Modern Machine Shop and MoldMaking Technology present ADDITIVE MANUFACTURING, a quarterly supplement reporting on the use of additive processes to manufacture functional parts. More at additivemanufacturinginsight.com.
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racy limitations inherent to most unconventional toolmaking processes. Plus, the leanest mold suppliers are discovering that machining molds does not need to take months. Here are some general differences between AM and CNC machining: • Surface fnish. AM is rough without secondary operations. A system with layers at 0.0005-0.001 inch might produce an Ra finish of 100-600. CNC can produce surfaces that are smoother. • Feature detail. AM typically is better for part features in special situations where CNC cannot make the geometry. Examples include internal features and trapped geometries. • Part size. 24 × 36 × 24 inches is typical for AM, though larger systems exist from such manufacturers as Materialise, Stratasys and Voxeljet. • Geometry/complexity. AM handles geometric complexity easily. CNC's geometric limitations include deep slots, deep holes and undercuts. • Accuracy. AM offers tolerances of +/-0.005 to Component made by pattern-based plaster casting (rubber plaster mold). Courtesy of Mydea Technologies. 3D-printed tool for silicone casting. Courtesy of Objet and Mydea Technologies. 0.020 inch. The comparable tolerance range for CNC is +/-0.0005 to 0.005 inch. • Speed. AM is faster for small, complex parts, while CNC wins for large, less-complex parts. • Labor is low for AM in terms of both the amount required and needed skill level. Setup time, operator attendance at the machine and the requisite skill level are higher for CNC. Direct Tooling Direct approaches to tooling using AM do not require a pattern, and numerous additive options exist for making metal or plastic components. These can reduce the number of steps in the toolmaking process, saving cost and time. Some manufacturers have been using AM to produce metal inserts for injection mold tooling, including Linear Mold of Livonia, Michigan, which has been successfully producing injection mold components off of DMLS inserts for several years. (Editor's note: See our article on Linear Mold at short.moldmakingtechnology.com/linmld.) One of the most popular forms of direct tooling from the '90s, Direct AIM, used stereolithography (SL) parts as molds. It was developed for small runs of injection molded parts off of a relatively cheap tool. Though this process had been in decline, a small rebirth has occurred in recent years thanks to tougher SL materials such as ceramicfilled Nanotool from DSM Somos. 3D printers also should not be overlooked. 3D printers from Objet, 3D Systems and Stratasys can be effective rapid tooling machines, especially when casting thermoset plastics and rubbers. Stratasys fused deposition modeling (FDM) prints have also been successfully used for thermo/ vacuum-forming direct molds. The porous nature of tooling produced this way enables air to pass through, possibly preventing the need for holedrilling. FDM tools are also being used for more demanding direct applications such as stamping and hydroforming tools. Direct tooling isn't necessarily limited to small components, either. ExOne and Voxeljet both have large systems that can produce direct tooling, including Voxeljet's VX4000, which is capable of building tooling larger than 12 × 6 × 3 feet. February 2013 — 5