A new type of bi-material coin

Abstract

This article presents a new type of bi-material coin with a polymer centre and a metal ring. The polymer-metal coin is fabricated by combination of coin minting and joining by forming in a single die stroke. The design of the coin is based on an analytical model built upon plasticity theory and plastic instability of circular plates under uniform radial edge compression. The analytical model and the bi-material coin concept are supported and validated by means of finite element modelling and experimentation. Destructive tests for pushing the polymer centre out of the metal ring demonstrate the effectiveness of the mechanical joint resulting from the interface contact pressure between the polymer and the metal. The new bi-material coin was developed to obtain new aesthetic effects for the collection market, and its polymer core can additionally be used for other applications such as the incorporation of advanced security features in high-denomination coins.