rScotty
Super Member
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- Apr 21, 2001
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- Rural mountains - Colorado
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- Kubota M59, JD530, JD310SG. Restoring Yanmar YM165D
As far as shrinking or stretching, it is common to do with light sheet metal. However, it may well be different to do with heavy box steel.
If one can predict how metal moves with welding, perhaps one could control stretching/shrinking with heat.
However, I'd probably try to straighten it cold. A car body shop with a frame machine could likely either straighten the bent side, or bend the other side to match (which may avoid the length issue).
I think the problem here is simply definitions. We all shape metal when we need to. Metallurgy looks at the chemical structure, and metalworking at the physical shape.
Bending metal until it yields causes it to stretch in the plane of the bend - there's no getting around that. But as several posters have pointed out, there are some practical ways to deal with the stretched metal so that the stretching and thinnng is controllable to get to where we want to go.
For example, if bending has caused a box beam or loader arm to become too long in the plane of the bend, it is common to "shrink" the beam lengthwise by forcing it to become thicker in a plane at right angles to the original bend. So what posters are saying is that metal worker can compensate for the original change in length by forcing the metal to thicken in a different direction. That works of course - we all do that in the shop. The exact same thing works in sheetmetal - you flatten (shrink) a dent it in one plane by pounding it to make it flat - but it grows in the other plane so it is larger. A bent washer is easy to flatten on an anvil, but it becomes a slightly larger diameter on the outside edges.
The metal didn't "shrink", it can't. Without huge atomic forces we can't make it much more dense. All we can do is remove voids, and steel doesn't have many of those. What we do is bend it around to become thicker in a different plane. We "shrink" it in the direction we care about by making it stretch in a direction that doesn't matter.
The art of metalworking is moving the metal around so that it is right in the dimension that you care about and it bulges in a direction that doesn't matter.
rScotty
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