The effects of striking force on microstructure and mechanical properties of coinage

Circulating coins have been produced by the United States Mint since 1792. Coinage designs begin with legislation passed by Congress. During the manufacturing process of coins, the force used during striking is determined based on denomination and design. It is desirable to minimize the striking force used to fill the design in order to decrease die wear. Besides design fill, the striking force can also affect microstructure and mechanical properties. Coin test pieces composed of a cupronickel clad material were produced as a part of a progressive strike where each denomination was struck at increasing incremental forces. Metallographic cross-sections were prepared to observe the clad response, the microstructure, and the transverse hardness properties of the coinage. The test pieces were analyzed to determine how the force applied during the manufacturing process affects the microstructure and mechanical properties and ultimately, the visual appearance of the coin. By characterizing the microstructural changes with increasing striking force, manufacturing processes can be optimized by utilizing the minimum force required during operation. Selecting the lowest force for striking will improve die life and reduce the number of dies necessary for coinage, one of the consumable items used during any coining production process.