Metal working – Method of mechanical manufacture – Assembling or joining
Patent
1998-06-03
2000-04-04
Bryant, David P.
Metal working
Method of mechanical manufacture
Assembling or joining
40 275, 428579, 428609, B21D 3900
Patent
active
060445416
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to the manufacture of bimetallic coins of the type having a centrally disposed core from one metal or alloy, and an annular outer member from another metal or alloy, the two being bonded to each other by plastic deformation under pressure.
One of the serious problems associated with the production of this type of coins is in that the bond between the core and the outer portion of the coin could be insufficient, particularly with respect to preventing axial displacement or even removal of the two sections from each other.
PRIOR ART
To this end, many solutions have been suggested in prior art. For instance, U.S. Pat. No. 632,938 (Greenburg) provides a reverse-bevelled inner edge on the annular member. A thicker and softer cylindical insert is positioned within the opening and is compressed such that the softer excess material of the insert flows over the bevelled edge of the annular member.
Japanese published application (Kokai) No. 58-3743 (Hisanobu) discloses a coin structure including a peripheral groove and key joint between the two elements. This is an expensive proposition requiring a complex manufacturing procedure which is particularly difficult if a very large number of coins is to be produced.
The same applies to other known proposals. For instance, Canadian Patent No. 1,103,431 (Hisanobu et al.) shows a method wherein two elements similar to the coin portions are coupled to each other by an insert which is forced by an impact to flow into grooves of the two elements. Such production is complex and expensive as an additional component is required for the manufacture.
Canadian Patent No. 1,195,058 (lelpo) proposes an interlocking arrangement much in the fashion of a tongue-and-groove which is difficult to apply in a mass production due to relative complexity of the structure. In this case, the outer ring has a circumferential tongue disposed along its interior on which is provided a series of teeth. The softer material of the insert is forced under pressure over the tongue and teeth. The tongue prevents axial separation of the elements while the teeth prevent relative rotational movement therebetween.
The coin shown in Canadian Patent No. 1,317,746 (Lasset et al.) is likewise complex and expensive to produce. Here, one of the elements, the harder inner member, is provided with a series of cavities into which the material of the softer outer ring is forced to flow by the minting operation.
A somewhat similar structure is disclosed in Canadian Published Patent Application No. 2,092,941 (Seuster et al.), where continuous or discontinuous grooves are proposed to be made in the edge portion of the core to receive impact forced flow of material of the outer ring. As in the preceding example, the provision of the cavities in the periphery of the inner core would be very expensive as it would require special tools. The difference between the inner diameter of the outer ring and the outside diameter of the core is relatively small. This often gives rise to difficulties when it is desired to feed the cores into the rings at a high speed as too many core blanks do not reach their position in the centre resulting in a high frequency of press stoppage.
European Patent Application No. 415,892 in the name of Lelpo describes a structure composed of an external ring and an insert. A series of spaced grooves is cut perimetrally in the edge surface of the ring. A perimetral ridge is formed on the edge surface of the insert. During the minting, plastic flow of material takes place from the ridge into the grooves in the external ring.
European Patent Application No. 678,251 in the name of Kim (Poongsan Corporation) describes a bimetallic coin and method of producing the same. The method involves forming a ring and an insert. A groove is formed on the edge of the insert. Emphasis is put on the thickness of the insert relative to the ring.
European Patent Application No. 080,437 (Instituto Poligraphico E Zecca Dello Stato) also describes a bimetallic composite coin blan
REFERENCES:
patent: 3636616 (1972-01-01), Remming
patent: 4472891 (1984-09-01), Ielpo
patent: 5094922 (1992-03-01), Ielpo et al.
patent: 5630288 (1997-05-01), Lasset et al.
Bryant David P.
Cozart Jermie E.
Royal Canadian Mint
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