What is Metal Forging?
Definition: Forging is defined as a metal forming technique in which the shape of metals is changed by applications of compressive forces.
For applying the compressive force to the steel or any other metals, the forging hammers, forging presses, ring rollers, etc are used.
Various useful shapes can be produced by metal forging due to the plastic deformation of the metal.
By metal forging, various parts like aircraft landing gears, jet engine shaft, turbine shaft, automobile parts and railroads, levers, crankshaft, gears, etc can be manufactured.
Well, this was just an introduction to forging. Now let’s see how the forging is done in industries.
Metal forging methods
There are mainly 5 metal forging methods that are used widely.
- Open die forging (Smith forging)
- Closed die forging or impression die forging
- Flashless forging
- Cold forging
- Warm forging
These methods are used mainly in forging of steels, hence they are also known as steel forging methods.
Let’s see each of these methods one by one.
#1) Open die forging (Smith forging)
Open die forging (also known as Smith forging) is a forging process in which the deformation of a workpiece takes place between the dies that do not completely enclose the workpiece.
In open die forging, the metal is heated above its recrystallization temperature which improves its plastic deformation with less force.
Open die forging is basically used to forge larger metal pieces that are not possible to forge with closed die forging.
#2) Closed die forging or impression die forging
Closed die forging (also known as Impression Die Forging) is a process in which the deformation of a workpiece takes place between the dies that completely encloses the workpiece.
In closed die forging process, the pair of matched dies having contoured impressions are used.
The dies used in impression die forging are such that it restricts the flow of metal within the die during its deformation.
The metal fills up in the space within the die cavity as it gets compressed into the molds.
Because of this, the impression of the die is left on the workpiece and in this way, the final forged metal is obtained.
Sometimes two or more progressive impressions are used in conjunction to get the desired impression on the workpiece.
During the cold forging process, some excess metal will flow out of the die in the area between the two dies.
This section is like a flash (or fin) produced at the parting line around the workpiece.
#3) Flashless forging
Flashless forging is an advanced form of closed die forging in which the entire volume of metal is contained within the die, and no material is allowed to escape the forging operation.
In flashless forging, no material can leave the mold. So there is no flash (or fin) formation in this forging process.
Flashless forging process is difficult as it requires a perfectly calculated amount of raw metal to be kept in the die.
If the quantity of metal kept in the mold is less, then it will not fill the mold completely. And if the quantity of metal is more than required, then it will create unnecessary forces on the dies.
#4) Cold forging
Cold forging is a type of die forging process which is carried out at (or near) the room temperature and the deformation of metal takes place when a high amount of compressive forces are applied to it.
By using cold forging operation, the small components like cups, bolts, etc can be manufactured.
The main advantage of cold forging is that it saves time and cost for heating the metal, plus it also hardens the metal.
Cold forging process also avoids surface oxidation that occurs at high temperature and hence it provides better surface finish.
The disadvantage of cold forging is that it requires a high amount of compressive forces and the plastic deformation of the material is also limited.
#5) Warm forging
Warm forging is a type of die forging process which is carried out above the room temperature but below the recrystallization temperature and the plastic deformation of metal takes place when compressive forces are applied to it.
The temperature range in warm forging is higher than the temperature of cold forging and lower than the temperature of hot forging.
Warm forging is carried out in order to get the advantages of both hot forging and cold forging.