“3D printing” covers very different processes. The right one depends on what the part must do: look good, fit precisely, survive load, or be produced in a small series. Here is a practical comparison of the four technologies buyers ask about most.
Comparison
| Factor | FDM | SLA / DLP | SLS | MJF |
|---|---|---|---|---|
| Process | Extruded thermoplastic filament | UV-cured liquid resin | Laser-sintered nylon powder | Fused nylon powder (inkjet agents + heat) |
| Common materials | PLA, ABS, PETG, ASA, PC, PA, TPU | Standard, tough, clear, high-temp resins | PA12, PA11, glass-filled PA | PA12, PA11, TPU |
| Surface | Visible layer lines | Smooth, fine detail | Slightly grainy | Slightly grainy, uniform |
| Supports | Needed (marks) | Needed (marks) | None | None |
| Mechanical | Weaker between layers | Can be brittle (material dependent) | Tough, functional | Tough, consistent |
| Best for | Fast, low-cost concept parts, jigs | Appearance models, small detailed parts | Functional prototypes, complex geometry | Functional parts and small series |
Typical accuracy depends on machine, part size and orientation. As rough guidance: SLA is usually the most accurate on small parts, SLS and MJF are commonly quoted around ±0.3% (with a minimum of about ±0.3 mm), and FDM is the least precise. Confirm tolerances for your specific part before relying on them.
How to choose
- Looks-like model or presentation sample → SLA, then paint
- Snap fits, hinges, brackets that must flex or take load → SLS or MJF (nylon)
- Large, simple parts on a tight budget → FDM
- 10–500 end-use parts without tooling → MJF or SLS, dyed black
- Rubber-like parts → TPU via MJF or FDM
- Metal parts → consider metal printing or CNC machining
Design tips for printed parts
- Keep wall thickness at or above the process minimum (roughly 1 mm for nylon powder processes, more for large FDM parts)
- Add clearance between mating printed parts — typically a few tenths of a millimetre
- Avoid large flat areas in SLA and FDM, which can warp
- For powder processes, add escape holes so unsintered powder can be removed from hollow parts
- If the part will later be injection molded, design with draft and uniform walls from the start
When to move away from 3D printing
As quantities grow, unit cost of printing stays roughly flat while molding becomes much cheaper per part. The crossover depends on part size and complexity; many plastic parts become cheaper to mold somewhere between a few hundred and a few thousand units. See injection molding and small batch manufacturing, or compare with CNC machining vs 3D printing.