Rapid prototype

Rapid prototype is a term referring to several methods used to create a solid free form model. Generally this process involves using a CAD (computer aided design) model to slice into layers. Usually the smallest layer thickness of the rapid prototype machine being used. Be it stereo lithography (SLA), stereo lithographic sintering (SLS), fusion deposition modeling (FDM), poly of mulitjet modeling (MJM) or one of several other methods.

Fusion Deposition Modeling using ABS plastic

The Dimension® FDM machines owned by Protomatix print Acrylonitrile Butadiene Styrene (ABS) plastic in .010" (10 * 1/1000) layer thickness. Yielding a part with the following mechanical properties:

Mechanical Properties         Test Method            ABS rating

Tensile Strength                    ASTM D638             3,132psi
Tensile Modulus                     ASTM D638             238,000psi
Tensile Elongation at Break    ASTM D638             10%
Flexural Strength                   ASTM D790             4,975psi
Flexural Modulus                   ASTM D790             176,000psi
Hardness                              DIN53505/2240      78 Shore D
Melting Temp                                                       221°F

A water-soluble support material is always incorporated by the machine to aid in holding the part to the work surface, and in supporting overhanging features of the part during the deposition process to assure correctly formed parts. After the deposition process the part may require an elevated temperature wash step to remove support material, especially if the part is fragile or complex. Overhanging features can affect part cost.

Part cost vary depending on several factors include overhanging features of the part, plane of parts relative to machine axis, and if the part is solid or "sparse" filled. Sparse fill yields a web like internal structure of the part. Considerations include load bearing features, surface finish of key surfaces, and accuracy of round features.

Examples of part cost:
1 cubic inch square sparse filled part with no features would cost $4.55. Machine time 26 minutes. This part may be slightly fragile.
1 cubic inch square solid filled part with no features would cost $10.19. Machine time 53 minutes. This part will be very strong.
1-inch diameter by 1-inch length by .125-inch thick helix solid filled part would cost $27.60. Machine and required wash time 3.5 hours. This part will act like a spring.

Very fine threads, raised letters, or features smaller than .03 inch may not form correctly. Glass jar sized and pitched threads will form correctly. Caution when applying a coarse thread with a low pitch as the thread action may be slightly ratchet like due to .01-layer thickness of the machine. Parts may also be machined depending on the form and internal structure.

Wikipedia definitions

RPM - Rapid_Prototype Modeling
CAD - Computer Aided Design
SFF - Solid freeform fabrication
FDM - Fusion deposition modeling