Rapid Prototyping

Rapid prototyping developed as an outgrowth of liquid photopolymer research. This is a class of plastics that solidify under high intensity ultraviolet laser light. Early rapid prototyping (RP for short) was created in units called  "SLA's" or stereoithography apparatus.

More recently, a different approach FDM (Fused Deposition Modeling) uses a heated nozzle to extrude plasltic onto the work piece. This opened up a wider range of materials including polycarbonates, ABS plastics, and others.  Fused plastic is deposited layer by layer according to the 3D model.

Possible shapes

Almost any 3D shape.

Rapid Prototyping Design Guidelines

The following guidelines are recommended:

• Since parts are formed by extrusion onto successive layers, surfaces with empty space below require special processing. For example, a part the shape of a drinking glass is fine but if your turn the glass up-side down it becomes more difficult.
• Since the extrusion is .010", it is best to keep dimensions in multiples of this value - especially smaller dimensions (including material, air, diameters, etc.)
• Tolerance:
  - X, Y: .005" + 0.1%
  - Z: .010 + 0.1%
• Min wall:
  - .030" for horizontal walls (e.g. bottom of box)
  - .040" for vertical walls with no holes or cutouts
  - .1" for vertical walls with holes and slots in sides
  - .020" for very low walls that form letters/logos
• Min acute angle: 30 deg.
• Min diameter of holes in side of part: 0.25".
• Min height of horizontal slots in side of part: 0.25".
• Min material between hole and edge or between holes: .04" ideally, .02" absolute min and can create problems.
• Max size: 8" x 8" x 12"
• Long thin objects (max dim / min dim > 10) can't be longer than 8".

Example Rapid Prototyping Parts

Plates, covers, frames, assorted mechanisms.

Advantages of Rapid Prototyping

• Low cost runs - Since RP does not require tooling, short production runs can be made at lower cost and faster turnaround. This approach also provides higher confidence when committing to conventional tooling.
  
• Proof of Concept and Testing design concepts - allows engineers, designers, end users to check designs for usability, appearance, manufacturability, etc. RP speeds the design cycle.
  
• Performance and fit testing - allows to check that parts fit and operate properly in a new device being designed.

Specifications for Rapid Prototyping

• Material - eMachineShop currently offers ABS FDM which is  generally the best choice for most mechanical model applications.
• Alternative machines - milling.
• Tooling - Rapid Prototyping requires only software program tooling.
• Reducing costs - cost is determined mainly by weight - small or hollow shapes are significantly lower cost than large or solid shapes.

Rapid Prototyping Notes