Process selection
FDM 3D Printing vs SLA 3D Printing
FDM extrudes molten thermoplastic filament through a heated nozzle, building parts layer by layer. SLA cures liquid photopolymer resin with a UV laser or LCD mask. The core trade: FDM delivers cheap, tough parts in real engineering thermoplastics, while SLA delivers fine detail and smooth surfaces at higher material cost and lower toughness.
| FDM 3D Printing | SLA 3D Printing | |
|---|---|---|
| Layer height | 0.1 to 0.3 mm typical | 0.025 to 0.1 mm |
| Dimensional tolerance | ±0.2 to 0.5 mm | ±0.05 to 0.15 mm |
| Machine cost | $300 to $5,000 desktop, $20k to $60k industrial | $2,000 to $10,000 desktop, $25k+ industrial |
| Material cost | $20 to $60/kg commodity, $80 to $150/kg CF nylon | $80 to $200/L resin plus IPA |
| Materials | PLA, ABS, PETG, PC, nylon, TPU | Photopolymers only, tough and castable grades |
| Part strength | Anisotropic, Z axis 40 to 70% of XY | Isotropic but brittle, 2 to 6% elongation typical |
| Post-processing | Support removal only | IPA wash, UV cure, support scar sanding |
Choose FDM 3D Printing when
- Functional prototypes, jigs, and fixtures that see mechanical load
- Large parts over 200 mm where resin cost gets painful
- Real thermoplastic behavior needed: PETG, nylon, PC, TPU
Choose SLA 3D Printing when
- Features under 0.5 mm: threads, snap details, text, thin walls
- Cosmetic models and master patterns for vacuum casting
- Sealing surfaces or fluidic parts needing watertight smooth walls
The verdict
Default to FDM for functional prototypes, brackets, and shop fixtures where a 0.2 mm layer line does not matter. Switch to SLA when you need fine detail, an injection-mold-like finish, or casting masters. Many shops run both since combined entry cost is under $3,000.
Cost comparison
A desktop FDM machine runs $300 to $2,500 and prints PLA at $20/kg, so a 100 g bracket costs about $2 in material. SLA resin runs $80 to $200/L, plus roughly $500 for wash and cure stations and ongoing IPA at $30 per 5 L, so the same 100 g part costs $10 to $25. FDM wins on nearly every purely functional part; SLA pays back only when finish or fine detail would otherwise force outsourced machining or hand polishing.
Common questions
Are SLA parts strong enough for functional use?
Standard resins are brittle, with 2 to 6% elongation at break, and they creep under sustained load. Tough and engineering resins close some of the gap, but for snap fits, living hinges, or anything that takes repeated impact, an FDM part in PETG or nylon usually outlasts SLA.
Which process holds tighter tolerances?
SLA, by roughly 2 to 4x. A calibrated SLA printer holds ±0.05 to 0.1 mm on small features, while FDM typically holds ±0.2 to 0.5 mm depending on material shrink and nozzle size. For press-fit bores on FDM, plan to drill or ream to final size.