Figure 1-23.—Cold-drawing operations for rod, tubing, and wire.
or bulged. The advantage of hammering is that the
operator has control over the amount of pressure applied
and the finishing temperature, and is able to produce
parts of the highest grade.
This type of forging is usually referred to as smith
forging, and it is used extensively where only a small
number of parts are needed. Considerable machining
and material are saved when a part is smith forged to
approximately the finished shape.
Cold-Working
Cold-working applies to mechanical working
performed at temperatures below the critical range, and
results in a strain hardening of the metal. It becomes so
hard that it is difficult to continue the forming process
without softening the metal by annealing.
Since the errors attending shrinkage are eliminated
in cold-working, a much more compact and better metal
is obtained. The strength and hardness as well as the
elastic limit are increased, but the ductility decreases.
Since this makes the metal more brittle, it must be heated
from time to time during certain operations to remove
the undesirable effects of the working.
While there are several cold-working processes, the
two with which you are principally concerned are
cold-rolling and cold-drawing. These processes give the
metals desirable qualities that cannot be obtained by
hot-working.
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