8 Main Steps in Sand Casting

The sand casting process is a casting method in which sand is the primary modeling material used to prepare the mold. And it is a traditional casting method. We can refer to the definition of sand casting through Wikipedia.

Due to the advantages of not being limited by the shape, size, complexity, and alloy type of the part, short production cycle, and low cost, sand casting has always been the most widely used casting method in foundry production, especially for single pieces or small batches of castings!

The basic flow of the traditional sand casting process consists of the following steps.

Sand preparation, pattern making, core making, sand molding, pouring, sand removal, cutting & grinding, inspection, and other extra steps.

Let’s go through each step one by one.

Prepare sand and core sand for molding, generally using a sand mixer to mix the used sand and the right amount of clay.

Molds and core boxes are made according to the part drawings. Generally, we can use wooden molds for single parts production, plastic or metal molds for mass production, and pattern plates for large castings. Nowadays, molds are made by engraving machines, so the production cycle is shortened significantly, and it could take 2 to 10 days for mold making.

Molding includes sand molding, core making, and mold fitting.

Sand molding means forming the cavity for the casting from the molding sand.

Core making refers to the production of the cores, which are used to form the internal shape of the casting.

Mold fitting is the assembly of the upper and lower sandboxes after the cores have been placed inside the cavity.

Molding is a crucial part of the casting process.

The chemical composition needs to match the required metal. A suitable furnace is selected to melt the alloy material to form a qualified liquid metal (piece and temperature of the molten metal must comply).

Melting adopts cupolas or electric furnaces (due to environmental requirements, cupolas have mainly got outlawed, so electric furnaces are the primary choice).

The molten metal from the electric furnace is poured into the mold using a ladle. The speed of pouring is critical to ensure that the molten iron fills the entire cavity. It is also dangerous to pour the iron, so be careful!

After the molten metal solidifies, take a hammer to remove the sprue and shake off the sand from the castings.
The castings are then blasted with a sandblaster to give a clean surface!
The casting blanks are ready to leave the factory after inspection.

For castings with special requirements, or where the surface of the casting blanks cannot be up to expectation, simple grinding is necessary.

And grinding is usually done with a grinding wheel or grinder to remove burrs and give the casting a better finish.

Usually, during the cleaning and grinding phases, non-conforming castings have been picked out. But still, final inspection is required. And for castings with assembly requirements, we need to make a set of tools or through-stop gauges for review to ensure no problems with the assembly.

After the above eight steps, the castings have taken shapes. For castings requiring high precision, further machining is required. As this is not part of the casting range, we will not describe it here.

With the progress of casting technology, traditional sand casting is either improved or replaced by other casting methods. Therefore, constant innovation is the constant topic, which is the essential characteristic of the foundry.