What is Closed 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.
Closed die forging (or impression die forging) process
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 the desired shape is not achieved in a single impression. So two or more progressive impressions are used in conjunction to get the desired impression on the workpiece.
You can see the closed die forging process of a crankshaft in the above image.
The desired shape of crankshaft is achieved in several stages.
If the metal is hot worked properly, then it improves its plastic flow as well as it reduces the forces on the dies and other tools.
By impression die forging process, the flash or fins are formed around the forged part.
During the design of a forging process, the volume of starting workpiece is kept slightly more than the volume of the closed die cavity.
As the die closes, the workpiece gets deformed into it and the impression of the die is formed on the workpiece. During this stage, some excess metal will flow out of the die in the area between the two dies.
This section is like a fin produced at the parting line around the workpiece.
The flash (or fin) is trimmed out afterwards by machining process.