The main technological steps of the coin manufacturing process are:
- coin dies manufacturing;
- blank production;
- coin stamping.
Coin dies production actually starts in the artistic department, from the plaster model created by an artist, based on a special design. The plaster model is several times the final piece, so the future coin is as beautiful as the artist’s talent makes it.
Next, with the plaster model, a much harder one, in bronze or epoxy is produced.
The bronze or epoxy model is used on a pantograph, which reduces the big image onto a steel master die. The original model is mounted on one spindle, the blank is mounted on another, and as both turn in synchronized manner, one end of an arm reads the original and the other end of the arm, provided with a graver, carves in steel the reduced duplicate.
The master die is then patiently retouched by an engraver, who eliminates the processing defects and emphasises certain relief details “missed” by the pantograph. This is the final step in obtaining the coin design.
After being finished by the engraver, the master die is heat treated, covered with a protection coat and polished with diamond paste until a high quality striking surface is obtained.
With the heat treated positive master die, a proof negative die is obtained via hubbing. The negative die is also heat treated and used for hubbing a working positive die. This positive die is finally used for obtaining serveral working negatives. These working dies are the actual dies which will strike coins.
Coins are obtained by stamping coin blanks (the process is also called “coining”). Metal stripes are first feeded into a rolling machine and the process repeats until the plate gets the necessary thickness. A press cuts coin-shaped discs (called blanks) out of these plates .
In order to improve the material flowing and to ensure adequate filling of the relief by the striking process, blanks are put onto a rotary milling machine, which puts a ridge around their edge. If necessary, this is also the moment where inscriptions can be done on the edge. Afterwards, blanks are degreased.
Blanks are stamped into coins on high productivity presses.
In order to avoid circulation of defective coins, a quality control is performed after stamping. After the quality check, coins are packet in tubes and prepared for delivery.