Modern Day Coin Minting Process

Many-a-times, we do not tend to value coins, this page might help you to know how the are minted in Modern day using the power of technology. Ancient and medieval coins were struck using manual processes. 

Design or Galvano Creation

The first step in the minting process is the design creation of the coin. An experienced artist draws a sketch on paper or on digitalised. This design may include the specifics and detailed elements of the final coin design, but not always. The design is then handed over to expert sculptors and engravers who convert the 2D design into a 3D design using plaster or other similar materials that are used for creating an artwork. The plaster model is generally 10” to 16” in size and is always in positive relief, just like how it appears on coins. The final plaster sculpture is coated with epoxy resin which acts as a hardener and a preservative. The end product is called “galvano”. Two such galvano models are created, one for the obverse of the coin and the other for a reverse.

Master Hub Creation

Once the galvano is created, the Master Hub is the next step in the coin minting process. The 'Master Hub' is created in steel, with the galvano as the reference. The 'Master Hub' also has a positive relief as galvano, the 'Master Hub' is heat treated for obtaining higher hardness. 

Master Die Creation

The process of creating the master die using the Master Hub is known as hubbing. The 'Master Hub' is placed on hydraulic press at one end, and steel road at the other end which will become the master die.

The 'Master Hub' is pressed against the steel rod repeatedly under high pressure to have the inscription of required depth and to convert the steel road into master die with a mirrored impression or negative relief. A single high-pressure strike is avoided as it could weaken the die which would later develop into cracks.

Working Hubs Creation

The only difference between the coin minting process involved in making the 'Working Hubs' and 'Master Die' is that one end of the hubbing press has 'Master Die' for making the 'Working Hubs'. The 'Working Hubs' will have a positive relief and many such 'Working Hubs' are created.

Working Dies Creation

'Working Dies' are used to strike the coins in the coin press. The only difference in the coin minting process of making the 'Working Die and the Master Die' is that one end of the hubbing press has the 'Working Hubs'. 'Working Dies' have a mirrored image and a negative relief. In normal cases, a single working die can strike around 5,00,000 coins, after which they're replaced.

Mint marks and dates are added on the working dies using hand punches if more than one mint is issuing the coins. Errors like date doubling, double mint marks, and errors happen during this phase of the coin minting process. However, the mint marks and the dates are added to the 'Master Die' if the number of coins to be minted is very high. The mint mark and date are also added to the plaster sculpture itself if the Mint is creating their own design.

Planchets Creation

The raw metal of the required composition is made into long sheets. The composition and exact specification of the metal is a secret between the Mint and the metal provider. The metal sheet is fed into a punching machine after a thorough quality check. Blanks of the desired shape are created by the punching machine during this coin minting process. The remaining metal or webbing is recycled.

Imperfect blanks are now separated by passing them over a mesh of the size of the coin. Larger coins will not fall, but coins of same or smaller diameter fall through. The next mesh has holes of a size slightly smaller than the coins. The smaller blanks fall through the mesh holes. These correct sized blanks then undergo annealing and cleaning process after which they are put into the upsetting machine. This machine creates the raised edges around the blank. Raised edges help the metal flow into the die design rather than flow off. They also allow the coins to be stacked properly. The blanks are then fed into a furnace and given a chemical bath to give them a distinctive colour or tone based on the metal used. The final Blanks are called Planchets that are ready to be stuck.

Striking

The striking chamber has 2 working dies. The reverse working die is placed in the “Anvil die”. The “Hammer die” has the Obverse working die. The coins are fed through a funnel into the striking chamber during this coin minting process. The bottom of the funnel has feeder tubes with 2 feeder fingers. These place the planchet on the anvil and eject the stuck coins. A collar [metal ring] holds the coin and the hammer strikes the planchet with the desired force. The collar prevents the planchet to expand beyond the desired diameter of the coin. Some collars have reeds and security so that the planchets that are struck have a reeded or security edge. After the strike, the hammer moves back and the feeding fingers then slide this coin out of the striking chamber. The process repeats several times to mint coins.

Almost 120 coins can be struck per minute using modern technology. To increase the speed, multiple planchets are struck at the same time. The coins then go through a quality check process. Whenever a new die is introduced, the coins are manually inspected for errors.

Counting:

The coins are then sent to the counting and bagging area using a conveyor where they are counted mechanically and bagged. The bagged coins are also weighed to ensure that they are of the right weight. The bagged coins are put into gunny bags which are signed by the official of the mint during this coin minting process. The ready coins are then sent to the central bank which distributes them to the general public.

Proof Coins:

Extremely high grade die blanks are used to create dies for Proof coins. The dies are chosen from many working dies and are hand-polished achieve a mirror finish. Sometimes, 3-4 rounds of polishing with different diamond paste achieve high-mirror finish. Today mints also look for Frost finish where the entire die is covered with soft tape and just the key design is exposed and sand blasted. The background gives a mirror finish and the design gives a frost finish. The blanks used for striking proof are polished. The proof coins are hand struck sometimes more than 3-4 times so as to give a sharp edge to the design. New dies is used to reduce the wear on the coins. The dies are cleaned after 20 to 30 strikes. Minor imperfections are checked at regular intervals and are removed by polishing the die again. Each coin is manually inspected before packaging and shipping. The rate of coin production for proof is less than 500 per day.