DEVELOPMENT OF AN INDUSTRIAL-PROCESS FOR MINTING A NEW-TYPE OF BIMETALLIC COIN

This paper introduces a technology for minting a new type of bimetalli c coin. The coin is manufactured from two metal disks of different mat erials, one being very thin, joined together by mechanical means durin g the impartion of the surface details by the minting dies. The propos ed technology is based on a multi-stage process consisting of three co ld metal forming operations (preforming, rimming and coining) and one intermediate annealing before the coining operation. The main objectiv e of this work is to present the theoretical and experimental results obtained during the development of the process, which are essential fo r producing this new type of bimetallic coin. The theoretical analysis was based on the utilization of the finite-element method to characte rize metal flow, to establish the process sequence and related interme diate disk geometries, and to design an appropriate geometry for the m echanical joint between the two metal disks. Experiments consisted on the coinage of several bimetallic prototypes in order to confirm the t heoretical predictions and to validate the new proposed technology, wh ich latter can be seen as an alternative to the existing bimetallic co in technology based on the utilization of an outer ring and a central disk. (C) 1997 Elsevier Science S.A.