The original definition of forging is the "mechanical deformation of metal when heated to a plastic state". However, in recent years it has come to include similar operations done in the cold or room temperature state as well. There are two main types of forgings: open end forging and close end forging. However upset forging is also used for a number of applications.Upset forging is a metal shaping process in which a heated workpiece of uniform thickness is gripped between split female dies while a heading die (punch) is forced against the workpiece, deforming and enlarging the need of the workpiece. A sequence of die cavities may be used to control the workpiece geometry gradually until it achieves its final shape. This is a rapid "cold forming" process. It increases the diameter of the end of the central portion of a workpiece by compressing its length. Complex parts are usually formed gradually in a sequence of separate die cavities. It may produce diameters up to three times the original diameter. Impressions may be in the punch die, gripping die, or both .Usually requires no trimming may be performed cold on ductile materials upset forging increases cross-section by compressing the length, this is used in making heads on bolts and fasteners, valves and other similar parts. Upset forging increases the diameter of the workpiece by compressing its length. Based on number of pieces produced this is the most widely used forging process.
The machines are usually set up to work in the horizontal plane, to facilitate the quick exchange of work pieces from one station to the next. The initial workpiece is usually wire or rod, but some machines can accept bars up to 25 cm (10 in.) in diameter and a capacity of over 1000 tons. The standard upsetting machine employs split dies that contain multiple cavities. The dies open enough to allow the workpiece to move from one cavity to the next; the dies then close and the heading tool, or ram, then moves longitudinally against the bar, upsetting it into the cavity. If all of the cavities are utilized on every cycle then a finished part will be produced with every cycle, which is why this process is ideal for mass production e following three rules must be followed when designing parts to be upset forged: the length of unsupported metal that can be upset in one blow without injurious buckling should be limited to three times the diameter of the bar. Lengths of stock greater than three times the diameter may be upset successfully provided that the diameter of the upset is not more than 1.5 times the diameter of the stock. In an upset requiring stock length greater than three times the diameter of the stock, and where the diameter of the cavity is not more than 1.5 times the diameter of the stock, the length of unsupported metal beyond the face of the die must not exceed the diameter of the bar.
