3D printing is a manufacturing technology where parts are fabricated layer by layer, thus layers form an integral part of the process. Staircase effect is a phenomena associated with 3D printing when the layer marks become distinctly visible on the surface of the parts, giving the perception of a staircase. Hence the name. Staircase effect is omnipresent in 3D printing irrespective of the technology chosen. In some processes (FFF) the layers are highly distinct, whereas in some (SLA), they are not. Although this has got to do with the method of fabrication and the process parameters in general, one thing common across all the technologies is the layer thickness setting. So let’s see how layer thickness impacts the part geometry and results in the staircase effect.
Consider the images as shown in Fig. a, the layer thickness size varies across the images. The left-most image depicts a thicker layer, whereas the rightmost image depicts a finer layer thickness. Let’s assume that the curvature, marked in red color, corresponds to the curvature of the part geometry under consideration. As you can see, if the same part geometry is fabricated with a finer layer thickness, more number of layers are required and vice versa. More the number of layers, more true the shape of the final part with respect to the 3D CAD data. Because when the layer thickness is fine, more number of layer are cramped together in a smaller space and thus the distance between two consecutive layers is smaller, thereby resulting in a smooth, continuous surface. If the part geometry has a curvature or an angled surface, a finer layer thickness will result in mitigated staircase effect thereby leading to a better surface accuracy and finish. A 60µm layer thickness setting will result in a better surface finish as compared to a 100µm layer thickness setting.
Another important phenomena responsible for staircase effect is the nature of part geometry under consideration. It’s been an observed fact that, layer marks are prevalent on curved and angled surfaces. Since layers are sliced and deposited with respect to the vertical axis, any change in the nature of the part geometry with respect to this axis will result in a staircase effect.
Consider the image shown in Fig. b, there are two lines (marked in red) at an angle of 10˚ and 80˚ with the horizontal. It is evident from the image that, for a given layer thickness setting, as the slope becomes steeper, the aligned distance(d2) between two consecutive layers decreases, whereas as the slope becomes gradual, the aligned distance(d1) between two consecutive layers increases. As the aligned distance between the layers increases, you can easily demark one layer from the other, thus the surface looks discontinuous, and the staircase effect is more prominent. Whereas, in case of steeper slopes, the surface looks like a smooth, continuous geometry because the staircase effect is mitigated.
Thus, the staircase effect is more prevalent on part geometries having gradual surfaces as opposed to part geometries having steep angled surfaces. To validate this, we prepared an angle benchmark and we found that, the observations aligned with our assumptions.
Thus, part orientation is a critical phenomenon. Depending on the requirements, you can play around with the part orientation to avoid staircase effect on critical and aesthetically good looking surfaces. The layer marks can be mitigated by polishing the parts, too. But it is advised that care be taken during part fabrication, itself.