3D print post-processing

3D print post-processing (also called finishing) is the set of steps that follow the removal of a part from the printer and turn a raw print into a usable part. Some steps are essential for the given process (support removal, depowdering, washing, post-curing), others are optional and determine the appearance, accuracy and properties of the finished part.

For FDM prints, the main steps are support removal (breakaway supports or supports soluble in water or another solvent), sanding, filling and painting, and for ABS and ASA also acetone vapor smoothing. SLA and DLP parts are washed in isopropyl alcohol (IPA), post-cured with UV light, often at elevated temperature, and the support marks are sanded off. SLS and MJF parts are depowdered and bead blasted; they can then be dyed in a bath, vibratory tumbled, vapor smoothed or impregnated.

Post-processing is most demanding for metal 3D printing: stress relief annealing while the parts are still on the build plate, separating the parts from the plate by wire EDM or sawing, support removal, hot isostatic pressing (HIP) for demanding applications, and finally machining of functional surfaces, threads and precision holes, followed by blasting or polishing.

Finishing operations change both the dimensions and the properties of the part. Sanding and blasting remove material and round off edges, while primer and paint add a layer typically several tens of micrometers thick, or more with multiple coats. Vapor smoothing refines the surface but can blur small text and sharp details. Annealing plastics improves heat resistance, but the part may shrink or warp. Depending on the amount of manual work, finishing can take longer and cost more than the printing itself, especially for visual models.

Choose the extent of post-processing according to the purpose of the part. A functional prototype usually only needs support removal and bead blasting, while a visual model for a presentation or photo shoot needs sanding, filling and painting to the required color and gloss. For end-use parts from SLS and MJF, dyeing and vapor smoothing are common; they improve appearance, seal the pores and make cleaning easier.

Machining and other mechanical operations are appropriate where printing cannot reach the required accuracy or surface roughness: bearing seats, sealing surfaces, precision holes and threads. For screw joints that are tightened and loosened repeatedly, heat-set threaded inserts are pressed into plastic parts.

The most common source of misunderstanding is a vague specification. "Finished part" means something different to every supplier, so describe the required condition in your request: which surfaces are cosmetic, what surface finish and color you require (for example to a RAL reference) and whether support removal and surface finishing are included in the price. For larger runs, have a reference sample approved.

Mask functional surfaces with tight tolerances during sanding and painting, or design them with a machining allowance and have them machined after surface finishing. For resins, insist on complete post-curing, because an under-cured part is tacky and has poorer mechanical properties. For powder-based processes, check that no powder remains in cavities and channels.