Permanent Metal Mold Casting Process (7 things to know!)

Permanent metal mold casting process
Casting of soldier using permanent mold casting process

What is Permanent Mold Casting process?
Permanent Mold Casting process (also known as Metal Mold Casting process) is a metal casting process which uses permanent molds (or reusable molds) that are usually made of metal.
In simple words, the mold in which the molten metal is to be poured is made up of metal (and not sand).

As the mold is made up of metal, it can be used repeatedly for multiple castings.
Steel, iron or other metals or ceramics are used for preparing the mold.

Permanent mold casting process (6 steps)

The steps involved in permanent mold casting process are mentioned below

Step 1: Creating a mold

The very first step in permanent mold casting process is to create a metal mold.

Permanent metal mould casting process

Generally, the molds are machined from two separate blocks.

Both these parts are machined very precisely so that they fit together and its opening and closing is also easy and accurate.

The gating system is made in the mold by machining process only.

All these steps lead to increase in the initial cost of permanent mold casting process.

But the advantage is that, once the mold is manufactured, it can be used for preparing many castings.

But due to high temperatures of molten metal, all the molds decay gradually at some point and they cannot be used for manufacturing good quality castings.

The total number of castings that can be manufactured by using a particular mold before its replacement is termed as mold life.

Various factors affects the mold life, such as;

  • Temperature of molten metal
  • Mold material
  • Casting metal, etc.

Step 2: Spraying the slurry of refractory materials

Metal mould casting process

In the second step, the liquid slurry of refractory materials is sprayed on the internal surface of the permanent mold.

This slurry of refractory acts as a lubricant which helps in easy removal of the casted component.

Also, by applying the refractory slurry, the mold life also increases.

Step 3: Pouring a molten metal

Permanent mold casting process

The parts of the mold are brought together and they are closed by some mechanical means.

Now before pouring the mold, the metal mold is preheated so that the molten metal can flow easily in the mold cavity.

Generally the molds are heated at the temperature around 175 °C.

Preheating also reduces the thermal gradient caused by the very high temperature of molten metal and the lower temperature of metal mold.

Thus preheating of metal mold increases the mold life.

After preheating the mold, the molten metal is poured into the mould cavity.

Step 4: Solidification

metal mold casting

After the pouring of molten metal, it is allowed to solidify in the mold.

Step 5: Removing the casting

Permanent mold casting process (2)

Generally the solidified part is removed from the mould before much cooling occurs. This is done to prevent the contraction of solid casting in the mold.

Also the cracking of casting can be prevented in this way.

Step 6: Finishing of casting

Permanent mold casting process (3)

The final casting is separated with the help of ejector pins built inside the mold.

In manufacturing industries, sometimes disposable cores are also used along with the permanent metal mold for achieving complicated shapes. 
This type of process is known as semi permanent mold casting.

Now let’s discuss the Advantages and Disadvantages of permanent mold casting process.

Advantages of permanent mold casting

The advantages of permanent metal mold casting process are mentioned below.

  1. By using a permanent mold casting process, the automation in manufacturing can be achieved.
  2. Production rate is higher in the permanent mold casting process.
  3. The rejection of castings is very less as most of the castings are accurately manufactured.
  4. Good dimensional accuracy is achieved with the help of metal mold casting process.
  5. Excellent smooth surface finish is obtained.
  6. The casted component has uniform properties throughout the component.

Disadvantages of permanent mold casting

The disadvantages of permanent metal mold casting process are mentioned below.

  1. For steel castings, a specific refractory material like graphite is required.
  2. Permanent mold casting process is suitable for casting metals which have low melting temperatures.
  3. Initial cost of equipment and mold making is higher.
  4. This process is not economical if a small number of castings are needed to be manufactured.
  5. Limited size of castings can be manufactured by this process.

Applications of permanent mold casting

The applications of permanent metal mold casting process are mentioned below.

  1. Permanent mold casting process is used for casting metals like aluminum, magnesium, and copper alloys.
  2. Metal like zinc, tin, iron, steel and lead alloys are also casted in graphite molds.
  3. Various parts like gears, engine pistons, pipe fittings, wheels, gear housing, etc can be manufactured using permanent mold casting.

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