Purposes and types of metal casting

Metal casting is a very old technology that originated in Egypt and China. It is a familiar processing method in Japan and has produced many products ranging from valuable historical artifacts such as bronze bells and the Great Buddha of Nara to everyday items such as Nambu ironware. What are the types of metal casting methods and their purposes?

What is metal casting?

Metal casting is a technique in which metal is melted, poured into a mold made of sand or another type of metal, and cooled and solidified (coagulation). A wide range of materials can be used, including any metal that can be melted.

Purposes of metal casting

Metal casting is used for the following three purposes

Form complex shapes

By preparing a mold of the desired shape in advance, casting can be used to form much more complex shapes than can be achieved by cutting with tools.

Form hollow shapes

Hollow shapes can be formed by fitting a sand mold called a core into the mold. Huge structures such as the Great Buddha of Nara were made by casting because the hollow shape not only reduces the amount of raw materials used, but also makes the manufacturing process easier.

Mass production

The same mold can be used multiple times for mass production in a short period of time. Another advantage is that mass production can reduce the cost per product.

Types of metal casting

There are various types of casting methods available today. This is because many techniques have been developed over a long history. Each has its own merits and demerits, so it is important to select a method that best suits the application and the characteristics of the metal to be used. Some of the representative construction methods are introduced below.

Raw casting

This method uses a mold made by combining quartz sand, clay (bentonite), mold release agent, and water. It has various advantages such as easy removal of castings, reusable molds, no generation of toxic gas, and low cost. Because of these features, this method is suitable for castings that require mass production, such as automobile parts, and is still a popular method today.

Full mold casting

In this method, a model made of foamed polystyrene is embedded in sand and cast into the sand. During casting, the high temperature of the metal vaporizes the polystyrene foam and the mold will be replaced with a metal mold. Since there is no need to align the molds, the process is simple and burr-free castings can be produced. On the other hand, careful attention must be paid to avoid adhesion of polystyrene foam residue (insoluble material left behind without dissolving).

Mold casting

This is a casting method in which molds are made of cast iron or heat-resistant alloys. The use of metal molds produces precise castings with excellent dimensional accuracy, which is useful for casting automotive brakes and other products that require high precision. However, the production of molds is expensive.

Lost-wax casting

This method uses a mold made by making a model with wax, coating the model with casting sand, and melting the wax inside the model. Since castings can be produced in the same shape as the wax model, even complex shapes can be produced with high dimensional accuracy.

Die casting

In this method, molten alloy is injected into a mold at high speed and high pressure. It has high dimensional accuracy and can be expected to produce a finish with excellent dimensional accuracy even for complex shapes. On the other hand, the disadvantage is that air and oxides may be entrained in the product because cast iron is injected at high speed.

Centrifugal casting

A casting method that uses centrifugal force to obtain cylindrical castings by casting in a rotating cylindrical mold. Hollow molding is possible at low cost without the use of cores. However, depending on the characteristics of the metal used, centrifugal force may cause segregation, so you must pay attention to it.

Continuous casting

This is a process to obtain castings continuously from molten metal. Molten steel is continuously injected into the mold, and the resulting strip castings are cut as needed to produce the same type of castings in large quantities without interruption. However, it is not suitable for small-lot products due to the high investment in machinery.

Plaster casting

This is a casting method using molds made of plaster. It can produce castings with excellent dimensional accuracy at low cost. In addition, since the molds are easy to produce, this method is best suited for prototype production and for small-lot production in a short period of time. On the other hand, it is not suitable for mass production due to its durability.

Summary

Metal casting is a process that can produce castings of complex shapes and hollow shapes at a relatively low cost. There are various casting methods, each of which has its own merits and demerits, so it can be useful if you select a method well suited to the scene of use. Proper research will be required on what you want to make and the most suitable casting method.