Process of Sand Casting

The process cycle for sand casting consists of six main stages, which are explained below.

1. Mold-making – The first step in the sand casting process is to create the mold for the casting. In an expendable mold process, this step must be performed for each casting. A sand mold is formed by packing sand into each half of the mold. The sand is packed around the pattern, which is a replica of the casting’s external shape. When the design is removed, the cavity that will form the casting remains. The casting’s interior features that the pattern cannot include are created by separate cores made of sand before starting the mold.
   Further details on mold-making will be described in the next section. The mold-making time includes positioning the pattern, packing the sand, and removing the print. The mold-making time is affected by the size of the part, the number of cores, and the type of sand mold. If the mold type requires heating or baking time, the mold-making time is substantially increased. Also, lubrication is often applied to the mold cavity surfaces to facilitate the removal of the casting. The use of a lubricant also improves the metal flow and can improve the casting’s surface finish. The oil that is used is chosen based upon the sand and molten metal temperature.
2. Clamping – Once the mold has been made, it must be prepared for the molten metal to be poured. The surface of the mold cavity is first lubricated to facilitate the removal of the casting. Then, the cores are positioned, and the mold halves are closed and securely clamped together. The mold halves must remain securely closed to prevent the loss of any material.
3. Pouring – The molten metal is maintained at a set temperature in a furnace. After the mold has been clamped, the molten metal can be scooped from its holding container in the stove and poured into the mold. The pouring can be performed manually or by an automated machine. Enough molten metal must be rushed to fill the entire cavity and all channels in the mold. The filling time is concise to prevent early solidification of any one part of the metal.
4. Cooling – The molten metal that is poured into the mold will begin to cool and solidify once it enters the cavity. When the entire cavity is filled, and the molten metal solidifies, the casting’s final shape is formed. The mold can not be opened until the cooling time has elapsed. The desired cooling time can be estimated based upon the wall thickness of the casting and the metal temperature. Most of the possible defects that can occur are a result of the solidification process. If some of the molten metal cools too quickly, they may exhibit shrinkage, cracks, or incomplete sections. Preventative measures can be taken in designing both the part and the mold and will be explored in later sections.
5. Removal – After the predetermined solidification time has passed, the sand mold can be broken and the casting removed. This step, sometimes called shakeout, is typically performed by a vibrating machine that shakes the sand and casting out of the flask. Once removed, the casting will likely have some sand and oxide layers adhered to the surface. Shot blasting is sometimes used to remove any remaining sand, especially from internal surfaces, and reduce the surface roughness.
6. Trimming – During cooling, the material from the channels in the mold solidifies attached to the part. This excess material must be trimmed from the casting manually via cutting or sawing or using a trimming press. The time required to trim the extra material can be estimated from the casting’s envelope’s size. A more extensive casting will require a longer cutting time. The scrap material that results from this trimming is either discarded or reused in the sand casting process. However, the scrap material may need to be reconditioned to the proper chemical composition before combined with non-recycled metal and reused.