The process of upset forging, at one time, was only used for gathering and upsetting metal to form heads on the bolts. However, the machine used for this process has now been developed to do multiple other forgings.
Also known as hot heading, the upset forging is a process that includes the increasing of the cross-sectional size of a bar. The size is increased at either an end or point along the length. The process is completed using special upsetting machines that use closed dies to control size and shape.
The dies in the machine are placed at different stations. The parts are passed from one die or cavity to another until the forging has been completed.
Upset forging is commonly used in the manufacturing of bolts of different configuration including the hexagon, square, mill, countersunk, liner, and fish. Nuts and rivets are also made using the same process.