Page 366 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Chapter 14 Metal-Forging Processes and Equipment

Incremental Forging. In this process, a tool forges a blank into a shape in several
small steps. The operation is somewhat similar to cogging (see Fig. 14.4a), in which
the die penetrates the blank to different depths along the surface. Because of the
smaller area of contact with the die, the process requires much lower forces com-
pared with conventional impression-die forging, and the tools are simpler and less
costly.

Isothermal Forging. Also known as hot-die forging, this process heats the dies to
the same temperature as that of the hot workpiece. Because the workpiece remains
hot, its flow strength and high ductility are maintained during forging. Also, the
forging load is low, and material flow within the die cavity is improved. Complex
parts with good dimensional accuracy can be isothermally forged to near-net shape
by one stroke in a hydraulic press. The dies for hot forging of high-temperature al-
loys usually are made of nickel or molybdenum alloys (because of their resistance to
high temperature), but steel dies can be used for aluminum alloys. Isothermal forg-
ing is expensive and the production rate is low. However, it can be economical for
specialized, intricate forgings made of materials such as aluminum, titanium, and
superalloys, provided that the quantity required is sufficiently high to justify the die
costs.

Rotary Swaging. In this process (also known as radial forging, rotary forging,
or simply su/aging), a solid rod or tube is subjected to radial impact forces by a
set of reciprocating dies of the machine (Figs. 14.14a and b). The die movements
are obtained by means of a set of rollers in a cage in an action similar to that of
a roller bearing. The workpiece is stationary and the dies rotate (while moving
radially in their slots), striking the workpiece at rates as high as 20 strokes per
second. In die-closing swaging machines, die movements are obtained through
the reciprocating motion of wedges (Fig. l4.14c). The dies can be opened wider
than those in rotary swagers, thereby accommodating large-diameter or variable-
diameter parts. In another type of machine, the dies do not rotate, but move
radially in and out. Typical products made are screwdriver blades and soldering-
iron tips.
Swaging also can be used to assemble fittings over cables and wire; in such
cases, the tubular fitting is swaged directly onto the cable. The process is also used
for operations such as pointing (tapering the tip of a cylindrical part) and sizing
(finalizing the dimensions of a part).
Swaging generally is limited to a maximum workpiece diameter of about
150 mm; parts as small as 0.5 mm have been swaged. Dimensional tolerances
range from ;i:0.05 to d:0.5 mm. The process is suitable for medium-to-high rates
of production, with rates as high as 50 parts per minute possible, depending on
part complexity. Swaging is a versatile process and is limited in length only by the
length of the bar supporting the mandrel (if one is needed).

Tube Swaging. In this process, the internal diameter and/or the thickness of the
tube is reduced with or without the use of internal rnandrels (Figs. 14.15a and b).
For small-diameter tubing, high-strength wire can be used as a mandrel.
Mandrels also can be made with longitudinal grooves, to allow swaging of inter-
nally shaped tubes (Fig. 14.l5c). For example, the rifling in gun barrels (internal
spiral grooves to give gyroscopic effect to bullets) can be produced by swaging a
tube over a mandrel with spiral grooves. Special machinery has been built
to swage gun barrels and other parts with starting diameters as large as 350 mm.