Every coin originates with an artist's sketch. The engraver then uses this to create a virtual, three-dimensional image on the computer. If that corresponds to the desired result, a CNC milling machine is subsequently used to create a synthetic model with a diameter of approximately 20 cm on the basis of the data. This mainly serves to assess the result obtained. The engraver can modify this model by hand if need be, giving the relief a somewhat longer life in certain cases. Once the model is okay, the data can be used to reduce the effigy directly to coin size, i.e. milled in an untempered steel cylinder. If changes were made by hand, the model is scanned using a 3D scanner and reduced using the new data. The positive steel die thus produced is known as an original or reduction die. Between 8 and 14 hours may be required for reproducing all the minutiae of the model in mild steel. The steel die thus produced is known as an original or reduction die.
Behind the scenes at Swissmint
The finishing touches are applied by a master engraver, who, with infinite care, meticulously perfects the contours and fillet work. Afterwards, the reduction die is hardened, and during a multi-stage pressing procedure a positive die is produced. During this process, the hardened steel is pressed into mild steel, whereby an exact copy of the coin image is transferred onto the latter. Finally, this positive die is used to produce the actual negative minting dies. After pressing, these are turned into the correct shape, hardened, and chromium-plated to enhance durability. Depending upon the variety of coins being minted, the service life of a pair of minting dies generally suffices for producing up to one million coins.
Most of the requisite properties of minted coins must already be reflected in the size and weight of the circular minting blanks - also known as planchets or flans. After the changeover from silver to cupronickel coins in the year 1968, the Federal Mint ceased manufacturing planchets, but now rather orders finished minting blanks primarily from foreign suppliers of non-ferrous metals. In the production of blanks, the coinage metals are melted in electric smelting furnaces. A sample is extracted from the molten mass for the purpose of checking - and also adjusting if need be - the alloy composition by means of X-ray fluorescent spectrometer analysis.
The molten metal is cast into ingots, which are then reduced in thickness by being repeatedly passed through large rolling mills until the sheets are of the required dimension. The actual minting blanks are afterwards stamped out of these metal strips. A rimming machine is used to flatten the blanks between a block and a roller, thereby forming a smooth raised edge. This bead or rim is necessary to ensure that there is enough metal around the perimeter of the blanks in order that the edge of the coin can also be embossed or lettered during the subsequent minting process. The edge is intended to protect the coin image from wear. The finished blanks are then delivered to Swissmint in special steel containers.
Swissmint has six high-performance minting machines which operate with a pressure of 50 to 150 tonnes. Depending upon the coin, the coining presses mint between 150 and 750 coins a minute. The obverse, reverse and edge are invariably minted with a single stroke. Between the upper and lower minting dies there is a so-called ferrule or steel collar in which the blanks are held, and the diameter of which corresponds to that of the coins to be struck. The ferrule serves to retain the perfectly circular shape of the coin and to also prevent the metal from flowing outwards under the immense pressure of the dies. In the case of coins with a raised legend on the edge, for instance the 5-franc piece, a ferrule consisting of three segments is used so that after striking the coins can be ejected without damage to the edge.
On state-of-the-art packaging lines, the minted coins are first counted and then packed in rolls of 25 or 50 pieces respectively. Conveyor belts take the rolls to the scales and, once the correct weight has been confirmed, they are packed in collapsible cardboard boxes by an industrial robot. After the filled boxes have been sealed shut with bands, they are weighed once again, labelled and palletised. The entire packaging process is fully automated. At regular intervals, the pallets are collected by the Swiss National Bank and stocked in their safes. The SNB is also responsible for the distribution of the coins into the appropriate channels (bancs, post offices, etc.). It puts coins for a new year into circulation only when those from earlier years have been depleted for the unit in question.
As opposed to circulation coins which are continuously struck in normal quality, collector's coins are either minted in reduced quantities in brilliant uncirculated quality, or individually with two strokes for coins in polished plate quality (also known as proof, PP, or mint gloss). The minting of collector's coins in normal quality is identical to that of circulation coins. Whereas the blanks supplied for coins to be minted in normal or brilliant uncirculated qualities require no further preparation (as is also the case with blanks for circulation coins), those reserved for proof-quality coins are subjected to a series of preparatory processes, including annealing, pickling, peen-finishing, washing, and stain-free drying with the aim of achieving optimum surface quality. In order to obtain the best possible contrast between the lustre of the field and the frosted appearance of the relief, the minting dies used for proof coins are also specially polished.
Commemorative coins in proof quality are hand-packed first in coin capsules and then in elegant cardboard boxes with slipcase, those in uncirculated quality are sealed. The annual circulation coin sets in both proof and brilliant uncirculated qualities are presented in a modern outfit of transparent shell packaging, as well as the special coins sets for birth, birthday and Christmas.
Last modification 28.05.2021