One of metalcasting’s strongest selling points is its ability to encompass several parts, often in the form of  a welded assembly, into one component. This is possible because the nature of the metalcasting process lends itself to complex geometries. At the heart of many of these complex geometries is a core or core assembly.

A core is a shaped body, usually made of sand, which forms the interior part of the casting, like the cavity the pit makes in the flesh of a peach. In metalcasting, the mold provides a space for the molten metal to go, while the core keeps the metal from filling the entire space.

Sand cores are made in a wide range of sizes, weights and complexities. Advances in corebox technology, such as improved venting, have increased coremaking productivity and quality.

Cores allow you to incorporate holes in your design, but these holes don’t have to be limited to the see-through kind you’d find in a length of pipe.  Cores can take on a variety of angles and shapes, and more than one can be used per casting. Sometimes, an assembly of cores is constructed to create a web of internal passageways and chambers.  For many seemingly impossible parts, imagination and cores can turn a floundering design into a winning engineered component.

“Go after the geometry you want and let the metalcaster figure out how to accomplish it with the best balance of economics and properties,” said Mike Gwyn, vice president of metals technology at Advanced Technology Institute Corp., Mt. Pleasant, S.C.

How a Core Works

Most cores are made of sand, although they also can be made of ceramic or metal. The core acts as a negative, displacing molten metal as it is poured into the casting mold. Following the solidification of the metal, the sand core is shaken out, revealing the void. In investment casting, a cored hole is formed by the ceramic shell mold and then knocked out after solidification. In permanent mold casting, metal cores are used, and semi-permanent molding makes use of sand cores. Although cores usually are used to form interior passageways in a casting, they also can be used to shape an external part of a more intricate casting. If a section of a casting is undercut, for example, a core can be used to help the pattern be withdrawn from the mold without distorting it. Additionally, sometimes cores are used to strengthen or improve an inner or outer surface of the mold.