I use 3D printing a lot at NK; it’s a great tool to prototype parts, but a common issue we face is that those printed prototypes can’t come close to the strength of a machined or molded part of the same shape. I have found that a quick way to improve the strength of my 3D prints is to put more consideration into the orientation and build direction of my prints.
The problem stems from the anisotropic nature of 3D printing. Essentially, a 3D print is formed by building a bunch of individual layers of a material and stacking them on top of each other, giving them a directionality. Each layer is very thin, so it behaves differently along its surface (the plane) than it does perpendicular to it. Though each individual layer may be strong, the connections between the layers have the lowest yield strength and, in turn, tend to be the point of failure (See picture above). Imagine an Oreo cookie. The cookie is composed of multiple layers which are adhered together. When you try to split the cookie, it is much easier to pull the layers apart from each other than it is to crack all three layers down the middle. In the picture below, the left image is easier to break than the right, a concept which holds true for any anisotropic material (3D prints, wood, baked goods, etc.).
Left: The layers inherent to a 3-D printed part
Right: How the build direction can cause prints to fail
(courtesy of Simplify3D.com)
This is especially an issue for lower-end printers which tend to have lower resolution and minimal post-processing. The FDM printers I have worked with in the past have had particularly directional prints, and thus, could easily cause structural flaws. This is when it can be very important to carefully choose the print’s build direction. Proto Labs makes it easy by recommending they choose the orientation, and that is fine for many situations, but, at the end of the day, you are the one who knows the actual function of the part. Thus, you are the one who has the best idea of where parts need greater strength. At NK Labs, we have a Form 2 printer from Formlabs, which I’ve been pretty impressed with so far. For an inexpensive system, this printer has shown good resolution and strength of prints. A big reason for this is that the Form 2 is a stereolithography (SLA) printer, which builds differently than FDM, and even includes a curing step to melt all of the layers of the print together, making a more uniform structure.
Anisotropic nature of an Oreo cookie
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