One consideration when designing for additive manufacturing is the size of the part you are building. Each technology has an optimal build volume, some larger than others. The largest build volume is accomplished on our Fused Deposition Modeling (FDM) machines at 36” x 24” x 36” (X, Y, and Z).
Parts bigger than the available build volume of any given technology can be sectioned prior to manufacturing in CAD and expertly bonded together post-build. The size of a part impacts the amount of time it will take to build and the minimum feature size possible. A bigger part will take longer to build and require more material, adding to the overall cost of the part.
Layer resolution is the thickness of each slice laid out during the build of a 3D printed part. Depending on the technology, a thinner layer height can reduce “stair-stepping,” or the visible ridges that appear on the surface of a part post-build. Resolution attributes to the surface quality and definition of the part before post-processing. The thinner the layer lines, the better the detail and smoothness, but the longer the build time.
The smallest resolution possible with the greatest amount of detail is accomplished with PolyJet at a layer resolution of .00063”. Stereolithography (SLA) also achieves a thin resolution at .0002” and Selective Laser Sintering (SLS) can produce a layer thickness of .004”-.006”. Slice thickness for FDM is recommended at .007”- .020” because of the build style. The thickest FDM resolution is a great option for large, non-cosmetic parts that can be built faster and cheaper.
After deciding on the optimal layer resolution, your wall thickness comes into play. Wall thickness is a fundamental design feature that ensures stability, accuracy and tolerance for an additively manufactured part. Thinner walls can shorten build times, but too thin and there may be flimsy or less than accurate features.
Thin-walled parts built with SLS are more likely to warp because of the build style. SLS parts are subject to high temperatures and the weight of the surrounding powder during the build, and SLS plastic materials experience slight shrink as the build cools and they solidify. With a wall thickness between .040”-.120”, geometric stability of these features is much more achievable.
With FDM, the recommended minimum wall thickness is four times the layer height. For example, if you are designing with the minimum FDM layer height at .007”, your minimum wall thickness should be .028”. Implementing this recommended ratio will eliminate brittleness in your piece.
Another important consideration for optimal geometric stability is build orientation. Orientation in 3D printing refers to how and which direction a part is placed on the 3D printing build platform (X, Y or Z). The part might be oriented at an angle, lying flat or standing vertical. Build orientation is a crucial step that affects part quality, in particular, geometric dimension and tolerance errors on the part, the energy expended and the extent of support structures needed, all contributing to the overall cost of the part.
Considerations for different technologies lead to building parts at different orientations. With FDM, the extruded plastics used in the technology have its strongest strength at the tensile mode along the X-Y plane and the lowest strength in the Z-direction because of the technology’s build style of one layer cooling and solidifying while the other is laid on. Building large flat surfaces horizontally could affect the accuracy of the part and result in warp because the large surface area of the part is parallel to every new layer of material.
Some build orientations are better for curved or square features. Others result in more visible layer lines affecting the aesthetics of the final part. Certain orientations will deliver more overhangs, resulting in the need for supports.
Size, resolution, wall thickness and build orientation are corresponding units in a seamlessly composed design for 3D printing. When these four considerations are in balance, you are ready to build your part.
Learn more about the design guidelines for 3D printing technologies here or speak with one of our experts in Design Services.
