The various coining facilities of the United States Mint are factories, whose products happen to be coinage of the realm. Like any other metal-working factory, the U.S. Mint has a variety of presses, engraving and reducing machines and metal-working equipment.
Like any metal product, coins don't "just happen." A number of intricate steps must be taken, from the preparation of the raw metal used in the coins to the striking of the coins. And before the coins can be struck, dies must be produced.
Modern United States coins have their beginnings in the private sector, where a number of companies produce some coinageblanks and planchets and all coils of strip metal the Mint purchases. Blanks and planchets represent the same product at different stages of production: the unstruck, circular pieces of metal that become coins when struck between the dies. The Mint produced its own strip metal as late as Fiscal Year 1982 at the Philadelphia Mint, but the operations were closed officially in Fiscal 1983. The Mint still produces some of its coin blanks and planchets.
In preparing the raw metals used in coining, the coinage metals are assayed, melted and formed into slabs which are then rolled to the proper thickness. For clad coinage, bonding operations are required to bond the two layers of copper-nickel to the core of pure copper. The strip is then coiled and shipped to the Mint for blanking.
Blanks are unfinished planchets that haven't been through all of the processing steps necessary before they can be struck into coins. Once a blank has been through all of the processing steps, it becomes a planchet and is ready to be struck.
Blanks are produced on blanking presses, which are simply punch presses similar to those found in any machine shop. They have a bank of punches (or rams) which travel downward through the strip of coinage metal and into a steel bedplate which has holes corresponding to the punches. The presses punch out blanks each time the punches make their downward cycle. The blanks made at this stage are slightly larger than the finished coins. Because of the shearing action of the punches, the blanks have rough edges. Most of the rough edges (or burrs) are removed during succeeding operations.
The blanks are next passed over sorting screens which are supposed to eliminate all of the defective pieces. Thin and incomplete blanks will fall through the screens. Rejected blanks are remelted.
During the finish rolling and blanking press operations the blanks have again been hardened and must now be softened (heated) to controlled temperatures, approximately 1400 degrees Fahrenheit, changing their crystal structure to a softer state. Planchets are "frozen" into that state by a water quench bath. The annealing process prolongs the life of the coining dies by ensuring well-struck coins with lower striking pressures.
Despite a protective atmosphere, annealing causes some discoloration on the surfaces of the blanks which must be removed. The blanks are tumbled against each other and passed through a chemical bath. Then they are dried by forced hot air. Many of the blanks' next stop is an upsetting mill. (The Mint no longer finds it necessary to upset the rims of 5-cent blanks.)
The upsetting mill consists of a rotating wheel with a groove on its edge. The grooved edge of the wheel fits into a curved section (or shoe) which has a corresponding groove. The distance between the wheel and the shoe gets progressively narrower so that, as the blank is rolled along the groove, a raised rim is formed on both sides of the blank. This raised rim serves several purposes. It sizes and shapes the blank for better feed at the press and it work-hardens the edge to prevent escape of metal between the obverse die and the collar.