Die Casting Overview

What Is Die Casting?

Die casting is a metal casting process that employs a mold cavity to apply high pressure to molten metal. The mold is typically machined from a stronger alloy, and the process is comparable to injection molding.

Main Characteristics

The die casting process is characterized by the use of liquid metal under high pressure, resulting in a high flow rate and short filling time. High pressure and high speed are the two main characteristics of the die casting liquid metal filling molding process. They represent the most fundamental difference between die casting and other casting methods:

1. The die casting process begins with the pouring of the metal liquid into the pressure chamber. This is followed by the application of pressure and injection into the mold. This process allows for faster filling speeds than those achieved through ordinary gravity casting.
2. In the die casting process, the application of pressure is employed to increase and hold pressure, thereby facilitating the internal densification of the metal, which is superior to that achieved in traditional casting techniques.

The injection of high-pressure molten metal into a mold results in a rapid filling of the mold, allowing the metal to fill the entire mold before any part solidifies. This process can be used to avoid surface discontinuities in thin-walled parts that are difficult to fill. However, this method can also lead to the formation of air pockets within the mold, as it is difficult for air to escape when filling the mold quickly. This issue can be mitigated by incorporating exhaust ports along the parting line. However, even with the most sophisticated processes, air pockets may remain in the center of the casting. Secondary operations, such as drilling and polishing, can be employed to complete structures that cannot be achieved through casting.

The Pros & Cons

Advantages

1. The product exhibits good quality. The rapid thermal conductivity of the die casting allows for the metal to cool rapidly while undergoing crystallization under pressure, resulting in a fine solid surface. This improves the strength and hardness of the casting, in addition to its dimensional stability and interchangeability. Furthermore, the casting can be manufactured in complex shapes, clear contours, thin-walled, and deep-cavity metal parts.
2. High production efficiency. And longer lifetime for the die-casting mold.
3. The economic benefits of the die-casting process are considerable, with a high material utilization rate. Only after a small amount of follow-up processing can the required product shape be achieved, thus saving a significant amount of raw materials, processing equipment, and labor-hours.

Disadvantages

1. The most significant disadvantage of die casting is its high cost. The equipment, molds, and mold-related components required for this method are expensive relative to other casting techniques. Additionally, the preparation period is lengthy. Consequently, only when the production of a large number of products is necessary is die casting a more economical choice.
2. Die casting is a rapid process, yet the cavity in the gas is difficult to completely discharge. Furthermore, the metal type undergoes fast solidification, rendering it practically impossible to compensate for shrinkage. This results in castings prone to the formation of small pores and shrinkage, as well as the presence of oxidized inclusions. The thicker the casting wall, the more severe such defects become.
3. Die casting is subject to size limitations and alloy type limitations. Die casting of high-melting-point alloys results in a limited mold life, which in turn affects the expansion of die casting production applications.

In summary, the advantages and disadvantages of the process must be considered when determining the suitability of die casting for specific applications. While die casting is suitable for non-ferrous alloys, small, thin-walled, complex castings, and the production of stereotyped products, it is not a viable option for large-scale production of non-stereotyped products. The demand for more than 2000-3000 pieces of the die casting process will be more advantageous.

Die Casting Machine

The type of die casting determines the necessity of utilizing a cold chamber die casting machine or a hot chamber die casting machine. In the case of zinc alloy die casting, the former is employed, whereas aluminum alloy die casting is commonly processed using the latter.

Hot-Chamber die casting machine

A hot chamber die casting machine is a die casting machine in which the ejection chamber and ejection punch are immersed in molten metal. The ejection chamber is connected to the gate of the die casting model through a gooseneck pipe. It is suitable for die-casting zinc, lead, and other low melting point non-ferrous alloy parts. It can be widely used in automobiles, motorcycle parts, instruments and meters, daily-use hardware, household appliances, and other industrial sectors.

Hot-chamber die casting uses the same process previously mentioned — molten metal is forced through the cavity of a pre-shaped mold using pressure. The defining characteristic of hot-chamber die casting is that metal is heated inside the casting machine rather than a separate machine or furnace.

Also known as goose-neck machines, hot-chamber casting machines feature a built-in furnace in which metal is heated to achieve a molten state. They use a hydraulic-powered piston that forces molten metal out of the furnace and into the die. Hot-chamber die casting is a relatively fast process, with a typical cycle lasting just 15 to 20 minutes. While not suitable for metals with a high melting point, it’s ideal for zinc alloys, tin alloys and lead alloys.

Cold-Chamber Die Casting

Based on its name, you may assume that cold-chamber die casting involves forcing cold metal through the cavity of a mold, but this isn’t necessarily true. Cold-chamber die casting still requires the use of molten metal that’s forced into a mold. The difference between these two processes is that hot-chamber die casting heats metal inside the casting machine, whereas cold-chamber die casting involves heating metal in a separate furnace and then transferring the newly molten metal into the casting machine.

With cold-chamber die casting, metal is first heated to achieve a molten state in a separate furnace. The molten metal is then transported to the casting machine where it’s fed into the machine’s chamber. The machine uses a pressurized plunger to force the molten metal into the cavity of the mold.

Certain types of metals — those with a high melting point — can only be processed using cold-chamber die casting. The high temperatures required to achieve a molten state for metals such as aluminum, magnesium and copper means a separate furnace must be used, which is why some manufacturers choose cold-chamber die casting over hot-chamber die casting.