Die casting is a popular manufacturing process for the casting of metal products. There are two main die casting process types and several variations in process design. When molten metal is forced into mold cavities at high pressure, it is known as die casting. The process is best suited for speedy production of bulk metallic parts that require minimal post-production machining. The main benefits of the die casting process include:
- High quality: Parts created through die casting deliver a long service life.
- High reliability: Uniformity of mass-produced parts is exceptional.
- Quick production: Die cast tooling requires minimal maintenance.
- Versatile design: Die casting can create virtually any size, part geometry, surface texture or luster.
- Minimal assembly: Assembly features such as studs, drill holes, and bosses can be integrated into mold design.
Applications of Die Casting Processes
Die casting is a process that has far-reaching applications. Any part production process that creates high-volume metal components will likely benefit from die casting. A variety of manufacturing industries currently rely on one or many types of die casting processes, including the auto, aerospace and power tools industries.
Types of Die Casting Processes
All die casting process types are designed with the same goal in mind—cast a mold using injected molten metal. Depending on the type of melted metal, part geometry and part size, different die casting processes can deliver superior results over alternative methods. The two main types of die casting processes are hot-chamber and cold-chamber die casting. Variations on these two types of die casting include:
- Low-pressure die casting
- Vacuum die casting
- Squeeze die casting
- Semi-solid die casting
The Hot-Chamber Die Casting Process (Hot Casting)
Hot-chamber die casting, sometimes called gooseneck casting, or hot casting, is the more popular of the two main die casting processes. In this process, the cylinder chamber of the injection mechanism is completely immersed in the molten metal bath. A gooseneck metal feed system draws the molten metal into the die cavity. This process lends itself to higher rates of part production than with the cold-chamber process.
While direct immersion in the molten bath allows for quick and convenient mold injection, it also results in increased corrosion susceptibility. Due to this fact, the hot-chamber die casting process is best suited for applications that utilize metals with low melting points and high fluidity. Suitable metals for the hot-chamber die casting process include lead, magnesium, zinc, and copper.
The Cold-Chamber Die Casting Process
The cold-chamber die casting process is very similar to hot-chamber die casting. With a design that focuses on minimizing machine corrosion rather than production efficiency, the melted metal is automatically- or hand-ladled into the injection system. This eliminates the necessity for the injection mechanism to be immersed in the molten metal bath.
For applications that are too corrosive for the immersion design of hot-chamber die casting, the cold-chamber process can be an excellent alternative. These applications include the casting of metals with high melting temperatures, such as aluminum and aluminum alloys.
The Low-Pressure Die Casting Process
What is low pressure die casting? Low-pressure die casting is a process best suited for aluminum components that are symmetric around an axis of rotation. Vehicle wheels, for example, are often fabricated through low-pressure die casting. In this type of process, the mold is situated vertically above the molten metal bath and connected via a riser tube. When the chamber is pressurized (usually between 20 and 100kPa), the metal is pulled upward and into the mold. The elimination of feeders from this type of low pressure aluminum casting process delivers the high casting yields.
The Vacuum Die Casting Process
Vacuum pressure casting (VPC) is a relatively new die casting process that delivers enhanced strength and minimal porosity. This process is similar to low-pressure die casting, except the locations of the die-cast mold and molten metal bath are reversed. The cylinder chamber can become a vacuum, which forces the molten metal into the mold cavity. This design reduces turbulence and limits the amount of gas inclusions. Vacuum die casting is especially beneficial in applications destined for post-casting heat treatment.
The Squeeze Die Casting Process
Squeeze casting was created as a workable solution for casting metals and alloys with low fluidity. In this process, the molten metal fills up an open die, which then squeezes closed, forcing the metal into the recessed portions of the molding. The squeeze casting process delivers extremely dense products and is a complementary process to subsequent heat-treating. The process is most often associated with molten aluminum and is used in applications that call for fiber reinforcement.
The Semi-Solid Die Casting Process
Semi-solid die casting, sometimes called Thixoforming, is another process that delivers minimal porosity and maximum density. A machine cuts the workpiece into smaller slugs, and then heated. Once the metal has reached the phase transition between solid and liquid, resulting in a somewhat slushy texture, a shot sleeve forces it into the mold cavity, where it hardens. The benefit of this is improved precision. Non-ferrous metals such as magnesium alloy and aluminum alloy are most often used with the semi-solid die casting process.
Advantages of Die Casting
Notwithstanding the specific process employed, die casting is widely used in metal part manufacturing, because of several significant advantages that it offers, including:
- High accuracy and repeatable reproduction of designs of varying complexity and level of detail
- The use of a single mold design (die set) to impart all features in one process
- Reduced cost from one process vs. several, as well as a reduction in waste material and scrap
- Faster production rates or speeds
Types of Alloys Used in Die-Castings
Aluminum
Aluminum is commonly employed in die-casting, but is prone to cracking or shrinking at high temperatures, so it is often alloyed with copper or silicon. Combining aluminum with these metals greatly increases its hardiness and fluidity. Since it has high dimensional stability, aluminum is used to create components with thin walls and complex shapes. Due to its corrosion resistance, aluminum is also beneficial in components that will face exposure to thermal or electrical energy.
Copper
Copper-based alloys are also commonly employed in die-casting. Many of these alloys are quite durable, making them an effective choice for mechanical products. Due to copper’s very high resistance to corrosion, it is often used to create plumbing and electrical material.
Zinc
Zinc die casting is a relatively easy process as it maintains high strength at room temperature, but can be alloyed with aluminum to further improve these qualities. Zinc has a lower melting point than aluminum and is suitable for hot-chamber casting. It is also valuable in the manufacture of products that require high precision and sturdiness, such as connectors and gears.
Magnesium
Magnesium has a high strength-to-weight ratio despite being a relatively light alloy, and it is useful for die-casting operations that require thin-structured walls and close precision.
Considerations When Choosing Die-Casting Alloys
The function and use of the final product will dictate die-casting alloy selection. For example, if the component requires high strength and corrosion resistance, an aluminum or copper based alloy could be an effective choice. Another consideration is production volume. With proper maintenance, aluminum die-casts can have a life of approximately 100,000 cycles, while zinc molds can last up to one million cycles before being replaced. For long-term, high-volume production, it may be more cost-effective to use alloys that maximize the life of the molds.
When considering various fabrication methods, it may be helpful to examine the advantages and disadvantages of using a die-casting process.
Potential advantages include:
- Dimensional Strength: die-casting parts are stronger than plastic components.
- Rapid Production: die-cast components can be produced in high volume with relatively little tooling or machining.
- Smooth Surfaces: the die-cast process can create finished parts with curved or seamless surfaces.
- Accuracy: die-casting parts can be created with close adherence to specifications.
Possible disadvantages include:
- High Volume: smaller production runs may reduce cost-effectiveness.
- Limited Metal Fluidity: alloy malleability varies, which can limit the complexity and shape of the finished product.
- Size and Weight Limits: a casting machine’s capacity limits the range of product dimensions.
Summary
Die casting is a very effective manufacturing process to produce parts that have accurate dimensions and sharp definition in large quantities, made possible using reusable metal dies. To locate potential sources for die casting services other manufacturing service, visit our capabilities.