Die casting is a process that involves rapid injection velocities at high pressures. During this process, liquid metal enters the die at speeds up to 80 m/s. Rapid injection increases the risk of air being trapped in the die. This is one of the reasons why ramping piston velocity is critical for minimizing air in the die. Using 3D flow and modeling is also helpful for optimizing the design of dies. Another key aspect to die casting is maintaining pressure on the melt to combat the solidification shrinkage. This process also requires large clamping forces to hold the mold closed. The clamping force is calculated by multiplying the projected area of the mold cavities by the pressure.
The cold chamber die casting process is similar to hot chamber die casting except that it uses less pressure. This process increases the life of machinery. The advantages of cold chamber die casting are high strength, minimal porosity, and minimal post-casting heat treatment. Hence, it is used for items that require post-casting heat treatment.
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The process is performed in stages. First, the die prepares the shot by moving the piston. Then, the mold is coated. Next, the shot is added to the shot sleeve. The plunger then returns, allowing residual molten metal to flow back through.
Although hot chamber die-casting is the more popular process, it does have some disadvantages. In addition to being slower than hot chamber die-casting, it can lead to high levels of oxidation and other contaminants. These contaminants are exposed to the molten metal during the process, which may negatively impact the finished product.
Another difference between hot chamber die casting and cold chamber die casting is the temperature at which the metal is molten. Hot chamber die-casting uses a built-in furnace and hydraulic-powered piston. The metal is formed in approximately 15-20 minutes. This type of process is better suited for metals with low melting points, such as lead and zinc. Cold chamber die-casting can be a faster and easier method for certain materials, but it is not appropriate for metals that have high melting points.
While hot chamber die-casting uses the same metal source and die, the molten metal is forced into a pre-shaped mold by pressure. Cold chamber die-casting requires a separate furnace for heating the metal. This method is usually more expensive but offers faster production rates.
Both methods of die-casting are advantageous in different applications. Hot chamber die-casting is a good choice for parts requiring high strength and low weight. Cold chamber die-casting is best suited for magnesium and aluminum alloys. While hot chamber die-casting yields are lower, cold chamber die-casting yields are higher. Cold chamber die-casting is generally preferred when large volume casting is needed, as it is more accurate and versatile. Cold chamber and hot chamber die-casting have many advantages, but they differ in the setup of machinery and delivery of molten metal.
Cold chamber die-casting is the more common process in metal manufacturing. It is most suitable for alloys with a high melting point. It is also more versatile and suitable for industry applications. Cold chamber die-casting requires additional equipment such as an outside furnace and a ladle.