Die casting
Die casting is a metal casting process that involves injecting molten metal into a mold cavity under high pressure. The die casting method can create metal parts that can be machined for precision and an excellent surface finish. Die casting can also produce exceptional parts where close tolerances are needed straight out of the die.
There is a difference between die casting, investment casting, and sand casting. In this article, you’ll learn about these differences and get a detailed view of the die casting process, its types, what materials can be die cast, and the applications for manufacturers.
What Is the Die Casting Process?
The die casting process relies on forcing molten metal into a die cavity with the impression of the desired part. The die casting mold is made of hardened tool steel that can withstand extreme temperatures and pressures.
The key components of die casting include:
- Fixed die
- Moveable die
- Cavity
- Cores
- Die inserts
- Injection system (plunger)
- Clamping mechanism
Molten metal is heated to its melting point or higher to a liquid metal state in an industrial furnace within the casting machine and injected using a hydraulic system. The hydraulic system provides the pressure needed for the metal flow to fill every crevice of the mold cavity. Once the metal is cold and solidified, the casting is removed, the part is ejected, and the same die is prepared for the next cycle.
Step-by-Step Die Casting Process
Die cast mold
- Mold Preparation: Before each die casting cycle, the mold is lubricated or sprayed with a release agent to help with ejection. This also reduces die wear and ensures a longer die life.
- Metal melting: Metal like aluminum, zinc, magnesium, or any other material is melted in a furnace (hot chamber) within the casting machine, while metals with higher melting points are melted in external furnaces (cold chamber), achieving a uniform liquid metal state.
- Injection of Molten Metal: Molten metal is injected into the die under high pressure. This ensures complete filling of the mold cavity.
- Solidification: The molten metal cools rapidly inside the die, forming a solid cast part that has a fine grain structure when observed.
- Ejection: Ejection and finishing of the part are the last steps in the die casting process. The solidified casting is removed from the mold. Excess material, like casting flash, is removed in the finishing. You can also use additional surface finishing processes like painting, powder coating, or anodizing for aluminum that can enhance durability and corrosion resistance.
Types of Die Casting
Die casting is a versatile process that can have several variations. Each type of die casting is suitable for specific materials and applications. The primary types of die casting include:
Hot Chamber Die Casting
Hot chamber die casting is useful for metals with lower melting points. These metals include zinc, tin, and magnesium. The furnace within the casting machine can melt metal and inject it into the die cavity. Most hot chamber die casting machines rely on a gooseneck mechanism.
Hot chamber die casting is ideal for high-volume production of medium-sized parts like valves and fittings.
Cold Chamber Die Casting
Plunger for injection material into casting
Cold chamber die casting is useful for metals with higher melting points, like aluminum or copper alloys. In this, molten metal is melted in an external furnace and poured into a cold shot chamber. After this, it is injected into the die cavity under high pressure (around 20 – 70 MPa).
Cold chamber die casting is ideal for larger components, like engine blocks and transmission cases. Low-pressure die casting is useful for structural parts. It forces molten metal into the mold cavity at low pressures (around 0.1 to 1 MPa). The key difference is that the molten metal comes from a furnace below the die in low pressure die casting.
Low casting creates parts with minimal porosity and uniform mechanical properties in all directions. It is commonly used for large part castings like aluminum wheels and structural components.
Vacuum Die Casting
Vacuum die casting is different from other die casting types because when casting the die, the air is removed before injecting molten metal. This is done to reduce porosity and to achieve uniform mechanical properties of the cast part.
Gravity Die Casting
Gravity die casting, or permanent mold casting, involves using gravitational pull to fill the mold with molten metal. This die casting method is simpler and more cost-effective for low-to-medium production runs.
Gravity die casting produces parts with a better surface finish than sand casting. It is often used to cast the dies for engine blocks, pumps, and casings used in the automotive industry. The key difference in this casting process is the avoidance of using high-pressure requirements.
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What are The Die Casting Materials?
The choice of materials in die casting depends on the application and project requirements. Here, choosing a material that can be cast cost-efficiently is critical.
Common die casting materials include aluminum, zinc, magnesium, and copper alloys.
Aluminum Alloys
Aluminum die-cast
Aluminum casting is widely used due to its lightweight and corrosion-resistant nature. Aluminum alloys like A380 and A413 are popular aluminum die casting materials due to their castability. Aluminum alloys are used in casting automotive components and electronic enclosures, and aluminum’s versatility makes it a great choice for die casting.
Zinc Alloys
Zinc alloys are easy to cast and highly ductile. They are suitable for plating and are also used for their decorative appeal. Zinc die casting is useful for high-impact strength and abrasion proofing applications.
Magnesium Alloys
Magnesium is a lightweight casting material. It has a high strength-to-weight ratio and is commonly used in die casting. Some car panels and seats are cast using magnesium alloys to save weight without compromising strength.
Copper Alloys
Copper alloys include brass and bronze, popular materials for their durability and corrosion resistance. These materials are commonly used for making valves and plumbing fittings. Copper alloys are highly machinable and aesthetic.
Advantages of Die Casting
Die casting is a great material for subsequent manufacturing and producing high-quality metal parts. It has many benefits as a manufacturing process.
- Dimensional Accuracy: Die casting can produce parts with high dimensional accuracy and tight tolerances. This removes many secondary CNC machining operations.
- Surface finish: The die casting process can produce surface finishes of 1.6 to 6.3 μm Ra.
- High Production Runs: Die casting is a cost-effective method of producing metal parts with low melting points, making high-volume production cost-effective.
- Thin-walled geometries: High-pressure injection can allow the material to form into thin walls supporting complex parts. CNC machining of thin walls can lead to issues like warping and extra costs.
- Material versatility: Die casting can be used for various materials, including aluminum, zinc, and magnesium alloys.
- Durability and strength: Die-cast parts have a uniform grain structure that adds strength in all directions and enhances mechanical properties and fatigue resistance.
Challenges with Die Casting
Despite its many benefits, die casting has some limitations and challenges.
- High Initial Costs: Die casting machines and materials require initial investment, and mold machining can be expensive.
- Simpler Material Choices: Die casting is unsuitable for ferrous metals because of their high melting temperatures. This means you cannot produce parts with high melting alloys like steel.
- Porosity: Like most casting processes, die casting also has porosity issues if little injection pressure is used or the mold is not designed to facilitate the complete flow of molten metal.
- Die Wear: The tooling or die can wear over time, and it is expensive to produce another mold. Wrong parameters, high temperatures, and high injection pressures can wear the die quickly.
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Comparing Die Casting, Sand Casting VS Investment Casting
Sand casting
Die casting is a highly efficient metal casting process. There are other casting processes, such as sand casting and investment casting.
Sand Casting
Sand casting involves pouring molten metal into a mold, except this mold is made from sand and can be discarded later. It is less expensive and more flexible for intricate designs. However, it is not as accurate because it lacks dimensional accuracy and has a poor surface finish compared to die casting.
The challenge with sand casting is that it adds to costs, due to the post-processing and surface finishing required. Sand casting is useful when large parts must be made in low volume.
Investment Casting
Investment casting uses a wax pattern instead of a metal mold. Investment casting is highly precise and can produce complex geometries with an excellent surface finish. Compared to die casting, it is more time-consuming and not ideal for high-volume castings.
Applications of Die Casting
Die casting is commonly used across many industries, but the most common is the automotive industry.
- Automotive Uses: Die casting is popular for engine blocks, transmission cases, and gearbox casings.
- Aerospace Uses: Lightweight, high-strength parts like airframe and secondary engine components are made with die casting.
- Furniture: Many mass-produced furniture pieces are made with die casting, especially chairs with metal legs or couches with metal pieces.
Die Casting Services at Prolean-Tech
Prolean-Tech offers high-quality die casting services for automotive components like engine parts and brackets, aerospace parts that require high-strength and low weight and many other industries, from medical to lighting.
Take advantage of our DFM support with our die casting services today–Request a free quote.
Conclusion
Die casting is a manufacturing process that can produce high-precision metal parts. It offers high-dimensional accuracy and excellent surface finish, making it ideal and suitable for high-volume production.
Types of die casting, like hot chamber, cold chamber, and low-pressure die casting, provide many choices for your project requirements and volume. Die casting is a key part of metal casting processes for high-quality parts in aerospace, electronics, and automotive.
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