Views: 0 Author: Site Editor Publish Time: 2025-09-05 Origin: Site
Die casting is an efficient manufacturing technology in which molten metal is injected into a mold under high pressure and rapidly cooled to form the shape . The core process includes six steps: mold design, smelting, die casting, cooling, demolding and post-processing. Among them, mold design and pressure control have a significant impact on the quality of the finished product . The castings produced by this process feature high surface finish and are suitable for thin-walled and complex structures, making them particularly suitable for mass production.
1. Core Principles and Characteristics of Die Casting Process
Core principle: Under the action of high pressure (usually tens to hundreds of megapascals), liquid or semi-liquid metal fills the mold cavity at an extremely high speed (usually 30-80 m/s) and solidifies and forms under high pressure.
Main features：
（1） High efficiency and high productivity: The die-casting cycle is extremely short, ranging from tens of seconds to several minutes, making it highly suitable for large-scale batch production.
（2） High dimensional accuracy and surface finish: The castings have small dimensional tolerances and good surface quality (Ra 1.6-3.2μm), and can usually be used directly with little or no mechanical processing required.
（3） High casting strength: Due to rapid solidification under high pressure, the casting structure is dense, the grains are fine, and it has a relatively high mechanical strength (tensile strength is about 25% to 30% higher than that of sand casting).
（4） Capable of manufacturing complex thin-walled parts: High-pressure filling ensures excellent fluidity of the molten metal, allowing for the production of castings with extremely complex shapes and very thin wall thicknesses (as thin as 0.5mm).
（5） Insert casting: It is easy to place parts made of other materials (such as insulators, bushings, thread bushings, etc.) in the mold and then die-cast them together to form assemblies.
Limitations：
（1） High cost of equipment and molds: Die-casting machines and mold manufacturing are extremely expensive and are only suitable for mass production to spread out costs.
（2） Material limitations: It is mainly used for non-ferrous alloys such as zinc, aluminum, magnesium and copper, and is rarely used for die-casting cast iron and steel.
（3） Presence of pores: During high-speed filling, the air in the cavity is difficult to be completely discharged, which easily leads to the formation of pores inside the casting. Generally, heat treatment (to avoid surface blisters caused by gas expansion) and welding cannot be carried out.
（4） Limited part size: Restricted by the tonnage of the clamping force of the die-casting machine.
2. Main Types of Die Casting Processes
Die casting is mainly divided into two categories based on the differences in injection systems:
（1） Hot Chamber Die Casting
• Working principle: The injection mechanism (gooseneck, punch, etc.) is directly immersed in the molten metal furnace. During injection, the machine uses hydraulic pressure to push the punch, pushing the molten metal through the gooseneck and nozzle into the mold.
• Advantages: Fast cycle speed (about 1,000 times or more per hour), extremely high efficiency; Less metal loss; The process is simple and easy to automate.
• Disadvantage: The injection mechanism is prone to corrosion when it is constantly immersed in molten metal.
• Applicable materials: Mainly suitable for low-melting-point alloys, such as zinc, tin, lead, etc. It is sometimes also used for small magnesium alloy die-casting.
• Application examples: toys, zippers, gears, small ornaments, small hardware parts.
（2） Cold Chamber Die Casting
• Working principle: The furnace is separated from the injection mechanism. First, a certain amount of molten metal is scooped from the furnace with a spoon and poured into the injection sleeve (cold chamber). Then, the machine uses a high-pressure punch to push the molten metal into the mold.
• Advantages: It avoids the prolonged contact between the injection system and the high-temperature molten metal.
• Disadvantage: The cycle time is slower than that of hot chamber die casting; There is a possibility of heat loss and oxidation during the transfer process of molten metal.
• Applicable materials: Mainly suitable for high-melting-point alloys, such as aluminum alloys, copper alloys, and magnesium alloys. The vast majority of aluminum alloy die-castings are produced by this method.
• Application examples: engine blocks of automobiles, transmission cases, aluminum alloy wheels, electrical enclosures, water pump housings.
3. Die Casting Process Flow (Taking Cold Chamber Die Casting as an Example)
（1） Mold preparation and spraying: Clean the mold, close the mold, and spray the mold release agent (which has both lubricating and cooling functions) on the surface of the cavity.
（2） Mold closing and pouring: The mold is locked under high pressure, and the precisely measured molten metal is poured into the injection sleeve using an automatic pouring machine or manually.
（3） Injection: The die-casting machine pushes the punch in two stages:
• Slow injection: The punch advances slowly, pushing the molten metal to the gate of the mold and expelling the gas inside the sleeve.
• High-speed injection: The punch is pushed at an extremely high speed, and the molten metal fills the entire cavity at high speed under high pressure.
（4） Pressure holding and cooling: After the injection is completed, the punch maintains pressure (pressure holding), allowing the metal to contract and solidify under pressure.
（5） Mold opening and ejection: After the casting solidifies, the mold is opened, and the ejection pin mechanism pushes the casting out of the mold.
（6） Post-treatment: Remove the casting, cut off the gating system and the overflow system (cake, runner, flash, slag bag, etc.), and perform deburring, polishing and surface treatment if necessary.
4. Main application Fields of Die Casting
Die-castings have almost permeated every aspect of modern industry.
Application fields | Main feature | Examples of typical parts |
Automobile Industry | Complex structure, high load-bearing requirements and an extremely large batch size | transmission housing, motor housing, steering knuckle, integrated die-cast body |
Electronics & Electrical Appliances | High appearance requirements,thin and light, and has good heat dissipation | notebook shells, mobile phone frames, router shells |
Daily Used Hardware | Strong decorative effect, surface treatment required, medium batch size | faucets, door locks, zippers, cookware |
Mechanical Equipment | High structural strength and good sealing performance | motor housing, pump body, industrial robot components |
Aerospace | Lightweight, high reliability, and small batch size | unmanned aerial vehicle components, instrument casings |
The selection of application fields for die-casting processes is mainly based on the balance of the following factors:
(1) Production batch size: It must be large enough to spread out the high mold cost.
(2) Part complexity: The more complex the shape and the higher the degree of integration, the more obvious the advantages of die-casting become.
(3) Material requirements: Mainly applicable to non-ferrous alloys such as aluminum, zinc, magnesium and copper.
(4) Performance requirements: For parts with high strength and high density (no porosity) requirements, more advanced die-casting processes should be adopted.
5. Conclusion
Die casting is a highly efficient and precise Near-Net-Shape manufacturing process, and it is an indispensable cornerstone technology in modern large-scale manufacturing, especially in the automotive and 3C industries. In the context of the pursuit of lightweight and integrated design, its status is becoming increasingly important.
