The first step in the sand casting process is creating the sand mold. Sand casting is known as an expendable mold process, that means that a new mold must be made for each part.
The video above illustrates the entire process, but the first part is what we'll focus on right now. You may have noticed that a pattern is used. A pattern is a part or parts that have the geometry of the final part with a gating system. The patterns are used to create the mold cavity, the space that the molten metal will fill and take the shape of. The pattern actually has to be slightly bigger than the intended part size because as the metal solidifies, it will shrink.
The top half of the mold, called the cope, (the bottom half is called the drag) has holes in it, one of which is a pouring cup. The pouring cup is the first part of the gating system, the path by which the molten metal flows into the mold cavity.
The video above illustrates the entire process, but the first part is what we'll focus on right now. You may have noticed that a pattern is used. A pattern is a part or parts that have the geometry of the final part with a gating system. The patterns are used to create the mold cavity, the space that the molten metal will fill and take the shape of. The pattern actually has to be slightly bigger than the intended part size because as the metal solidifies, it will shrink.
The top half of the mold, called the cope, (the bottom half is called the drag) has holes in it, one of which is a pouring cup. The pouring cup is the first part of the gating system, the path by which the molten metal flows into the mold cavity.
Diagram of a sand mold. Found here.
In this image, you can see that sand is being packed around a pattern inside of the drag. Then, after taking out the pattern, the cope is placed onto the drag, the cope has a gating channel, called a sprue leading to the mold cavity. Once these steps have been completed, the mold creation part of the sand casting process is done.
I like this video because it demonstrates that this process is really quite simple, and that there are many ways to perform sand casting.
Many parts created with sand casting have hollow sections. Hollow sections are created using cores. Cores are placed into the mold where the manufacturer doesn't want metal to flow.
A core and its corresponding part. Found here.
The yellow part is a core that allowed for the creation of the hollow metal part on the right.