Post Processing for SLS Parts

Introduction

SLS parts have high accuracy and good strength, which is always applied for functional parts. However, in reason of the nature powder based fusion in SLS, SLS parts normally have a powdery and grainy surface finish. So post processing techniques are available to increase surface finishes, and costing is normally applied to improve performance.

There are common SLS post processing methods as following:

Finish typeVisual rankToleranceSpeed
StandardPoorHighHigh
Media tumbled & Vibro polishExcellentMediumMedium
DyeingMediumHighMedium
Spray paint & LacqueringExcellentMediumMedium
Water-tightnessMediumMediumMedium
Metal coatingExcellentMediumLow

Standard Finish

This is the most common finish for SLS parts. Compressed air is used to remove all powder form parts once printing finish, then apply plastic bead blasting to clean any un-sintered powder sticking on surface. This finish is rough like medium grit sandpaper or slight matte grainy, which is best surface preparation for painting or lacquering.

Finish typeAdvantageDisadvantage
Standard finishCommon finish otherwise specified

High accuracy as overall geometry

Low cost
Matter, grainy surface

Limited color option(typically white)

Media Tumbled & Vibro Polish

Media tumbled or vibro polish are applied for SLS parts, in order to polish parts into smoother surface texture. Small ceramic chips in a tumbler can vibrate against parts and erode outer surface to polished surface. In order to have less effect on part dimensions and get rounding sharp edges. However, it is not suitable for parts with fine details and intricate features.

Finish typeAdvantageDisadvantage
Media tumbled & Vibro polishExcellent smooth surface

Multiple parts in one process

Remove sharp edges
Unsuitable for delicate features

Remove sharp edges with negative effect on part geometry

Dyeing

Dyeing is the most cost-effective way to color SLS parts, the porosity in SLS parts are perfect for dyeing. In this process, SLS parts are immersed in a hot color bath with a wide range of available color, this color bath will guarantee full coverage of internal and external surface. However, the typical dye only penetrates parts with a depth of 0.5 mm, which means continued wear will expose the original powder color on surface.

Finish typeAdvantageDisadvantage
DyeingA wide range of colors

Never affect part dimensions

Multiple parts in one process

Cost effectiveSuitable for complex geometries
Dyeing penetration depth is only 0.5mm

Not glossy finish

Spray Paint & Lacquering

SLS parts can be spray painted or coated with lacquer. These processes will make parts surface with various finishes, like high gloss, or metallic sheen. Lacquer coating can improve parts surface hardness, wear resistance, water tightness, and limit marks or smudges on parts surface. In reason of SLS parts nature porous, we recommend to apply 4-5 thin coats rather than 1 thick coat. This will increase the paint drying time and reduce the likelihood of paint moving.

Finish typeAdvantageDisadvantage
Spray paint & LacqueringImprove mechanical properties

Improve UV protection

Glossy smooth surface with color or clear
Labor intensive

Impact overall dimensions

Require good surface preparation

Water-tightness

Normal SLS parts have some inherent water resistance. Coating is always applied to enhance this properties. Silicones and vinyl-acrylates are verified to improve this properties greatly, while Polyurethane (PU) is not recommended. For complete water resistance, a dip coating method is required.

Finish typeAdvantageDisadvantage
Water-tightnessFurther improve water resistance

Improve mechanical strength
Coating thick affect overall accuracy

Metal Coating

Electroplating can be applied of SLS parts, stainless steel, copper, nickel, gold and chrome are able to deposited on parts surface, in order to increase strength, electrical conductivity in shielding applications. Parts are cleaned and a conductive layer is applied on surface, then the parts go through traditional metal coating process.

Finish typeAdvantageDisadvantage
Metal coatingImprove strength and functionality

Excellent aesthetic appearance

Part conductivity

Excellent surface finish
Increase lead time

Increase cost greatly

High level of skill

Limited number of metals