Designers and engineers in the permanent mold aluminum casting industry have quickly recognized the benefits of prototyping parts early in the design stage. With the increased utilization of three-dimensional (3D) CAD models, the application of rapid prototyping has become more popular. Today, there are numerous technologies available for producing rapid prototypes of cast aluminum parts.The most publicized rapid prototype processes include the group of Additive Rapid Prototyping (ARP) technologies, such as: Stereolithography (SLA), Laminated Object Manufacturing (LOM), Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and Solid Ground Curing (SGC). The recent introduction of these technologies have significantly expanded the application of rapid prototyping, in addition to creating an entirely new industry dedicated to the production of rapid prototype parts.The growing popularity of the new ARP technologies has overshadowed one technology that has been utilized in the mold tooling industry for over 20 years - Computer Numerical Control (CNC) machining. Today, CNC machining is used extensively in the manufacture of permanent mold tooling, such as: mold models/patterns, graphite electrodes for Electronic Discharge Machining (EDM), and direct machining of mold cavities into tool steel. This traditional, as well as proven, technology has demonstrated the capability to quickly produce prototype models of parts, much like the new ARP technologies. In addition, CNC machining can provide several key capabilities not yet available with ARP technologies, namely: tight dimensional accuracy, exceptionally smooth surface finish, high level of aesthetic detail, wide selection of materials, and ability to directly produce functional prototypes without secondary casting processes.