Key Factors for an Ideal Design
Four figures in particular have to be in balance with one another in order to build an ideal and accurate part. Within that balance, size, layer resolution, wall thickness and orientation will contribute to the ultimate functionality and aesthetics of your part.
3. Wall Thickness
1. Size: 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 Fused Deposition Modeling (FDM) machines at 36” x 24” x 36” (X, Y, and Z).
2. Resolution: 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 (SL) also achieves a thin resolution at .0002” and Laser Sintering (LS) 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.
3. Wall Thickness: Thin-walled parts built with LS are more likely to warp because of the build style. LS parts are subject to high temperatures and the weight of the surrounding powder during the build, and LS 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.
4. Orientation: 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.