metallization, chroming and zinc plating, all of which can radically transform the appearance of a printed part.

Electroplating options use a vat of plating solution and an electric current add the metal surface layer, producing a professional-grade metallic surface finish in a very short space of time.

Contact 3ERP to find out how your 3D printed FDM parts can be improved with post-processing treatments.

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