Exploring The Casting Processes of Different Types of Die Casting Techniques

Die casting is the most common metal parts fabrication method. The goal of this process is to turn molten metal into different shapes. Technicians use various machines and follow different processes to achieve the desired shape. As such, die casting can be classified into several types. In this article, you will learn all about these types and how they happen.

What is Die Casting?

Die Casting

As we started by saying, this process aims to shape molten metal into desired shapes. Die casting has been used in various industries, such as automotive, to manufacture parts with intricate geometry. 

Select types of metals are heated to their melting point and transferred into a die cavity either under high pressure or by gravitational flow. The die cavity consists of a mold that the molten metal mimics as it solidifies. Essentially, this is the basic idea behind die-casting. 

Types of Die-Casting 

The different types of die-casting result from the various ways in which this process occurs. These types also account for the diverse parts that the casting technique can produce. Factors such as the type of metal, desired shape, and other parameters influence the die-casting technique to be used. Let’s learn about these types.

Cold chamber die-casting

This technique is set apart because the furnace used to melt the metal is separate from the casting machine. In other words, the molten metal comes into contact only during the injection stage of the process. This means that the chamber (die cavity) will be cold when the metal is being ladled in it. 

The cold chamber is used to cast metals with high melting points, such as brass, magnesium, and aluminum. This is to avoid damaging equipment with the high heat required to melt these metals.

The casting process 

The casting process

In the cold chamber die-casting process, the four basic steps that occur are as follows;

  • Heating the metal to its melting point,
  • Transporting the molten metal into the casting machine
  • Ladling the metal into the shot chamber
  • Plunging the metal into the die cavity

Evidently, cold chamber die casting is relatively straightforward. Depending on the production scale, these steps are either manual or automated. Automation helps increase production quality, while a manual approach is used when quantity is not the main focus. 

Still, with the right system, machines, and personnel, automated systems can produce high-quality and quantity die-cast parts using the cold chamber approach.

Hot chamber die-casting

This die-casting method differs from the cold chamber technique in that the plunger is connected to the furnace using the shot chamber. As soon as the metal melts, it is forced into the die cavity by pressure or gravity. 

In contrast, the hot chamber method is used for metals with a low melting point, such as zinc and lead. The furnace’s connection directly to the shot chamber ensures a continuous supply of metal to mold, making hot chamber die casting effective in terms of cost and speed of manufacturing.

The casting process

In hot chamber die casting, the process is related to that of cold chamber, with slight differences. It follows the following steps;

  • The die cavity is closed, and the ports opened,
  • Molten metal is plunged into the die cavity via the gooseneck
  • Pressure is maintained until the metal solidifies
  • Ejector pins are opened to release the cooled part

During the process, high pressure is required to force the liquid metal into the cavity and ensure it fills it. 

High-pressure die casting (HPDC)

Both cold and hot chamber die-casting techniques require pressure when injecting liquid metal into the die cavity. However, the pressure can be relatively small, and the casting will take place. On the other hand, in high-pressure die casting, the pressure required is relatively high, reaching up to 10,000 Mpa.

A hydraulic shot chamber applies this pressure in this process. Due to these high pressures, HPDC can be used to achieve highly precise shapes, details, and complex shapes. The process of a hot chamber resembles the regular cold or hot chamber process, with slight differences in the application of high pressure. 

Squeeze die casting

This technique combines forging and casting. It is unlike other die-casting processes because the die needs to be preheated. Squeeze casting is also known as liquid forging, and it is further classified into direct and indirect die casting.

Direct squeeze casting

The approach used to shape metals in this subcategory of squeeze casting can be likened to regular forging. Here, the molten metal is poured on the bottom half of the die cavity, and the top is closed under high pressure. The squeezing action allows the liquid metal to fill the cavity before solidification begins.

Indirect squeeze casting

This technique can be likened to high-pressure die-casting since it uses a shot chamber similar to that technique. The shot chamber can be vertical or horizontal. The only difference is that the velocity is lower in this process compared to the pressure flow used in high-pressure die-casting.

Low-pressure die casting

This type of die-casting technique is unusual since the furnace containing the liquid metal is placed below the die cavity. A gas supplied to the enclosure injects the molten metal into the cavity, allowing the metal to flow into the cavity at a pressure of about 10 psi. During the process, the pressure from the gas holds the liquid metal steady as it solidifies.

Gravity die casting

Gravity die casting

GDC is a low-pressure casting process that involves transferring the molten metal directly to the die cavity. This is the traditional approach of gravity die casting. To improve the efficiency of the cast, the die can be titled before the molten metal is poured in.

The speed of the die and tilting angle control the liquid metal’s flow. Usually, the die is returned to its previous position after the molten metal is poured in. Tilting die casting is also known as metallic static casting.

Semi-solid Die Casting

This is another die-casting process that includes both casting and forging techniques. It differs quite a bit from the regular die-casting processes in several ways. For one, the metal is partially melted. Rather, it is heated to a semi-solid state (40 – 60 % solid) and injected into the die cavity.

The casting process 

The semi-solid die casting process is considered a casting process since the metal is not in a liquid state when it is injected into the die.

This semi-solid die casting is categorized into;

  • Thixomolding – A semi-solid die-casting process of molding semi-solid magnesium 
  • Rheocasting – The metal is melted completely and then cooled into a slurry of semi-solid metal for casting.
  • Thixocasting – This approach uses a precast billet that is heated into a semi-solid state by induction heating and then transferred into the die.

Vacuum die casting

In this type of die casting, a vacuum is used to remove gases from the liquid metal before it is transferred into the die cavity. The process is similar to other die-casting processes but with the addition of a vacuum system.

The vacuum system’s significance is to improve casting quality when the vacuum removes gases and impurities from the molten metal. Other benefits include reduced oxidation, improved surface strength, mechanical stability, and reduced porosity.

Conclusion

The various types of die-casting processes allow you to choose the most suitable technique based on what you are casting. Each method has advantages and recommended applications based on its capabilities. Therefore, always discuss the most appropriate casting approach with your metal parts manufacturer beforehand.

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