A question regarding tube bending
A question regarding tube bending
(OP)
Good day guys,
Can anyone let me know, why the cold bending is preferred by the fabricators instead of hot bending? Even in the hot bending there is very little chance of cracking and tubes also get bend easily.
Regards
Zebmahar
Can anyone let me know, why the cold bending is preferred by the fabricators instead of hot bending? Even in the hot bending there is very little chance of cracking and tubes also get bend easily.
Regards
Zebmahar





RE: A question regarding tube bending
Cold bending also can offer tighter control of the dimensions.
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P.E. Metallurgy, Plymouth Tube
RE: A question regarding tube bending
RE: A question regarding tube bending
RE: A question regarding tube bending
A hot bend MUST BE exactly the same temperature across the entire bend length (and be very, very carefully kept exactly at the same temperature EVERY time the same part is made.) Otherwise, the part is ruined - it bends too far at the hot spots and too little (is still straight) at any or all of the cold spots. So, as you do more and more bends, the mandrel and die and machine heat up - you get different results. Then you go to lunch, or lose power, or do something else for a few minutes, and the parts change again., Start up again the next day, you make all of the same differences in each part.
You need more energy for a cold bend, but that bend is simple and repeatable. Build the machine for a big tube, buy a new mandrel and die and you can use it for any smaller tube diameter, wall thickness, and bend diameter. A cold bend is the same bend across the whole tube every time because the metal yields predictably every time. (Unless wall thickness changes.)
RE: A question regarding tube bending
Need to bend tighter than 3D? Now you need the bother of either internal guiding or heat. The bother associated with heat has been very articulately explained by racookpe1978.
RE: A question regarding tube bending
We actually use mandrels up to about r=4d, that way we can control the balance between wall thinning on the extrados and ovality in the bend.
And in most cases we post bend anneal the ubends. Clamp the legs just past tangent point and pass DC current through them using optical pyrometers to control the temp. The real critical part is the cooling. You need fast enough to preserve the structure, but slow enough to not introduce severe residual stresses.
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P.E. Metallurgy, Plymouth Tube
RE: A question regarding tube bending
Zebmahar