"A TWO-SIDED FLAT PRODUCT AND I TS MANUFACTURING PROCESS "

FIELD OF THE INVENTION

The present invention is related to a two-sided flat product. Specifically, is related to a coin, a medal which comprises two materials, such as a non-metal and a metal .

The present invention is also related to a process to manufacture the two-sided flat product abovementioned, by combination of coin minting and mechanical joining by interface contact pressure between the centre and the ring, at room temperature, in a single press stroke.

STATE OF THE ART

Proof coins for collection purposes make use of a very restricted set of metals that are mainly taken from groups 10, 11 and 12 of the periodic table, after exclusion of the radioactive (Ds, Rg and Cn) , toxic (Cd) and liquid (Hg) metals.

The main reasons behind the choice of metals belonging to the above-mentioned groups of the periodic table, to manufacture these products are corrosion and wear resistance, high fracture toughness and good formability at room temperature resulting from the fact that all of these metals, with the exception of Zn, have face centered cubic (FCC) crystal structures. Another important reason is the fact that some of these metals (Pd, Pt, Ag and Au) are very expensive and, therefore, appropriate for high denomination coins for collection and investment. Globalization and the opportunity of selling high denomination coins around the world justify the reason why mints are nowadays strongly committed to the development of innovative coins made from alternative materials.

This trend is here to stay as it was recently shown by the internationally awarded "Chinese Porcelain Vase Qing Dynasty" coin manufactured by the Mint of Poland in 2016 that incorporates a fine porcelain relief etched on the reverse of a silver coin.

The first attempt to use polymers as alternative coining materials was made in 2015 by the German central bank who issued the 5 Euro 'Planet Earth' coin.

Although 'Planet Earth' may be considered the first polymer-metal coin, the use of polymer is marginal and is limited to a relatively thin ring.

The use of polymers in coin minting of the present invention is entirely different from that employed in tokens for shopping trolleys, which are produced by plastic injection moulding.

The process of manufacture of the two-sided flat product of the present invention is based on an analytical model developed by the inventors. The analytical model enables the selection of the appropriate geometries of the polymer and metal blanks. The accuracy of the analytical model and the overall feasibility of the bi-material coin concept are validated by means of finite elements and experimentation . Still, Kiran and Shaw (1983) developed an analytical model that allowed understanding flat disc minting, specifically a coin minting as a net-shape precision forming process involving indentation, gross upsetting and interaction between adjacent relief coin features. The model was developed for metal coins under plane strain deformation conditions and the reliefs were approximated by simple saw tooth profiles characterized by a pitch and a feature included angle.

In the following year, Delamare and Montmitonnet (1984) applied the upper bound method to develop an analytical model for calculating the energy and shape of a blank to strike a metal coin with a central circular design and an outer annular legend. Finally, Brekelmans et al . (1988) applied the upper bound method to setup an analytical model to calculate the pressure for producing a conical axisymmetric relief in the centre of a metal coin.

The abovementioned analytical models cited in prior art are limited to applications concerning about minting of mono-metallic coins. There are no analytical models and finite element investigations focused on the design and fabrication of polymer-metal coins.

In the present invention, is proposed a two-side flat product two-sided flat product which forms a flat plane and comprises a metal at least non-metal part, in particular the non-metal part consisting a polymer or a composite material, the metal part entirely surrounding the non-metal part along the flat plane such that, i) in the referred two sides, the non-metal part and the metal part form the surface of the flat plane, and ii) the metal part thereby forms a radial boundary of the flat plane. Is also proposed an analytical model that allows to calculate and select the interference between the non-metal part and the metal part, i.e. the analytical model associated to the process to obtain the two-sided flat product allows fixing the non-metal part to the metal part by calculating the interface contact pressure after unloading.

The different solutions of the state of art mentioned are where, such as the case of the "planet Earth" coin, use form fitting to mint the coin and only apply a thin ring of the polymer between the metal ring and the metal centre .

Under these circumstances, the main purpose of this invention is to give a step forward, extending the technology of coin minting to bi-material coins having a large area ratio between the non-metal part and the metal part, with high reliefs imparted on the surfaces of the non- metal part.

The present solution overcome such issues, namely with the use of a non-metal material, such as a polymer or a composite, which enables joining a metal part with a non- metal part, (particularly in the laminated polymer or in a composite material), with durability and resistance properties. In another aspect the two-sided flat product of the present invention can be produced on the presses that are normally used in the manufacture of the current coins.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention a two-sided flat product, preferably a coin or a medal, that it forms a flat plane and it comprises a metal part and at least non-metal part, in particular the non-metal part consisting of a polymer or a composite material, the metal part entirely surrounding the non-metal part along the flat plane such that, i) in the referred two sides, the non-metal part and the metal part form the surface of the flat plane, and ii) the metal part thereby forms a exterior edge of the flat plane.

In an inventive aspect of the flat product of the present invention, it is obtained by the following steps: i. providing a metal blank with at least one hole and at least non-metal blank, each non-metal blank fitting a corresponding hole with an clearance, the clearance being such that simultaneous mechanical lock of each hole of the metal blank and corresponding non-metal blank, obtaining a two-sided flat blank;

ii. minting of the two-sided flat blank with two punches and a collar , wherein the collar consists of a die surrounding the two-sided flat blank when of minting with a reverse punch and a obverse punch, such reverse punch making contact first on an exterior edge of the metal blank, thereby a) each non-metal blank forming a non-metal part, b) the metal blank forming a metal part and thus c) the two-sided flat blank forming the two-sided flat product.

This embodiment provides that the at least two different materials that are comprised in the two-sided flat product remain permanently fixed. Step i) provides that with the clearance - which is calculate by the analytical model - enables the non-metal and the metal part to be joint to each other after, and on step ii) and prevents, in a preferred embodiment, the non-metal part to have an inadmissible buckling deformation.

It is also an object of the present invention process for manufacturing a two-sided flat product, preferably a coin or a medal, characterised in that it comprises the following steps:

i. providing a metal blank with at least one hole and at least non-metal blank, each non-metal blank fitting a corresponding hole with a clearance, the clearance being such that simultaneous mechanical lock of each hole of the metal blank and corresponding non-metal blank, obtaining a two-sided flat blank;

ii. minting of the two-sided flat blank with two punches and a collar , wherein the collar consists of a die surrounding the two-sided flat blank when of minting with a reverse punch and a obverse punch, such reverse punch making contact first on an exterior edge of the metal blank, thereby a) each non-metal blank forming a non-metal part, b) the metal blank forming a metal part and thus c) the two-sided flat blank forming a two-sided flat product.

Preferably, the manufactured product is the two- sided flat product of the present invention, in any of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The description below is made with reference to the accompanying drawings which are presented solely as reference, having no limitative character, and wherein: Figure 1 (a) - is a schematic representation of the new proposed two-sided flat product on step (i) of the punch stroke with the notation utilized in the analytical model;

Figure 1 (b) - is a schematic representation of the new proposed two-sided flat product on step (ii) of the punch stroke with the notation utilized in the analytical model.

Figure 2 - represents the process curve showing the interference i as a function of the clearance j between the non-metal part and the metal part blanks.

List of reference numbers:

- a metal part after coining (1);

- a non-metal part after coining (2);

- a metal blank (3) ;

- a non-metal blank (4);

- a collar ( 5 ) ;

- a reverse punch (6) ;

- a obverse punch (7);

- a clearance between the non-metal blank and the metal blank ( j ) ;

- a clearance between the metal blank and the collar

(jc) ;

- a critical clearance between non-metal blank and the metal blank (j _cr) ;

- a interference (i);

- a critical interference (i _cr) ;

- outer radius of the metal blank (R _mo) ;

- radius of the non-metal blank (R ₀₎ ;

- final radius of the two-sided flat product (R) ;

- thickness of the metal blank (t _mo) ;

- thickness of the non-metal blank (t ₀₎ ; and

- final thickness of the two-sided flat product (t) ; DE TAILED DESCRIPTION OF THE INVENTION

The more general and advantageous configurations of the present invention are detailed below in accordance with other advantageous and/or preferred embodiments of implementation of the present invention.

In a preferred embodiment the minting is performed at room temperature, without any adaptation of the tools and presses utilizes in current minting. The use of a polymer or a composite material in the present invention do not modify the conditions of manufacture.

In a preferred embodiment on the two-sided flat product each non-metal part after coining (2) is centred relating to the boundary formed by the metal part after coining ( 1 ) .

To calculate the clearance is necessary to apply the developed analytical model. In fact, joining by forming is carried out simultaneously with coin minting with the reverse punch (6) and the obverse punch (7) to produce a mechanical lock between the non-metal part after coining (2) and the metal part after coining (1) by interface contact pressure (step i) .

In the present invention the two-sided flat product has a large area ratio between the non-metal part after coining (2) and the metal part after coining (1) and high reliefs imparted on the surfaces of the polymer. The non-metal part after coining (2) and the metal-part after coining (1) are locked together during coin minting by interface contact pressure resulting from radial interference between the two parts.

The process to manufacture the usual and circulating bi-metal coins (for example, the 1 and 2 Euro coins), are based in form-fit joints resulting from the plastic deformation of the ring into a groove placed on the outside edge of the centre part. The analytic method proposed and associated to the present invention considerer that Ro is the radius of the non-metal blank (4) with thickness to, and R _m o is the outer radius of the metal blank (3) with thickness t _mo , j is the clearance between the non-metal blank (4) and the metal blank (3) and j _c is the clearance between the metal blank (3) and the collar (5) . The thickness t and the radius R relating to the coin and i is the interference between the non-metal blank (4) and the metal blank (3) at the end of punch stroke.

The analytical model considers plastic deformation of the non-metal blank (4) and of the metal blank (3) to be homogenous and isotropic under axisymmetric material flow conditions. Volume incompressibility during plastic deformation of the metal blank (3) allows writing its final thickness t as a function of the main geometric parameters of Figures la and lb, as follows,

The same procedure applied to the plastic deformation of the non-metal part leads to the following equation, Matching equations (1) and (2) because must be identical at the end of punch stroke, one obtains the following relation between the clearance j and the interference i,

The above equation gives rise to the process curve, which is plotted as a black solid curve in Fig. 2. The vertical-axis interception of the process curve is the maximum achievable interference (i _max ) and the horizontal- axis interception corresponds to the maximum clearance (j _max ) that is capable of ensuring a mechanical lock by interface contact pressure between the non-metal blank (4) and the metal blank (3) .

The process curve in Fig. 2 provides the design values for the bimaterial polymer-metal coins and its position will move upwards or downwards by decreasing or increasing the initial radius of the non-metal blank (4) or the ratio between the thickness of the polymer and the thickness of the metal blanks (3) .

As shown in Fig. 2, above the critical values of clearance (j _cr ) and interference (i _cr ) the non-metal part after coining (2) will buckle under uniform radial edge compression imposed by metal part after coining (1), triggering a concave shape in the non-metal part after coining (2) . In a preferred embodiment of the present invention, the interference (i) and the clearance between the non-metal blank and the metal blank (j) are substantially close to the respective critical values, but without promoting a buckle on the non-metal part after coining (2) .

In a preferred embodiment the two-sided flat product of the present invention is obtained by the described process and for step i) is necessary previously calculate the clearance j, which is necessary to estimate the interference i and the resulting interface contact pressure. The referred clearance j is obtained from a solution of the following equation:

Where,

R _m o is the outer radius of the metal blank (3); t _m o is the thickness of the metal blank (3);

Ro is the radius of the non-metal blank (4);

to is the thickness of the non-metal blank (4); j _c is the collar clearance between the metal blank (3) and the collar (5), the collar (5) consisting of a die component surrounding the two-sided flat blank when of minting with the reverse punch (6) and the obverse punch (7) ;

i is the interference; and

j is the clearance between the non-metal blank (4) and the metal blank (3) .

The interference depends on the initial clearance and initial thicknesses of the non-metal blank and the metal blank, and the initial clearance between the metal blank and the collar. The analytical model calculates the interference as a function of the above-mentioned geometric parameters. Absence of interference leads to separation of the two parts after coin minting while large interferences give rise to buckling of the non-metal part. In a preferred embodiment of the present invention on the two-sided flat product each non-metal part consists of a polymer, in particular one of the following: a thermoplastic laminated polymer or a thermoplastic polymer, providing a multiply uses, as such incorporate different elements preferably such element consisting of a security, optical, graphic, design or electronic element, whereby the additional element is embedded in the thermoplastic laminated polymer during lamination of such thermoplastic laminated polymer, providing enhanced security of the coin and subsequently reduce the risk of counterfeiting.

In another preferred embodiment at least one non- metal part of the two-sided product consists of a composite material, providing a multiply uses, as such incorporate different elements preferably, such elements consisting of a security, optical, graphic, design or electronic element providing enhanced security of the coin and subsequently reduce the risk of counterfeiting.

In another preferred embodiment in piece blank of the two-sided flat product the non-metal blank are such that the two sides have no rimmed edges, to ensure that the minting and the mechanical joint are effective.

In another preferred embodiment the plane forms a flat disc, such disc preferably being circular.

In a preferred embodiment the metal part is of a single metal or a metal alloy, preferably the metal being a non-toxic element from the groups 10, 11 or 12 of the periodic table. The main reasons behind the choice of metals belonging to the above-mentioned groups of the periodic table, to manufacture this products are corrosion and wear resistance, high fracture toughness and good formability at room temperature resulting from the fact that all of these metals, with the exception of Zn, have face centered cubic (FCC) crystal structures. Another important reason is the fact that some of these metals (Pd, Pt, Ag and Au) are very expensive and, therefore, appropriate for high denomination coins for collections and investment.

In a preferred embodiment the non-metal part is transparent providing a enhanced security.

In another embodiment the single non-metal blank is circular, and the corresponding metal blank is a circular ring with a corresponding circular hole.

In an inventive aspect of the process of the present invention, in step i), it is performed for a single non-metal blank (4) and corresponding non-metal part after coining (2), and where the respective hole of the metal blank (3) is centred in such metal blank (3), and the referred clearance j is obtained from a solution of the following equation :

Where

R _m o is the outer radius of the metal blank (3); t _m o is the thickness of the metal blank (3);

Ro is the radius of the non-metal blank (4);

to is the thickness of the non-metal blank (4); j _c is the collar clearance between the metal blank (3) and the collar (5), the collar (5) consisting of a die component surrounding the two-sided flat blank when of