FDM and SLA: Working Principles

1. Fused Deposition Modeling (FDM)

FDM is a material-extrusion process that normally uses thermoplastic filament.

Working:

1. Filament is fed from the spool into a heated extrusion head.
2. The filament is heated until it becomes sufficiently soft or molten.
3. The nozzle deposits the material along the programmed path of the current layer.
4. The deposited material cools and bonds with the previous layer.
5. The build platform or print head moves by one layer height.
6. The process repeats until the complete part is formed.

Advantages: relatively simple equipment, low material cost for common polymers, and easy prototyping.

2. Stereo Lithography (SLA)

SLA is a vat photopolymerization process that uses liquid photosensitive resin.

Working:

1. A build platform is positioned in a vat of photopolymer resin.
2. A UV laser or projected UV light selectively exposes the resin according to the current layer.
3. The exposed resin polymerizes and becomes solid.
4. The platform moves by the layer thickness and fresh resin covers the next layer region.
5. Exposure is repeated until the part is complete.
6. The printed part is removed, washed and normally post-cured.

Comparison: FDM deposits melted/softened filament, whereas SLA selectively cures liquid resin using light. SLA generally provides finer details and smoother surfaces, while FDM is often simpler and economical for many prototype applications.