Flash Forging and Flashless Forging

What is flash forging?

In the forging process, when the upper die applies the pressure on the hot object inside the bottom die, excess metal squirts out of the cavity as a thin rubber slit is called flash and the process is called flashless forging. Flashes are forms in the closed die forging. These flashes are getting cool very fast and help to cool the main part as well.

Before going to study flash forging, let’s discuss what is closed die forging?

Closed Die Forging

Closed die forging is also known as Impression die forging. In closed die forging, the lower die is attached to the anvil, and the upper die or hammer die is movable. During the process, the upper die or hammer die strikes on hot metal, which is placed on the lower die. Due to the striking of the hammer, the metal flows in the die and fills the cavity as per the design of the die.

This striking occurs only for milliseconds depending upon the type of die and metal. The metal strike depends on the size of the die and the type of metal.

When the metal fills the die cavity, excess metal is squirt out of the cavity and this is called flash. Flash gutter is used to prevent the excessive formation of flash. This flash can remove by the machining process generally by trimming operation.

In closed die forging, flash cools faster than other metals because it directly comes into contact with the environment. This metal is strong as compared to metal in the mold. This flash forces the metal to cool down and helps to fill the cavity faster.

Function and importance of flash forging:

1. Flash cools faster as compared to the rest of metal because it directly gets in contact with the environment. So, it gets stronger and helps other metals cool.

2. Flash regulates or controls the flow of metal. Due to that, flow resistance increases, and pressure builds upon the rest of the metal in the die. So, metal fills the die cavity at a faster rate. 

Forging pressure mainly depends upon the flash thickness and flash width. When the flash thickness decreases and flash width increases, forging pressure is automatic increases. So, there is a chance to fill the die cavity in faster.

3. Flash acts as a safety valve for the rest of the metal in the die.

What is flashless forging?

In closed die forging, deformation takes place in the die only, and there is no excess metal squirt during the deformation. So, this forging is called flashless forging.

In actual practice, a thin layer of metal or flash forms in-between clearance of upper or hammer punch and die. This layer of flash can be removed by the blasting process, and it does not require any trimming operation.

This flashless forging is carried out in certain temperatures in between cold working and hot working.


  1. No waste of material
  2. Energy Saving
  3. High production rate
  4. High Dimension accuracy
  5. The finished part has a clear shape
  6. High Strength to finished part
  7. The finished part is more ductile


  1. In the automotive industry, for manufacturing of connecting rod and special piston used in a racing car.
  2. Tracks in a military vehicle.
  3. Aerospace component.

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