Design tips for SLS and MJF 3D printing

This article points out design tips that are crucial for successful SLS and MJF 3D printing

Xometry Europe · Mar 31, 2020

Design is the first stage of most manufacturing processes including SLS (Selective Laser Sintering) and MJF (Multi Jet Fusion) 3D printing technologies. These technologies are capable of producing superb parts with complex features, and using design for additive manufacturing (DFAM) in your 3D model will make the print flawless. The following are some tips that would improve and optimize your designs for SLS and MJF 3D printing.

(Want to know the differences between MJF and SLS? They are all explained in this article)

Size limitations

The consideration of size limitations is very important when designing for SLS or MJF 3D printing. The following are some of the size limitations in these technologies.

Wall thickness: To prevent collapse during printing or breakage during post-processing or use, it is necessary to design parts with sufficiently thick walls. The recommended minimum wall thickness is 1mm for MJF and from 0.7mm (PA 12) to 2.0mm (carbon-filled polyamide) for SLS. It’s possible to have walls as thin as 0.6 mm, provided support structure is provided. For either process, a wall thickness of 1.3 mm is preferred for repeatable results, and in most cases walls do not need to go beyond 4 mm.

Walls thinner than 0.5 mm are likely to over thicken as a result of the heat from the laser (SLS) or infrared source (MJF).

Minimum wall thickness for MJF and SLS
Minimum wall thickness

Hole size: The SLS and MJF technologies can print holes directly in parts (rather than drilling holes after printing. However, the holes you design must not be smaller in diameter than 1.5 mm for SLS and 1.0 mm for MJF. This is to prevent unsintered powder from getting stuck in the holes. It is recommended to design holes to standard drill sizes in case they need to be mechanically opened.

Minimum hole size for SLS and MJF
Minimum hole size

Part size: The maximum printable part size for SLS is 600 x 350 x 560 mm, with a minimum printable feature size of 0.8 mm. MJF, on the other hand, can print parts as large as 360 x 284 x 360 mm and features as small as 0.5 mm.

Tolerancing

When designing for MJF or SLS 3D printing, limit tolerances to areas where they are important such as mating parts. Excessive tolerancing would only increase the printing effort.

Achievable dimensional accuracy depends on the printer and the size of the printed part. MJF and SLS are both capable of printing with very high accuracy of up to ±0.2% of feature dimensions.

Avoid excess tolerance
Avoid unnecessary tolerancing

Hollow parts

To reduce weight and material use, SLS and MJF parts can be designed hollow. For such parts or features, escape hole(s) must be included for the removal of residual unsintered powder from the hollows. The recommended minimum size of the hole(s) is 3.5 mm. Sufficiently large holes are also necessary to allow the interior of hollow parts to be polished via media tumbling.

Escape holes for hollow parts
Escape holes for hollow parts

Interlocking parts

SLS and MJF parts can print mating and moving parts in a single build. This means that using these 3D printing technologies, you don’t need to print separate parts before assembling them as you build entire functional assemblies in one cycle. For interlocking parts, models must be designed with a minimum clearance of 0.5mm, with larger clearance preferred if possible. This is to ensure the thorough removal of excess powder to ensure that printed assemblies do not become one solid part.

Minimum clearance for interlocking parts
Minimum clearance for interlocking parts

Engraving and Embossing

Certain details of parts are engraved or embossed during printing. For such details to be visible, we recommend designing them with a minimum depth or height of 1 mm. This depth is also important for post-processing as any engraving or embossing less than 1 mm may wear off during media tumbling.

Texts can also be printed on parts using SLS and MJF technologies. To ensure readability, texts should have a minimum height of 2 mm. Also, the Sans serif font is recommended not only for legibility but also to reduce details. Adding height to text can help assure that more fragile letters, like the lowercase letter “i” will withstand post processing and handling.

Minimum depth and height of embossings  and engravings
Minimum depth and height of embossings  and engravings

Warping

One of the most important design tips for MJF 3D printing is to avoid large flat surfaces. This tip also applies to SLS. In these two technologies, large flat surfaces are susceptible to warping and should, therefore, be avoided. If they are a crucial feature of a part, ribs should be included in the design to provide support. Note, however, that this may not always solve the problem, hence, Large flat surfaces should be avoided whenever possible.

Warping of large flat surfaces
Warping of large flat surfaces

Conclusion

Following these tips, you can rest assured that your 3D printed parts would be flawless. Have your designs ready? Head over to our Instant Quoting Engine to upload them and get a quote in seconds.

Posted in Design