Development of an industrial process for minting a new type of bimetallic coin

Abstract

This paper introduces a technology for minting a new type of bimetallic coin. The coin is manufactured from two metal disks of different materials, one being very thin, joined together by mechanical means during the impartion of the surface details by the minting dies. The proposed technology is based on a multi-stage process consisting of three cold metal forming operations (preforming, rimming and coining) and one intermediate annealing before the coining operation. The main objective of this work is to present the theoretical and experimental results obtained during the development of the process, which are essential for producing this new type of bimetallic coin. The theoretical analysis was based on the utilization of the finite-element method to characterize metal flow, to establish the process sequence and related intermediate disk geometries, and to design an appropriate geometry for the mechanical joint between the two metal disks. Experiments consisted on the coinage of several bimetallic prototypes in order to confirm the theoretical predictions and to validate the new proposed technology, which latter can be seen as an alternative to the existing bimetallic coin technology based on the utilization of an outer ring and a central disk. © 1997 Elsevier Science S.A.