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Warping/bending when welding


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I thought this time would be fine, i'd learnt my lesson from previous mistakes of not clamping things down when welding them.

 

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I need to weld 10mm square bar to 20x30mm bar (twice in fact to create a recess on a bar that looks like 30x30, if that makes sense.)

 

I clamped the whole lot down and proceeded to weld the length up and clean up all the weld.

 

When i released it i found it had still warped upwards of an 50-60mm in two planes across the 2m length!!!

 

What can i do to prevent this on the others i have to do. and what is my best course of action to rectify the bend i've created here?

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Nic,

 

I don't think you will ever stop that from warping by clamping it down. It sounds like you have a bend and a twist, which makes things that bit more difficult.  You could try and spot weld on the other side to where you have already welded it, that may pull it back. Or get the hole thing hot and try and knock it back into shape.

 

Failing the above efforts, is there anyway you can fix the 10mm square by using countersunk screws. If the piece is going to be painted afterwards they can be easily hidden by some body filler or make a feature out of the fixings. 

 

Mick.

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There are whole books written on warping and straightening weldments, but the short answer is:

 

(1) Prebend the metal so that the welding pulls it straight, and/or

 

(2) Alternate welding from all sides so that you end up with equal strain, and/or

 

(3) Do a post weld heat treatment and counterbend to straighten.

 

Water is pretty much the only common material that expands when it becomes solid, everything else contracts. There are tables and guidelines for welding engineers to use to compute the weld stress and contraction, but they are not much help to the layman.

 

If I understand you correctly, you welded one 10mm bar down, starting at one end and going to the other. One continuous bead the entire length of the bar. That will cause the bar to bow up as one end and one side is hot and the other end/side is cool. (The same effect you get when you change a large tire on a vehicle. You don't tighten the lug nuts 1-2-3-4-5, that will warp the rim. You tighten 1-3-5-2-4.)   Then you welded the other bar in the same manner after the first one had cooled somewhat. That would cause the corkscrew effect, as well as increase the bow.

 

How I would set this up would be to but a 10mm shim under the center when clamping, and put both bars on the top at the same time. I would tack weld the bars in three or four places, 5-10mm tacks only. When cool, I would "skip weld" a half dozen or so 25mm long beads on each bar, alternating top/bottom left/right to spread the stress. Done. Go get a cold or hot beverage of your choice, as indicated. Take the clamps off when the welds are cool to the touch.

 

If you beveled the edges of the spots that you were going to weld, there will be less grinding to do, and more strength in the weld that is left.

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you can bend it cold, place a block of wood on its edge and lay the length of metal across it. Hold it like you would a sledge hammer and belt it on the timber block working along the length of metal from both ends. if you look along the piece and mark the spots to be fine tuned with chalk it is possible to get a perfect result.

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Greenbeast,

What welding process and parameters are you using ? Where did it warp the most, in between the
C-clamps?
It can be VERY frustrating when this happens but using a well configured setup and proper technic
will make all the difference in the world.
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Happy New Year,

 

If you want a simple straight bar, buy it the size you want! If you are going to weld it and it pulls all over the place, make a 3 foot long propane forge (one brick wide, 3 bricks tall, 4-5 bricks long, aim your burner in one end and semirestrict the other end) and heat and straighten 3 feet at a time. The good part about heating and straightening, all the internal stress and strain from welding will be gone.

 

Neil

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Clamping does not always help. There is a lot of stress left in the weld even after cooling. I have seen very large weldments that were perfectly square get stress relieved simply by the vibrations and movements of the delivery truck. They arrive out of square and need to be repaired.

 

In addition to the already mentioned techniques.  Backstep and skipstep welding can really make a difference. With backstep weld in the opposite direction of travel ie: if you are progressing from left to right down the bar, weld from right to left. Skip step simple skip very second or third weld. then come back an do this again.

 

You can also peen the weld with an air chisel as it cools this will help to stress relieve it so that the contraction of the weld metal will not be so pronounced.

 

These techniques are particularly helpful for large weldments that can not be restrained.

 

brad

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There is a good book called flame bending/straightening that deals with how sheet and other things move when heated in a particular section.  I have been able to straighten things out by doing a little stick here or a little stick there but you have to have an idea of how the heat will affect the steel.  When you do it is like magic.  

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the 20x30 is 6 times the volume of the 10x10, so it has area to transfer heat and hold heat reducing the contraction, clamping a second 20x30 offcut on the top as a heat-sink will help a little, John has nailed the pre-flex and stitch technique, that is exactly how I would jig it up.

 

I find welding is like golf or painting a car, its 95% preparation and planning, 4% luck and 1% basking in the glow of satisfaction after a perfect weld.

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Greetings Green,

 

I guess I would have to ask if the end product is structural or ornamental.   If you are using the 10 mm bar for a reveal that's  one thing .. If it is structural I would follow the master.. Johns advice ...  Sometimes if it is only ornamental its wise to counter sink screws from the back... Than stitch weld.. after bevel .

 

Is a full weld required ??

 

Forge on and make beautiful things.

Jim

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It is purely ornamental, i thought it might be aesthetically better to lose the seam between the bars

 

I'm debating minimal welding or the countersunk screws.

 

The piece will be galvanised and powder coated. my concern is getting a proper coating in between the pieces, if it was screwed at least it would be removable but the 10x10 might be more likely to warp in galv (i think?).

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If you are looking for minimal heat and penetration then choosing a small diameter all position rod and welding in the vertical down position is the way to go. With practice and a good welder  it can make an almost seamless look.

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If you are looking for minimal heat and penetration then choosing a small diameter all position rod and welding in the vertical down position is the way to go. With practice and a good welder  it can make an almost seamless look.

Yes, 7014 would work well for that and vertical down imparts the least heat. 

Personally though, I would go the countersunk screw methods, easiest by far. 

 

When such a weldment MUST be made however,John McPherson covered it pretty well indeed.

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You think thats bad, make that from 316 stainless!!! You've already welded one and now it smiles at you, turn it over so it frowns and measure how much arch it has from the table to the inside if the arch.... Shim the next one in the middle that much and clamp only at the ends after you get the three pieces tacked together then weld using the same parameters as you did before. Once you finish welding, let it cool just a bit (not till ice cold) and release it.

To straighten the one thats already welded, take your oxy-fuel torch and heat the outside of the arch down the length only on the edges where the pieces got welded on. Not till it's red hot, just till you start to move colors. Apply a clamp to the center and drive the arch down slowly, little but at a time and let cool. Keep doing this until straight.

-Hillbilly

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Heat straightening or a press would work, but a length of pipe that would slide over the piece and a bending fork on a table or a vise would do for that as well. You'd just need to go a long and bump it where needed to take the bend out of it using the pipe to help make sure it only bent where you wanted it to. Lots of small bends would work better than trying to do just a few bigger ones. I'd probably go thru it two or three times minimum working on getting it close 1st before fine tuning where needed if I used that method..

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Thanks guys, i do have a reasonably sized fly press.

 

I have enough steel to continue with this project using alternative fixing methods. Although i do like the pre-bending method as it will allow me to use welding which will seal the seam/gap ready for galv/powercoat

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  • 3 months later...

E-7014 will leave porosity and holes!!! The ONLY stick electrode that is designed for (let alone rated) downhill progression is E-6010 & E-6011. Thats it. Keep it in the horizontal position, counter-bow as I've explained, and carry on.

-Hillbilly

You should have gone to Lincoln School son.

 

I can only imagine you are thinking of 7018, which should only go up, although with practice can also make downhill welds. 7014 however was designed for downhill.

 

“High Speed” Group
Operates in all positions, but most widely use downhill, horizontal or in the flat posi-
tion. Ideal for irregular or short welds that change direction or position. Medium
deposit rates and medium penetration. Appearance ranges from smooth and ripple-
free to even with distinct ripples.
Sizes & Current Ranges (Amps)
Electrodes are manufactured in those sizes for
which current ranges are given
Product AWS Electrode Fleetweld 7 E6012 DC- ---
Name Class Polarity AC ---
Fleetweld 37 E6013 AC 75-105 (1) 110-150 160-200 205-260
                   DC± 70-95
                       100-135 145-180 190-235
Fleetweld 47 AC 80-100
             DC- 75-95
(1)
E7014
3/32”
1/8”
5/32”
3/16”
7/32”
80-135 110-180 155-250 225-295
90-150 120-200 170-275 250-325
---
---
110-160 150-225 200-280 260-340
110-145 135-200 185-235 235-305
1/4”
245-325
275-360
---
---
280-425
260-380
Range for 5/64” Fleetweld 37 is 50 - 80 amps AC or 45-75 amps DC. 1/16” Fleetweld 37 is

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