What post-processing options are available for 3D printed parts?
- Share
- Issue Time
- Oct 20,2026
The short answer
Every process needs its own mandatory step: support removal on FDM and SLA, powder removal on SLS and MJF, solvent wash and UV cure on resin. Beyond that, bead blasting, vapour smoothing, dyeing, epoxy sealing, annealing, inserts, machining and plating are chosen to match the part's job.
Two buckets: mandatory and chosen
Post-processing is quoted badly because it is quoted as one line. In practice it splits into work that cannot be skipped without the part being wrong, and work that is chosen to meet a specification. The mandatory list is short and process-specific: supports and rafts have to come off an FDM or resin part and the witness marks dressed; loose powder has to come out of an SLS or MJF part, including internal channels; a resin part has to be washed of uncured resin and then cured under UV to reach its stated mechanical properties. Skip any of those and the part is not a cheaper version of the finished item, it is a different and usually unusable item.
The chosen list is where the money and the arguments are: bead blasting, sanding and polishing, vapour smoothing, dyeing, painting, epoxy sealing, annealing, thread inserts, secondary machining, plating and, for metal, hot isostatic pressing. Each one buys a specific property and each one has a side effect on dimension or surface. The useful discipline is to name the property first, cosmetic, colour, strength, tolerance or conductivity, and then pick the shortest route to it rather than the longest menu.
| If the part must | The sequence is | What to watch |
|---|---|---|
| look moulded | smooth, prime, paint or texture | build-up on mating faces |
| hold a colour | dye the nylon, or paint | dye lot-to-lot match |
| resist wear or fluid | seal, plate or coat | added thickness, masking |
| carry load | anneal, then machine critical faces | shrinkage after annealing |
| take a thread | install a heat-set insert | boss wall thickness |
| hold a tolerance | print oversize, machine after | fixture and datum choice |
Supports, rafts and loose powder
FDM and resin processes build on supports, and the marks they leave are the first thing a buyer notices. Breakaway support on FDM leaves a rough patch that has to be sanded through a grit progression, typically from 80 up to 2000 for a cosmetic surface, and soluble support removes the problem inside cavities at the cost of a wash station and time. Resin parts printed with supports on a cosmetic face will show witness pits no matter how carefully the support is placed, so the orientation decision is really a finishing decision made at the quoting stage.
Powder-bed processes have the opposite problem: nothing to break off, but powder everywhere. Depowdering is blowing and blasting loose powder out of the part, and on SLS and MJF it is followed by bead blasting to even out the surface and remove the last of the cake. That blast is also what makes the part paintable without a primer, because it gives a uniform matte key. Parts with internal channels need the powder removed before any coating, or the coating seals the powder in.
Resin parts: wash, cure and the tacky failure
A stereolithography or DLP part straight off the platform is not fully cured. It comes out coated in uncured resin, and its mechanical properties are a fraction of the datasheet until it has been washed in solvent, usually isopropyl alcohol, and post-cured under UV. A part that is wiped rather than washed, or cured for too short a time, stays tacky, creeps under load and can be chemically reactive on skin. That is not a cosmetic defect; it is a part that will fail a functional test and, in a medical or consumer context, fail a safety review.
The practical consequence is that resin printing has a fixed labour content per batch that does not scale down with part size. Small parts in a full build are cheap per unit; one large part in a half-empty build carries the whole wash and cure cost. When comparing a resin quote with an SLS or MJF quote, ask whether wash and cure are inside the price or billed as a separate operation, because that single line often explains a gap that looks like a material or machine difference.
Vapour smoothing: what it buys, what it moves
Solvent vapour dissolves the outer skin of an ABS or ASA part so that the layer valleys flow together. Done properly it takes a visibly layered FDM surface to something close to a moulded finish, with roughness down to about 0.8 micrometres, in roughly twenty minutes, and it improves inter-layer bonding at the same time, which is why impact strength can rise by 10 to 25 percent. It is the single most effective cosmetic step available for a thermoplastic print.
It is not dimensionally neutral. The process removes something like 20 to 50 micrometres of surface, rounds sharp edges, and moves dimensions by roughly 0.05 to 0.15 mm depending on exposure. Any feature that must hold a tolerance after smoothing has to be either masked, machined afterwards, or printed oversize. Vapour smoothing is therefore the wrong last step on a part with a press fit; it is the right step on a cover or a handle where appearance matters and fits are loose.
Colour: dyeing against painting
Nylon powder parts take dye exceptionally well because the sintered surface is porous. Dyeing in a hot bath penetrates 0.3 to 0.5 mm into the surface, so the colour cannot chip or wear off the way paint can, and colour matching to a reference is achievable to within a small colour difference. That makes dyeing the default for functional parts, jigs, housings and anything that will be handled. The limits are that it works best on light-coloured nylon, deep blacks and saturated reds are harder, and the process adds moisture that has to be dried out before the part is measured.
Painting gives colour plus surface in one step, and it can hide layer lines that dye cannot. The cost is thickness: a primer and a topcoat add tens of micrometres and can bridge small holes, fill engraved text and change a press fit. It is also the right choice when the colour must match an existing product exactly, or when the part needs a gloss, metallic or soft-touch effect that a dye cannot produce.
Functional finishing: annealing, inserts, machining, plating
Annealing is the cheapest strength upgrade for an FDM part. Holding at 80 to 120 degrees Celsius for one to four hours relieves the internal stress locked in by extrusion; annealed PETG shows 15 to 20 percent better impact resistance and less creep under sustained load. The side effect is shrinkage, roughly 0.3 to 0.5 percent linear for nylon, which has to be allowed for before printing or removed by machining afterwards. For metal parts the equivalent step is hot isostatic pressing, which closes residual porosity and can add up to 40 percent fatigue life and 30 percent elongation at break, at the cost of several days of lead time.
Threads are the other common functional finish. A printed thread in nylon is weak and wears; a heat-set brass insert gives a reusable thread that survives repeated assembly, provided the boss around it has enough wall, usually at least twice the insert diameter. Secondary machining covers everything printing cannot hold: a bearing bore, a sealing face, a flat that has to sit square. And plating, applied over an electroless copper seed and then built up electrolytically, turns a plastic part into a conductive or metallic-looking one for shielding cans, RF enclosures and display models.
How to specify it in a quote
Do not write "finished part". Write the property and the measurement: surface roughness or a comparison sample, colour to a reference with the acceptable difference, the dimensions that must be held after finishing, and whether the finish is inside or outside the quoted tolerance. State whether the part will be measured before or after finishing, because on a smoothed or painted part those are two different parts. And ask which operations are done in-house: the split between printing and finishing is where lead times and quality arguments usually start.
The processes behind these finishes are described on the 3D printing page, with resin parts under SLA printing and powder parts under SLS printing.
Scope and sources. The split between mandatory steps and chosen operations, and the list of operations by material, are from a post-processing and finishing guide. The vapour smoothing figures of 20 to 50 micrometres removed, roughness down to 0.8 micrometres in about 20 minutes, impact strength up 10 to 25 percent and dimensional movement of 0.05 to 0.15 mm are from a post-processing techniques guide, as are the epoxy build of 0.3 to 0.5 mm per side, the annealing window of 80 to 120 degrees Celsius for one to four hours, the 15 to 20 percent impact gain on annealed PETG, the 0.3 to 0.5 percent shrinkage on annealed nylon, the dye penetration of 0.3 to 0.5 mm, the colour difference tolerance, the 80 to 2000 grit sanding progression, the 40 percent fatigue and 30 percent elongation gains from hot isostatic pressing, and its 10 to 14 day lead time. The bead blasting step for powder parts and its role as a paint key are from the same guide. Ranges are typical workshop values and will vary with geometry, exposure time and resin grade; they are planning figures, not a specification.