In the sand casting process a pattern is made in the shape of the desired part. The pattern is typically made of wood, plastic, or metal. A single piece or solid pattern is used for simple designs. Patterns that are more complex are made in two parts, called split patterns. The upper part of a split pattern is called a cope, while the bottom section is called a drag. The parting line is where the cope and drag meet. Both solid and split patterns can have cores inserted to create internal cavities or detailed external features. When making a pattern, it is necessary to taper the edges so the pattern can be drawn put of the sand without breaking the mold.
The pattern is housed in a box called the flask, and then packed with sand. A binder helps harden the sand into a semi-permanent shape. Once the sand mold is cured, the pattern is removed. This leaves a hollow space in the sand in the shape of the desired part. The pattern is made larger than the casting to allow for shrinkage during cooling. Sand cores can then be inserted in the mold to create holes and improve the casting's overall shape. Simple patterns are usually open on top, allowing molten metal to be poured into them. Two-piece molds are clamped together. Molten metal is poured into a pouring cup where it will then travel down a sprue and into the gating system. Vent holes are created to allow hot gases to escape during the pour. Ideally, the pouring temperature of the molten metal is a few hundred degrees higher than the melting point, assuring good fluidity. The temperature difference also prevents premature cooling and resulting voids and porosity. After the metal cools, the sand mold is removed and the metal part is ready for additional operations, such as cutoff and grinding.