Open-die forging shapes heated metal between flat or simple dies that do not enclose it, and suits large, simple shapes in small numbers. Closed-die forging, also called impression-die forging, squeezes metal into shaped dies that form the whole part, and suits complex shapes in larger volumes.
Both give a stronger part than a casting of the same shape, because forging closes internal voids and aligns the grain flow with the part. The choice between them comes down to shape, size and quantity. A casting may still win where the shape has large internal cavities that forging cannot form.
Open-die forging
In open-die forging, a hammer or press works the hot billet step by step. The operator turns and moves the workpiece between blows. Parts come out near the final shape but need significant machining.
It is used for shafts, rings, discs, blocks, sleeves and large flanges. Tooling is simple, so there is little upfront cost, and single pieces or short runs are practical. It also handles very large parts that would need huge closed dies. The trade-off is lower dimensional accuracy and more machining stock.
Closed-die forging
In closed-die forging, the billet is placed in a die cavity shaped like the part. A hammer or press forces the metal to fill the cavity. Excess metal squeezes out as flash, which is trimmed off afterwards.
It is used for connecting rods, gear blanks, crankshafts, levers, hand tools, flanges and fittings. Parts are close to final shape, with good repeatability. The dies are a real upfront cost and take time to make, so closed-die forging pays off at medium and high volumes.
Dies also wear. Agree who owns them, how they are maintained, and how often forgings are checked for size as the dies age. The same ownership points apply as for casting patterns.
Side by side
- Tooling: open-die uses simple flat or shaped dies, while closed-die needs a dedicated die set for each part.
- Volume: open-die suits one-offs and short runs, while closed-die suits repeat production.
- Size: open-die handles very large parts, while closed-die is limited by press or hammer capacity.
- Accuracy: closed-die gives closer tolerances and less machining.
- Lead time: open-die can start quickly, while closed-die must wait for dies to be made and proved.
Related processes
Seamless rolled rings are made by piercing a forged disc and rolling it out to a larger ring. They are common for bearing races, gear rims and large flanges. Upset forging gathers metal at the end of a bar to form heads and collars, as on bolts and shafts.
Whichever process is used, the steel grade and heat treatment largely decide the final properties. See steel grades for forgings and heat treatment for forgings.
Next step
We match your part to forging units with the right presses, hammers and heat treatment, and we check samples and test reports before you commit. To discuss your forging, book a free sourcing review.