Die Casting Process, Types, Properties, and Metals – Everything You Need to Know

Some of the key benefits of die casting as a metal fabrication method are its reliability, speed, and cost-effectiveness. If anything, about 77% of aluminum parts in automotives are die-cast. This shows you the significance of the die casting process. This article explores all there is to know about the die-casting process.

What is Die Casting?

The process of die casting entails the molding of metal components from molten metal under certain conditions. Metals are heated at high temperatures and cooled in a mold cavity that resembles the shape and size of the end product.

The mold cavity used in die casting is made of two dies made of steel. The cavity contains the mold on the bottom, while the top die acts as the cover. 

Apart from die casting, there are other casting methods such as sand casting used to create metal parts from molten metal. Regardless, die casting is preferred since it is efficient. Still, the process of making an individual die is relatively expensive and time-consuming.

The Die Casting Process

The Die-Casting Process

Die casting can be carried out in a few steps. Each step in this process has control measures to ensure to optimize production and achieve quality results.

Pre-production processes

Every production process has mandatory preparatory procedures. In this process, the standard operations are strategizing, making prototypes, and material selection. These are requisite steps because they influence the quality of the finished product. 

Preparation of the mold

Die casting is beneficial since the dies can be reused. ScienceDirect reported that a single die used for aluminum die casting can make over 150,000 castings before it needs repair or replacement. Industry 4.0 practices are improving the damage tolerance of dies to increase this number for effectiveness and profitability.

There are two types of molds; custom and generic. Custom molds are much more expensive to make as compared to generic ones. 

Since making the mold is a one-time thing, this stage in the subsequent casting involves readying the mold for the next casting cycle. Technicians will open the mold cavity for aeration, lubricate it, and close it for the next injection.

Molten metal injection

After the desired metal is gathered, it is heated under extreme temperatures in a furnace until it melts. Moreover, additives such as fluxes are also added to the furnace to remove impurities from the metal. 

The different melting points of the various metals used in die casting are as follows;

MetalMelting Point  
Aluminum 660.3 °C (1220°F)
Zinc419.5 °C (787.2°F)
Copper1,084 °C (1,983°F)
Magnesium650 °C (1,202°F)

Injecting the molten metal into the die requires many safety precautions to avoid accidents. At this stage, the liquid metal is transferred to the shot sleeve where it will be pushed to the mold cavity under high pressure. The molten metal has to be delivered at high pressure to ensure it fills up the die cavity.

The die-casting process produces parts with smooth finishes and intricate details due to the controlled injection of molten metal. Aspects like insulating the shot sleeve and maintaining high pressure ensure that the molten metal does not solidify prematurely. 

Cooling

Cooling

Primarily, steel is the go-to die material due to its high thermal conductivity. This means steel transfers the heat of the molten metal to the die cavity. Resultantly, this promotes rapid solidification. 

Cooling of the molten metal is also facilitated by coolants such as water. Also, note that the type of cooling will depend on the specific type of die-casting process in use. This is because of the different parameters required for each process.

Ejection

On the die cavity, there are ejector pins that push the solid part out. For ejection to happen, the mold cavity has to open first. Technicians have to be sure that the molten metal has solidified completely before opening the cavity.

If the cavity is opened before the part has cooled and solidified properly, it has to be melted and taken through the whole process again. At that stage, the part is considered an unsuccessful cast.

Post-production processes

Parts that are ejected from the cavity are not ready for use. This is because they usually contain excess metals that need to be trimmed in a process called de-flashing. For small-scale productions, de-flashing is done manually. However, large-scale production lines use methods such as cryogenic deflashing.

Types of Die Casting You Should Know

hot/cold chhamber die casting

There are four major types of die casting processes. While the objective is the same, each method has specific conditions and procedures for how it works. Generally, the major difference lies in the injection and cooling methods.

Hot chamber die-casting

The most popular method of die casting. In hot chamber die casting, the molten metal is rapidly pushed to the cavity via the shot chamber. The most suitable metals in this process are magnesium and zinc.

Cold chamber die-casting

In cold chamber die casting, the delivery approach is different. Rather than pushing the metal to the die using the shot chamber, a ladle is used to pour the metal directly into the die cavity. This promotes better control of the casting process. The cold chamber technique is suitable for metals with higher melting points like aluminum and copper.

Low-pressure die casting (LPDC)

This method of die casting relies on pressure to fill the molten metal in the die. The pressure used ranges anywhere between 1 and 15 psi. Specifically, LPDC represents the different ways in which the feedstock is delivered to the die.

Gravity die casting (GDC)

GDC is the other die casting method that represents the different approaches to feeding molten metal into the die cavity. Here, the molten metal is let to flow naturally to the die without any artificial pressure. 

Properties of Metals Used in Die Casting

On top of having low melting points, the metals used in die casting have other properties that make them suitable.

Excellent mechanical properties

For metals, mechanical properties describe their behavior when exposed to mechanical force. Die-casting metals have excellent properties such as strength, ductility, malleability, and stiffness.

Enhanced fluidity

This characteristic of metals defines their ability to flow in the molten state. Flow dynamics are essential to facilitate filling the die cavity. Metals used in die casting can be said to have low viscosity.

Low shrinkage

The mold/die cavity used in the die-casting process has set dimensions depending on the shape of the part. This means the die should generate the part with those dimensions. This is only possible if the metal has a low shrinkage rate.

Conclusion

Die casting is among the most common ways of fabricating metal parts from molten metal. Before it was invented, producing complex shapes out of metal was a major challenge. This explains the growing demand for die-cast parts in major industries. Learn more about our die casting services here.

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