There are many different types of casting in the industry today, and each type accomplishes a common goal. When our company gets calls or emails reviewing new projects and opportunities, you would be amazed how many times different casting processes are actually used interchangeably.
Just because the names of different casting processes are used by a potential buyer incorrectly doesn’t mean they are created equal. Because of that, it can be difficult to tell which type is best for your project. Two of the most common casting processes are die casting and sand casting. Let’s take a look at each term, how the processes are different, and why you should choose one process over the other for your next project.
What Is Die Casting?
In the die casting process, liquid or “molten” metal is forced into a die under high pressure. In this case, “die” refers to the steel mold created to shape the actual product that will be made. Following the pour and injection into the mold, the molten metal solidifies and is removed from the mold. When the metal cools, the gating material gets removed and a product has been manufactured! The steel mold can then be closed and prepared for the next “shot,” which allows it to be reused immediately. The cycle on making a die cast part can be from 30 seconds to one minute, making the process extremely fast. The image to the left shows the ejector half of a die cast mold and the shot from the mold on the right.
There is a distinct difference between die-cast and cast iron. Die casts use an iron-carbon composite like stainless steel, which is similar to cast iron. However, cast iron is not a candidate for die casting because cast iron has a melting point similar to stainless steel. Although it’s not technically impossible, most manufacturers prefer to die cast their iron.
What Is Sand Casting?
In the sand casting process, molten metal is poured directly from a ladle into a sand mold – no high pressure necessary. The mold is created when a pattern made out of wood or plastic — typically called a matchplate — is placed inside an enclosure. Sand is then filled in around the matchplate and inside the enclosure. Once the sand is added and packed densely, the matchplate is removed and the remaining cavity is filled with molten metal. Following the pour, the metal solidifies, the mold is opened and the sand is shaken off the hot casting, which leads to a product being manufactured. At this point, the gating material can be removed and the casting is complete.
The mold in a sand casting will then need to be prepared for the next “shot,” but there will be a bit of downtime while sand is placed around the matchplate and inside the enclosure. Because of the downtime that occurs — up to 5 minutes per casting — sand casting is best applied to parts that are lower quantity. The materials used in this process also typically lead to less detail in the final products, which usually require more secondary operations than die casting. The image above shows multiple sand casting molds.
How Does Die Casting Differ From Sand Casting?
Aside from the biggest difference in the two processes – the materials being used to form the molds – die casting and sand casting have differences in application as well. Medical device manufacturers, for example, will require precision with complex shapes in their castings. Because of their needs, die casting most likely makes more sense for their project.
In contrast, a furniture manufacturer may find sand casting to be more cost-effective for their production. Sand-casted parts often come with a thicker wall, so the larger size of the final product can still be accurately produced with less precision. The products also often have textural imprints. These imprints can improve the aesthetics of a piece of furniture or decor item with a granular finish or imperfections that imply antique-like qualities. By comparison, this would be a disadvantage to a smaller-shaped product with more complexity that require a precise application.
While there are fundamental differences in the processes for creating a die-casted product and a sand-casted product, both have legitimate applications in commercial manufacturing. For companies that have a sufficient lead time and are able to front the higher cost of having their molds made out of steel, die casting is going to save them money in the long run. Reusing the dies not only ensures accuracy, but production costs are also lower over time. This is because all the items that require casting can be set up and produced in one session, and then repeated as necessary. Die casting can also produce features that cannot be made in sand casting, reducing the secondary costs over sand.
If your company is a high-volume producer of products with a long service life (casting runs of 1,000 or more), the die casting process is most likely going to be the right choice over sand casting.
In summary, the main differences between the sand and die casting processes include:
- Dimensional accuracy: Die casting provides very accurate dimensions, while sand casting is less predictable with a medium to a low accuracy rate.
- Lead time: Die casting can take anywhere from six to ten weeks, while sand casting only needs one to two weeks to complete.
- Parts complexity: Although sand casting produces high complexity parts, die casting can perform to create very high accuracy parts for advanced applications.
- Production volume: Sand casting ranges from one to 1,000 castings, while the production volume for die casting typically begins at 1,000 scales higher.
Whatever method you choose, die and sand casting are efficient production types that suit various applications.
If you have any further questions about these casting processes or want to discuss how die casting may work for your next project, contact Premier Engineered Products online.