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Ahmet Çelik
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Ch20 Rapid Prototyping

MECH306

Rapid prototyping (RP) quickly builds a physical model from a CAD file — for visualization, fit/interference checks, troubleshooting, and even tooling. Speed-to-market matters.

Three groups:

  • Subtractive: machine away material (turning/milling/drilling) from soft stock (polymer, wax).
  • Additive: build up layer by layer from CAD slices.
  • Virtual: software/VR visualization only.

Additive Processes

  • Fused-deposition modeling (FDM): a heated extruder lays a thermoplastic/wax filament in the x–y plane; table lowers for each layer. Overhangs need a support material (less dense, broken off later). Most-sold RP system; ~$30,000. Oblique faces show a stepped surface (coat to smooth, at the cost of tolerance).
  • Stereolithography (SLA): a UV laser cures a liquid photopolymer layer on a platform that lowers into the vat; unused resin reused; supports removed; sanding/painting may follow. Machines ~100,000–100,000–400,000; resin ~$100/L.
  • Selective laser sintering (SLS): a laser sinters cross-sections in a powder bed; surrounding loose powder supports the part; shaken off at the end.
  • 3-D printing (3DP): a binder (e.g. silica) is sprayed onto powder layers; post-process by curing ~150°C then firing ~1000°C.
  • Laminated-object manufacturing (LOM): glued paper sheets laser-cut layer by layer; very cheap; paper parts unsuitable for further processing.

Virtual Prototyping

Software-only (CAD + VR) to examine a part. Boeing 777 fits/interferences were checked on CAD before building the first aircraft.

Applications

  • Individual parts: polymer/paper parts are usually non-functional, but serve as investment-casting patterns (CAD-scaled for shrinkage). Economical only for very short runs (often one part).
  • Rapid tooling: RP-made pattern plates feed conventional sand casting — fast to make, but shorter pattern life (polymer wears faster than metal).

Main advantage of a physical prototype: design visualization — directly assess manufacturability (section thickness for casting, tooling room, ejectability) and interferences that a CAD drawing alone may hide.