Permanent Mold Casting
Aluminum Permanent Mold Casting, Permanent Alloy, Zinc Standard Mold and Gravity Die Casting
 Permanent mold castings, while not as flexible as sand castings in allowing the use of different patterns (different part designs), lower the cost of producing a part. At a production run of 1000 or more parts, permanent mold castings produce a lower piece cost part. Of course, the break-even point depends on the complexity of the part. More complex parts being favored by the use of permanent molds. Instead of using sand as the mold material, a metal is used as a mold. Typically cast iron or Meehanite (a dense cast iron) is used as the mold material and the cores are made from metal or sand. Cavity surfaces are coated with a thin layer of heat resistant material such as clay or sodium silicate.
Permanent Mold or gravity die-casting is mainly used for nonferrous metals and alloys. The mold (or die) is usually iron, steel, or graphite, and is cooled by water channels or by air jets on the outer surfaces. Cavity surfaces in metal dies are coated with a thin layer of heat-resistant material. The mold or die design is usually in two halves, although many multiple-part molds are in use, with loose sand or metal cores to form "undercut" surfaces.
The cast metal is simply poured into the bowls on the side of the mold.
During the period after solidification and before ejection, cooling continues but shrinkage of the casting(s) is restricted by the die. The alloy being cast must be sufficiently ductile to accommodate these restrictions without fracturing. Dimensions of the casting(s) at shop temperatures will be related to the die temperature and the dimensions at ejection.
Tilting mechanisms are used to control the passage of metal into (and emergence of air from) the remote portions of die cavities.
Because the die temperature varies during the casting cycle, its dimensions vary correspondingly. The die is opened and ejectors push the casting(s) out as soon as their temperature is low enough for sufficient strength to build up.
The permanent mold process employs gravity pouring of metals using steel, cast iron or graphite molds. The castings produced have excellent grain structure and extremely low porosity which result in superior ductility and outstanding strength. The castings can be designed with thinner walls and less weight with good dimensional accuracy. Used primarily for low melting temperature metals such as aluminum & zinc, permanent mould castings produce excellent finishes & pressure tightness when compared to sand castings.
Savings in reduced machining operations can also be realized due to the dimensional uniformity of the castings and details that can be cast in, as well as reducing some secondary operations such as polishing due to the excellent surface finish. Permanent molds have a production life of 10,000-50,000 parts, casting sizes range from a few ounces to 50lbs.
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Mr. Palmer may be reached by calling toll free:
888.494.0414 or email: (dick@castingreps.com)
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