Exploring Casting Processes for Automotive Parts, Pumps, and Valves

Jan 24, 2023

Casting Process and Mold Design

Casting foundries produce customized castings with various shapes and dimensions, by pouring molten metal into a mold. As a result, mold design and production is a key capability for any experienced and reliable casting foundry. A poorly designed and manufactured mold, whether permanent or perishable, will produce poor quality castings.

Material shrinkage and uniformity are other important factors to consider when designing molds. Molten metal tends to shrink when it cools off, so an experienced foundry will always consider the shrinkage amount and factor it into the mold design. Another important aspect is the uniformity of the casting material as it solidifies. For example, long and slim parts cool down faster and more evenly than thick, round shapes.

Casting Methods  

The most commonly used casting methods are centrifugal casting and sand casting, for the automotive, steel mill, and heavy manufacturing industries such as power plants.

• Centrifugal casting uses a mold that rotates on a vertical or horizontal axis at high velocities to separate any impurities from the molten metal.
• Sand casting uses a pattern of the finished part, which could be a lot more intricately shaped than those made from centrifugal castings.

There are many advantages of sand casting, such as lower cost, but the most common reason to choose sand casting over centrifugal casting is its ability to produce complex geometries with thin wall sections such as fluid control valve, pump casings, petrochemical tube supports, impellers and volute covers. This is where mold design becomes crucial – if the mold pattern is designed without calculating the shrinkage portion, or the mold is not properly maintained, the sand casting’s shape will be far from the net shape of the finished products.

In recent years, the application of 3D printing technology to mold design has become popular, enabling foundries to build molds with intricate designs for near-net-shape casting.

Types of Sand Casting

Sand casting can be further divided into green casting and shell mold sand casting, based on the type of sand used. Shell mold sand casting uses silica sand, which is finer than that used in green casting. The fine grained sand packs better than large grained sand, leading to lower porosity,  better material conformity, and increased surface smoothness.

Although mold preparation time is longer for shell mold casting than green sand casting, overall production time is shorter for shell mold casting because its smooth surface finish requires no further machining. In addition, the higher porosity of green sand castings can sometimes cause quality issues and impact end product performance, or simply be rejected for cosmetic reasons, due to the pinholes on the casting surface.

Shell Mold Sand Casting for Automotive Parts, Pumps and Valves