Abstract
This chapter addresses ongoing developments in the engineering design of coin minting processes by application of the finite element method. The presentation draws from a brief overview on the fundamentals of the quasi-static and dynamic finite element formulations based on implicit and explicit solution procedures to the application of the quasi-static finite element flow formulation to the numerical simulation of coin minting. Validation of the results from numerical simulations involved 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, confirmation of the estimates of the progressive filling of the relief coin features, and comparison of the numerical and experimental force versus die stroke evolutions for coins with different diameters and relief profiles produced by the Portuguese Mint. Results show that finite element analysis can be successfully applied to predict material flow and filling of the intricate relief coin features, to estimate the required coin minting forces, and to improve the design of the dies before fabrication.
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Acknowledgements
Luis Alves and Paulo Martins would like to acknowledge the support provided by the Portuguese Mint (Imprensa Nacional Casa da Moeda) and IDMEC under LAETA-UID/EMS/50022/2013.
The authors would also like to acknowledge the technical assistance of Elisabete Novais and Nuno Caetano from Imprensa Nacional Casa da Moeda.
The support of Dr. Silvia Garcia and Dr. Alcides Gama from Imprensa Nacional Casa da Moeda is also acknowledged.
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Glossary
- Coin minting
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A net-shape metal forming processes in which a disk (coin blank) is compressed between two dies while it is being retained and positioned by a collar (side ring) with the objective of producing well-defined imprints of the dies in its opposite faces.
- Finite element method
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The governing equations of engineering problems solved by the finite element method are typically formulated by partial differential equations in their original form. These are rewritten into a weak form, such that domain integration can be utilized to satisfy the governing equations in an average sense. The domain integration is solved numerically and approximated by a summation over a number of elements utilized for discretizing the domain.
- Force–displacement curve
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A graphical representation showing the evolution of the compression force with the die stroke.
- Knuckle-joint press
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A special press design very appropriate for coin minting in which the connecting rod driven by the eccentric actuates a knuckle-joint system in order to provide a short stroke length and high load capacity.
- Stack compression test
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An alternative experimental procedure for evaluating the stress–strain curve of raw materials. The test makes use of circular disks that are cut out of the coin blanks and stacked to form a cylindrical specimen with an aspect ratio in the range of solid cylinders commonly employed in the conventional compression test.
- Stress–strain curve
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A graphical representation showing the stress response of a material and the corresponding deformation (strain).
- Tool system
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The main components of a coin minting tool system are the obverse and reverse dies and the collar (also known as side ring).
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Alexandrino, P., Leitão, P.J., Alves, L.M., Nielsen, C.V., Martins, P.A.F. (2018). Coin Minting. In: Davim, J. (eds) Introduction to Mechanical Engineering. Materials Forming, Machining and Tribology. Springer, Cham. https://doi.org/10.1007/978-3-319-78488-5_3
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DOI: https://doi.org/10.1007/978-3-319-78488-5_3
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