Cold Chamber Die Casting: A High-Strength Precision Forming Process for High-Melting-Point Metals

As a high-strength and precision metal forming process, Cold Chamber Die Casting has become the core process for mass production of high-melting-point metal components, relying on its core advantages of strong adaptability to materials, large forming capacity, and excellent part compactness, and plays an irreplaceable role in various fields such as automotive, aerospace, and heavy machinery. Although it has limitations in production efficiency and initial equipment investment, these limitations are gradually being optimized with the continuous upgrading of automation and mold technology.

I. What is Cold Chamber Die Casting?

Cold Chamber Die Casting, a key branch of the die casting process, is a specialized metal forming technology designed for high-melting-point, high-corrosion metal materials that are not suitable for hot chamber die casting. Its core feature is that the injection chamber (also known as the cold chamber) is separated from the molten metal furnace—unlike the hot chamber die casting where the injection mechanism is immersed in the molten metal. Instead, molten metal is manually or automatically scooped from the separate furnace and poured into the cold injection chamber, then pushed by a high-pressure plunger into the closed mold cavity for rapid cooling and solidification, ultimately forming high-precision metal components.

The fundamental difference between Cold Chamber Die Casting and Hot Chamber Die Casting lies in the separation of the injection chamber and the furnace. This design avoids the damage to the injection mechanism caused by long-term immersion in high-temperature molten metal, making it possible to process high-melting-point metals such as aluminum alloy, copper alloy, and brass (with melting points above 600℃). It is precisely this structural difference that makes Cold Chamber Die Casting the preferred process for large, thick-walled, and high-strength metal components, complementing Hot Chamber Die Casting to cover almost all die casting application scenarios.

In simple terms, Cold Chamber Die Casting is like "scooping boiling oil from a pot into a mold with a ladle"—the injection chamber remains at room temperature (or slightly preheated) before receiving the molten metal, ensuring the stability of the injection mechanism while handling high-temperature materials. It is an indispensable "high-strength tool" for producing large, load-bearing metal components in industrial manufacturing.

II. Core Structure and Working Principle of Cold Chamber Die Casting

(I) Core Equipment Structure

The equipment structure of Cold Chamber Die Casting is more robust than that of Hot Chamber Die Casting, mainly consisting of five core components: separate melting furnace, injection mechanism, mold clamping mechanism, control system, and feeding device. Each component is designed to adapt to high-temperature, high-pressure working conditions, ensuring stable and efficient production:

• Separate Melting Furnace: Independent of the injection mechanism, it is specially used for melting high-melting-point metals (such as aluminum alloy, copper alloy). The furnace is equipped with high-efficiency heating elements and temperature control systems, which can heat the metal raw materials to 600-1200℃ (depending on the material) and keep them in a stable molten state. The furnace is usually made of high-temperature-resistant refractory materials to prevent deformation and corrosion under long-term high-temperature conditions.

• Injection Mechanism: The core component, including the cold injection chamber, injection plunger, and nozzle. The injection chamber is made of high-strength heat-resistant steel, which is not in direct contact with the furnace and remains at a relatively low temperature (cold state) during normal operation. The injection plunger is driven by a high-power hydraulic system, which can generate extremely high pressure (50-150MPa) to push the molten metal into the mold cavity at high speed. The nozzle is designed with a heat insulation structure to reduce heat loss of the molten metal during injection and prevent leakage.

• Mold Clamping Mechanism: Due to the higher injection pressure of Cold Chamber Die Casting, the mold clamping mechanism needs to provide greater clamping force (usually 100-2000 tons) to resist the high-pressure impact of the molten metal and avoid mold overflow or damage. It is driven by a dual hydraulic cylinder system, which can realize rapid mold clamping and stable locking, ensuring the precision of the formed parts.

• Control System: Adopting advanced PLC and touch screen control, it can accurately set and adjust key process parameters such as molten metal temperature, injection pressure, injection speed, mold clamping force, and cooling time. High-end models are also equipped with intelligent monitoring and fault alarm functions, which can real-time monitor the production process and reduce the occurrence of defects.

• Feeding Device: Used to transfer molten metal from the separate furnace to the injection chamber, which can be divided into manual feeding (ladle) and automatic feeding (robot or quantitative pouring device). Automatic feeding is widely used in mass production, which not only improves production efficiency but also ensures the consistency of the amount of molten metal poured each time, reducing quality fluctuations.

(II) Working Principle (Complete Process)

The working process of Cold Chamber Die Casting is slightly more complex than that of Hot Chamber Die Casting, but it is still highly automated. The core process can be divided into 7 steps, which cycle repeatedly to achieve mass production of high-quality metal components:

1. Metal Melting: Put high-melting-point metal raw materials (such as aluminum alloy ingots) into the separate melting furnace, heat them to the specified molten state through the heating system, and keep them warm at a stable temperature to ensure good fluidity and purity of the molten metal.

2. Mold Clamping and Locking: The mold clamping mechanism drives the fixed mold and moving mold to close tightly, and applies sufficient clamping force to lock the mold, ensuring that the mold cavity can withstand the high-pressure impact of the molten metal during injection without deformation or overflow.

3. Molten Metal Feeding: Use a feeding device (ladle or robot) to scoop a fixed amount of molten metal from the furnace and pour it into the cold injection chamber, ensuring that the molten metal fills the injection chamber evenly without splashing.

4. High-Pressure Injection: The injection plunger moves forward rapidly under the drive of the hydraulic system, pushing the molten metal in the injection chamber into the mold cavity at high pressure (50-150MPa) and high speed (2-8m/s), ensuring that the molten metal fills every corner of the cavity and eliminates air bubbles.

5. Pressure Holding and Solidification: After the mold cavity is filled with molten metal, the injection plunger maintains a certain pressure to compensate for the shrinkage of the molten metal during cooling and solidification, ensuring that the formed parts are dense and free of shrinkage holes. The molten metal in the cavity is rapidly cooled and solidified into the shape of the cavity under the action of the mold cooling system.

6. Mold Opening and Part Ejection: After the parts are completely solidified, the mold clamping mechanism drives the mold to open, and the ejection system ejects the formed parts from the mold cavity. The ejection speed and force are precisely controlled to avoid deformation or damage to the parts.

7. Part Cleaning and Inspection: Take out the ejected parts, remove the gate, runner, and burrs through post-processing, then inspect the parts for size, surface quality, and internal defects to ensure they meet the production standards. After inspection, the qualified parts enter the next process, and the unqualified parts are recycled and remelted.

III. Process Characteristics of Cold Chamber Die Casting (Advantages and Limitations)

The process characteristics of Cold Chamber Die Casting are determined by its "separate injection chamber and furnace" design, which is complementary to Hot Chamber Die Casting. It has unique advantages in processing high-melting-point metals and large parts, but also has certain limitations in production efficiency and cost. It needs to be reasonably selected according to product requirements.

(I) Core Advantages

1. Wide Adaptability to Materials: This is the biggest advantage of Cold Chamber Die Casting. It is not limited by the melting point and corrosion of metals, and can process almost all commonly used die casting metals, including high-melting-point metals such as aluminum alloy, copper alloy, brass, and even some special alloys. It solves the problem that Hot Chamber Die Casting cannot process high-melting-point metals, expanding the application range of die casting technology.

2. Large Forming Capacity: The mold clamping force and injection pressure of Cold Chamber Die Casting machines are larger, which can produce large, thick-walled, and heavy metal components. The weight of the parts can reach tens or even hundreds of kilograms, and the size can exceed 1 meter, which is far beyond the forming capacity of Hot Chamber Die Casting. It is suitable for producing large load-bearing components in automotive, aerospace, and heavy machinery fields.

3. High Part Strength and Compactness: The injection pressure of Cold Chamber Die Casting is much higher than that of Hot Chamber Die Casting (up to 150MPa), and the pressure holding process can effectively compensate for the shrinkage of the molten metal, making the internal structure of the formed parts dense, free of shrinkage holes and air bubbles, and the tensile strength and hardness are significantly higher than those of parts produced by Hot Chamber Die Casting. It can meet the performance requirements of load-bearing and wear-resistant components.

4. Good Part Precision and Surface Quality: With the optimization of mold design and injection control technology, Cold Chamber Die Casting can achieve high forming precision. The dimensional tolerance grade of parts can reach IT10-IT12, and the surface roughness can be as low as Ra≤1.6μm. The parts can be directly used for assembly after simple post-processing, reducing production costs.

5. Long Service Life of Equipment: Since the injection chamber of Cold Chamber Die Casting is separated from the furnace and not immersed in high-temperature molten metal for a long time, the wear and corrosion of the injection mechanism are greatly reduced, and the service life of the equipment and mold is longer than that of Hot Chamber Die Casting, reducing the cost of equipment maintenance and replacement.

(II) Limitations

1. Lower Production Efficiency: Compared with Hot Chamber Die Casting, Cold Chamber Die Casting adds the link of manual or automatic feeding of molten metal, and the injection cycle is longer (each cycle takes 15-60 seconds). The production efficiency is about 30%-50% of that of Hot Chamber Die Casting, which is not suitable for mass production of small and micro components.

2. High Initial Equipment Investment: Cold Chamber Die Casting machines need to be equipped with separate melting furnaces and high-power hydraulic systems, and the equipment structure is more complex. The initial purchase and installation cost is much higher than that of Hot Chamber Die Casting machines, which increases the access threshold for small and medium-sized enterprises.

3. Higher Requirements for Operators: The production process of Cold Chamber Die Casting involves more links, and the control of key parameters (such as molten metal temperature, injection pressure, and feeding amount) is more strict. Operators need to have professional technical knowledge and rich operation experience to ensure stable production and product quality, which increases the cost of personnel training.

4. More Serious Molten Metal Oxidation: During the feeding process, the molten metal is exposed to the air, which is easy to oxidize and generate oxide inclusions, affecting the internal quality and surface finish of the parts. It is necessary to take measures such as adding flux or using protective gas to reduce oxidation, which increases the production process and cost.

IV. Control of Key Process Parameters for Cold Chamber Die Casting

The quality of parts produced by Cold Chamber Die Casting (dimensional precision, surface quality, internal compactness, and mechanical properties) mainly depends on the control of key process parameters. Due to the high melting point of the processed materials and large forming size, the parameter control is more strict than that of Hot Chamber Die Casting. The core parameters that need to be focused on are as follows:

(I) Temperature Control

Temperature control is crucial for Cold Chamber Die Casting, which directly affects the fluidity of molten metal and the solidification quality of parts. Two key temperatures need to be strictly controlled:

• Molten Metal Temperature: Set according to the type of metal material. For aluminum alloy, it is usually 650-720℃; for copper alloy, it is 900-1100℃. Excessively high temperature will accelerate the oxidation of molten metal, increase oxide inclusions, and cause defects such as burning and deformation of parts; excessively low temperature will reduce the fluidity of molten metal, leading to defects such as material shortage, cold shut, and insufficient filling.

• Mold Temperature: Usually controlled at 180-300℃, which needs to be kept uniform and stable. For large and thick-walled parts, the mold temperature should be appropriately increased to prolong the cooling time and avoid defects such as cracks and shrinkage holes; for small and thin-walled parts, the mold temperature can be appropriately reduced to improve production efficiency. The mold temperature is usually adjusted through the built-in cooling channel and heating device.

(II) Injection Pressure and Speed Control

Injection pressure and speed are the core parameters affecting the filling effect and internal quality of parts. Cold Chamber Die Casting adopts high-pressure injection, and the parameters need to be adjusted according to the material and part structure:

• Injection Pressure: Generally controlled at 50-150MPa. For high-strength and dense parts (such as automotive engine parts), higher pressure (100-150MPa) is needed to ensure that the molten metal fills the cavity completely and the internal structure is dense; for parts with complex shapes and thin walls, moderate pressure (70-100MPa) is adopted to avoid mold overflow and part deformation.

• Injection Speed: Divided into slow injection speed and fast injection speed. The slow speed (0.3-1m/s) is used in the initial stage of plunger movement to push the molten metal to the nozzle smoothly and avoid air entrainment; the fast speed (2-8m/s) is used when the molten metal enters the mold cavity to ensure that the molten metal fills the cavity quickly and reduces defects such as cold shut and insufficient filling. The speed switching time needs to be accurately controlled to avoid impact on the mold and parts.

(III) Pressure Holding Time and Cooling Time Control

• Pressure Holding Time: Usually 5-20 seconds, which is longer than that of Hot Chamber Die Casting. The purpose is to compensate for the shrinkage of the molten metal during cooling and solidification, ensuring that the parts are dense and free of shrinkage holes. The pressure holding time is determined by the thickness and material of the parts—thicker parts require longer pressure holding time.

• Cooling Time: Usually 10-60 seconds, which accounts for a large proportion of the entire production cycle. It needs to be adjusted according to the thickness and material of the parts to ensure that the parts are completely solidified before mold opening, avoiding deformation and cracks. For large and thick-walled parts, the cooling time can be prolonged by optimizing the mold cooling system to improve production efficiency.

(IV) Feeding Amount Control

The feeding amount directly affects the filling effect and weight precision of the parts. Too much feeding will lead to mold overflow, increase the amount of burrs, and increase post-processing workload; too little feeding will cause insufficient filling, material shortage, and other defects. In mass production, automatic quantitative feeding devices are usually used to ensure that the feeding amount is consistent each time, improving the consistency of product quality.

V. Industrial Application Scenarios of Cold Chamber Die Casting

Based on the core advantages of "wide material adaptability, large forming capacity, and high part strength", Cold Chamber Die Casting is mainly used for producing large, thick-walled, high-strength metal components, and is widely applied in industries that require high-performance metal parts, covering automotive, aerospace, heavy machinery, and other key fields. The following are typical application scenarios:

(I) Automotive Industry (Core Application Field)

The automotive industry is the largest application field of Cold Chamber Die Casting. With the trend of lightweight and high performance of automobiles, aluminum alloy and magnesium alloy components produced by Cold Chamber Die Casting are widely used in automotive engines, transmissions, chassis, and other key parts, accounting for more than 60% of automotive die casting parts:

• Engine Components: Engine cylinder blocks, cylinder heads, crankcases, piston tops, etc. These parts require high strength, high temperature resistance, and good sealing performance, which can be perfectly achieved by Cold Chamber Die Casting with aluminum alloy.

• Chassis and Transmission Components: Transmission cases, differential cases, suspension brackets, steering knuckles, etc. These parts need to bear large loads and wear, and Cold Chamber Die Casting can produce parts with dense structure and high strength to ensure the safety and stability of automobile operation.

• Body Components: Automobile door frames, engine hood frames, trunk lid frames, etc. Using aluminum alloy Cold Chamber Die Casting can reduce the weight of the automobile body, improve fuel economy and battery life (for new energy vehicles).

(II) Aerospace Industry

The aerospace industry has extremely high requirements for the strength, precision, and reliability of metal components. Cold Chamber Die Casting is widely used for producing small and medium-sized precision components of aircraft and rockets, mainly using high-strength aluminum alloy, magnesium alloy, and copper alloy:

• Aircraft Components: Aircraft engine brackets, landing gear accessories, cabin structural parts, hydraulic system connectors, etc. These parts need to have high strength-to-weight ratio and corrosion resistance, and Cold Chamber Die Casting can meet the strict quality requirements.

• Rocket Components: Rocket engine nozzles, fuel tank accessories, satellite structural parts, etc. Cold Chamber Die Casting can produce parts with complex shapes and high precision, ensuring the stability and reliability of aerospace equipment during launch and operation.

(III) Heavy Machinery and Equipment Industry

Heavy machinery and equipment (such as construction machinery, agricultural machinery, and mining machinery) need to withstand large loads and harsh working environments, so the requirements for metal components are extremely high. Cold Chamber Die Casting is used for producing large, thick-walled, and wear-resistant components:

• Construction Machinery Components: Excavator bucket teeth, hydraulic cylinder blocks, gearbox cases, etc. These parts need high strength and wear resistance, and Cold Chamber Die Casting with copper alloy or high-strength aluminum alloy can meet the service life requirements.

• Agricultural Machinery Components: Tractor engine blocks, transmission cases, plow blade brackets, etc. Cold Chamber Die Casting can realize mass production of these large components, reducing production costs while ensuring quality.

(IV) Other Fields

In addition to the above three fields, Cold Chamber Die Casting is also widely used in electrical and electronic, hardware tools, and marine engineering fields:

• Electrical and Electronic Field: High-voltage switch housings, transformer shells, motor end covers, etc. These parts require good electrical conductivity and mechanical strength, and copper alloy Cold Chamber Die Casting is the preferred choice.

• Hardware Tools Field: Large wrench bodies, pliers handles, hammer heads, etc. Cold Chamber Die Casting can produce parts with thick walls and high strength, ensuring the durability of hardware tools.

• Marine Engineering Field: Marine engine components, ship hull connectors, hydraulic system parts, etc. These parts need to have good corrosion resistance and high strength, and Cold Chamber Die Casting with special alloys can meet the requirements of marine working environments.

VI. Development Trends of Cold Chamber Die Casting

With the continuous development of global manufacturing towards high precision, high efficiency, greenization, and intelligence, Cold Chamber Die Casting, as a core metal forming process, is constantly upgrading and optimizing, breaking through existing limitations, and expanding application boundaries. In the future, it will mainly show the following four development trends:

(I) Automation and Intelligence Upgrade

To solve the problem of low production efficiency, Cold Chamber Die Casting will gradually realize full-process automation and intelligence. Industrial robots, machine vision, and AI algorithms will be widely used in feeding, part taking, post-processing, and quality inspection links, forming an automated production line. At the same time, the intelligent control system will realize real-time monitoring and adaptive adjustment of process parameters, automatically optimizing injection pressure, speed, and temperature according to the production status, reducing human intervention, improving production efficiency and product consistency.

(II) Precision and Lightweight Development

With the increasing demand for high-precision and lightweight parts in automotive, aerospace, and other fields, Cold Chamber Die Casting will develop towards higher precision and thinner walls. By optimizing mold design (using 3D printing technology to produce complex molds), improving injection control precision, and adopting new materials, the dimensional tolerance grade of parts can be improved to IT9 or above, and the wall thickness of parts can be reduced to 1-2mm, realizing the integration of precision and lightweight, and further reducing the weight of products.

(III) Green and Energy-Saving Transformation

Under the background of global carbon neutrality, green and energy-saving has become an important development direction of Cold Chamber Die Casting. On the one hand, new energy-saving melting furnaces and heat insulation materials will be adopted to reduce energy consumption during the melting and injection process; on the other hand, the recycling technology of waste parts and molten metal will be optimized to improve the utilization rate of raw materials (up to 98% or more). At the same time, environmentally friendly fluxes and protective gases will be used to reduce oxide emissions and realize green production.

(IV) Expansion of Material and Application Boundaries

With the development of material science and mold technology, Cold Chamber Die Casting will gradually expand the applicable material range, and can process more high-performance special alloys (such as titanium alloy, magnesium-lithium alloy) to meet the needs of high-end fields such as aerospace and military industry. At the same time, it will expand to new fields such as new energy (wind power, photovoltaic) and medical equipment, producing large-scale and high-precision components, and further expanding the application space of Cold Chamber Die Casting.

VII. Conclusion

As a high-strength and precision metal forming process, Cold Chamber Die Casting has become the core process for mass production of high-melting-point, high-strength metal components, relying on its core advantages of wide material adaptability, large forming capacity, and excellent part compactness. It complements Hot Chamber Die Casting, forming a complete die casting technology system, and plays an irreplaceable role in promoting the development of automotive, aerospace, heavy machinery, and other key industries. Although it has limitations in production efficiency and initial investment, these limitations are constantly being optimized and solved with the upgrading of automation, intelligence, and material technology.

In the future, with the integration of new technologies such as industrial 4.0, 3D printing, and AI, Cold Chamber Die Casting will enter a new stage of development, achieving higher precision, higher efficiency, greener, and more intelligent production. It will not only provide more high-quality, high-performance metal forming solutions for global manufacturing but also play an important role in promoting the upgrading and development of the manufacturing industry, helping the manufacturing industry move towards high-end, high-value-added, and sustainable development. For enterprises, mastering the core technology and parameter control of Cold Chamber Die Casting will become the key to enhancing core competitiveness and seizing market opportunities in the high-end manufacturing field.