Closed Die Forgings
Closed die (impression die) forging presses heated metal into shaped die cavities to produce near-net-shape parts with consistent dimensions and excellent strength. It is the standard process for high-volume forged components like connecting rods, gears and levers.
What it is
Upper and lower dies contain the part shape; the hot billet fills the impressions under hammer blows or press force, with excess metal forming flash that is trimmed off. Multiple impressions (blocking, finishing) shape complex parts progressively.
Dies are costly but produce thousands of consistent parts, with much less machining than open-die forgings or bar stock.
Typical applications
- Connecting rods and crankshafts
- Gears, hubs and flanges
- Levers, yokes and forks
- Hand tools and spanners
- Automotive and tractor parts
Suitable materials
- Carbon steels (EN8, C45, 1045)
- Alloy steels (EN19, EN24, 42CrMo4, 20MnCr5)
- Stainless steels (304, 316, 410, 17-4 PH)
- Aluminium, brass and copper alloys
Points to consider
- Die cost is justified at volumes of thousands of parts.
- Design with draft (5–7° typical), radii and a clear parting line.
- Flash trimming leaves a line; mark areas where it's acceptable.
- Specify heat treatment and grain flow requirements for critical parts.
Frequently asked questions
What is the difference between open and closed die forging?
Closed-die forging uses shaped dies that enclose the part, giving near-net shapes in volume. Open-die uses simple dies for larger or low-volume parts.
What is flash in forging?
Excess metal squeezed out between the dies, trimmed off after forging.
When is closed die forging economical?
At medium to high volumes, where die costs are spread and machining is reduced.