Straight out of the machine, an SLS part has a uniform matte finish with a slightly grainy texture, a little like a piece of fine sandstone. For a great many functional parts that finish is perfectly good exactly as it is, and no further work is needed. But when appearance, feel or sealing matter, there is a useful range of post-processing options to choose from, each one adding a little time and cost.
Knowing what is available helps you specify the right level of finish for your particular job and budget, rather than paying for a premium finish a hidden part does not need, or under specifying a part that customers will see and handle. We carry out all of our SLS finishing in house as part of our MJF & SLS printing service, so we can advise exactly how far to take each part.
The standard finish
Every part is bead blasted after it comes out of the powder, a step that uses fine media to clean off any residual powder clinging to the surface and to even out the texture. This is the baseline finish, and it suits the large majority of functional parts and prototypes without any further work, which keeps both cost and lead time down for the everyday jobs that make up most of what we print.
A nice side effect of the matte texture is that it hides layer lines very well, so SLS parts rarely show the stepped, ribbed appearance that you sometimes see on parts made with other layer based processes. The surface looks intentional rather than like the trace of a print head, which is part of why blasted nylon parts present so well even without extra finishing.
Colour and sealing
Because raw nylon is naturally pale, SLS parts take dye beautifully. Vat dyeing immerses the part in heated dye, which soaks into the porous surface to produce deep, even colour right through the outer layer, with black being by far the most popular choice. For a smoother, sealed surface we can vapour smooth or coat parts, which reduces porosity and gives a more finished look closer to a moulded item.
Sealing genuinely matters for parts that need to resist liquids or that you want to look and feel like a moulded product, while dyeing is mostly about appearance, branding and hiding marks. The two can be combined, smoothing first and then dyeing, for parts where presentation is important and you want a uniform, professional result.
Painting and premium finishes
For show pieces and customer facing products, painting takes things further again. Because the blasted nylon surface is slightly porous, parts usually benefit from a primer coat first, which fills the texture and gives the topcoat something even to grip, after which the part can be sprayed to almost any colour or gloss level you like.
Painted finishes suit display models, marketing samples and consumer products where the part needs to look manufactured rather than printed. It is the most labour intensive option, so we reserve it for parts that truly need it, but the difference on a presentation piece can be dramatic.
Choosing a finish level
The right finish depends on whether the part is hidden away, regularly handled, or on show to customers, and on how much it needs to resist the environment it will live in. Matching the finish to the role of the part keeps you from over or under spending.
- Raw bead blasted finish for hidden functional parts.
- Dyed black or colour for visible and branded parts.
- Smoothing or sealing for a moulded look and liquid resistance.
- Painted or coated finishes for premium presentation pieces.
- Combine smoothing and dyeing where appearance really matters.