SLS Powder
SLS powder consists of thermoplastic micro-particles (45 to 90 microns in diameter). Unlike the resin used in SLA or the filament in FDM, SLS powder serves a dual purpose: it is both the building material and the support structure since the unsintered powder surrounds and supports the part during the print, allowing for incredible geometric freedom and nested batch printing.
General Properties and Characteristics
When working with SLS materials, you aren't just looking at a solid plastic part; you are looking at a porous, sintered structure. Key traits include:
- Isotropic Mechanical Properties: Unlike FDM prints, which are weaker along the Z-axis (layer lines), SLS parts exhibit nearly uniform strength in all directions.
- Surface Texture: Parts typically have a grainy, "sugar-cube" matte finish. This is due to the nature of fused powder particles.
- Porosity: SLS parts are naturally slightly porous. While they are structurally sound, they may require sealing if they need to be airtight or watertight.
- Thermal Stability: Most SLS powders have high heat deflection temperatures, making them suitable for high(er)-temp applications.
Refresh Rate
In SLS, you don't throw away the unsintered powder but mix it with "virgin" powder to compensate the aging/degradation of the powder beforr the next build.
Health and Safety
Working with SLS powder requires a bit more discipline than your standard desktop printer. Because the particles are so fine, they behave more like a fluid or a gas than a solid.
1. Respiratory Risks
The primary concern is inhalation. Fine polymer dust can irritate the lungs and, with chronic exposure, lead to more serious respiratory issues. So the use of a protective mask during post-processing and powder recovery is advised.
2. Combustibility
Like many organic dusts (including flour or sugar), high concentrations of polymer powder suspended in the air can be explosive if met with an ignition source. Special equipment (ATEX-certified) for the post processing and minimizing "dust clouds" is essential.
3. Skin and Eye Irritation
The powder is a desiccant; it loves to suck moisture out of whatever it touches. Handling it with bare hands can lead to dry, cracked skin, and a stray puff of powder in the eyes is not a pleasant experience. Nitrile gloves and safety goggles are therefore also advised.
PA12 as the best option for the space
If you want to change the material used, the necessary clean up to avoid cross contamination is a tedious task. Therefore it is reasonable to decide only to use a single material for most applications. For this Nylon 12 (PA12) is the best choice based on it's good fitting properties. While other materials like PA11 (bio-sourced) or TPU (flexible) have their niches for special applications, PA12 is the most used SLS material for several reasons:
Exceptional Versatility
PA12 strikes a good balance between stiffness and impact resistance. It is rigid enough to hold its shape under load but ductile enough to be viable for snap-fits and some living hinges without snapping like brittle resins.
Environmental and Chemical Resistance
PA12 is remarkably stable:
- Low Moisture Absorption: Unlike PA6 (standard nylon), PA12 doesn't swell and loses very little mechanical integrity when it gets humid.
- Chemical Inertness: It is highly resistant to oils, greases, aliphatic hydrocarbons, and alkalies, making it ideal for various environments.
Refresh Rate
From a cost perspective, PA12 is also one of/the best choice because it has a very predictable refresh rate (usually around 20%–50% virgin powder), meaning you can run a highly efficient, low-waste production.
Specific PA12
There are several variations of PA12 powder depending on manufacturer and additives. Important factors would be the mechanical properties, how easy it is to source and the price (/kg).
From my research, it would be best to choose a material from the same company that the SLS printer is from (SinterIT) since they should have optimal print settings for this powder. Also their offers are quite affordable.
- SinterIt PA12 Smooth: cheaper kg-price and has a higher refresh rate
- SinterIt PA12 Industrial: a bit better mechanical properties
The printer allows the use of 3rd party materials so these could also be considered, but they would definitely need testing to find the right print settings:
