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Condition that occurs when a flat-rolled metal or alloy is cold-worked; upon release of the forming force,
the material has a tendency to partially return to its original shape because of the elastic recovery of the material.
This is called Springback and influenced not only by the tensile and yield strengths, but also by thickness,
bend radius and bend angle.
Three ways to eliminate springback
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The obvious way to counter springback is simply to over bend the piece and let it open up to the desired shape.
You make your bend and the, by trial and error, find how much the part springs from the bend. This method will
probably be the choice for most parts when the tolerances are generous. Where the tolerances are exacting,
the obvious problem is that springback is not consistent. It will vary from one coil of wire or strip to the nest.
A further complication exists if the finished part is heat treated - it will change shape in the furnace and the
amount it will "open up" is another inconsistent and unpredictable factor.
An experienced toolmaker usually knows several ways of modifying tooling to correct springback. These
ideas are often based on trial-and-error experiences.
There is another interesting way of preventing springback. If, during the forming of the part, the wire
has been heated, it will not have a tendency to spring back after the forming slides have been released.
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All strip stock and wire has a "yield point," as does any metal. The yield point is the point at which
it will no longer spring back to its original size. When strip or wire is stretched or compressed, the material
is put under strain. If the metal is stressed enough, it will fail at some point or become stressed. "Fail," in
this case, does not mean that it will be broken, but that it is permanently "set". A piece of mind steel might
yield at 20,000 psi but it might require 40,000 psi to actually make it break apart. We are interested in that
point at which it yields but does not break.
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