Rapid prototyping and additive manufacturing

Rapid prototyping (RP), now called additive manufacturing (AM) or 3D printing, builds a part directly from the CAD model by adding material layer by layer, instead of removing it (machining) or forming it.

Process chain

 CAD solid -> STL file -> slicing into layers
      -> build (layer by layer) -> post-processing -> part

1. Create the 3D solid model in CAD.
2. Convert it to STL (triangulated surface).
3. Choose the orientation and add supports; slice into thin layers (0.05 to 0.3 mm), generating the machine code.
4. Build the layers on the machine.
5. Post-processing: remove supports, clean, cure, sand, infiltrate or heat treat.

Two common processes

• Fused deposition modelling (FDM): a thermoplastic filament (PLA, ABS) is melted in a heated nozzle and deposited along the layer path; the layer solidifies and the platform moves down. Low cost, good for prototypes.
• Stereolithography (SLA): a UV laser traces the cross-section on a bath of photopolymer resin, curing it layer by layer; high accuracy and surface finish.

(Others: selective laser sintering (SLS) of powder, laminated object manufacturing (LOM), and binder jetting.)

Advantages

• Very complex shapes (internal channels, lattices) with no tooling.
• Fast models for design review and fit checks; lower cost for one-offs.
• Direct link from CAD, with little human work; low waste.

Limitations

• Stair-step surface finish; STL approximation errors.
• Limited materials and strength; anisotropic properties.
• Slow and costly for large production runs; size limits.