Closed Die Forging

Closed die (impression) forging forms heated metal in shaped dies to create strong, near-net parts with good repeatability at medium to high volumes.

Overview

Closed die forging, also called impression die forging, uses matched upper and lower dies to form heated metal into a precise cavity. The process produces near-net-shape parts with excellent mechanical properties, refined grain flow, and good dimensional consistency, especially for complex 3D geometries that will see high loads or fatigue. Typical production runs range from hundreds to hundreds of thousands of parts, where tooling can be amortized over volume.

Choose closed die forging when you need strong, reliable parts with better properties than castings and more efficiency than hogging from bar. It excels for moderate-sized parts with defined parting lines, generous fillets, and some machining stock left on critical surfaces. Tradeoffs include upfront die cost, required draft angles, flash and parting line cleanup, and limits on extremely thin sections or sharp internal features. Expect a forged blank that still needs finish machining on sealing, bearing, and precision locating surfaces.

Common Materials

  • Carbon steel 1045
  • Alloy steel 4140
  • Stainless steel 304
  • Aluminum 6061
  • Titanium Ti-6Al-4V
  • Inconel 718

Tolerances

±0.010" to ±0.020" on as-forged dimensions (tighter features typically finish machined)

Applications

  • Automotive connecting rods
  • Crankshafts and gear blanks
  • Aircraft landing gear components
  • Hand tools and wrenches
  • Axle shafts and yokes
  • Off-highway suspension and linkage arms

When to Choose Closed Die Forging

Use closed die forging for medium to high volume parts that need high strength, good fatigue life, and consistent geometry from heat-to-heat. It suits moderate-sized components with well-defined parting lines, generous radii, and a plan for finish machining on critical surfaces. Ideal when you can justify tooling cost in exchange for part performance and repeatability.

vs Open Die Forging

Choose closed die forging when the part has defined geometry, tighter tolerances, and you need consistent, repeatable shapes at higher volumes. Open die fits very large, low-volume, simple shapes; closed die fits smaller to medium parts with detailed features, flash control, and a predictable machining envelope.

vs Cold Forging

Choose closed die hot forging when the part is larger, has more complex geometry, or requires alloys that do not cold form easily. Cold forging works well for smaller parts with excellent surface finish and tighter as-formed tolerances, but hot closed die handles thicker sections, deeper cavities, and higher deformation without cracking.

vs Ring Rolling

Choose closed die forging when you need solid or irregular-shaped parts rather than seamless rings. Ring rolling is efficient for toroidal and ring geometries with large diameters; closed die forging is better for yokes, arms, and complex 3D shapes that cannot be reduced to a ring form.

vs Upset Forging

Choose closed die forging when the part has complex multi-axis geometry that cannot be formed by upsetting the end of a bar. Upset forging excels at simple headed parts like bolts, valves, and shafts with localized enlargements; closed die forging allows more intricate cavities, varying cross-sections, and integrated features in one hit sequence.

vs Casting

Choose closed die forging when mechanical properties, toughness, and fatigue life are critical, especially under shock or cyclic loading. Casting can achieve very complex shapes and internal passages, but forged parts offer denser microstructure, better grain flow, and reduced defect risk at the cost of tooling, draft, and added machining stock.

Design Considerations

  • Define a clear parting line and align major geometry to simplify die design and reduce flash volume
  • Use ample fillet and corner radii (typically ≥ 0.06–0.12") to promote metal flow and extend die life
  • Include 3–7° draft on forged surfaces depending on depth to allow reliable ejection and avoid die galling
  • Avoid thin isolated walls and abrupt section changes; transition thickness gradually to prevent laps and underfills
  • Specify realistic as-forged tolerances and clearly indicate which surfaces will be machined and how much stock is required
  • Orient the part so critical load paths follow grain flow; share load cases so the forger can optimize preforms and fiber direction