What is Open Die Forging (or 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.
Open die forging (or Smith forging) is a hot working process, in which the standard flat dies, V-shaped dies or Swage dies are used.
In open die forging, the metal is heated above its recrystallization temperature which improves its plastic deformation with less force.
The dies used in open die forging are generally flat, but some dies can have specific shapes for different applications. For example, a die may have a round shape or concave shape, or convex shape.
Open die forging is basically used to forge larger metal pieces that are not possible to forge with closed die forging.
The simple type of Smith forging process is also called upsetting forging in which the metal piece is placed between the two flat dies and its height is reduced by compressive forces.
As the height of the workpiece is reduced by the compressive forces, its width increases since it has constant volume.
Types of open die forging
Open die forging is mainly classified into 3 main types.
Let me tell you a few important things about each type of open die forging process.
Cogging is a type of forging process in which a flat or slightly contoured die is used to forge a workpiece by decreasing its thickness and increasing its length.
Generally the cogging process is used to properly size the raw workpiece to its required dimensions.
As shown in the diagram above, the metal is advanced along its length after the compression is being done.
The compression process or forging process is then repeated for another section of the workpiece.
The distance that is travelled by the die in forward direction on the workpiece between each forging step is called bite.
For longer workpieces, the cogging process can be done on smaller machinery with less power and force.
In some forging operations, cogging is included as one of the steps in shaping the metal to a specific dimensions.
Sometimes, the final product is made just by cogging process only.
Fullering operation is an earlier step to prepare the metal for further forging processes.
Fullering operation is generally used when the metal forming process requires several forging operations to get the finished part.
Die having a convex surface is used to forge the metal piece using a fullering operation.
Because of the convex dies, the material flows in an outward direction on both sides (see above image).
Edging is a type of open die forging process in which the forging of a workpiece is carried out at the edges.
In the edging process, a die with a concave surface is used to forge the workpiece.
The edging of the material causes it to flow into the material from both the sides.
Fullering process and edging process are used to bulk distribute the metal at a particular area of the workpiece.