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  1. #1
    Airborne is offline Stainless
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    What's the best way to stress relieve a welded steel frame? 3" x 3/16" square steel tube in case you're wondering. Various sizes... 3' x 2' for starters.

    Small shop, don't have any fancy equipment. I'm guessing probably a torch, or maybe a homemade brick oven. How hot and what would the procedure be?

    Or maybe I can try using the vibratory method with a big subwoofer. Neighbors won't like it. [img]tongue.gif[/img] [img]tongue.gif[/img] [img]tongue.gif[/img]

  2. #2
    Ries's Avatar
    Ries is offline Diamond
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    I really dont think using a torch will work.
    The main thing you need for stress relief like that is a constant, controllable, all over heat- that means a thermocouple controlled oven.

    A torch will make it warp, as any time you apply localised heat to steel, it moves.

    Why does it need to be stress relieved?
    To meet some engineering standard?
    Or is it warped from welding and you want it straight again?

    If that is the case, heat wont help.

    Some people use air powered needle peeners to stress relieve welds on higher carbon steels, when they might crack from just cooling at room temp.

  3. #3
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    I think a torch will work but it's a very high form of skill.

    A man I respect once told me of a guy he met who stress-relieved welds with just a torch, and I suspect lots of experience and expensive testing-training iterations. His technique was something like pulse-width modulating the time the torch was on the weld, at first hot, but then to promote a slower bulk cooling curve. Analagous to using the "ANNEAL" button on a bandsaw blade welder.

    Homebrew, for a project about a foot cube as a welded machine element, I had considered building sort of a "cave" out of firebrick, to retain heat. Then point a propane weedburner torch inside there and adjust by calibrated eyeball.

    I have also heard of welding 1 inch, then quickly removing the helmet and peening the heck out of the hot weld. Then weld 1 more inch and repeat ad nauseaum. However, that was for a cast-iron repair but I suspect the technique would work on steel.

  4. #4
    Airborne is offline Stainless
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    Not warped, I just don't want it to relieve itself later on.

  5. #5
    Mebfab is online now Diamond
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    I saw a machine at auction once that did this. Looked like black magic.

    Basicly a small DC motor. Double ended. Had weights attached so as it ran it vibrated. THere was a chart on the machine so you would strap it down to the weldment, adjust the knob to the size (?weight ??) of the frame and let it run.

    Dont remember the name, dont know if it really did any good. Do know that everything at that sale went high and nobody wanted this.

  6. #6
    Mike W is offline Stainless
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    Just keep it square when you weld it up and don't worry about it. I don't recall having any problems later on.

  7. #7
    Gary E is online now Diamond
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    Zumba
    Not warped, I just don't want it to relieve itself later on.
    You should ask yourself...
    Self, do I feel lucky??
    Lucky that this thingie wont bend outa shape, become useless and waste and ruin all of the time and material I put into it?
    So self, are you lucky that it's a cheap thingie that I can aford to throw away and start over? and this time SEND IT TO A HEAT TREATER for proper stress relieving ???

  8. #8
    Airborne is offline Stainless
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    I feel lucky enough not to spend the money on a commercial heat treater, but not lucky enough to do nothing about it. If I were only making one part, it'd be a different story, but I'm making a ton of them.

  9. #9
    Gary E is online now Diamond
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    That many ehh..

    You could be VERY SORRY you didnt have it done correctly

    And there's NO way you will do it correctly yourself, or you would not of asked this question

  10. #10
    3t3d is online now Titanium
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    Basicly a small DC motor. Double ended. Had weights attached so as it ran it vibrated. THere was a chart on the machine so you would strap it down to the weldment, adjust the knob to the size (?weight ??) of the frame and let it run.
    I met the manufacturer of those, either at IMTS or National Manufcturing Week, in Chicago.
    They had a way to measure the stress in the part by dynamic analysis, and would then run the gizmo on a weldment. You could watch the stress go away.. .
    Then they could weld on it again, and stress relieve it again.
    I was amazed that that would work, apparently form your story, it is not commonly used.

    Basiclly it was a vibration that would jiggle it,to stress releive it. Not unlike the kneedle scaler idea, only more electronic controls, and a larger scale effect.
    Pete

  11. #11
    Gary E is online now Diamond
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    Will these FRAMES be machined after your done welding ?
    If yes... better send it out for proper Stress Relieve

    Sounds like this is a customers design.. what does he expect?

  12. #12
    johnoder's Avatar
    johnoder is online now Diamond
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    ASME "ramped" PWHT is just what you are looking for, but is hardly a home shop exercise.

    John

  13. #13
    gbent's Avatar
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    3/16 x 3" square tubing is hardly the stuff of precision weldments. The tubing probably has as much stress from the mill as you induced by welding. Just weld them up and don't worry about it.

    If you plan on precision machining weldments, start with all hot rolled steel.

  14. #14
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    bluchip is offline Stainless
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    I saw a machine at auction once that did this. Looked like black magic.

    Basicly a small DC motor. Double ended. Had weights attached so as it ran it vibrated. THere was a chart on the machine so you would strap it down to the weldment, adjust the knob to the size (?weight ??) of the frame and let it run.

    Dont remember the name, dont know if it really did any good. Do know that everything at that sale went high and nobody wanted this.
    No, it's not black magic....it's fact and it works. Been welding molds with this on an isolated table for years. Also, set mold on blocks of iso rubber and shake the $%^#& out of it. Saves from sending to heat treaters. Works wonders for weldments. It will stress relieve all THERMALLY induced stresses. If MECHANICALLY induced it still will require a thermal treatment. I have bolted it to engine blocks and heads, weldments, big mold inserts after rough machining, entire die cast machines, etc.
    It is wild watching the harmonic peak shift. Takes minutes and is fascinating.

    http://www.meta-lax.com/Home/home.html

  15. #15
    LL
    LL is offline Senior Member
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    Very high end, high carbon steel, blacksmith-made Japanese
    hand saws (pullsaws of various types: backsaw,
    crosscut and rip) are prone to cracking if
    not handled properly. They are forged, heat treated and tempered, then further stress-relieved after scraping, thicknessing and tapering, with
    highly skilled peening on both sides, a process that makes the blade flat and straight and tensioned for maximum performance in the hands of an expert joiner. After the teeth are cut it is ready for use.

    A Hitachi or Bosch rotary hammer drill might make a good peening tool. Many different types of points are available, in addition to masonry drills, such as chisel, sharp point, curved and blunt. You could modify these on a grinder to suit your needs.

    [ 12-29-2006, 03:39 AM: Message edited by: LL ]

  16. #16
    Airborne is offline Stainless
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    3/16 x 3" square tubing is hardly the stuff of precision weldments. The tubing probably has as much stress from the mill as you induced by welding. Just weld them up and don't worry about it.

    If you plan on precision machining weldments, start with all hot rolled steel.
    Can you elaborate on this? Are you referring to the inside weld on A36 tubing that creates stress? What would constitute "all hot rolled steel"?

    I guess I should've asked a different question right from the start...

    "In what applications is thermal induced stress relieving required, and in those cases, how much would the material actually move over a few years?"

    Another question...

    "How do I minimize thermal induced stress (that might haunt me later) when welding?"

    Thanks for the replies, everyone.

  17. #17
    Rick Rowlands's Avatar
    Rick Rowlands is offline Titanium
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    Of course Gary E thinks you can't do it correctly. In his world you are incapable of learning by asking questions on this forum, so why bother?

  18. #18
    gbent's Avatar
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    Hot rolled steel is the stuff with the blue scale on the outside. Any steel that has been cold finished has compressive stresses from the finish rolling. The shape is held straight by matching stresses on both sides. If the stresses on one side are relieved by heat or removed by machining, the steel will bend.

    I think A36 only refers to low carbon hot rolled flats and shapes. Structural tubing is cold finished and is often A500.

    Your question as to how much the weldment will move, in my experience very little. Without external stresses I expect almost no movement due to internal stress relief.

    The James F. Lincoln Arc Welding Foundation has published several good books on welding. One is on the design of weldments, most specifically to replace castings.

    If you define your view of precision it would be easier to answer your question. Some here think of 6 decimal places for precision, others work to the closest 1/8". Neither is wrong, its just a case of what job you are doing. To me, its in the range of .002/10" true position and that would be challenging on a light weight weldment.

  19. #19
    Airborne is offline Stainless
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    Thanks for the good info, gbent. You're right, the tubes I have are A500... printed right on the metal!

    The precision I'd like to achieve is .010/12" overall. However, I'd like to achieve .005" or better in certain spots by grinding after welding (places where bearing blocks, motor mounts, etc will be mounted).

  20. #20
    bernie_l is offline Member
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    Zumba-

    If what you are trying to acheive is a weldment that is flat, square, and to dimension then I suggest a welding fixture may go a long ways to achieving this. For 3" square tube a very robust fixture. This will not relieve any stress, but it will hold the parts and pieces in the correct relative alignment during assembly and if allowed to cool in the fixture has a pretty good chance of maintiaining that alignment. Using a well designed fixture will also greatly reduce your assembly time. Also if you are making many of these structures it will be important to get a good handle on your welding process so that each unit is welded as close as possible to the others. You may also want to experiment with the sequence of the welds, this can make a very significant difference to the outcome of the assembled structure. Develop the process parameters and sequence and stick to it. To completely eliminate stress in a welded structure seems to be pretty ambitious, not impossible but challanging, and probably expensive. I think what frequently happens in weldments is not so much an elimination of stresses as it is a balence or offsetting of stresses. If all else fails and the weldments are all pretty much out of flat, square, or whatever about the same then a straightening fixture could be made to correct that. Once the structure is welded and cooled it seems pretty unlikely that any residual stress is going to change it at a later date unless further welding, heating, or machining is done on it.

    Good luck and take care

    Bernie

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