Model design rules for SLM/DMLS 3D printing

Different 3D printing processes have different capabilities and different design restrictions. In this article we will talk about key design considerations that apply to all 3D printing processes.

Here are 7 tips I have found helpful when designing and modeling for 3D prints. these tips should work on most 3D modeling software.

Keep Your Parts Manifold
For modelers coming from animation, illustration, or gaming backgrounds, one important thing to remember is that your 3D prints must be composed of watertight manifold volume parts. Always check your model for artifacts, loose faces or unwelding edges and verts.

That means:
No one dimensional planes,shells or extruded edges
No double sided faces
No self intersecting faces
No open faced holes
No unwelded verts or edges

Multi-object Prints
Does my part need to be one continuous mesh? This is a question that many new modelers have when creating for 3D printing. The simple answer is that a continuous mesh is not required. You can design prints from overlapping or intersecting objects so long as all components involved are manifold parts.

Know Your Build Area
When designing your part, keep in mind your build area. However, your printer’s build volume does not have to limit the size of your final model. Be creative! Clever layout in your build area can help you get larger prints. For instance, the diagonal space from top to bottom in your build area will give you the longest build size of your printer.

Small prints and exaggerated details
When sculpting small parts, it’s often very helpful to slightly exaggerate details. This means making your surface details with slightly deeper cuts and more pronounced surface texture. If possible, making slender parts slightly thicker will help ensure that they will print clean.

Save Material
Making your model hollow using shell and boolean functions available in your modeling software will save you resin material. Be sure to make a large enough “vent hole” that connects to your hollowed area to the outside of your model this will allow uncured material to flow out.

Clean Up Well
After your print is finished you have to soak your finished print in IPA for 12-15 minutes. I find that towards the end of the soak you can give your part a gentle rubdown with your gloved hand to help break down and remove any resin stuck to the surface of your print. Using a soft brush also helps to reach area that you can’t reach with your hand, this added step this helps get a quality finish to your print.

Remove Supports Carefully
Take your time when removing your support material. Rushing this process could ruin an otherwise flawless print. Using an X-acto knife to score a line at the connection point will give a cleaner break. Give thicker supports a gentle wiggle, don’t pull or use excessive force.

Especially for SLS/MJF,How do you design for SLS/MJF printing?

Designing for metal printing
General guidelines for designing metal printed parts are:

Wall thickness
The minimum wall thickness to ensure a successful 3D print with most materials is 0.4mm. Finer structures are possible, but are dependent on material, orientation, and printer parameters.

Pin diameter
The minimum reliable pin diameter is 1mm. Smaller diameters are possible, but will have reduced contour sharpness

Hole size
Holes diameters between 0.5mm and 6mm can be printed reliably without supports. Support free building of hole diameters between 6mm and 10mm is orientation dependent. Horizontal holes with a diameter greater than 10mm require support structures.

Escape holes
Holes are required on hollowed metal parts to remove unmelted powder. A bore hole diameter of 2-5 mm is recommended. Using multiple escape holes will greatly improve the ease of powder removal.

Overhanging Surfaces
The minimum angle where support material is not required on an overhanging surface is 45º relative to the horizontal in most cases. It is possible to reduce this angle further by optimizing the laser parameters.

Unsupported Edges
The maximum length of a cantilever-style overhanging surface is 0.5 mm. An overhanging horizontal surface supported on both ends can be 1 mm long. These rules will apply to embossed and engraved features with unsupported surfaces as well.

Aspect Ratio
The maximum ratio between the vertical print height and the part section is 8:1 to ensure stability of the printed part on the build plate.

Tolerances
Part tolerance in the print direction is ± 1-layer thickness. In the XY plane, the achievable tolerance is ± 0.127 mm

Support material
Due to the high temperatures involved in the metal printing process and the layer by layer nature of part construction, support structures are required to connect unsupported geometry to the build platform and act as a heat sink for thermal energy. Support therefore plays is an essential factor to consider when designing for metal printing.

Surface quality
Some designs require one side of the part to have a smooth surface (also known as the presentation side). If a smooth surface finish is desirable, post-processing is generally required. There are some steps that can be taken when selecting part orientation to improve the surface quality of a print. These include:

Upward facing surfaces of a part will have sharper edges and better surface quality than downward facing surfaces. The greater than angle of a downward facing surface relative to the horizontal, the better the downward facing surface quality.

A visible “stepped” effect can occur on angled surfaces depending on the layer thickness. In general, to avoid steps on the surface, the angle of the plane should be greater than 20º relative to the horizontal.