If the casting experience hasn’t ever been witnessed first hand, it’s hard to wrap your head around. In such a large industry with so many different methods of casting, people often find it hard to differentiate between casting processes.
Many terms are accidentally used interchangeably, when in fact they don’t apply. I will be differentiating between two terms that often lose their identity: Die Casting vs. Sand Casting.
Think of this as a quick reference guide that will provide insight into the industry without actually having to be immersed in it.
In this case the term “die” simply refers to the mold that is used to shape the product. The words “die” or “mold” refer to the same thing – and the die is made out of steel in die casting. The first step in the die casting process is to fill the mold with molten metal. As this process ends the metal will solidify. Once the metal cools it is removed from the die and then the die is closed and made ready for the next “shot” or filling of the die. In die casting the die is reusable.
Reusing the dies provides accuracy as the same process is continuously repeated without change. Dies are known for supporting complex shapes and designs under high pressure settings. Being able to mass produce products that have a long service life has made die casting very popular with many commercial industries.
A slightly less complex process, sand casting requires higher levels of hand crafting and is more labor intensive. There are two main parts; the top and the bottom of the mold which form the flask. This top and bottom, are also called the flask assembly, and this flask assembly “holds the whole thing together.” The upper or top-most section of the flask is called the cope, while the bottom of the flask is called the drag. There is always an impression device, in the middle of the flask assembly. This is called the pattern. The sand around the pattern is called the, holding medium.
To cast an object, the mold maker, uses the pattern to make the impression in the holding medium, the sand. He then sets the pattern aside. At that point, the molder closes the cope and drag, to complete the flask, and forms the mold, with the impression of the pattern captured in the sand. What the mold maker wants, is the potential “CASTING” or the void left from the impression of the pattern, in middle of the sand. To get that “CASTING,” the mold maker fills that void with a molten material; which could be almost anything, but here just imagine the material is aluminum.
Unlike die casting, sand casted final products have heavy textual imprints from the sand and required further finishing. The tolerances that can be held by sand casting is much less than die casting so any close tolerance dimensions need to be machined into the sand casting. The sand process better serves those looking to produce low quantity and products with less detail than die casting. This is due to the cost of tooling in sand casting which usually is lower than die casting.
While this is still a general description, hopefully it will help the next time you find yourself trying to decide what casting process to use. Review the diagram for a more abbreviated process overview.
We’d Love to answer any further questions you have on this matter. Feel free to ask a question!
By Leonard Cordaro, President of Premier Engineered Products