What is Die Casting?
Die casting is a metal casting process that involves feeding molten nonferrous alloys into dies under high pressure and at high speed to rapidly create molded products. The main materials used in die casting are alloys of aluminum, magnesium and zinc.
The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process.
Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter, and tin-based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high-volume production.
Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low.
It is especially suited for a large quantity of small- to medium-sized castings, which is why die casting produces more castings than any other casting process. Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency.
How Does Die Casting Work?
Die casting is a manufacturing process in which molten metal is poured or forced into steel molds.
The molds also known as tools or dies are created using steel and are specially designed for each project. This allows each component to be created with accuracy and repeatability.
The die casting process involves several steps, including mould design, metal preparation, injection, casting, and finishing.
#1. Mould Design.
The initial step in the die casting process is creating a mould called a die. This mould is usually made from steel or aluminium and is designed to withstand the high temperatures and pressures of the die casting process.
The mould design begins with developing a CAD design of the required mould. This design is then used to create a mould by CNC machining, which is further used in the casting process.
#2. Metal Preparation.
The next step is to prepare the metal for injection. This metal is typically an alloy, such as aluminium, magnesium, or zinc. The metal is melted in a furnace and then poured into a ladle.
#3. Injection Process.
Once the metal is in a liquid state, it is injected into the mould under high pressure. The molten metal fills the mould cavity and cools to create the desired shape.
#4. Casting Process.
After the metal has cooled and hardened, the mould is opened, and the part is ejected. Ensure that the part has cooled entirely before handling to avoid any potential injuries.
#5. Finishing Process.
The final step in the process is to finish the part. Surface finishing plays a vital role in die casting, as it can impact the durability and function of the part. Standard finishing processes include anodizing, powder coating, wet plating, and many more.
Types of Die Casting
The aim of all die casting process varieties is to cast a mold using injected molten metal. Various die casting processes may produce better results than competing techniques depending on the type of molten metal, the part geometry, and the size of the part. Here are the types of die casting.
Hot-Chamber Die casting
The hot chamber die casting process is ideal for materials with low melting points, such as magnesium alloys, tin, zinc, and lead.
This is done to prevent damaging the pump, which could occur when it comes into contact with metals or alloys with a higher melting point.
The injection of the melted metal into the die is achieved by applying pressure from a hydraulic system.
Cold Chamber Die Casting
Cold chamber die casting is the ideal method when working with materials that have a high melting point, like aluminum.
Since the high temperature required to melt these materials can damage the pumping system, this procedure is perfect for such metals.
This is a high-pressure die casting process that involves pouring the melted material into a cold chamber and then injecting it into the die.
The hydraulic system used in a cold chamber process is similar to that used in a hot chamber process. However, a higher pressure of between 2000 and 20000 psi could be necessary.
Different Variations of Die Casting
The following variations were suitable to tackle defects, mishaps, distortions, and other problems that might arise during the casting process.
Semisolid Die Casting(SSDC)
This process, also known as thixoforming, involves heating the shot, which consists of small pieces, to the liquid-solid phase transition temperature (the thixotropic state).
This allows the pressure to feed the material into the cavity. Since most of the melt expansion occurs at or shortly after phase change, this process minimizes shrinkage, shortens processing times, and increases precision due to the lower operating temperature.
Vacuum Die Casting
It is a special way to make high-quality metal parts with better precision. The charge is sucked up by a tool placed above the molten reservoir, using a vacuum delivered to the cavity.
They remove the air and gases from the mold before pouring in the hot metal. This makes the parts better and more precise.
Vacuum die casting is commonly done with aluminum and magnesium. It helps create strong and detailed parts that are used in cars, airplanes, and electronics.
Squeeze Die Casting
In this process, the tool is filled and then squeezed shut, forcing the fill into small cavity sections that wouldn’t typically fill easily. This casting is ideal for use with metals with a high level of viscosity like zinc, nickel, and copper.
Gravity or Low-pressure Die Casting
This less intricate method reduces tooling costs and equipment complexity by allowing parts with thicker portions to be low-pressure cast using gravity-fed (or even hand-ladled) fill.
Ideally, this method should be used with symmetrical, round aluminum die casting components.
Materials used in Die Casting
When you are ready to begin your die-casting project, one of the most important decisions you will make is choosing the suitable material.
The material you select must be able to withstand the high temperatures and pressures of the die casting process, as well as the demands of your end-use application.
Furthermore, it is important to choose a material that is compatible with the die casting operation you have selected.
With so many factors to consider, working with an experienced die-casting partner who can help you navigate the many options and make the best decision for your specific project is essential.
However, aluminium, magnesium, and zinc are three of the most popular die casting materials, as they all are strong and lightweight:
Aluminum die casting alloys
Aluminum is one of the main die casting metals, and aluminum alloys are used in cold-chamber die casting. These alloys typically contain silicon, copper, and magnesium.
Aluminum die casting alloys are lightweight and offer good dimensional stability, which makes them a good choice for complex, fine-featured parts. Other advantages include good corrosion resistance, temperature resistance, and thermal and electrical conductivity.
Common die casting aluminum alloys include:
- 380: A general-purpose aluminum alloy which balances castability with good mechanical properties. It is used in a very wide variety of products, including engine brackets, furniture, electronics enclosures, frames, handles, gearbox cases, and power tools.
- 390: An alloy with excellent wear resistance and vibration resistance. It was developed specifically for the die casting of automotive engine blocks and is also suitable for valve bodies, impellers, and pump housings.
- 413: An aluminum alloy with excellent casting properties. It has good pressure tightness and is therefore used for products like hydraulic cylinders, as well as architectural parts and food and dairy industry equipment.
- 443: The most ductile of die casting aluminum alloys, this alloy is suitable for consumer goods, especially those that require plastic deformation after casting.
- 518: A ductile aluminum alloy with good corrosion resistance. It is used in a variety of products, including aircraft hardware fittings, ornamental hardware, and escalator components.
Magnesium die casting alloys
Magnesium is another very popular die casting material. It is even lighter than aluminum, with the added advantage of being highly machinable making it suitable for cast parts that require additional machined details or machined surface finishing.
A major advantage of magnesium die casting alloys is their suitability for hot-chamber die casting, making them easier to use than die casting metals like aluminum. Other elements in magnesium alloys include aluminum, zinc, manganese, and silicon.
Common magnesium die casting alloys include:
- AZ91D: A general-purpose alloy with good castability, corrosion resistance, and strength-to-weight ratio. Applications include mechanical and power-train components.
- AM60: An alloy with good castability, strength, vibration dampening, and ductility. It is used in automotive components such as seat frames and panels.
- Rare earth alloys AS41B and AE42: Alloys with superior temperature resistance, as well as good creep resistance, corrosion resistance, and ductility. Both alloys are found in engine parts.
Zinc die casting alloys
Another major category of die casting metals is zinc alloys. Castable in a hot-chamber die casting machine, zinc is the most manufacturer-friendly of die casting materials and offers other benefits like impact strength, ductility, and suitability for plating.
Due to its castability, it also results in minimal die wear. Zinc is heavier than aluminum and magnesium and is usually alloyed with aluminum, copper, and magnesium.
Common zinc die casting alloys include:
- Zamak 3: A general-purpose zinc alloy that is easy to cast and offers excellent dimensional stability. In North America, more than two thirds of zinc die castings use Zamak 3. Example uses include ceiling fans and plumbing components.
- Zamak 2: A slightly stronger and more expensive alloy with added copper content. It is often used to produce tooling for plastic injection molding.
- Zamak 5: A zinc alloy close in composition to Zamak 3 but with greater tensile strength and lower ductility. Popular for products like automotive parts and wheel balancing weights.
Other die casting alloys
Other die casting materials include copper, silicon tombac, lead, and tin alloys, in addition to zinc-aluminum alloys.
Copper alloys exhibit high strength, hardness, and corrosion resistance, in addition to excellent dimensional stability. Meanwhile lead and tin alloys are very dense and can be resistant to corrosion.
Zinc-aluminum alloys are recognizable by the ZA prefix; those with a lower aluminum content can be hot-chamber die cast, but those with 11% or more typically cannot.
How Do You Design A Mold For Die Casting?
When designing molds for use in die casting, it is important to consider factors such as wall thickness, draft angles, and the placement of gates and runners.
You should also factor in the material being used and any specific requirements for strength, durability, or resistance. Here are a few tips for designing a mold for die casting.
#1. Design and Specification.
The journey of creating a die casting mold commences with meticulous planning and mold design. Engineers and designers collaborate to conceptualize the product and translate its specifications into a detailed design.
This involves understanding the geometry, tolerances, and intricacies of the final component. CAD software plays a pivotal role in this phase, enabling the creation of 3D models and intricate designs that adhere to industry standards and the specific requirements of the end product.
In addition, it is important to know what type of die casting machine will be used in the manufacturing phase, a hot chamber die casting machine or cold chamber die casting machine.
#2. Tooling And Mold Base Preparation.
Once the design is finalized, the focus shifts to the die cast tooling and mold base preparation. Skilled toolmakers meticulously craft the mold components, including the mold die cavity and core, using high-grade steel or other materials capable of withstanding high temperatures and pressures.
Precision machining techniques such as CNC milling and EDM (Electrical Discharge Machining) ensure accuracy in shaping these components, maintaining the integrity of the intended design.
#3. Mold Assembly and Finishing.
With the individual components crafted, the assembly of the die cast molds takes center stage. This intricate process involves meticulous fitting, aligning, and securing the various parts together.
Every detail matters, from ensuring proper venting and cooling channels to integrating ejector pins and slides that facilitate the ejection of the final part.
Finishing touches and surface treatments are applied to enhance the mold’s durability, prevent corrosion, and facilitate smooth operations during casting.
#4. Testing and Validation.
Before the mold is put into full-scale production, rigorous testing and validation are imperative. Trial runs are conducted to assess the mold’s functionality, integrity, and the quality of the cast parts it produces.
Adjustments and fine-tuning may be necessary to optimize the mold’s performance, ensuring that it meets the required specifications and consistently produces high-quality parts.
#5. Production and Maintenance.
Once the mold passes the validation phase, it’s ready for deployment in the production environment.
The die casting process begins, where molten metal is injected into the mold cavity under high pressure, taking the shape of the mold to form the desired component.
Regular maintenance and upkeep of the mold are crucial to sustain its longevity and preserve the quality of the manufactured parts.
This includes cleaning, lubrication, and periodic inspections to identify and address any wear or potential issues during mass production.
Advantages of Die Casting
#1. Complex Thin-walled Parts.
Aluminun die casting can manufacture complex-shaped and light components but with an excellent strength to weight ratio, giving it an edge over other metal molding castings and investment castings.
Die casting parts with aluminum alloys can have a thickness as low as 0.5mm; the wall thickness of cast parts made with zinc can even be as low as 0.3mm.
#2. High Mechanical Properties.
Die casting products feature excellent mechanical properties. As the liquid metal solidifies under high pressure, the product appears to be fine, compact, and crystalline.
Die casting parts are rigid with high hardness and strength. Also, they have improved durability and high conductivity.
#3. High Dimensional Tolerance.
Die casting produces parts with high durability and dimensional accuracy. Even when exposed to harsh conditions, the parts maintain their dimensional accuracy over time.
As a result, die casting is used in fabricating complex and internal parts of machines that require high standards of precision and accuracy.
Die casting maintains tighter tolerances over other casting processes. That is, parts are produced with minimal variations. The typical tolerance class of die castings is IT13~IT15 in GB/T 1800-2009.
Higher precision can reach IT10~W 11. Therefore, the excellent dimensional accuracy of die casting avoids the need for machining and improves the utilization of the alloy.
#4. Smooth Surfaces.
Die casting parts have a smooth, consistent crystalline surface. Die casting process alloys molten metal alloy to fill up the dies and create the exact shape.
Therefore, provided the die is well shaped and the process is in the right condition, the parts will be fine and smooth.
Because of making glossy parts, there is less need to proceed with additional post-processing operations, except for custom needs.
What’s more, after die casting is done, products can be shipped off for delivery. This can reduce the total cycle production time.
#5. Cost-Effective for Mass Production.
Since the surface of die castings is often smooth with excellent mechanical features, die-cast parts often require less machining.
In some cases, no machining at all. As a result, there is less need to spend on secondary operations. The ability of die casting to reduce post-processing costs helps ensure its cost-effectiveness.
Notably, die casting machines, molds, and other related types of equipment are quite expensive. However, mass production aids in better distribution of cost through the production process, thereby making the die casting process economical.
Disadvantages of Die Casting
#1. Easily Generate Porosity.
In the die casting process, molten metal rapidly fills the mold cavity at high speed, but the cavities lack gas permeability. Hence, gas bubbles that affect the structural integrity of fabricated parts tend to get trapped within castings.
The presence of gas cavities in die castings would affect such parts when exposed to harsh conditions, such as hardening by heat treatment.
Additionally, such parts are predisposed to machining difficulties. Therefore, the machining allowance of the parts should be kept minimal.
If not, the hardened layer on die casting surfaces would be removed, thereby exposing the surface.
#2. Usually Support Non-ferrous Metals Only.
Generally, die casting is perfect for non-ferrous metals with lower melting points than ferrous metal alloys. However, the process supports ferrous alloys like iron and steel.
Ferrous metals have very high melting points and low corrosion resistance, which causes low die life. Therefore, manufacturers always choose non-ferrous metal alloys for die casting.
Moreover, casting ferrous metals come with lots of complexity and several unforeseen complications. Consequently, manufacturers stick to non-ferrous metals only for die casting operations.
#3. Not Suitable for Low Volume Production.
Die casting is not a practical choice for low volume production, because the tooling cost of die casting machines and maintenance are quite expensive. Therefore, the process is costly and seems complex for small-scale production.
However, large-scale production becomes cost-effective as costs are well distributed over the many items produced.
Suppliers don’t recommend die casting services for low-scale projects, as the process appears to be more expensive than other production methods.
#4. Low Die Life.
High melting point metals and alloys compromise the effectiveness of steel dies. These metals, like copper, have extensive requirements to resist thermal deformation.
The continued presence of alloys with high melting points strains the molding die, thereby reducing its durability.
#5. Large Capital Investment.
Unlike other casting processes, the casting machine, the dies, and other related equipment for die casting are costly. Without the essential equipment, it is impossible to carry out die casting.
Although cheap materials like zinc are used to cut costs, the overall production process is still expensive. The only time die casting becomes cost-effective is in large volume production.
Applications of Die Casting
Die casting has many applications in various industries. Some of the most common applications include:
- Automotive: Many automotive parts, such as gears, pistons, and housings, are made using die-cast parts.
- Aerospace: Die-cast aluminum is especially popular for aerospace components due to its lightweight.
- Electronics: Electronic housings and connectors are commonly made from die-cast aluminum, zinc, or magnesium, providing good shielding from radio frequency interference (RFI) and electromagnetic interference (EMI).
- Construction: Window frames, cladding, and other structural components are commonly made from die-cast metals, especially aluminum.