A better appreciation by design engineers of the function of cores can improve a cast part design and decrease final cast component cost. Cores are separate shapes made of sand and they are placed in the mold to provide castings with contours, pockets, holes, and passageways not otherwise obtainable. Sand cores are made in a core box that is part of the pattern equipment for each casting. Just like the pattern, the core box cavity must have a parting plane. For a complex casting, several cores may be assembled in a fixture before being placed into the mold.
The use of cores allows additional freedom in casting design and usually adds to the cost of casting production. However, cores in most cases reduce the cost of secondary operations such as machining and assembly. As illustrated in the drawing below, cores can sometimes be combined or eliminated, without affecting the utility of the casting, as a result of design modification, thereby achieving production economies.
Dimensional accuracy of a mold assembly can be improved by reducing the number of cores in a cast component because the variations in core assemblies are additive.
Basic principles of coremaking. Shown are examples:
(a) One of the simplest and most common core shapes.
(b) Boss A is formed by the core box and boss B by a loose piece.
(c) Core box requiring two loose pieces.
(d) Core box with loose piece used to make core and replaced with bedding sand.