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OverviewMolding and casting is a manufacturing procedure in which an object is created by introducing material into a mold of the exterior surface of that object, so that the material becomes an exact copy of the object. The mold can be thought of as a "negative" of an object, a way of transfering the details of the object to another batch of material. In urethane molding, the mold is created from polyurethane rubber which is poured as a liquid around an object. When the rubber hardens, the object is removed and the cavity created is used to produce duplicates. These duplicates are made of a hard, rigid urethane compound, also introduced into the cavity as a liquid. The resulting piece is capable of displaying very accurate details of the original.Urethane molding is not strictly a prototyping technique. Molding requires a premade piece to be used as a master for the mold. This master piece must be manufactured through some other process, such as LaserCAMM, stereolithography, or some other prototyping system. More likely, molding will be used to duplicate objects that have already been produced. Notably, unlike the prototyping systems listed, molding is a purely physical, rather than digital, process. The part design is transmitted from piece to piece by a physical imprint upon the mold. In any case, urethane molding is a useful method of producing many parts. |
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UsageWhat is molding good for?
A mold can be reused many time, making urethane molding an inexpensive way to produce many copies of the same part We found that surface details and textures, such as engravings or embossings, could be reproduced quite well. Molding is useful for copying a part in order to attempt alterations or modifications without harming the original Solid pieces are much easier to produce than thin pieces. In fact, Por-A-Kast appeared to harden more quickly in the thicker portions of a piece than the thin sections. |
What is molding not good for?
Thin walled pieces are very difficult to cast and remove from the mold. Any air bubbles trapped in the casting materials will cause the cast to become brittle or prevent thin walls from filling completely. Molding can not be used to produce hollow parts and pieces with holes are more difficult to produce as they require a two-part mold. There is a limit on the practical volume for urethane molding (see limitations). |
ADVANTAGES
Molding is very cheap when compared to other methods of rapid prototyping. Molding is a great way to produce a limited quantities of identical parts. |
LIMITATIONS
Water is 100 times as reactive as the curative, accelerating the curing process. Molds are fairly temperature sensitive, cannot endure extended periods of time above 270 degrees Fahrenheit. Details of molding are theoretically possible, but very difficult to implement. They involve a lot of hand work which introduces errors. Also thin walls are extremely difficult to create. Mold takes 24 hours to cure, and casts each take at least an hour. Batch size is recommended to be under a half gallon for the molding mixture. Large parts require a rigid "mother mold" which surrounds the urethane mold. |
COSTS |
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| POR-A-MOLD S111 | |
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$ 20.00 |
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$ 60.00 |
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$ 250.00 |
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$ 1925.00 |
| POR-A-CAST Mark 1 | |
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$ 22.00 |
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$ 60.00 |
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$ 260.00 |
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$ 2125.00 |
| Synlube 1711 release agent | |
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$ 6.50 |
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$ 15.00 |
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$ 55.00 |
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$ 250.00 |
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$ 2500.00 |