Cold-Working

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. 1-26