Additive manufacturing process comparison

The analyzed additive manufacturing processes build parts layer by layer from a digital model, but differ in the way material is deposited and consolidated:

• FDM (Fused Deposition Modeling): extrudes a thermoplastic filament through a heated nozzle that moves in the X‑Y axes, depositing the molten material onto a platform. The part is formed as each layer solidifies.
• SLA (Stereolithography): an ultraviolet laser selectively solidifies a liquid photosensitive resin contained in a tank. A platform descends progressively and a new layer of resin is spread over the previous one to be cured by the laser.
• SLS (Selective Laser Sintering): a high-power laser (typically CO₂) sinters or fuses powder particles (nylon, elastomer, etc.) spread in thin layers on a bed. The bed is preheated just below the powder’s melting point and no supports are required because the unsintered powder acts as such.

Applicable materials

| Process | Material | Form | | — | — | | FDM | ABS, PLA, PETG, TPU, PC, ASA, nylon, fiber composites | Filament (∅ 1.75 mm / 0.069 in or ∅ 2.85 mm / 0.112 in) | | SLA | Standard, engineering (rigid, flexible, castable), biocompatible, ceramic-filled resins | Liquid photosensitive resin | | SLS | Nylon PA12, PA11, TPU (elastomer), polypropylene, reinforced polyamides (glass fiber, carbon fiber), polystyrene (lost wax) | Spherical powder (mean size 20–80 µm / 787–3150 µin) |

Process parameters

Process	Material	Layer thickness	Operating temperature	Power / source	Typical build speed
FDM	PLA	0,1–0,3 mm / 0.004–0.012 in	Nozzle: 190–220 °C / 374–428 °F; bed: 50–60 °C / 122–140 °F	—	40–100 mm/s (Z axis variable per layer)
FDM	ABS	0,1–0,3 mm / 0.004–0.012 in	Nozzle: 220–250 °C / 428–482 °F; bed: 90–110 °C / 194–230 °F	—	30–80 mm/s
SLA	Standard resin	0,025–0,15 mm / 0.001–0.006 in	Controlled environment 25–30 °C / 77–86 °F	UV laser 355 nm, up to 500 mW	10–20 mm/h (Z advancement)
SLS	PA12 (nylon)	0,1–0,15 mm / 0.004–0.006 in	Powder bed preheated 170–180 °C / 338–356 °F (≈ 5–10 °C below Tm)	CO₂ laser 30–50 W, pulsed beam	10–20 mm/h (Z advancement)
SLS	TPU (elastomer)	0,1–0,12 mm / 0.004–0.005 in	Preheated bed 80–100 °C / 176–212 °F	CO₂ laser 20–40 W	8–15 mm/h

Tolerances and surface quality

Process	Typical dimensional tolerance	Surface roughness (Ra)
FDM	±0.5 % of nominal (minimum ±0,2 mm / 0.008 in)	8–25 µm / 315–984 µin
SLA	±0,1 mm / 0.004 in (up to ±0,05 mm / 0.002 in on high-precision equipment)	0,5–1,5 µm / 20–59 µin
SLS	±0,3 mm / 0.012 in (Z may be larger)	5–15 µm / 197–591 µin (powdery surface without sealant)

Advantages and limitations

Process	Advantages	Limitations
FDM	Low cost, wide variety of thermoplastic materials, ease of use, functional parts, possibility of composites.	Lower surface resolution, mechanical anisotropy (lower strength in Z), requires supports for overhangs.
SLA	Very high dimensional precision, excellent surface finish, possibility of transparent or castable materials, suitable for visual prototyping and molds.	Limited to photosensitive resins (lower mechanical and thermal durability than thermoplastics), post-curing required, lower impact resistance.
SLS	Materials very close to engineering thermoplastics (nylon, elastomers), no supports needed, allows complex geometries and functional parts, possible 3D nesting of parts.	Porous and powdery surface finish unless sealant is applied, Z precision less predictable than SLA, high machine cost, requires powder handling and controlled preheating.

Selection guide

Select the process based on the primary criterion:

• Low cost per part and varied material → FDM. Ideal for functional rapid prototyping, low-stress parts, and form/fit testing.
• Maximum precision and surface finish → SLA. Recommended for presentation models, master molds, casting patterns, and applications requiring tolerances below ±0,1 mm / 0.004 in.
• Functional parts without supports and with properties close to engineering thermoplastics → SLS. Suitable for short runs, components with living hinges, housings, and geometries inaccessible by other processes.
• Medium mechanical or thermal loads → FDM (with ABS, PC) or SLS (with PA12). SLA is ruled out if toughness or temperature resistance (> 60 °C / 140 °F) is required.
• Urgent delivery deadline → FDM (lower machine time for simple parts). For highly detailed parts, SLA may be competitive.
• Low production volume (up to 100 units) → SLS, thanks to nesting and the absence of supports which reduces post-processing.

Frequently Asked Questions (FAQ)

What is the typical dimensional accuracy of SLA?

SLA routinely achieves tolerances of ±0,1 mm / 0.004 in, and can reach ±0,05 mm / 0.002 in on high-end machines.

What layer thickness does SLS use for nylon PA12?

The standard layer thickness for PA12 in SLS ranges from 0,1 mm / 0.004 in to 0,15 mm / 0.006 in, which determines surface roughness and build time.

What is the nozzle temperature in FDM for ABS?

The extruder temperature for ABS is typically maintained between 220 °C / 428 °F and 250 °C / 482 °F, and the heated bed between 90 °C / 194 °F and 110 °C / 230 °F to prevent warping.

What surface roughness can be expected in unsealed SLS parts?

The average roughness (Ra) of an SLS part without surface treatment is between 5 µm / 197 µin and 15 µm / 591 µin, due to the powdery nature of the sintered powder.

How long does a 100 mm tall SLA print take?

A 100 mm / 3.94 in tall part typically completes in 5 to 10 hours with a 0,1 mm / 0.004 in layer setting, depending on geometric complexity and cross-sectional area.

What is the minimum wall thickness that can be guaranteed in FDM with a 0.4 mm nozzle?

The functional minimum wall thickness in FDM is 0,8 mm / 0.031 in (twice the nozzle diameter) to ensure structural strength, although decorative details can reach 0,4 mm / 0.016 in.

References

• efunda.com: https://www.efunda.com/processes/rapid_prototyping/sls.cfm
• manufacturingguide.com: https://www.manufacturingguide.com/en/stereolithography-sla