#11
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Yes, and no. Just inspect the open side of one of your bends, and if you see the grain opening up to the point where the valleys start looking pretty deep, then increase the radius a bit. I have seen flanges crack off because of bend radii being too tight on 1100 and 3003. Another area of caution is when making hems. Leave the hem rounded at the bend and then just set it down at the return. I've seen more than a few hems suffer cracking at the fold from over-zealous mashing down.
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#12
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I deal with this issue on a daily basis. While we are normally dealing with harder and much thicker steel alloys (armor plate) than is used in normal automotive applications, many of the rules still apply. Most materials will have a minimum bend radius (measured to the inside of the bend). The minumum radius is when bending perpendicular to the grain.
A couple things come into play: material, material temper or hardness, and thickness. A quick rule of thumb is to double the minumum bend radius when bending parallel with the grain. If you are bending a square/rectanular box or tray, or have to make two bends 90° to each other, try to cut the piece so that the bends are 45° across the grain. This is typically for mission critical parts, or simple straight bends on thing subjected to high loads or vibration. Things like hems across curves, like a fenderwell, pick up a lot of strength since the panel is more rigid than a large straight panel. For larger radii like 4T (4 times the thickness) on material under .120" you don't have much to worry about unless you are using high-hard steel or 2024 Aluminum. For 1100, 3003-H14, and 5052-H32 Aluminum, and AISI 1008CRCQ Steel the minimum bend radius would be 1T. As crystallographic suggested, check for spreading of the grain on the outside of the bend. I suspect that this might be the reason for wire formed edges on older vehicles. For what most of us are doing, you would never have a problem with sharp bend radii Oh yeah. . .never ever ever scribe a bend line. Use a fine tip sharpie. Those of us who do failure analysis thank you.
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Andrew Slater HANGAR 18 FABRICATION |
#13
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Quote:
Well said. Experience speaks. Kent |
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