Automatic hot forging, cogging, impression die forging, open die forging, press forging, roll forging, swaging, and upsetting are the most common forging processes.
Automatic hot forging involves feeding mill-length steel bars into one end of the machine at room temperature, and hot forged products emerge from the other end.
Cogging is the successive deformation of a bar along its length using an open-die drop forge. The common application is to work a piece of raw material to the desired thickness.
Open die and impression die (also called closed die) forging are drop forging processes, meaning there is a need for a raised hammer then “dropped” onto the workpiece to deform it according to the shape of the die. As their names imply, the difference between the two depends on the shape of the die, with the open die not fully enclosing the workpiece and the closed die enclosing it.
Unlike the nearly immediate impact of drop hammer forging, press forging involves a slow application of continuous pressure or force. Press forging can be either hot or cold. The amount of time that the dies are in contact with the workpiece is measured in seconds in contrast to milliseconds with drop hammer forging.
Roll forging is a forging process where there is a reduction of round or flat bar stock in thickness and an increase long.
Swaging is a forging process in which the operator alters the dimensions of a workpiece thanks to the dies into which the workpiece is forced. Usually considered a cold working process, swaging may also be hot-worked.
Upsetting also called upset forging, increases the diameter of the workpiece by compressing its length. It is the most widely practiced forging process based on the number of pieces produced. Engine valves, couplings, bolts, screws, and other fasteners are some examples of common parts made using the upset forging process.
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