What is the primary difference between a pattern and a core in sand molding?

The primary difference between a pattern and a core in sand molding is that a core creates the internal cavity of the part while a pattern defines the outer shape. In the molding process, the pattern is a pre-made model that represents the external features of the final product. It is used to form the mold by being placed in the sand, which is compacted around it to create a cavity. This cavity corresponds to the shape of the outer surface of the desired part.

On the other hand, cores are additional components crafted separately from patterns. They are inserted into the mold to shape internal features, such as holes, channels, or other voids that are not accessible through the pattern alone. By allowing the creation of more complex geometries, cores enable manufacturers to produce parts that meet specific design requirements.

Other options touch on aspects that do not accurately define the roles of patterns and cores. For instance, the notion that a pattern gives internal geometry while a core gives external shape misrepresents their functions, as it conflates their primary roles in the molding process. Similarly, while there are permanent and expendable molds, the distinction does not directly address the specific functions of patterns and cores. Additionally, patterns being used only in closed molds is misleading, as open