In order for a core to successfully produce a quality casting, it must have several different types of strength. It must be strong enough to maintain its form while it is prepared and handled, withstand the hot metal poured into a mold, and exhibit minimal expansion or contraction in order to maintain good dimensional accuracy. These necessary strengths should be considered during casting design in order to ensure an accurate component can be cast in an efficient and productive manner.

“You have to keep in mind the mechanical and physical limitations of the core itself,” said Larry Stahl, General Motors. “Despite one’s best efforts, you can’t overcome physics.”

Sand cores can be made in a handful of ways, and most metalcasting facilities use more than one type of core in their production. The metalcaster chooses the type of core based on what would fulfill the application’s physical and dimensional requirements in the most economical way. While a core’s strength is important, care also must be made to ensure it will easily disintegrate after the metal solidifies in order to be removed during shakeout.

As a customer, it’s beneficial to have a clear understanding of the properties that are truly required for the part. This can save you money and time.

“You don’t want to pay dearly for perfection if you don’t need it,” said Wayne Rossbacher, president and owner of Foundry Consulting, Sugar Grove, Ill. “For example, you want to use the coarsest grain possible to give an acceptable finish.”  

Core Considerations

Stahl suggests including core design in your initial discussions with the metalcaster to avoid potential setbacks in the coreroom. One of the primary core design issues is the location of the cavities needed in the component.

“How are you going to support those cores? How are you going to keep the cores in place when the metal comes?” Stahl asked. “What are the production requirements that have to be met? These all become questions that have to be answered.