Below is a list of Closed Die Forging manufacturers from Spring Grove, Illinois. Closed die forging, also known as impression die forging, involves the pressing or hammering of preformed metal blanks into a set of dies shaped as a three dimensional negative of the part to be produced. In closed die forging the hammer and anvil fully enclose the workpiece, forcing the metal to fill all areas of the die. Closed die forging can produce a nearly limitless variety of 3-D shapes, and is capable of producing complex parts with tight tolerances.