Sand Castings vs. Die Castings:
Considerations to Help You Decide
Sand castings and die castings have lots of common ground. Many parts can be
produced using either method. So, how to decide, and to make sure decisions made
in the past are still based on valid assumptions?
First, the easy part. Sand castings are used when parts are hollow; there’s no practical
alternative. An example is automotive (intake exhaust) cylinder heads. Internal water
passages preclude the use of die castings for these applications. Engine blocks
such as the one shown above are traditionally sand cast because they, too, have
internal passages, although many modern automotive engines use blocks cast with “hybrid”
processes, which may include permanent mold, sand, and multiple injections of metal.
Sand castings are more costly, but can produce shapes that are not possible with
die castings. Tooling is less expensive as well. Lightweight, thin wall castings,
such as those found on simple BBQ enclosures are almost always die castings;
a grill lid that costs $10 to die cast costs $100 to produce as a sand casting,
even though die castings require more machining. Die castings generally have
smoother surfaces, however.
Sand castings are preferable for components such as housings for medical
diagnostic equipment. One reason is that tooling changes are more economical
to make for sand castings, in part because the material for sand castings is wood
or plastic, which is far easier to modify than the metal used for die castings. Die castings
and common sand castings both require draft angles to eject the part from the mold.
Note: the V-Process castings supplied by AccuForm do not require draft angles.
One advantage of sand castings over die castings is that, given the short life cycle
of many of today’s products, the substantial upfront investment in hard tooling for
die castings is less palatable. Sand castings do not commit the customer to costly
tooling for a part life with a brief life. Changes are also quite costly for a die casting.
Die casting is economical only for very high-volume production.
Die castings typically have a uniform wall thickness. Sand castings can vary greatly
in wall thickness – a substantial design advantage for many product developers.
Sand castings can also be wider in gauge than die castings.
Sand castings are also typically stronger than die castings, by virtue of the material used;
sand cast alloys are typically stronger than die cast alloys.