August 2026 Volume 8

EQUIPMENT & TECHNOLOGY

Figure 3: Tonnage reduced by 20% and maximum principal stress reduced by 30% as a result of utilizing a better forging design.

Buster and blocker dies should be designed with die life in mind. In most cases the finisher cavity will require replacement before the buster and blocker cavities have worn out. That is mainly because the finisher cavity is the one producing the final product, so even a relatively small amount of wear will cause the forgings to fall out of tolerance. Blocker cavities usually wear faster than finisher cavities because they are doing more work, but a badly worn blocker cavity paired with a good finisher cavity can usually still produce good parts. However, parts coming out of a worn blocker will no longer be optimized to the finish cavity, so using a blocker cavity past its prime will accelerate wear in the finisher. The buster cavity will often outlast several finisher die cavities before it needs replacement. The design of the buster and blocker cavities has a large influence on the life of the finisher cavity. This is particularly important when all three cavities are cut into the same block of steel, since in that case they must all be re-sunk at the same time. If you can design the blocker cavity to produce

something closer to the finish part, you will reduce wear in the finish cavity but increase wear in the blocker. Since it is the finish cavity that governs when the entire die needs to be reworked, this trade-off can produce a net gain in die life. Finally, we need to discuss gas trapping. Gas trapping occurs when the partially formed forging seals off a portion of the cavity from the outside, trapping whatever gases, die lube, and possibly water are in the die. As these gases are compressed and heated, they can produce enormous pressure. This pressure can cause non-fill in the forging and significant stress in the dies, which can lead to crack formation. The solution to trapped gas is to create a path for the gases to escape. A small hole or a segmented die design can provide that path, alleviating the problem. A segmented die can offer additional advantages as well: it can reduce die stresses, and it allows high-wear components to be replaced individually rather than replacing the entire die.

Figure 4: Gas trapping occurs above the collar in the top die. Implementing a segmented die allows the gases to escape through the gap between the top die and the top plug.

22 FIA MAGAZINE | AUGUST 2026