SLA, FDM, and SLS are additive manufacturing processes, but they form layers differently. SLA cures liquid resin, FDM deposits molten filament, and SLS fuses powdered material. Consequently, each produces prototypes with different properties, costs, and finishes.
All three begin with a three-dimensional CAD model digitally sliced into layers. Their key difference is the mechanism used to manufacture each layer.
| Process | How it works | Main characteristics and uses |
|---|---|---|
| SLA (stereolithography) | A laser or projected light selectively cures liquid photopolymer resin in a vat. | Produces high accuracy, fine detail, and a smooth finish. Parts need supports, washing, and ultraviolet post-curing. Suitable for appearance prototypes, intricate models, and dental applications, although standard resins may be brittle. |
| FDM (fused deposition modelling) | A heated nozzle melts and deposits thermoplastic filament, such as PLA or ABS, layer by layer. | Usually the least expensive and most accessible method. Suitable for quick concept models and functional prototypes, but visible layer lines, lower accuracy, and weak interlayer bonding may occur. Supports are needed for significant overhangs. |
| SLS (selective laser sintering) | A laser selectively fuses particles in a powder bed, commonly nylon powder. | Produces strong, complex functional parts. Surrounding powder supports the component, so separate supports are normally unnecessary. Equipment is expensive, and parts typically have a rough, grainy finish. |
Selection depends on the design specification: SLA suits visual detail and surface quality; FDM suits low-cost, rapid iteration; SLS suits complex geometry and durable functional testing.
A common misconception is that one process is always “best.” In A2.2 Prototyping techniques, choose and justify the process against accuracy, material properties, surface finish, production time, complexity, and cost.
For compare, identify similarities and differences. For justify, select a process and link its characteristics directly to the design specification, rather than listing advantages.