Coining is a closed die forging process, in which pressure is applied on the surface of the forging in order to obtain closer tolerances, smoother surfaces and eliminate draft. Closed die forging is a process in which forging is done by placing the work piece between two shaped dies. This process may be done in hot or cold working conditions, but is predominantly a cold work process.
In coining, pressure is applied to a portion or the entire surface of a forging. The surface of the metal work piece is positioned parallel to the dividing line of the forging. This process is considered a method of precision stamping, in which the metal work piece is subjected to high stress to induce plastic deformation in the shape of the die.
This article will elaborate on the technique of coining, aong with its advantages and applications.
Technique of Coining
Completely closed dies are used for this process. High pressure is applied on the closed die containing the metal work piece. As a result of the high deformative stress, the metal conforms to the shape of the die. Coining produces finer details and provides a smooth surface finish to the metal work piece.
Coining can be done using a gear driven press, a hydraulic press, or a mechanical press. Lubricants are not used in coining as they are incompressible. The presses required for coining are high tonnage presses in order to produce plastic deformation of the metal work piece.
Advantages of Coining
The advantages of coining process are listed below:
- Produces finer and detailed surface finish
- Provides accurate bends in a consistent manner
- Does not require expensive machinery
- The work hardened surface can resist impact and abrasion
- Eliminates the need for complex finishing processes
- Plastic flow reduces the surface grain size and work hardens the surface.
Industrial Applications
Some of the typical applications of coining are listed below:
- Minting of coins and medallions
- Making of jewelry
- Making badges, buttons, precision-energy springs
- Making complex electronic parts
- Making precision parts that require finer polished surface finishes.