The essence of pressure die casting is to cause molten or semi-molten metal to fill the die cavity at extremely high speed under high pressure, and to solidify under this pressure to form the casting. High pressure and high speed are the two key characteristics of metal filling and forming in die casting, and they are also the fundamental differences between die casting and other casting methods.
In die casting, the injection pressure generally ranges from 5 ~ 30 MPa, and can even be higher. The filling speed ranges from 0.5 ~ 120 m/s, and the filling time is very short—usually between 0.01 ~ 0.2 seconds. In addition, die castings have very high dimensional accuracy and low surface roughness. These features make die casting unique in terms of its process, production, casting structure, quality, and related performance.
Compared to other casting methods, pressure die casting offers the following advantages:
1. High dimensional accuracy and low surface roughness. Most die castings can be used without machining, or only require minimal machining on certain parts.
2. High strength and surface hardness. Due to rapid cooling of the die and solidification under pressure, the grains on the surface layer of die castings are fine and the structure is dense, resulting in higher hardness and strength in the surface layer.
3. Ability to cast complex thin-walled components. The minimum wall thickness for zinc alloy castings is about 0.3 mm, and for aluminum alloy castings about 0.5 mm.
4. Very high productivity. Among all casting methods, die casting has the highest productivity. This is mainly due to the nature of the process. With increasing mechanization and automation, productivity continues to rise.
5. Good interchangeability. High precision and dimensional stability make die castings highly interchangeable, simplifying the assembly of machine parts.
6. Capability of insert casting. Metal or non-metal parts can be cast into the die, allowing for complex component shapes and improved performance. In some cases, insert castings can replace assembly parts altogether.
However, pressure die casting also has some disadvantages:
1. Air entrapment. Due to the extremely fast filling speed, it is difficult to completely eliminate air from the cavity. This often results in internal porosity in the casting, which makes die castings unsuitable for heat treatment or use in high-temperature environments. Machining is also discouraged, as it may expose internal pores.
2. Shorter mold life for ferrous metals. The high melting point of ferrous metals shortens the service life of die casting molds, so die casting of ferrous materials is less common in practice.
3. High cost and limited to mass production. Die casting molds have long manufacturing cycles and high costs. Combined with the high productivity of die casting machines, this process is only suitable for mass production.
Applications of Pressure Die Casting
Pressure die casting is widely used. Among non-ferrous alloys, aluminum alloy castings account for the highest proportion (about 30% ~ 50%), followed by zinc alloy castings.
Industries that use die cast products include: automotive, electrical and electronic instruments, agricultural machinery, aviation, and medical devices.
Die Casting Process
In die casting production, the three key elements are the die casting machine, the die casting alloy, and the die. The die casting process is the integration and effective use of these three elements.
There are two different concepts of speed in die casting: injection speed and filling speed.
• Injection speed refers to the speed at which the plunger advances inside the injection cylinder under hydraulic pressure.
• Filling speed refers to the linear speed at which the molten metal flows through the gate into the die cavity under pressure.
Filling Speeds of Common Die Casting Alloys (m/s)
| Alloy Type | Simple Thick-Walled Casting | General Casting | Complex Thin-Walled Casting |
| Zinc Alloy、Copper Alloy | 10 ~ 15 | 15 | 15 ~ 20 |
| Magnesium Alloy | 20 ~ 25 | 25 ~ 35 | 35 ~ 40 |
| Aluminum Alloy | 10 ~ 15 | 15 ~ 20 | 25 ~ 30 |
Die Casting Machines
Die casting machines are the fundamental equipment in die casting production. As the technology continues to advance, demand for die casting machines increases, and the level of automation in die casting is continuously improving.
Current trends in die casting machine development include: larger scale, series standardization, automation, and major improvements in structure—especially in the injection system, which is evolving rapidly to better meet the demands of die casting processes. These improvements help enhance injection speed and momentary boost pressure, which in turn improves dimensional accuracy and internal density of the castings.
Die casting machines are generally divided into two main types:
• Hot-chamber die casting machines
• Cold-chamber die casting machines
Post time: Jul-03-2025