×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

A question regarding tube bending

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

RE: A question regarding tube bending

Hot bending can induce changes in microstructure.
Cold bending also can offer tighter control of the dimensions.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: A question regarding tube bending

Because hot bending requires more time and cost. Actually, hot bending is preferred for most tight radius bends and to reduce residual forming strains.

RE: A question regarding tube bending

We cold bend from 1/8" to 4",SST and Inconels

RE: A question regarding tube bending

A hot bend is easier to bend = true. BUT, if you are doing hundreds of bends an hour, or even only two or three a day, both a hot bend and a cold bend require a form, a die and a process or machine to pull the tube through the bend. You are actually rolling the tube past a fixed die with a mandrel and lever arm against the fixed die.

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

The easiest, fastest and cheapest bend for stainless steel tubing is a 3D externally guided cold bend. From 1/8" through 1/2", you can do this with hand-operated lever tube benders- and at 3/4" and 1" you can manage with hand-operated crank benders.

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 cold bend SS and Ni alloy tubes, a lot.
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.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: A question regarding tube bending

(OP)
Many thanks for your replies

Zebmahar

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources