In high-production lost foam casting, foam patterns are molded and assembled on a cluster, coated with a refractory, placed in a flask and surrounded with unbonded sand. Molten metal then is poured over the pattern, evaporating the foam.
ecasting), low-pressure permanent mold casting and permanent mold casting. Unlike sand casting processes, in which the mold is destroyed after pouring to remove the casting, permanent mold casting uses the mold repeatedly. Diecasting—Diecasting is used to
produce small- to medium-sized castings at high-production rates. Te metal molds are coated with a mold surface coating and preheated before being filled with molten metal. Premeasured amounts of molten metal are forced from a shot chamber into the permanent mold or die under extreme pressure (greater than 15,000 psi). Castings of varying weights and sizes
can be produced. Nearly all die castings are produced in nonferrous alloys with limited amounts of cast iron and steel castings produced in special applications. Die castings and the diecasting
process are suitable for a wide variety of applications in which high part volumes are needed. Benefits include: • excellent mechanical properties and surface finish;
• dimensional tolerances of 0.005-0.01 in.; • recommended machining allowances of 0.01-0.03 in.;
• thin-section castings. Permanent Mold Casting (Gravity
Diecasting)—Another form of per- manent mold casting involves molten metal being poured into the mold either directly or by tilting the mold into a ver- tical position. In this process, the mold is made in two halves from cast iron or steel. If cores are to be used, they can be metal inserts, which operate mechani- cally in the mold, or sand cores, which are placed in the molds before closing (semi-permanent molding). Te mold halves are preheated, and the internal surfaces are coated with a
2014 CASTING SOURCE DIRECTORY METAL CASTING DESIGN & PURCHASING 9
Automated vertically parted molding machines, normally used for high-production runs, compact molding sand by squeezing.
refractory. If static pouring is to be used, the molds are closed and set into the vertical position for pouring; thus, the parting line is in the vertical position. In tilt pouring, the mold is closed and placed in the horizontal position, at which point molten metal is poured into a cup(s) attached to the mold. Te mold then is tilted to the vertical position, allowing the molten metal to flow out of
the cup(s) into the mold cavity. Te various permanent mold tech- niques—static pour and tilt pour—offer a variety of advantages for a range of metalforming applications. Benefits include:
• superior mechanical properties be- cause the metal mold acts as a chill;
• uniform casting shape and excellent dimensional tolerances because the
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