SLS (Selective Laser Sintering) is the only common additive process that requires no support structures. That single fact changes what you can design. Overhangs, undercuts, internal channels, interlocking assemblies, and living hinges all print cleanly in a single build without post-processing to remove supports. This opens geometry that is simply impossible in any supported process — and it is why SLS is the go-to process for production-intent functional parts.
The Physics of Powder Bed Fusion
A thin layer of polyamide powder (typically 0.1–0.12 mm) is spread by a counter-rotating roller across the build bed, which is preheated to just below the powder''s melting point (165–170 °C for PA12). The CO₂ laser scans the cross-section, locally raising the temperature above melt point and fusing the powder particles. The bed drops one layer, the roller deposits fresh powder, and the cycle repeats.
The unfused powder surrounding each part acts as self-supporting scaffold. When the build completes (typically 8–16 hours for a full 380×284×380 mm build volume), the entire powder cake — solid parts embedded in loose powder — is removed from the machine and cooled under controlled conditions for 4–8 hours before breakout.
Powder Management
PA12 powder can be partially recycled — unfused powder is sieved, mixed with fresh virgin powder (typically 50:50 ratio), and reused. The ratio is critical: too much recycled powder degrades mechanical properties and surface quality. Layer X tracks powder lot numbers and refresh ratios per build, maintaining documentation for AS9100 compliance. All powder is stored in sealed hoppers at <30% RH.
Part Extraction and Cleaning
Breakout is a manual operation. The cooled powder cake is scooped out into a breakout station and parts are located by reference to the build layout map. Each part is manually brushed, then bead-blasted to remove residual surface powder. Fine internal channels and recesses require compressed air flushing. This is where SLS quality separates — proper cleaning requires skill and time; rushed cleaning leaves powder in channels that later degrades in use.
Post-Processing Options for SLS PA12
As-built: Consistent matte grey surface. Ra ≈ 10–20 µm. Suitable for mechanical components, jigs, and internal parts. Ready for use without further processing.
Bead blast: Standard on all Layer X SLS parts. Ra ≈ 5–10 µm. Better surface consistency and primer adhesion.
Surface dyeing: Boiling reactive dye bath achieves RAL colour matching to ΔE ≤3. Penetrates 0.3–0.5 mm — permanent, unlike paint coatings. Ideal for consumer products and colour-coded tooling.
Tumble finishing: 4–8 hours in ceramic media. Ra ≈ 2–5 µm. Used for consumer product components where a smooth, tactile surface is required.
Epoxy sealing: Two-part coating seals porosity for pressure vessels and fluid-handling parts.
Mechanical Properties of Layer X SLS PA12
Tensile strength: 48 MPa. Elongation at break: 18%. Flexural modulus: 1,600 MPa. Impact strength (Charpy notched): 5.4 kJ/m². These are isotropic — identical in XY and Z — which is the critical advantage over FDM. HDT at 0.45 MPa: 172 °C. PA12-GF (glass-filled) option raises flexural modulus to 2,600 MPa for higher-stiffness applications.
Why SLS is Ideal for Production Quantities
SLS build economics reward batch density. A full build volume can contain 200–800 individual parts depending on geometry. The fixed cost of machine time (8–16 hours) is spread across all parts in the build. At 80% volume utilisation, SLS approaches injection moulding economics for small parts at quantities of 100–1,000 units — without any tooling investment. Layer X batch builds SLS weekly, combining customer orders to maximise density and minimise per-unit cost.