3.5.4.2 Design Rules For Parts Made From Upset Forgings

1. Parts that are symmetrical about an axis are the most economical for upset forging.
2. Upsetting generally increases the diameter of the beginning stock. Therefore, the stock size will generally correspond to the smallest as-forged diameter. This is the case for the flanged member shown in Figure 3-16. However, there are cases in which a nose can be extruded to achieve a smaller diameter.
   
   
   
   

   Figure 3-15 Design so that all datum targets and tooling points are in the same die member, preferably the moving member.

   Figure 3-16 The flanged shaft was an ideal candidate for upsetting from bar stock.

3. There are limits to the change in shape that can be achieved in one stroke of an upsetter. There are three rules, which are based on geometric proportions:

   Rule 1: The limit of length of unsupported stock that can be gathered in one upset blow without excessive buckling is not more than three times the diameter of the bar as shown in Figure 3-17^.

   Figure 3-17 Rule 1

   Rule 2: When the length of unsupported bar stock is more than three times its diameter, the bar can be upset in one blow provided that the diameter of the upset is not more than one and one-half times the diameter of the stock as shown in Figure 3-18.

   Figure 3-18 Rule 2

   Rule 3: Where the length of unsupported bar stock is more than three times its diameter, and the diameter of the upset is not more than one and one-half times the diameter of the stock, the bar can be upset in one blow provided the amount of unsupported stock beyond the face of the die is not greater than one and one-half times the diameter of the stock, as shown in 4. Upset forgings with very large ratios of maximum to minimum diameter, or with massive features that require gathering sections of bar stock that are long compared with the diameter, will require several forging operations to gather the metal and form it to the desired shape while preventing defects.

   Figure 3-19 Rule 3

4. Upset forgings with very large ratios of maximum to minimum diameter, or with massive features that require gathering sections of bar stock that are long compared with the diameter, will require several forging operations to gather the metal and form it to the desired shape while preventing defects.
5. Upset dies are essentially three-piece impression dies. Therefore, maximum radii should be used wherever possible to minimize forging pressure and promote die fill.
6. See Appendix B Tolerances for Hot Upset Forgings.