What is Drop Forging? (3 Types of Drop Hammers Explained!)

Drop Forging hammer

What is Drop Forging?
Definition: Drop Forging (also known as hammer forging) is a forging process in which the hammer is raised and then it is dropped on the workpiece to deform it into a desired shape.

The die used in drop forging process of steel (or other metal) is made in two halves, upper die and lower die.

The workpiece is positioned on a lower die (stationary die) which is kept on the anvil and the upper die is forced on this workpiece using a drop hammer.

Drop forging process is widely used in the automotive industry for manufacturing of crankshaft, gears, stub-axles, etc.

Well, this was just an introduction. Now further I have explained 3 different types of drop forging hammers that you must see.

Drop forging hammers

There are basically 3 different types of hammers used in drop forging (or hammer forging) process.

  1. Gravity drop hammers (or board hammers)
  2. Power drop hammers (or steam hammers)
  3. Counterblow hammers

Let’s see each of these drop forging hammers one by one.

#1) Gravity drop hammers (or board hammers)

Gravity drop hammers (or board hammers)

Gravity drop hammers (also known as board hammers) work on the principle of gravity.

The gravity drop hammer is the simplest type of hammer used for applying the impact force to the workpiece.

As shown in the diagram of gravity drop hammer, it consists of a free falling ram weighing 180 kg to 4500 kg.

The workpiece which is to be forged is kept on the lower die, and the upper die is attached with the ram which is connected with the board.

The upper die as well as the ram is raised upward with the help of friction rollers that grip the board (see diagram).

This raised ram contains gravitational potential energy. So when it is released, it falls back on the workpiece due to gravity.

The gravity hammers can strike the workpiece between 60 to 150 blows per minute.

The energy imparted to the workpiece due to the weight of the ram can be calculated by using a simple equation of gravitational potential energy.

Total energy = potential energy = mgh

Where;
m = mass of ram, board and upper die,
g = gravitational acceleration, 9.81 m/s2
h = height from where the ram freefalls

This potential energy of the falling ram causes the workpiece metal to deform plastically.

Gravity drop hammers are generally used for mass production of complex shapes.

#2) Power drop hammers (or steam hammers)

Power drop hammers (or steam hammers)

Power drop hammers (also known as steam hammers) are generally used to apply force to large and heavy workpieces.

In steam hammer forging, the steam is used to produce a high amount of forging force.

The lower die is kept on the anvil and the upper die is attached with the ram.

This ram is forced downward with very high force with the help of steam pressure along with the gravity force.

The upward movement of the ram is also made by the reverse steam pressure (see diagram).

The ram used in power drop hammers weights from 225 kg to 22500 kg.

The total energy produced by power drop hammers is the sum of kinetic energy and potential energy.

Total energy = kinetic energy + potential energy = ½ mv2 + mgh

Where,
m = mass of ram, board and upper die,
g = gravitational acceleration, 9.81 m/s2
h = height from where the ram freefalls
v = velocity of the ram falling downward

#3) Counterblow hammers

Counterblow hammers has two ram that approach each other horizontally and vertically to forge the metal piece.

Counterblow hammers operate at high speeds and they transmit less vibrations to the base.

The Counterblow hammers has a capacity range upto 1200 kJ.


External links:
Drop forging hammer: Image by Rainer Halama, CC BY-SA 3.0, via Wikimedia Commons

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