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A forging machine is also called a press or punch press; the machine presses down on a metal blank and creates a specific shape. Operated in one of three common temperatures — cold, warm and hot —, the designation is keyed to the temperature of the metal being shaped. Using enough pressure to stamp a basic shape from a solid piece of metal in a single strike, the forging machine often operates from a flywheel mechanism that powers a stamping die downward and into the second component piece of the total die, continually pressing due to the inertia of the spinning flywheel. It is a common design trait for a forging machine to drop or press the die or stamp straight down on the work piece, hence the name drop forge.
Forged steel and aluminum parts retain greater strength than a cast or machined item due to the grain of the forged material running in the same direction throughout the entire part. This greater strength retention lends to the forging machine being the preferred method of creating high-strength, durable products such as hand tools, machine parts and engine pistons. While the forging machine gives the basic shape to a part by applying severe pressure in a single strike and sandwiching the metal blank between the upper and lower press dies, it often requires several more steps to produce a finished product.
The process of cold forging is used on smaller and less critical parts since the amount of hardening of the metal directly out of the forging machine is less controllable. When a part is cold-forged, the heat created from pressing the metal into a particular shape also hardens the piece. Known as work hardening, the level of hardness is not fully controllable or uniform throughout the entire run of parts. One side effect of cold forging is that the work hardening of the piece typically makes further steps more difficult due to the level of hardness found in the metal.
Hot forging involves the forging machine stamping a red hot piece of metal into a basic design or shape. The forging machine typically uses a light oil film on the pressing dies in order to prevent the sticking of the part to the die as well as to provide a heat shield to the die. The worker operating the hot forging machine uses long steel tongs to place the hot piece of steel into the machine's dies. On larger parts, the hot steel is often fed into the forge by a steel belt.