2002 (Backfills for previous years) / DB reference years
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Author Dave Regnet, Taylor-Pohlman, Inc., 3925 California Road, Orchard Park, NY 14127 USA; Tel 716-662-1096; Fax 716-775-3407; Dregnet@tpicast.com
Source Rapid Prototyping & Manufacturing 2000
Abstract The need for converting 3-D models into aluminum castings has found a new niche where many of the V-Process's advantages can be utilized. The V-Process is unique as a form of sand casting in that the process does not require draft angles on the castings. The castings have a smooth surface finish and good dimensional accuracy. Tooling or patterns for the V-Process are constructed of machined plastic, SLA or LOM models. All of these methods of producing patterns result in unlimited life patterns capable of supporting both prototype and production requirements.
A plastic, SLA or LOM cope and drag pattern is prepared for mounting to specially designed cope and drag pattern boards, the wood gating system is installed and the pattern is vented. A vacuum is applied to the pattern and a thin sheet of heated plastic film is drawn over the pattern, the vent holes insure that the film is pulled down into all the nooks and crannies. After the pattern has been "shrink wrapped" a flask is precisely placed on top of the film that covers the pattern. The flask is then filled with very fine loose sand. This fine grain sand allows for the excellent surface finish, typically 125 to 150 RMS. A second sheet of plastic film is placed on top of the sand and flask. The sand is now sandwiched between the original sheet of plastic film that is conforming to the shape of the pattern and the second sheet of film on top of the sand, this is surrounded by the flask acting as a vacuum chamber. A vacuum is then pulled on the sand through the flask. This vacuum causes the sand to become hard mu ch like a vacuum packed brick of coffee. The flask is now stripped from the pattern. After both halves of the mold are made and any cores are placed, they are matched together. Throughout the entire molding and pouring process the vacuum is maintained. After the mold is filled with aluminum and had sufficient time to cool and solidify, the molds are placed in a chamber and the vacuum is released. The sand then reverts back to the un-bonded sand and falls away from the casting and is recycled.
The advantages of this casting process with concern to Rapid Prototyping are: Prototype castings in two to four weeks; Easier and less expensive pattern construction; Reduction or elimination of machining operations; Close tolerances and good surface finish; Easy revisions to patterns; Wall sections as thin as .090; Reduced design and CAD time due to Zero draft pattern requirements; Quick turnaround using SLA, LOM or CNC machined patterns; Unlimited life patterns that can be used for both prototypes and production quantities.
Because of these advantages, this process is an excellent choice for both prototype and production castings. XX