Die Casting Process (Step by Step Explanation with Diagram)

6 cylinder engine made by die casting process

What is Die Casting Process?
Die casting process is a type of permanent mold casting process in which a large amount of pressure is applied to the molten metal that forces it to flow in the mold cavity.
Because of the large amount of force applied to the molten metal, high accuracy can be achieved on the final casting product.

Few important things about die casting

  • The die used in the die casting process is made up of metal.
  • The mass of the die is kept far greater than the mass of the casting.
  • Due to the large amount of pressure and direct contact of the molten metal, wear of die may occur.
  • But if the die casting process is done in a maintained and controlled way, then it can last up to hundreds of thousands of cycles.
  • The casting products manufactured by using die casting process may vary from extremely small to around 23 kg.
  • Wall thickness of around 0.5 mm can also be achieved by using the die casting process.

Die Casting Process Steps

8 steps of Die casting process are mentioned below.

Detailed Step by step process of die casting is discussed below.

Step 1: Mold preparation

In die casting process, the first step is to prepare the mold.

The mold should be made in two halves such that it can be opened and closed so that the castings can be removed easily from the mold.

The mold used in die casting process is made up of steel.

Step 2: Making the Gating system

In order to insert the molten metal in the mould cavity, the gating system is required.

The mold of die casting itself consists of all the components of gating system.

In some manufacturing industries, multi cavity dies are used in order to manufacture several castings in a single cycle.

Unit dies which are combination of smaller dies are also used to manufacture castings in some industries.

The mass of the mold (or die) is kept far greater than the mass of casting to be manufactured.

Because of the exposure to higher temperatures of the molten metal, the wearing of die is a big problem.

However, this can be avoided upto some extent and die can be used for hundreds of thousands of cycles, if well maintained manufacturing practice is carried out.

Step 3: Lubricating internal surfaces

The internal surface of the mold is lubricated to prevent the sticking of metal with the mold.

This lubricant also helps in cooling down the dies.

Step 4: Holding the molds in die casting machines

Die casting machine

The opening and closing of die casting mold is necessary for the removal of final castings. But along with this, it is also very important that there is enough force that can be applied to hold the two halves of the mold together during the injection of the molten metal.

The pressure exerted on molten metal is so high that it can separate the two halves of the dies.

So die casting machines are used to hold the molds together against such forces.

There are various types of die casting machines which are designed to withstand the different range of forces.

The clamping forces of these machines vary from 25 tons to 3000 tons.

Step 5: Injection of molten metal

In the manufacturing process, die casting is basically of two types.

  1. Hot chamber die casting
  2. Cold chamber die casting

These processes are different from each other, but they have one thing in common. And that is they both employ a piston or plunger to force molten metal to the mold cavity.

die casting process

The pressure required to force the molten metal to the mold cavity can range from 7 MPa to 350 MPa.

This high pressure is necessary to apply in order to get the perfect surface details on the metal castings.

Step 6: Solidification

Once the mold cavity is filled with molten metal, the pressure is maintained until the hardening of the metal.

The molten metal is allowed for solidification in the die.

Step 7: Removing the castings

After this process, the mold is opened and the casting is removed.

The ejector pins attached with the casting helps in removing the metal casting from the mold.

After removing the casting from the mold, the lubricant is again applied to the internal surface and then the die is clamped together.

The number of cycles for which die can be used, depends on the details of each specific die casting manufacturing technique.

In some cases, high production rate can be achieved by using a die casting process.

Step 8: Insert molding process (optional)

Insert molding process

In die casting process, the parts like shaft, bushings, bolts, etc can be inserted into the mold and the metal casting can be formed around these parts.

This process is also known as insert molding, in which these parts look like a single piece casting after solidification.

Also in order to provide stronger contact with the casting, the joining parts can be grooved or knurled.

The above image shows the grooved bolts which are attached into the metal casting using Insert Molding Process.

Advantages of Die Casting process

The advantages of die casting process are mentioned below.

  1. By using the Die casting process, a close tolerance of cast components can be achieved.
  2. The components with thin walls can also be manufactured by using a die casting process.
  3. Castings manufactured by using die casting process have superior mechanical properties.
  4. Labour cost is less as most of the work is on high automation.
  5. High production rate can be achieved using the die casting process.
  6. This process is economical for large batch production.

Disadvantages of Die Casting process

The disadvantages of die casting process are mentioned below.

  1. The thin metal marking is usually formed at the parting lines, which is required to be trimmed out from the final casting.
  2. The mold is not permeable. Hence the vents are necessary to be provided which helps in removing the trapped hot gases.
  3. In die casting process, the equipment cost and setup cost is high.
  4. Die casting is not suitable for small scale production work.
  5. This process is also not suitable for all types of metals.

Applications of Die Casting process

The applications of die casting process are mentioned below.

Die casting process is applicable in industries for manufacture following things;

  • Tools 
  • Toys
  • Magnetos
  • Crank cases
  • Machine components
  • Various housings
  • Vehicle parts
  • Zip fasteners
  • Head lamps
  • Decorative items for automobiles, etc

External links:
Engine made using Die casting: Image by 160SX, CC BY-SA 3.0, via Wikimedia Commons.

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