What are the different types of casting processes?

There are many types of casting processes, each with its own advantages and disadvantages, depending on the needs of the user.

1. Sand Casting Process

Sand casting is a flexible casting process that can be used to cast any ferrous or non-ferrous metal alloy. It is often used in industrial units to mass produce automotive metal castings such as engine blocks, cylinder heads, crankshafts, etc.

The process uses a mold made of a silicon-based substance (such as natural bonded sand or synthetic sand) to produce a smooth mold surface. The mold surface is divided into two parts: the upper mold (upper half) and the lower mold (lower half). The molten metal is poured into the mold using a pouring cup and allowed to harden to form the final shape. Finally, the excess metal is removed to complete the final metal casting product.

The sand casting process has both advantages and disadvantages.

2. Gravity Die Casting

Gravity die casting, also known as permanent mold casting, uses reusable molds made of metals such as steel and graphite to manufacture metals and metal alloys. This metal casting process can produce a variety of items such as gears, gearboxes, pipe fittings, wheels, engine pistons, etc.

In this process, molten metal is poured directly into the mold cavity under the force of gravity. The mold can be tilted to adjust the filling for optimal coverage. To create the object, the molten metal can cool and solidify inside the mold. Therefore, casting materials such as lead, zinc, aluminum and magnesium alloys, certain bronzes and cast iron are becoming more popular. Compared with traditional pressure casting procedures, this casting process fills the mold from the bottom up. However, this method is faster than sand casting. However, it is much more expensive due to the high cost of metal molds. Please check out the advantages and disadvantages below.

3. Pressure Casting

Die casting has two forms depending on the pressure. There are two types of die casting: low-pressure die casting and high-pressure die casting. High-pressure die casting is more commonly used for mass production of complex geometries that require high precision. On the other hand, low-pressure die casting is the preferred casting process for large-scale simple component production.

In this type of metal casting, non-ferrous metals and alloys such as zinc, tin, copper and aluminum are injected at high pressure into a reusable mold coated with a lubricant. To avoid hardening of the metal, the high pressure is maintained throughout the rapid injection process. Finally, after the process is complete, casting extraction and finishing are performed to remove any remaining material. Pressure die casting differs from gravity die casting in the process of filling the mold. Pressure die casting involves injecting molten metal into a metal mold under high pressure. The molten metal then solidifies rapidly to produce the desired result.

4. Investment Casting

Investment casting, also known as lost wax casting, is a method of producing metal castings by encasing refractory materials and binders in a wax pattern to form a disposable ceramic mold, and then pouring molten metal into the mold.

Investment casting is a costly and labor-intensive process that can be used for large-scale production or complex castings to make metal castings such as gears, bicycle trunks, motorcycle wheel discs, and sandblasting machine replacement parts.

5. Plaster Casting

Plaster casting is the same as sand casting, but the mold is made of a material called "Plaster of Paris". Because gypsum has limited thermal conductivity and heat capacity, it cools the metal more slowly than sand molds, which helps achieve high precision, especially for workpieces with narrow cross-sectional areas.

However, it is not suitable for high-temperature ferrous metal materials. Plaster mold casting can produce small castings of 30 grams as well as large castings of 45 kilograms. For example, the figure below shows a casting made by this process with a cross-section thickness of 1 mm.

6. Centrifugal casting

Centrifugal casting, also known as spin casting, is a method of producing cylindrical objects in an industrial setting using centrifugal force.

In this metal casting method, molten metal is poured into a prepared rotating mold. Under high pressure, centrifugal force helps distribute the molten metal within the mold.

There are three centrifugal casting processes: pure centrifugal casting, semi-centrifugal casting, and vertical centrifugal casting. Unlike pure centrifugal casting, semi-centrifugal casting uses a pouring gate to completely fill the mold. However, due to the constant rotation, in pure centrifugal casting, the molten metal adheres to the sides.

On the other hand, vertical centrifugal casting uses directional molding in the same way as true centrifugal casting. Centrifugal casting generally produces rotating structures such as cylinders. Parts include bushing bearings, clutch plates, piston rings, and cylinder liners, among others. In addition, placing the metal in the middle of the mold helps reduce defects such as porosity, shrinkage, and cavitation. However, it is not suitable for all metal alloys.

7. Lost Foam Casting

The lost foam casting method is similar to the investment casting method, except that the model is made of foam instead of wax. Once the design is completed, the model is covered with refractory ceramics by dipping, coating, spraying or brushing. The molten metal is then poured into the mold to make the desired product.

The process is suitable for a variety of materials, including alloy steel, carbon steel, alloy cast iron, ferroalloys, etc. The lost foam casting process is used to manufacture products such as pump casings, fire hydrants, valves and fittings. Lost foam casting has several advantages, including high precision and high accuracy production. However, this technology has some disadvantages that make it unsuitable for small batches.

8. Vacuum Casting

As the name suggests, vacuum casting is a casting method that is manufactured under a vacuum pressure of 100 bar or less to exhaust the gas in the mold cavity. In order to eliminate bubbles and cavitation, the molten metal is poured into the mold cavity inside a vacuum chamber.

Vacuuming the mold cavity prevents gas from being trapped in the mold cavity during metal injection. Finally, the metal solidifies in the heating chamber and is then removed from the mold. Vacuum die casting is widely used in several industries such as automotive, aerospace, electronics, marine and telecommunications. Therefore, structural chassis components and body elements are among the components produced using this manufacturing technology.

9. Squeeze Casting

Squeeze die casting is a promising casting process for safety-critical elements in automotive systems. For example, space frame joints, aluminum front steering knuckles, chassis frames, brackets or nodes. This metal casting process combines the advantages of casting and forging. For example, the high pressure used during solidification helps prevent shrinkage and porosity. However, it is not as common as other casting processes in large-scale production due to the need for specialized tools.

Liquid forging, also known as squeeze casting, is a metal forming hybrid process that combines permanent mold casting with die forging in a single operation. In this process, a certain amount of molten metal alloy is poured into a mold and formed under pressure. The metal part is then heated to the melting temperature and removed from the mold.

10. Continuous Casting

As the name suggests, it can continuously mass-produce metal profiles with a constant cross-section. This type of casting is often used in rebar manufacturing.

In addition, vertical casting can produce semi-continuous castings such as billets, ingots, bars, etc. Molten metal is poured into a water-cooled open mold at a calculated rate so that a solid metal surface forms over the liquid metal at the core. Thus, metal solidification occurs from the outside inward. Once this is done, the metal wire can be removed from the mold indefinitely. The material can be cut to predetermined lengths using mechanical shears or a moving oxyacetylene torch.

Products produced by continuous casting are generally uniform, consistent, and dense. However, it is limited to such uses. Other advantages and disadvantages include:

11. Shell Molding

Shell casting is a mold casting process that uses a disposable mold. It is similar to the sand casting process, except that instead of a sand box, a hardened sand shell is used. The sand used in sand casting is finer and is combined with a resin so that it can be heat treated and bonded into a shell around the design. Shell casting is used to manufacture industrial products such as gearbox housings, connecting rods, small ships, vehicle hoods, cylinder heads, camshafts, valve bodies, etc. The cast products have a smooth surface and precise dimensions.

However, the size and weight restrictions of the workpiece are a constraint to this type of casting.