Swage

Swaging (pronunciation note below) 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.^[1] Swaging is a forging process, usually performed cold, however it can be done hot.^[2]

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

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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. The second category is when two 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).

A swaging machine works by using two split dies which separate and close up to 2000 times a minute. This action is achieve by mounting to 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 crossover the rollers they push the dies together because of their larger size.^[3]

Other types of swaging

Pipes and cables

The most common use of swaging is to attach fittings to pipes or cables (also called wire ropes); the parts loosely fit together, and a mechanical or hydraulic tool compresses and deforms the fitting, creating a permanent joint. Pipe flaring machines are another example. Flared pieces of pipe are sometimes known as swage nipples, pipe swages, swedge nipples, or reducing nipples.

Saw blade teeth

In sawmills, a swage is used to flare large bandsaw or circle saw teeth, which increases the width of the cut, called the kerf. A clamp attaches a mandrel and die to the tooth and the eccentric die is rotated, swaging the tip. A much earlier version of the same operation used a hardened, shaped swage die and a hand held hammer. Saw teeth formed in this way are sometimes referred to as being "set". A finishing operation, shaping, cold works the points on the tooth sides to flats. It might be considered as a side swage. This slightly reduces the tooth width but increases the operating time between "fittings". Swaging is a major advance over filing as the operation is faster, more precise and greatly extends the working life of a saw.

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.

Rubber components with mold bonded metal sleeves

This process provides a more controlled and cost-effective alternative to 'shooting' the rubber part into a metal sleeve, where an intensive and less dependable secondary operation is needed to finish the product. A metal can with a bonding component (such as phosphate) is painted to the inside diameter, and molten rubber is injected into the metal sleeve. This creates a product that when cooled may be swaged to the desired size. The second reason for this is that the product is more reliable, and during the swaging process the rubber is more relaxed when the outside can to which the rubber is bonded has its diameter reduced, changing the springrate (K) values and dampening the co-efficient (C) of the rubber. After swaging, any inconsistencies in the metal and rubber have been minimized.

Drawing Tubes

Tubes may be tagged using a swager which allows them to be drawn on a draw bench.

Suture needles

In surgery, the thread used in sutures is often swaged to an eyeless needle in order to prevent damage as the needle and suture thread are drawn through the wound.

Musical Instrument Repair

In Musical Instrument Repair the usual term on both sides of the Atlantic is invariably swedging, not swaging, though it is generally acknowledged that the former derives from the latter. Keyed instruments such as the clarinet, bassoon, oboe and flute need swedging when years of key movement has worn or compressed the metal of the hinge tube they swivel on and made it slightly shorter, so that the key can travel along the rod it's mounted on instead of being held firmly between the posts attaching the rod to the body of the instrument. This gives rise to floppy keys and a poor air-seal and needs to be corrected by lengthening (swedging) the hinge tube. This is a job that needs to be done by hand, and swedging pliers with highly-polished oval holes in the jaws to fit common sizes of hinge tubes are often used to achieve this, though various proprietary designs of swedging tools are available to do the same job more efficiently.

Pronunciation note

Swage is most often pronounced /ˈsweɪdʒ/ (AHD format: swāj).^[4][5] Another (less common) pronunciation sometimes heard in the metalworking industries is /ˈswɛdʒ/ (AHD format: swĕj)^[6] (perhaps influenced by sledge as in sledgehammer).

See also

• Manufacturing
• Flare fitting
• Cold work

References

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