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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.

Additive manufacturing is proposed as a novel alternative to coin blank’s production routes based on rolling, blanking and edge rimming. The presentation draws from laser powder bed fusion of cylinders, slicing into individual coin blanks by electro discharge machining and surface preparation by polishing, to coin minting in a laboratory press-tool system. Special emphasis is given to material deposition and coin minting due to the originality of producing coin blanks with complex intricate contoured holes and to the necessity of subjecting the additive manufactured coin blanks to extreme compressive stresses that are typical of coin minting. Numerical and experimental results confirm the excellent performance of the additive manufactured coin blanks. The new design layouts included in the additive manufactured coin blanks open the way to produce high value-added singular collector coins, which are disruptively different from those available in the market nowadays.

This paper describes a numerical and experimental route for application and validation of finite elements in coin minting based on an industrial case study. The numerical work encompasses virtual prototyping of the dies from three-dimensional models prepared by the sculptor and finite element simulation of the coin minting process. The experimental work comprised independent determination of the stress–strain curve of the disk material by means of stack-compression tests, verification of the force values provided by the industrial coin minting press and validation of the numerical estimates of the progressive filling of the relief coin features and of the force vs. die stroke evolution. Results show that finite elements can be successfully applied to predict material flow and filling of the intricate relief coin features as well as to estimate the required coin minting forces before fabricating the actual dies.

This paper presents a new finite element based design procedure for correcting the coining die profiles in order to optimize the distribution of pressure and the alignment of the resultant vertical force at the end of the die stroke. The procedure avoids time consuming and costly try-outs, does not interfere with the creative process of the sculptors and extends the service life of the coining dies by significantly decreasing the applied pressure and bending moments. The numerical simulations were carried out in a computer program based on the finite element flow formulation that is currently being developed by the authors in collaboration with the Portuguese Mint. A new experimental procedure based on the stack compression test is also proposed for determining the stress-strain curve of the materials directly from the coin blanks.

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.