Open Die Forging

Open die forging shapes large, simple metal sections between flat dies, creating strong directional grain flow with low tooling cost for heavy-duty parts.

Overview

Open die forging deforms hot metal between flat or simple contoured dies, usually under a hammer or press, to produce large bars, disks, shafts, and blocks. The process excels at creating sound, low-porosity material with controlled grain flow, ideal for highly stressed components and large cross-sections that are difficult to produce by other methods.

Choose open die forging for low to medium volumes, large part sizes, and relatively simple geometries where you plan to machine critical features afterward. Tooling is minimal, so upfront cost and lead time stay low, but as-forged tolerances and surface finish are relatively coarse. Expect to leave machining stock and use secondary processes for final dimensions and finishes. The tradeoff: excellent mechanical properties and material integrity in exchange for more machining and less geometric precision in the forging step.

Common Materials

  • Carbon steel 1045
  • Alloy steel 4140
  • Stainless steel 316
  • Inconel 718
  • Titanium Ti-6Al-4V
  • Aluminum 6061

Tolerances

Approximately ±0.06" to ±0.12" on as-forged dimensions; tighter features require machining

Applications

  • Large stepped shafts
  • Pressure vessel shells and nozzles
  • Rotors and generator shafts
  • Forge blocks and plates for machining
  • Disks and flanges for oil and gas
  • Heavy-duty crane and mining components

When to Choose Open Die Forging

Use open die forging for large, simple shapes where mechanical integrity, grain flow, and low tooling cost matter more than near-net geometry. It fits low to medium production volumes, parts that will be extensively machined, and components with heavy sections or long lengths.

vs Closed Die Forging

Choose open die forging when part geometry is simple, sizes are large, or volumes are too low to justify expensive impression dies. It’s better when you need flexibility to tweak dimensions between heats and are willing to machine final profiles rather than chase near-net as-forged shapes.

vs Cold Forging

Choose open die forging when you’re dealing with very large sections, high-alloy or hard-to-form materials, or when you need significant deformation at elevated temperatures for improved toughness. It’s more appropriate for heavy-duty structural parts where surface finish and tight as-forged tolerances are less critical than internal quality and grain flow.

vs Ring Rolling

Choose open die forging when you need solid disks, blocks, or irregular shapes rather than seamless rings, or when your volumes don’t justify dedicated ring-rolling tooling. It’s also useful for preforms that will later be ring-rolled, letting you keep one flexible process for multiple part families.

vs Upset Forging

Choose open die forging when you need long shafts, stepped profiles, or large blocks that exceed typical upset forging length-to-diameter limits. It’s a better fit when part geometry varies often and you want to avoid dedicated upset dies for each configuration.

Design Considerations

  • Keep geometries simple—bars, blocks, disks, and stepped shafts forge more consistently and quote faster
  • Specify realistic as-forged tolerances and clearly call out machining stock, especially on critical surfaces
  • Include generous corner radii and avoid sharp transitions to reduce cracking risk and forge loads
  • Define required grain flow direction relative to critical load paths so the shop can plan forging sequences
  • Provide maximum envelope, weight, and material specs early so the forge can confirm press capacity and handling limits
  • Call out required UT/NDT, heat treatment, and mechanical properties so the forge can design a suitable process route