Closed Die Forging

Closed die (or impression die) forging have been a key metal working process for gears for many years.


Forging is the process of forming and shaping metals through the use of localized compressive forces.  Forgings are worked above their recrystallization temperature and are gradually shaped into the desired configuration through the skillful hammering, pressing, or rolling of the work piece.  Since both ferrous and nonferrous metals can be forged and raw material mills allow for the development of custom-melt materials, the options for grades as well as physical and mechanical properties are endless. (Figure 1)

Figure 1

Closed die (or impression die) forging have been a key metal working process for gears for many years. Forging suppliers have long used tooling to achieve near net or finish size and shape. Each forging process utilizes forge tooling in different ways to best reduce input material and machining reduction. Tooling has allowed this process to continue to be cost competitive when compared to machined bar or casting options while taking advantage of the plasticity of metals at high temperatures. The plasticity allows forgings to deliver significant economic, manufacturing, and quality advantages when compared to alternative metalworking processes such as directional strength, structural strength, and impact strength. (Figure 2)

Figure 2

Die tooling is the cornerstone for impression or closed die forgings. This application is ideal for higher volume repeatable products.  The tolerances achieved offer reduced machining needed to attain finish shape or sizes. Open die forging has long provided gear blanks for pieces historically too large or in non- ideal shapes for impression die. (Figure 3)

Figure 3

However open die forging also offers a unique solution for gearing with the application of loose tooling.  Many open die manufacturers stock a wide variety of loose tools that can be used to achieve various shapes closer to finish than would be achievable through a pure open die process.  This offering is ideal for prototype or low volume production where the die block cost for impression die does not provide economic justification. The immediate availability of this tooling can also allow for a shorter production lead time offering flexible order quantities and reduced lead time in situations where needed. (Table 1)

Table 1.