Following the heading stage, the shaped bars may be subject to further hot forged processes to form the material into shapes that are unachievable by using upset forging alone. For example, drop forging is required to punch the hole out of the middle of an eyebolt.
The upset forging process uses a specialised forging press which was initially designed for, and is often still used for, forging the head of a bolt.
Although the upset forging process is fairly flexible due to the use of tools, there are limitation to the change in shape that is achievable by a single blow of an upsetter. The following three rules should be followed to ensure maximum strength in the component:
1. The length of unsupported material should be no more than three times the diameter of the bar. This results in a reduced likelihood of buckling during each upsetting blow
2. If the length of material is greater than three times the diameter, this is still achievable provided that the diameter of the upset is not larger than one and a half times the diameter of the bar.
3. Where neither rule 1 nor 2 can be met, the length of the unsupported material beyond the die must not exceed the diameter of the bar.