Die Casting Process Types

Die casting is a popular manufacturing process for casting metal products. There are two main die casting process types and several variations in process design.  When molten metal is forced into mold cavities at high pressure, it is known as die casting. The process is best suited for speedy production of bulk metallic parts that require minimal post-production machining. The main benefits of the die casting process include: 

• High quality: Parts created through die casting deliver a long service life.
  
• High reliability: Uniformity of mass-produced parts is exceptional.
• Quick production: Die cast tooling requires minimal maintenance.
• Versatile design: Die casting can createvirtually any size, part geometry, surface texture or luster.
• Minimal assembly: Assembly features such as studs, drill holes and bosses can be integrated into mold design.  

Applications of Die Casting Processes 

Die casting is a process that has far-reaching applications. Any part production process that creates high-volume metal components will likely benefit from die casting. A variety of manufacturing industries currently rely on one or many types of die casting processes, including the auto, aerospace and power tools industries. 

Types of Die Casting Processes 

All die casting process types are designed with the same goal in mind—cast a mold using injected molten metal. Depending on the type of melted metal, part geometry and part size, different die casting processes can deliver superior results over alternative methods. The two main types of die casting processes are hot-chamber and cold-chamber die casting. Variations on these two types of die casting include: 

• Low-pressure die casting
• Vacuum die casting
• Squeeze die casting
• Semi-solid die casting
  

The Hot-Chamber Die Casting Process 

Hot-chamber die casting, sometimes called gooseneck casting, is the more popular of the two die casting processes. In this process, the cylinder chamber of the injection mechanism is completely immersed in the molten metal bath. A gooseneck metal feed system draws the molten metal into the die cavity.

While direct immersion in the molten bath allows for quick and convenient mold injection, it also results in increased corrosion susceptibility. Due to this fact, the hot-chamber die casting process is best suited for applications that utilize metals with low melting points and high fluidity. Good metals for the hot-chamber die casting process include lead, magnesium, zinc and copper. 

The Cold-Chamber Die Casting Process 

The cold-chamber die casting process is very similar to hot-chamber die casting. With a design that focuses on minimizing machine corrosion rather than production efficiency, the melted metal is automatically- or hand-ladled into the injection system. This eliminates the necessity for the injection mechanism to be immersed in the molten metal bath.

For applications that are too corrosive for the immersion design of hot-chamber die casting, the cold-chamber process can be an excellent alternative. These applications include the casting of metals with high melting temperatures, such as aluminum and aluminum alloys. 

The Low-Pressure Die Casting Process

Low-pressure die casting is a process best suited for aluminum components that are symmetric around an axis of rotation. Vehicle wheels, for example, are often fabricated through low-pressure die casting. In this type of process, the mold is situated vertically above the molten metal bath and connected via a riser tube. When the chamber is pressurized (usually between 20 and 100kPa), the metal is pulled upward and into the mold. The elimination of feeders from this type of die casting process delivers the high casting yields. 

The Vacuum Die Casting Process

Vacuum pressure casting (VPC) is a relatively new die casting process that delivers enhanced strength and minimal porosity. This process is similar to low-pressure die casting, except the locations of the die cast mold and molten metal bath are reversed. The cylinder chamber can become a vacuum, which forces the molten metal into the mold cavity. This design reduces turbulence and limits the amount of gas inclusions. Vacuum die casting is especially beneficial in applications destined for post-casting heat treatment. 

The Squeeze Die Casting Process

Squeeze casting was created as a workable solution for casting metals and alloys with low fluidity. In this process, the molten metal fills up an open die, which then squeezes closed, forcing the metal into the recessed portions of the molding. The squeeze casting process delivers extremely dense products and is a complementary process to subsequent heat-treating. The process is most often associated with molten aluminum, and is used in applications that call for fiber reinforcement.

The Semi-Solid Die Casting Process

Semi-solid die casting, sometimes called Thixoforming, is another process that delivers minimal porosity and maximum density. A machine cuts the workpiece into smaller slugs, and then heated. Once the metal has reached the phase transition between solid and liquid, resulting in a somewhat slushy texture, a shot sleeve forces it into the mold cavity, where it hardens. The benefit of this is improved precision. Non-ferrous metals such as magnesium alloy and aluminum alloy are most often used with the semi-solid die casting process.