Coins come from blank disks of metal that are fed into the coin press. These blanks may be purchased from an outside source or produced by the mint itself. If produced by the mint, long, flat sheets of the appropriate metal(s) will be fed into a blanking press, which will punch out the blanks much like a cookie cutter. The left over sheet of metal is known as "webbing" and it will be chopped up and then recycled.
In their current condition the blanks are too brittle to be placed in the coin press. To correct this, they are heated in an annealing furnace, which will make the metal more workable.
After cooling, the blanks pass through a washer to remove the tarnish that was acquired during the annealing process. The blanks are then dried and passed through a "riddler," which screens out any blanks that are not the proper size or shape.
The final step in the process is to pass the blanks through an "upsetting mill," which will create the raised rim around the edge of the coin. The upsetting mill will also smooth the edges and harden them.
Inside the upsetting mill, blanks follow a slot-like channel on a spiral track. A rapidly rotating wheel forces blanks in the channel against a curved structure (the "shoe"), which remains stationary. The curvature of the shoe is such that the channel containing the blanks gradually narrows as it progresses along. Thus, the distance between the wheel and the shoe is constantly decreasing and the edges of the blank are squeezed with great force. As the blank is compressed along its edges, a raised rim is forced up. This will occur on both the front and the back of the blank.
The blank with raised edges that is ejected from the machine is now known as a "planchet" and it is ready to be struck as a coin. Planchets are very slightly smaller in diameter than the coins they will become.