Swage

Swaging is a metal-forming technique in which the dimensions of an item are altered using a die or dies, into which the item is forced. Swaging is a forging process, usually performed cold, however it can be done hot.

The term swage can apply to the process of swaging (verb to swage), a die or tool used for swaging (noun swage).

Swaging as a manufacturing process

As a general manufacturing process swaging may be broken up into two categories. The first category of swaging is when the workpiece is forced through a confining die to reduce its diameter, similar to the process of drawing wire. This may also be referred to as tube swaging. The second category is when two or more dies are used to hammer a round workpiece into a smaller diameter. This process is usually called rotary swaging or radial forging.

Rotary swaging

Rotary swaging process is usually a cold working process, used to reduce the diameter, produce a taper, or add point to a round workpiece. It can also impart internal shapes in hollow workpieces through the use of a mandrel (the shape must have a constant cross-section). Swaging a bearing into a housing means flaring its groove's lips onto the chamfer of the housing.

A swaging machine works by using two or four split dies which separate and close up to 2000 times a minute. This action is achieved by mounting the dies into the machines spindle which is rotated by a motor. The spindle is mounted inside a cage containing rollers (looks like a roller bearing). The rollers are larger than the cage so as the spindle spins the dies are pushed out to ride on the cage, as the dies cross over the rollers they push the dies together because of their larger size. On a 4 die machine the number of rollers cause only one opposite pair of dies to close at a time; if the number of rollers cause all 4 dies to close at the same time then the machine is called a rotary forging machine, even though it is still a swaging process.

A variation of the rotary swager is the creeping spindle swaging machine where both the spindle and cage revolve in opposite directions, this prevents the production of fins between the dies where the material being swaged grows up the gap between the dies.

There are two basic types of rotary swaging machine, the standard (also known as a tagging machine), and the butt swaging machine. A butt swaging machine works by having sets of wedges that close the dies onto the workpiece by inserting them between the annular rollers and the dies, normally by the use of a foot pedal. A butt swaging machine can allow a workpiece to be inserted without the dies closing on it, for example a three foot workpiece can be inserted 12 inches and then the dies closed, drawn through until 12 inches remain and the dies are then released, the finished workpiece would then be for example be four feet long but still of its initial diameter for a foot at each end.

Other types of swaging

Firearms and ammunition

In internal ballistics, swaging describes the process of the bullet entering the barrel and being squeezed to conform to the rifling. Most firearm bullets are made slightly larger than the inside diameter of the barrel, so that they are swaged to engage the rifling and form a tight seal upon firing. Compare to obturate.

In ammunition manufacture, swaged bullets are bullets manufactured by swaging room temperature metals into a die to form it into the shape of a bullet. The other common manufacturing method is casting, which uses molten metals poured into a mold. Since metals expand when heated and contract when cooled, cast bullets must be cast with a mold slightly larger than the desired finish size, so that as the molten metal cools, it will harden at just the right point to shrink to the desired size. In contrast, swaged bullets, since they are formed at the temperature at which they will be used, can be formed in molds of the exact desired size. This means that swaged bullets are generally more precise than cast bullets. The swaging process also leads to fewer imperfections, since voids commonly found in casting would be pressed out in the swaging process. The swaging process in reference to cold flow of metals into bullets is the process not of squeezing the metals into smaller forms but rather pressing smaller thinner items to form into shorter and slightly wider shapes.

Individuals who make their own bullets usually are not aware of available manual specialized equipment and dies required for swaging bullets, and thus choose to make cast bullets. To get high precision results, it is common to cast the bullets slightly oversized, then swage the resulting castings through a die to do the final forming. Since the amount of pressure required to size the bullet is far less than that required to form a bullet, a simple mechanical press can be used, often the same press used for handloading ammunition.

Swaging bullets using the cold flow method with manual hand tools, presses and dies is often credited to Ted Smith author of the 45 page book The Bullet Swage Manual.

Many reloading equipment manufacturers started by marketing both reloading and bullet swaging dies and equipment. Originally formed by Fred Huntington the name RCBS was an acronym for Rock Chuck Bullet Swage. Historically many swage dies sold by well known reloading manufacturing companies were actually made by Ted Smith in his die shop then stamped with the name of the marketing company.

All of the larger manufacturers of reloading equipment have abandoned making or marketing bullet swaging equipment due to the downturn in the popularity of the manual methods and the subsequent loss of sales. Currently there are only a few die makers who manufacture and market bullet swaging equipment, three die and equipment makers CH/4D, RCE, and Corbin manufacture the bulk of bullet swaging equipment in the United States.

References

• Degarmo, E. Paul et al., (2003). "Materials and Processes in Manufacturing", 9th Ed., pp. 398 - 409. Wiley. ISBN 0-471-65653-4