Correcting for warpage

[joshuabardwell]

It sounds like there is general agreement that holding the pieces in place until the weld cools will eliminate much distortion. As basic as that might be, I didn't realize that. I guess I thought that the weld would put tension into the structure and the tension would still be there when the clamps were removed, unless you did something like peen the weld. Leaving the piece clamped will be the first thing I try.

[mikehaugen]

yes, and the peening is still a good idea. It's not to technical to "peen", or maybe it is but I have never treated it as such.

[Shield Arc]

I take it as the back side is a corner joint? If so, I would have tacked everything up good. Check for squareness. Smacked it back in shape, placed a large C-clamp on the front side. Back step welded the backside corner joint. Let cool, remove the C-clamp, no doubt it would want to open up some, then I would place a fillet weld inside to pull it back square.

[Johnp33]

What I do is stitch weld one side then the other, in short welds, using as many clamps as posible, I use a spray bottle to cool it off, wait about 5 minutes, while I chip it off and clean it, many times I use my air chisel to clean and stress relieve it, then stitch it some more, I will many times tack it to my welding table. I like to keep the material cool, just above, being able to handle it without gloves. It is not a race.

[muddstopper]

What I try to do, with some luck, is aline everything up just like I want it. I will tack weld, starting in the center then go to each corner. Flip the piece and tack again, opposite of the first tacks. I will do the flip and tack thing two or three times, checking for straightness as I go. Once everything is tacked and true, I will start running short stitching beads, again starting in the middle and working toward the edge and flipping the piece between each stitch. I keep a heavy hammer handy and I aint afraid to use it.

[joshuabardwell]

I've been doing some work on a small welding table, and had some ideas about how to help make sure it's square. The table is mostly made of 2" square tubing. For the top, to make sure it ended up square, I realized that I could easily put tacks as shown below, allowing them to act as a hinge and allowing me to make final adjustments to the angles before welding the legs into the corners.



Getting the legs square in both directions was a little challenging. I came to see that the order the tacks were put in was critical. If the tack is put in on the inside of a joint, then the joint can hinge inwards on the tack without breaking the tack, but if you were to pull outwards, it would break the tack. The opposite would be true if the tack was put on the outside of the joint. What I finally ended up with was this.



If the vertical leg is perfectly square, then don't bother with this silliness, but since it probably isn't perfectly square, rotate it so that it angles outwards rather than angling inwards in any direction. Then tack the inside corner. This tack location allows the leg to hinge inward in both directions.



Next square up the leg in one direction and, holding it square, tack the opposing outside part of the joint. The two existing tacks now hold the leg square in the one direction, while creating a hinge that can be easily bent inwards in the remaining direction.



Finally, square up the leg in the remaining direction and tack the opposing outside part of the joint. These three tacks should now hold the leg square to the frame. If the leg is not square in any direction, simply grind out the opposing tack, leaving the remaining two tacks to act as hinges while you square it up.

Hope this made sense, and I'm definitely receptive to any feedback on alternative or improved methods of accomplishing the desired outcome. Obviously, this is a problem that has been well solved by fabricators through the years, and I'm certainly reinventing the wheel. This is the inevitable consequence of not getting formal training.

[CNC Dan]

Josh, you got it nailed. There is a good video from
www.weldingtipsandtricks.com
that shows how to do, what you just did.
Here's the link to that vid:
http://www.youtube.com/watch?v=ulzR8...e_gdata_player

[tommu56]

that weld in the middle is to long as some said stitch it work in short 1" beads


like this alternating sides slowly from the center out.

then fill in the spaces after it cools and is correctly alignment.


_ _ _ _ _ _ _ one side

. _ _ _ _ _ _ _ other side

Another trick for the bushings is to make them go all the way through piece ream or bore to size after welding is done then cut out the center for needed clearance.

[kcender]

One rule of welding is:Provided the total heat input is the same,the quicker the rate of input,the less the distortion for a given weld.What this means is that the quicker the weld can be deposited,the less distortion there will be,provided the total amount of weld is the same.This is one reason I prefer flux core(with shielding gas) over other welding processes.It has a higher deposition rate than mig or stick and helps to reduce distortion.Even so,other procedures such as backstepping and patience should still be used.