Swaging
Swaging hammers or presses the end of a tube or bar inward against a die to reduce or taper its diameter without removing any material.
- Part
- Forming
- Variants
- 2
- Revised
- 2026-08-11
At a glance
- Family
- Metal
- Typical tolerances
- Roughly ±0.002–0.005 in (±0.05–0.13 mm) on swaged outside diameter; inside diameter holds a comparable tolerance only when a mandrel is used
- Surface finish
- Burnished by the repeated die contact, typically smoother than the incoming bar or tube surface
- Typical volumes
- 100–1,000,000+ parts; practical in dozens on a manual machine
- Lead time
- 2–6 weeks including a new die set; days for repeat work on existing tooling
- Materials
- Metal
What it is
Swaging reduces or tapers the end of a tube or bar by hammering it inward against shaped dies. In rotary swaging — the production form — a spindle spins a set of dies past a ring of rollers, and each roller passage drives the dies closed and lets them spring open again, delivering thousands of light blows per minute while the workpiece is fed in.
Nothing is removed. The material is displaced, so the metal cold works, gets stronger, and takes on a burnished surface, and a swaged tube end has continuous grain rather than a cut edge. Diameters can be held to a few thousandths of an inch.
It is how cable and wire rope fittings are attached, how tube ends are reduced for assembly, how tapered tubes such as golf shafts and antenna sections are made, and how screwdriver blades and pointed bar ends are formed. Tooling is simple and inexpensive, so swaging is economic from small quantities up to millions.
How it works
- Die set selection. Two or four die segments are ground to the finished profile — a straight reduction, a taper, or a combination. The dies define the finished outside diameter directly.
- Spindle rotation. The dies sit in slots in a rotating spindle, with backers behind them. A stationary outer ring holds a set of rollers. As the spindle turns, each backer passes a roller and is driven inward, closing the dies; between rollers, centrifugal force opens them.
- Blow rate. The result is a rapid succession of light hammer blows — commonly on the order of 1,000–5,000 per minute depending on spindle speed and roller count. Each individual blow does very little work, which is precisely why the metal flows smoothly rather than cracking.
- Feed. The workpiece is pushed into the closing dies. Because material is displaced rather than cut, it flows both radially inward and axially — a swaged tube gets longer as it gets smaller.
- Mandrel (optional). For tube work where the inside diameter matters, a mandrel is inserted so the wall is compressed between the dies and the mandrel. Without one, the ID follows whatever the wall does, and thin walls can buckle inward.
- Multiple passes. Area reduction per pass is limited, commonly in the range of 10–30% depending on material. Deeper reductions are staged through successive die sets, with the metal work hardening at each stage.
Cold work is the point
Because the operation is cold, the swaged region ends up stronger than the parent material and with a smooth, burnished surface. On ductile alloys this is free strength. On material that is already hard or has low ductility, the same cold work causes cracking — swaging is a ductile-metal process, and heavily cold-worked material may need an intermediate anneal.
Design guidelines
Reduce gradually
Keep area reduction modest per pass — commonly 10–30% depending on material — and stage larger reductions through multiple die sets. Trying to take too much in one pass causes the metal to pile up ahead of the dies, producing folds and laps that show up as cracks in service.
Tapers should be gentle
A long shallow taper feeds smoothly through the dies. A steep taper makes material accumulate at the shoulder rather than flow, which needs staged dies and more passes. Where a design allows a longer transition, take it.
Use a mandrel when the bore matters
Swaging a tube without internal support controls only the outside diameter; the wall thickens and the bore follows unpredictably, and thin walls can buckle. A mandrel makes the inside diameter a controlled dimension and keeps the wall uniform. Say on the drawing whether the OD, the ID, or the wall is the controlled feature — all three cannot be.
Expect the part to grow longer
Displaced material has to go somewhere, and a proportion of it goes axially. Overall length after swaging is longer than the blank, and the growth has to be accounted for either as a cut-to-length allowance or a trim operation.
Ductile materials only
Low-carbon steel, austenitic stainless, copper, brass, aluminum, and titanium all swage. Hardened steels, cast alloys, and heavily cold-worked stock crack. Where a part needs a hardened final condition, swage first and heat treat afterward.
Sharp geometry does not swage
The process makes bodies of revolution with gradual transitions. Sharp shoulders, steps with square corners, and non-round sections are not swageable — the metal simply will not fill them under light repeated blows.
For fits between a swaged end and its mating part, see ISO 286 fits and tolerances; for base material comparison, the material properties chart.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Area reduction per pass | 10–20% | ≈30% in ductile alloys | Excess reduction folds and laps the metal |
| Taper transition | Long and shallow | Steep tapers need staged dies | Material must flow, not pile up |
| Bore control | Use a mandrel | ID uncontrolled without one | Wall thickens inward under the dies |
| Controlled dimension | Choose OD, ID, or wall | Cannot control all three | Displaced material has to go somewhere |
| Length allowance | Add for axial growth | — | Volume is conserved; the part lengthens |
| Material | Ductile, annealed or soft temper | Hardened stock cracks | Cold work accumulates with every blow |
| Geometry | Bodies of revolution, gradual transitions | No square shoulders | Light blows will not fill sharp corners |
Cost drivers
Swaging has the cheapest tooling of any of the bulk forming processes: a set of two or four ground die segments, plus a mandrel if the bore is controlled. Machines are small and setups are quick, so the entry cost is low enough that swaging is economic on hundreds of parts. At volume, cycle times of seconds and near-zero material loss make it very cheap per piece — there are no chips, unlike turning the same taper.
Volume breakpoints: dozens of parts are practical on a manual machine. From 1,000 to 100,000, a dedicated die set and semi-automatic feed pay back quickly. In the millions, fully automated swagers with in-line feed and part handling take over.
- Design one reduction rather than several. Every additional stage is another die set and another pass.
- Lengthen the taper. Gentle transitions swage in fewer passes with less die wear.
- Only control the bore when you need it. A mandrel adds tooling, setup, and lubrication requirements.
- Swage instead of turning a taper. The material savings are total — nothing becomes a chip — and the swaged surface is burnished, often eliminating a finishing operation.
- Specify an annealed starting condition. Cracking from over-hardened stock is the most common avoidable scrap in swaging.
Variants
2 named
Rotary Swaging
Hydraulic Swaging
Questions
6 questionsHow much can be reduced in one swaging pass?
Commonly 10–30% area reduction per pass, depending on material ductility. Larger reductions are staged through successive die sets. Attempting too much in one pass makes the metal pile up ahead of the dies and fold over on itself, creating laps that behave like cracks.
Does swaging control the inside diameter of a tube?
Only if a mandrel is used. Without internal support the dies control the outside diameter, the wall thickens inward, and the bore follows unpredictably — thin walls can buckle. Specify which of OD, ID, or wall thickness is the controlled feature, because all three cannot be held at once.
Does swaging make the part stronger?
Yes. The operation is cold, so the swaged region work hardens and gains strength, and the repeated die contact leaves a burnished surface. The same mechanism is the process limit: material that is already hard or has low ductility cracks instead of flowing, so parts needing a hardened final state are swaged first and heat treated afterward.
Why does a swaged part get longer?
Because no material is removed. Volume is conserved, so metal displaced radially inward by the dies also flows axially. The blank has to be cut short of the finished length, or the part trimmed afterward, to account for the growth.
What materials can be swaged?
Ductile metals: low-carbon steel, austenitic stainless, copper, brass, aluminum, and titanium. Hardened steel, cast alloys, and heavily cold-worked stock crack under the repeated blows. An intermediate anneal restores ductility when several stages of reduction are needed.
Swaging or turning a taper on a lathe?
Turning is more flexible and holds tighter tolerances, but it cuts the material away as chips and severs the grain flow. Swaging keeps all the material, work hardens the formed region, leaves a burnished surface, and runs in seconds per part with inexpensive tooling — but it only makes gradual, round transitions.