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Overall design considerations for 3D printing

3D printing is an umbrella term covering different additive manufacturing processes, but these design tips are nearly universal

Designing for additive manufacturing (DfAM) can seem daunting. Often, the phrase DfAM is juxtaposed with images of complex lattice structures or forms that look more organic than mechanical. In reality, 3D printing is inherently a very forgiving process when it comes to design best practices. It can easily perform internal sharp corners, complex undercuts and even build a structure that would be fully inaccessible to traditional cutting or tooled manufacturing. This is what has made additive manufacturing a powerful tool for prototyping parts destined for injection molding or casting since it can handle a broad mix of design features.

So what should you know about DfAM? What design traits can become problematic for 3D printing? These design best practices apply to nearly all the common additive processes, from laser powder bed fusion (SLS, DMLM), to fused deposition modeling (FDM), to vat photopolymerization (SLA).

Minimum wall thicknesses should be larger than 0.6 mm (0.024”) on self-supporting features like X-, T-, O-, or C-like shapes. This gives the material, and its method of 3D fusion, enough real estate to successfully deposit. If there is an unsupported area or needs to bear a load, the wall should be double at 1.2 mm (0.048”) or above.

Clearance between features should be above 0.5 mm (0.020”) to allow gaps to resolve without neighboring materials bonding to each other unexpectedly.

design considerations for 3D printing
Building “escape” channels at the bottom of long narrow gaps, such as screw bosses, will make 3D printed parts much easier to post-process.

Remove confined hollows allows for excess material removal. This can be printed support structure or unfused powders and resins. A balloon shape would be full of unused material without a means of removal. Adding ample exit holes for material clearing is needed. Often, parts can be digitally programmed to act hollow through modifications of material infill, which can create sparse geometric structures inside the part as it prints. Infill does not need to be designed in the part, the programming occurs during build preparation.

Design in escape holes to prevent trapped material that is difficult to clean. Many parts are cleaned with line-of-sight tools, bead blasting or liquid baths. Building exit channels, such as small perpendicular holes at the bottom of blind bosses, deep features or other gaps can help material freely exit while post-processing.

Fillet everything to mitigate acute stress points in the 3D printed parts. Fillets help evenly distribute strain load on a part and can generally make most features stronger. Fillets also tend to print more consistently versus sharp edges or corners.

Be mindful of cantilevers in the design that could easily break. A good rule of thumb is to think about holding a printed part from that cantilevered section, if you think the part will bend and break off, then you may want to reinforce that feature. Cantilevers grown vertically in a 3D build will be slightly weaker than those grown horizontally due to the layer-by-layer nature of 3D prints.

Design with even wall thicknesses as you would an injection molded part. Even walls help mitigate stress in the part while it is printing which can reduce twist or warping. In contrast, over-thick areas can build up a lot of stress, possibly deflecting thinner areas around the feature.

Provide the solid model, not just the STL, to your 3D printing service or internal manufacturing team. They have the right tools to convert the file and achieve the resolution you require without detail loss. Providing the solid model allows the operator to do any minor changes in a parametric environment – adding legacy to future prints.

design considerations for 3D printing
Coarse STL mesh will lead to printed parts with coarse features around rounded edges. By providing the CAD model, the printer operator can ensure the STL export is appropriate for the print job.

Many of the tips above outline minimum requirements. The best tip of all is to give some factors of confidence in the design by not always modeling to the minimums. Xometry offers free online design resources for seven 3D printing methods that go deeper into process-specific advice. Want to learn more? Check out Xometry’s Complete 3D Printing Guide.

This article was published in collaboration with Xometry.

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Greg Paulsen

Greg leads the Application Engineering team at Xometry, an online manufacturing marketplace. Greg handles special case projects that require attention on material selection, design-for-manufacturing, or technical engineering resources. Greg also plays a vital role in vetting new technologies and materials to add to Xometry's manufacturing portfolio. Greg’s background is in product development using rapid prototyping, focusing on the various applications of industrial additive manufacturing (3D printing) and advanced manufacturing.

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