If you are new to die casting, then you should know that this is a versatile process used for creating engineered metal components. This is done by forcing molten metal into reusable steel molds under high pressure. Also known as dies, these molds can be designed to generate complicated shapes with extreme accuracy and repeatability. These components can be perfectly defined with textured or smooth surfaces. Also, they are appropriate for different serviceable finishes.
Among the products produced by the metalworking industry, die castings are the ones that are mass-produced and have the biggest volume. Die casting can be found in a wide variety of commercial, consumer, and industrial products. Die-cast components are essential for a wide variety of products, ranging from toys to automobiles. These parts can either be as complicated as a connector housing or it can be something as simple as a sink faucet.
Throughout the years, the die casting process has evolved from the use of the low-pressure injection method to advanced techniques such as high-pressure casting, which has a pressure of more than 4500 pounds per square inch. Other methods include semi-solid die casting and squeeze casting. With these modern techniques, generating high-quality castings with remarkable surface finishes is possible.
Advantages of Die Casting
Die-casting is an effective, economical process that provides a wide range of shapes and parts than any other manufacturing method. These components can last longer and can be designed to complement the appearance of the surrounding parts. There are a lot of advantages that designers can gain from these specific die-cast parts.
Die casting offers complicated shapes with closer tolerances than any other mass-production method. Minimal or no machining is needed. Thousands of similar castings can be generated before additional tooling is needed.
Dimensional Stability and Accuracy
Die casting can generate parts that are not only dimensionally stable, but durable as well. At the same time, close tolerances are maintained. Die-cast products are also heat resistant.
Weight and Strength
Die-cast parts are more durable compared to plastic injection moldings with similar dimensions. Thin wall castings are lighter and more durable than those produced with other casting methods. Additionally, since die castings do not include separate parts that are fastened or welded together, then the strength comes from the alloy instead of the joining process.
Die castings offer essential fastening elements including studs and bosses. Holes can be cored and created to tap drill sizes, or exterior threads can be cast.
Several Finishing Techniques
Die-cast parts can be generated with textured or smooth surfaces. They can be easily finished or plated with less surface preparation.
The Die-Casting Process
The die casting process is accomplished by injecting molten metal into a steel mold under high pressure. Die-casting machines are typically rated in clamping tons equivalent to the total pressure they can implement on the die. The sizes of these machines range from 400 tons to 4000 tons. No matter the size, the only basic difference in die-casting machines is the technique used for injecting molten metal into a die. The two techniques being used are the cold chamber and hot chamber methods.
In both of these manufacturing techniques, it is important that before the start of the casting process, the mold is sprayed with a release agent. This is done in order to make sure that the cast part can be easily removed from the mold. However, the alloy will not be poured into the mold cavity directly. First, it will be placed into the casting chamber of the die casting machine. Then, the piston will press the alloy into the mold using one or more channels. These two processes differ based on the structure of the casting chamber.
Hot Chamber Die-Casting Process
One major characteristic of hot chamber machines is that the liquid alloy is always in contact with the casting chamber. The melt flows through a valve, then towards the casting chamber. Here, the piston will press the closed die-casting mold at high speed. Hot chamber machines are mainly used for copper, lead, zinc, magnesium, tin, and other alloys with low melting points. This is because they do not easily damage and erode cylinders, metal pods, and plungers.
Cold Chamber Die-Casting Process
In cold chamber die casting machines, the casting set is placed outside the melt. To generate a component, the alloy is poured into the casting chamber and pressure will be applied into the die casting mold using the channels. The molten metal will be poured either by an automatic ladle or manually by a hand ladle. The cold chamber port will be sealed by a hydraulically operated plunger, forcing the metal into the locked die at extreme pressures. Cold chamber machines are more suitable for alloys with high melting points such as aluminum, copper, and many more.
In both of these processes, once the alloy has been pressed into the die casting mold, the component turns into solid due to the strong pressure. As a result, it will now be easier to open the latches of the mold. With the automatically operated ejection pins, the part with the gate can now be taken from the mold. Additionally, it can be processed further when necessary. Simply put, we can divide the casting process into the following steps. In reality, the process can be done in hundredths of a second or thousandths of a second:
- Filling of alloy on the casting mold.
- Solidifying the component under high pressure.
- Open the mold and take out the component.
Among these two processes, cold chamber die-casting is quite popular when it comes to the mass production of lighter metal die castings.
How Long Will the Process Take?
An entire cycle of die-casting can vary depending on the weight and size of the components. For small components that weigh less than one ounce, the process could take one second. For parts that weigh several pounds, it could take two to three minutes. This means that the die casting process is the fastest method for generating accurate non-ferrous metal parts.
Additionally, there are multiple variations of the fundamental process that can be utilized for generating casting for certain applications. For instance, squeeze casting. In this technique, molten alloy is cast without any instability and gas entrapment at extreme pressure to produce dense, high-quality components that are heat treatable.
How Aluminum Die Casting Differs from Other Metals
Aluminum is a lightweight alloy that has extreme dimensional stability which is perfect for thin walls and complicated shapes. Aluminum has excellent mechanical properties and corrosion resistance. It has outstanding strength at high temperatures with high electrical and thermal conductivity. Other cast materials are magnesium, lead, zinc, copper, and tin.
How to Select the Appropriate Die-Casting Alloy
Various aluminum alloys are composed of various elements such as iron, manganese, nickel, tin, silicon, copper, magnesium, zinc, titanium, and others. There are also a variety of aluminum alloys that can be die-cast from recycled or primary aluminum.
Construction of Die-Casting Die
Die casting tooling or die, is created from alloy tool steels. It consists of at least two parts including the cover half or the fixed die half, and the ejector half, used for the removal of castings. Also, modern dies may also include move-able cores, slides, or any other sections to create threads, holes, and other intended shapes in the casting.
Sprue holes along the fixed die half to permit the molten metal to get inside the die and fill the cavity. Usually, the passageways and inlets can be found in the ejector half. They can guide the molten metal towards the cavity. Dies also consist of locking pins to keep the two halves secure, openings for lubricant and coolant, as well as ejector pins for removing the cast part.
Once the die casting machine is already closed, the two die halves are kept secured. It is the machine’s hydraulic pressure that keeps them together. The surface where the fixed halves of the die and the ejector meet. The lock is also known as the die parting line. The overall estimated surface area of the component being cast is measured through the parting line. Consequently, the pressure needed by the machine for injecting metal into the die cavity controls the clamping force of the machine.
Different Kinds of Dies in the Die Casting Process
- Single-Cavity Die produces one part.
- Multiple-Cavity Die produces several identical parts.
- Unit Die produces a variety of parts simultaneously.
Materials for Die Casting
When it comes to die-casting, typically, non-ferrous metals are used in producing components. Furthermore, when choosing the alloy to use for a specific application, there are some factors to consider such as weight, budget, and material properties.
One of the most relevant materials is aluminum, followed by magnesium and zinc. Furthermore, lead, copper, and tin can also be used. These alloys have varied properties. For instance, aluminum and magnesium have a high melting point, while zinc and lead have a low melting point. SEI produces high-quality aluminum die-cast products. For more details, you can call us at (408) 374-1031.