Swaging is a metalworking process that reshapes metal by forcing it through or between dies, compressing it into a new form without cutting away material. Unlike machining, which removes metal to create a shape, swaging displaces it. The result is a stronger part with an unbroken grain structure, and the process works on everything from surgical needles to aircraft landing gear components.
How Swaging Works
At its core, swaging uses compressive force to change the dimensions of a metal workpiece. There are two basic approaches. The first pushes metal through a confined opening to reduce its diameter, similar to how wire is drawn through a hole. The second uses two or more dies that repeatedly hammer the workpiece from opposite sides, gradually forcing it into a smaller or differently shaped cross-section.
The most common industrial version is rotary swaging. A set of split dies (usually two or four) are mounted inside a spinning spindle. As the spindle rotates, the dies ride outward from centrifugal force, then get pushed inward each time they pass over a set of oversized rollers in the surrounding cage. This open-close-open-close action happens rapidly, delivering hundreds or thousands of small hammer blows per minute. The workpiece is fed into the center of the dies, and each blow compresses it slightly. The cumulative effect reshapes the metal precisely and quickly.
Most swaging is done cold, meaning the metal stays at room temperature. Cold working is practical for most metals that can tolerate deformation without cracking, and it has the added benefit of strengthening the material during the process itself.
What Swaging Does to Metal
When metal is swaged, the internal grain structure gets compressed and elongated in the direction of the swaging. Grains that were roughly round become stretched and narrow, typically 5 to 10 micrometers wide. This refinement dramatically increases strength. In one study on a copper-chromium-zirconium alloy, rotary swaging nearly doubled the ultimate tensile strength, pushing it from 227 MPa to 433 MPa. A pre-processed version of the same alloy reached 597 MPa after swaging.
The tradeoff is ductility. That same copper alloy went from 61% elongation before swaging down to about 16% afterward. In practical terms, the metal becomes much harder and stronger but also less flexible. This is a well-understood characteristic of cold working: you gain strength at the expense of the material’s ability to stretch before breaking. For applications where stiffness and load-bearing capacity matter more than flexibility, that exchange is worthwhile.
Rotary vs. Radial Swaging
Rotary swaging and radial forging are closely related but serve slightly different purposes. Rotary swaging is best suited for reducing cross-sections on rods, tubes, and similar round blanks. It excels at creating tapers, points, and stepped diameters on relatively small workpieces, and it’s considered a cost-effective process that saves both material and weight compared to machining.
Radial forging is an open-die process typically used on larger parts: shafts, axles, stepped shafts, and tubes. One of its signature applications is creating internal profiles inside tubes, such as the rifling inside gun barrels. When shaping the inside of a tube, a mandrel (a shaped rod inserted inside the tube) acts as the inner die while the outer dies compress the tube wall against it. If the internal surface quality isn’t critical, or the geometry doesn’t allow it, the mandrel can be skipped.
Precision and Tolerances
Swaging can achieve remarkably tight dimensional control. In barrel manufacturing, for example, machine makers guarantee bore dimensions within plus or minus 0.0002 inches (about 5 micrometers). Under ideal conditions, precision of 0.0001 inches on diameter and straightness of 0.0005 inches per foot has been demonstrated, producing parts that are nearly stress-free. These tolerances rival or exceed what many machining operations can deliver, which is one reason swaging is favored for high-performance applications where consistency matters.
Where Swaging Is Used
Aerospace and Automotive
In aerospace manufacturing, swaging produces hydraulic tube fittings, control rods, and landing gear components. These are parts where both strength and weight savings are critical. In automotive manufacturing, the process creates drive shafts, axles, and steering components. Because swaging displaces rather than removes material, the finished part retains a continuous grain flow that resists fatigue better than a machined equivalent of the same shape.
Surgical Needles
One of the less obvious but widespread uses of swaging is attaching suture thread to surgical needles. The needle has a small channel or opening at its blunt end. A strand of suture material is inserted into that opening, and then a pair of dies compresses the needle around the suture, permanently locking them together. Automated machines perform this at a rate of about one needle per second, using a fixed die and a movable die that closes under controlled air pressure. The result is a needle-suture connection that won’t separate during surgery, with no knot or bulge that would tear tissue as it passes through.
Wire Rope and Cable Fittings
Swaged fittings are standard in wire rope and cable applications, from construction rigging to sailboat stays. A metal sleeve is placed over the cable end and then compressed with a swaging tool or machine, permanently gripping the wire rope. Swaged connections are compact and reliable, though the compression process does slightly reduce the cable’s breaking strength compared to its unmodified state. Spelter sockets (which use poured metal rather than compression) are the only fittings rated at 100% efficiency. Swaged fittings typically rate around 90%, but since most wire ropes have an actual breaking strength 5% to 15% higher than their published catalog rating, a swaged connection often still meets or exceeds the rope’s listed capacity.
Bearings and Assemblies
Swaging is also used to secure bearings into housings. Rather than using fasteners or adhesives, the process flares either the bearing’s groove lips onto the chamfer of the housing, or flares the housing material over the edge of the bearing. A pair of rolls travels around the hole and feeds downward, deforming the metal in a controlled pattern. This creates a permanent, vibration-resistant joint without adding separate fastening hardware.
Swaging vs. Other Forming Methods
Compared to machining (turning on a lathe, for instance), swaging is faster, wastes no material, and produces a stronger part because the grain structure stays intact. A machined shaft has its grain lines cut through at every surface, while a swaged shaft has grain lines that follow the contour of the finished shape.
Compared to traditional forging with a hammer and anvil, rotary swaging is more precise and better suited to long, thin, or tubular parts. It also requires less force per stroke because the deformation happens incrementally over many small blows rather than a few large ones. This makes it practical for shaping metals that might crack under a single heavy impact. The limitation is geometry: swaging works best on round or near-round cross-sections. Complex shapes with flat faces, sharp corners, or asymmetric profiles are better handled by other forging or stamping methods.