Planchets are small metal discs that are made into coins. Generally speaking, the mint uses raw materials obtained from commercial sources to create the planchets and begin the coin making process. The exception however is the cent. Cent planchets are prepared for the mint before they arrive. Nickel planchets are made at the mint, and dimes, quarters, half dollars, and dollar coins are all “clads” and made from the strips of metal that are pressed together to be made into planchets and eventually coins. This is why you see the copper center around the edge of each of those coins (post 1964 of course).
Planchets receive their edge from an “upsetting machine”. This serves multiple purposes. It gives coins their distinct raised edge and also hardens the edge to prevent the coin from projecting out the middle when going through the press. The process of giving dimes, quarters, halves, and dollars their ridged edge is known as “reeding”.
A common mint error is the misstrike, which will often leave a significant amount of the original planchet visible in the final coin.