Closed Die Forging

Closed die forging forms heated metal in shaped dies to create near-net components with high strength, repeatable geometry, and good grain flow.

Overview

Closed die (impression die) forging plastically deforms heated billet between matched dies to create near‑net shapes with strong, directional grain flow. It delivers high strength and fatigue performance, good repeatability, and efficient material use compared with machining from bar.

Choose it for medium to high volumes where tooling cost can be amortized and the part benefits from forged properties: load-bearing features, impact resistance, and reliable performance. Typical outputs need trim/flash removal and often finish machining on datum surfaces, bores, threads, and tight-tolerance features.

Tradeoffs: die design and lead time drive NRE; geometry must support metal flow (draft, radii, parting line control). Very thin webs, deep pockets, and sharp inside corners are difficult. Scale, decarb, and variation from forging/heat treat mean you should plan machining stock on critical surfaces and specify realistic tolerances and surface requirements.

Common Materials

  • 4140 steel
  • 4340 steel
  • 1045 steel
  • 17-4 PH stainless
  • Ti-6Al-4V
  • Aluminum 7075

Tolerances

±0.010" to ±0.030" as-forged; ±0.002" to ±0.005" after machining

Applications

  • Connecting rods
  • Crankshafts
  • Steering knuckles
  • Aircraft landing gear fittings
  • Wrenches and striking tools
  • Flanges and yokes

When to Choose Closed Die Forging

Closed die forging fits parts that need high strength and fatigue life with repeatable geometry, especially load-path components where grain flow matters. It’s a strong choice at medium to high volumes or for families of parts that share tooling concepts. Expect to finish machine critical features and plan for trim and heat-treat steps in the routing.

vs Open Die Forging

Choose closed die forging when you need repeatable near-net geometry, defined features, and higher production rates. It supports tighter shape control and lower per-part machining than open die forgings, at the cost of higher die tooling and less flexibility on size/shape changes.

vs Cold Forging

Choose closed die forging when the part is too large, thick, or complex for cold forming loads or when the alloy/work hardening makes cold forging impractical. Hot closed die forging handles tougher alloys and larger section changes, with less dimensional precision than cold forging and more need for machining/clean-up.

vs Ring Rolling

Choose closed die forging when the part is not axisymmetric or needs integrated bosses, lugs, or non-circular geometry. Ring rolling wins for seamless rings with controlled grain flow around the circumference; closed die forging wins for discrete 3D features and non-ring shapes.

vs Upset Forging

Choose closed die forging when you need multiple features beyond head/thickening operations, or when the geometry requires controlled flow into cavities and around fillets. Upset forging is efficient for axisymmetric parts with localized thick sections; closed die forging better suits complex profiles that need defined contours.

Design Considerations

  • Add draft on all die-pulled faces (often 3–7° hot forging) and align key features with the pull direction
  • Use generous fillet and corner radii to support flow and die life; avoid sharp internal corners
  • Place the parting line on a simple, accessible plane and keep critical datums away from flash/trim areas
  • Provide machining stock on functional surfaces and specify which surfaces are as-forged vs machined
  • Avoid thin webs, deep blind pockets, and abrupt section changes; keep thickness transitions smooth
  • Call out grain-flow critical directions and required post-forge heat treat early so the shop can design the preform and process route