One of the key questions when planning 3D printing jobs is considering the roughness or smoothness of surfaces of different materials. After all, their quality varies, depending on the material and printing process. We would therefore like to give you an overview of what needs to be considered in 3D printing with regard to rough and smooth surfaces.
This requires a look at the individual 3D printing processes.
Contents
3D printing with liquid polymers
The following additive processes work according to the active principle of selective curing of liquid polymers: Stereolithography (or SLA/STL printing), Digital Light Processing (DLP process), Continuous Liquid Interface Production (CLIP process) and the 2- Photon Polymerization. What all of these methods have in common is that supporting structures (support) always have to be printed at the same time.
Especially for stereolithography, the surface quality depends heavily on the orientation of the model in the 3D printer. The underside in particular is usually very rough due to the support structures, while the Ra value (the measure of roughness) on the top is in the low single-digit µm range even without reworking.
As a post-processing, it is particularly recommended to use spatula or fillers or sanding with sandpaper. Very good surfaces can be produced in this way.
Powder-based 3D printing processes
In addition to the widespread selective laser sintering (SLS printing), particular mention should be made of the HP Multi Jet Fusion and the ColorJet process. As a rule, these processes do not require any support structures. An exception to this, however, is the selective laser melting (SLM printing) commonly used in metal printing.
The surface quality in powder-based 3D printing proves to be of good quality overall. In addition, these models have largely homogeneous surfaces due to the omission of support structures. Depending on the material (∅ approx. 60 µm powder grains), however, holes/pores form on the surface. As a result, completely smooth surfaces cannot be produced even when grinding.
For post-processing, grinding, blasting or vibratory grinding are particularly recommended for these processes. It should be borne in mind, however, that an almost pore-free surface can only be produced with the powder-based 3D printing process with great effort (vacuum infusions; multi-stage process).
3D printing by plastic extrusion
The FDM or FFF process can undoubtedly be considered the most well-known 3D printing process in the field of plastic extrusion. Support structures are generally required here.
3D prints in these processes usually have a rather low to at best mediocre surface quality. For production reasons, the outer layers in particular are heavily grooved. On the other hand, the surfaces of these models prove to be almost non-porous. Above all, the underside is mostly very smooth in the areas without support.
Post-processing usually focuses on removing the support structures. In particular, FDM models made of ABS can be ground, blasted or vibrated/trowelized very well.
3D printing by photopolymer jetting
Among those 3D printing processes that are based on the selective application of photopolymer droplets, PolyJet or MultiJet modeling should be mentioned in particular.
These processes are characterized by the fact that they produce good to very good surfaces. As the discharged drops of material dissolve into very small layer heights, very homogeneous surfaces are created with barely perceptible layer thicknesses of only 15 – 30 µm.
However, support structures are also necessary here, which noticeably impair the quality of the “affected” areas. However, this does not apply to those PolyJet or MultiJet 3D printers that use thermally soluble or water-soluble support structures.
In the latter cases, post-processing is usually no longer necessary. In the other cases, blasting and grinding are used in particular, with which very good surface values can be achieved in each case.
Learn more about 3D printing processes and post-processing options on our website.
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