Explain "spring-back" in metal forming.

Spring-back refers to the tendency of metal to revert to its original shape after being deformed. This phenomenon occurs during processes such as bending or forming, where the metal is stressed beyond its elastic limit. Once the external force is removed, the metal experiences a recovery to some extent, creating a difference between the final shape and the intended shape. Understanding this behavior is crucial in metal forming because it impacts the accuracy of parts and the required adjustments in tool design and process parameters.

Knowing how much spring-back to expect helps tool and die makers anticipate necessary corrections to achieve the desired final dimensions after the forming process. Techniques such as compensation in the tooling design or applying post-forming processes may be used to manage spring-back in practical applications.

The other options do not accurately describe spring-back, as they relate to different aspects of metal forming, including heating, elongation, or the nature of support during shaping, rather than the specific characteristic of metal returning to its original form after deformation.