Sand Castings Process
The sand castings process is the oldest, most basic, simple, and cheapest method of casting ferrous and non-ferrous materials. In this process, a pattern is made in the shape of the desired part. The pattern can be made of wood, plastic, or metal. Simple sand castings can be made in a single or solid pattern. More complex designs are made in two parts, called split patterns.
The pattern is then packed into sand, mixed with a binder, which helps harden the sand into a semi-permanent shape. Once the mold is cured, the pattern is removed, leaving a hollow space in the sand in the shape of the desired part. The pattern is intentionally made larger then the cast part to allow for shrinkage during cooling. Cores can be inserted into the mold to create holes and improve the casting’s net shape.
The pouring temperature of the material should be a few hundred degrees higher than the melting point of the material to assure good fluidity, thereby avoiding premature cooling, which can create voids and porosity.
The sand castings process is the least expensive of all of the castings processes, but it also provides the least dimensional accuracy and a rough surface finish. This process is normally used to obtain only the basic shape of the part, which is less expensive than machining such a shape from bar stock. Sand castings will normally require several additional secondary operations to complete the component. The labor involved in those secondary operations is what makes this process an attractive candidate for off shore sourcing.