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Forging processes: open die, closed die, rolled ring, cold and upset
Part weight, shape and yearly quantity decide the process, and the process decides which suppliers can quote. Use this page to narrow it down, then send the drawing and we match suppliers.
Process comparison
Ranges are typical, not limits. Individual suppliers cover only part of each range.
| Process | What it makes | Typical size | Typical tolerance | Tooling cost | Sensible quantity |
|---|---|---|---|---|---|
| Open die | Shafts, blocks, discs, sleeves and step bars formed between flat or simple dies. | About 5 kg to over 50 t | Machining allowance of a few mm per side | Low. Standard flat and V dies | 1 to a few hundred |
| Closed die | Near-net shapes such as connecting rods, flanges, gear blanks, yokes and levers. Metal fills a cavity cut into the dies. | About 0.1 to 250 kg | About ±0.5 to ±1.5 mm, plus 3 to 7° draft | High. One die set per part number | A few hundred to hundreds of thousands |
| Seamless rolled ring | Rings, bearing races, slewing rings and flange blanks. A pierced blank is rolled out to size. | OD from about 100 mm to several meters | Machining allowance of a few mm | Low. Mostly standard rolls | 1 to thousands |
| Cold and warm forging | Small round parts such as shafts, fasteners, splined parts and gear blanks, formed at or near room temperature. | A few grams to a few kg | About ±0.05 to ±0.25 mm | High. Multi-station tooling | Tens of thousands and up |
Open die forging
The metal is pressed or hammered between flat or simply shaped dies and turned between blows. The operator shapes the part step by step, so no die is cut for the part number.
- Best forShafts, blocks, discs, sleeves and step bars. One-off and low-volume parts, and parts too large for any closed die.
- Typical sizeAbout 5 kg to over 50 t.
- ToleranceMachining allowance of a few mm per side on small parts, more on large ones.
- ToolingStandard flat and V dies. Lead time is driven by material and furnace time, not by tooling.
- Watch forThe forged shape is rough, so expect more machining than on closed die. For large shafts and pressure parts ask for the forging ratio.
- Put on the RFQFinished or rough machined dimensions, alloy, heat treatment, weight as forged, quantity and test requirements.
Closed die forging
A heated billet is pressed or hammered into a cavity cut into two dies. The metal fills the cavity and the excess escapes as flash, which is trimmed off.
- Best forConnecting rods, flanges, gear blanks, yokes, levers and valve bodies, from a few hundred to hundreds of thousands a year.
- Typical sizeAbout 0.1 to 250 kg.
- ToleranceAbout ±0.5 to ±1.5 mm, plus 3 to 7° draft.
- ToolingOne die set per part number. It is paid once and its cost depends on part size and complexity.
- Watch forDie cost and lead time. Below a few hundred pieces a year, open die or machining from bar can cost less. Flash and cropping often add 20 to 40% to the input weight.
- Put on the RFQDrawing of the forged shape or the finished part, weight, yearly quantity, alloy, and who pays for and owns the dies.
Seamless rolled ring forging
A pierced disc is heated and squeezed between a rotating mandrel and a drive roll. The wall gets thinner and the diameter grows. Shaped rolls make profiled rings.
- Best forBearing races, slewing rings, flange blanks and gear rings, plus rings for turbines and pressure vessels.
- Typical sizeOutside diameter from about 100 mm to several meters.
- ToleranceMachining allowance of a few mm.
- ToolingMostly standard rolls. Profiled rings can need shaped rolls.
- Watch forSeamless means no weld, and the grain runs around the ring. Each mill has its own limits on diameter, height and wall, so check OD, ID and height against the supplier range.
- Put on the RFQOD, ID and height as forged or finished, profile if any, alloy, heat treatment and tests.
Cold and warm forging
Cold forging forms the metal at room temperature. Warm forging heats it to a few hundred degrees, still below the range used for hot forging. Both use multi-station tooling and run at high volume.
- Best forFasteners, small shafts, splined parts, sockets and gear blanks. Simple, mostly round shapes.
- Typical sizeA few grams to a few kg.
- ToleranceAbout ±0.05 to ±0.25 mm, with a clean surface.
- ToolingHigh cost. Multi-station dies for each part number.
- Watch forHigh forming loads limit the process to formable alloys such as low and medium carbon steel, aluminum and some stainless grades. Below tens of thousands a year the tooling rarely pays back.
- Put on the RFQDrawing, alloy, yearly quantity, tolerance on critical diameters and any heat treatment.
Upset forging
The end of a heated bar is gripped and pushed along its axis so the end gets shorter and thicker. It forms heads and flanges on long, slim parts.
- Best forBolt heads, shafts with a flange or collar, valve stems and axle ends.
- Typical sizeDepends on the upsetter. Ask each supplier for its bar diameter range.
- ToleranceSimilar to closed die on the upset section. The bar section keeps the tolerance of the stock.
- ToolingGripping dies and heading tools for each part.
- Watch forThe unsupported length of bar in relation to its diameter limits how much can be upset in one stroke, so a long head can need several steps.
- Put on the RFQBar diameter, head or flange size, overall length, alloy and quantity.
Choosing a process
Start from the shape and the yearly quantity. These are rules of thumb. Edge cases are common, which is why suppliers read the drawing before they quote.
- Ring shape, any sizeSeamless rolled ring. A ring cut from plate or bar wastes material and cuts the grain.
- Small round part, tens of thousands a yearCold or warm forging. Tight tolerance and little machining pay for the tooling.
- Long slim part with a head or flangeUpset forging, which forms the head from the bar end.
- Up to about 250 kg, a few hundred pieces a year or moreClosed die. Near-net shape and a die set spread over the run.
- One-off, very large or under a few hundred a yearOpen die. No part-specific die and a larger machining allowance.
Questions about forging processes
How do I know which forging process my part needs?
Weight, shape and yearly quantity decide it. Rings go to ring rolling and small round parts in the tens of thousands go to cold or warm forging. Mid-size parts in the hundreds and up go to closed die, and one-offs or very large parts go to open die. If you are unsure, pick "Not sure" on the RFQ form and send a drawing.
Can one supplier do more than one process?
Some shops run two or more, for example closed die with open die or open die with ring rolling. Few run all of them. We match on the process your part needs, so you do not have to know who runs what.
Is forging always better than machining from bar?
No. Forging pays off when the part sees fatigue or impact load, when most of the bar would end up as chips or when the volume covers the tooling. For a few pieces of a simple shape, cutting from bar is often cheaper.
What is the difference between hot, warm and cold forging?
Hot forging heats steel to about 1100 to 1250 °C. Warm forging works at a few hundred degrees and cold forging at room temperature. Hotter means larger parts and more machining stock. Colder means tighter tolerance and a better surface, but smaller parts and more tooling cost.
Not sure which process your part needs?
Pick "Not sure" on the form and send the drawing, weight and yearly quantity. We match up to 3 suppliers and reply within 24 business hours.