How to prevent this angle from warping when I weld in plates

[tominboise]

I am working on a project and need to weld this 1/2" plate into the interior of this 3X3X1/4" angle. The angle is 50" long and there will be a plate welded in at each end and one in the middle. I have TIG and stick available and am planning on TIG welding this. I will grind bevels on the 1/2" plate to get good penetration at the root of the joint, and sand all the rust and scale off. How best to weld this out, as I would like the angle to be as square and flat as possible when I am done.

Also, should I preheat this plate and angle prior to welding it out?

 

[Walkers]

Just clamp it, tack it, and weld it. It is going to be difficult to get it wrong due to the joint design.

 

[readhead]

The angle will pull both ways quite a bit at the center plate. If you have enough material to do a test you can do a weld and see what the angle does. Once you know what the weld does you can shim the angle so that when the weld cools it will be close to straight. Clamping will not keep it from warping.

 

[jsaw]

How about if you tack weld it and then let it cool, and then weld a little more , then let it cool.

 

[tominboise]

Just clamp it, tack it, and weld it. It is going to be difficult to get it wrong due to the joint design.

I see what are you saying - that the 1/2" plate, being cut square and fit inside the angle, will help hold those flanges from either going in or out when I weld it. I hadn't thought about that.

 

[GeoBruin]

I have had tremendous luck with flame straightening. To the point where if I know a joint is prone warp, I don't pull out all the stops trying to prevent it, because many times it warps anyway and I'm out all that time. Instead, I just weld it, then flip it over, clamp it, and fire up the torch. I'm getting to where I can get back to "straight enough" in one shot but sometimes it takes a couple attempts.

As mentioned above, the center plate will pull the angle in the middle. If it were me, I would then flip it over, clamp it to something straight (and stiff) and then just run right along the HAZ on the backside of the welds with a torch. Get it just orange at first. Then see how close you are. If you need more, do it again.

 

[Jswain]

I have had tremendous luck with flame straightening. To the point where if I know a joint is prone warp, I don't pull out all the stops trying to prevent it, because many times it warps anyway and I'm out all that time. Instead, I just weld it, then flip it over, clamp it, and fire up the torch. I'm getting to where I can get back to "straight enough" in one shot but sometimes it takes a couple attempts.

As mentioned above, the center plate will pull the angle in the middle. If it were me, I would then flip it over, clamp it to something straight (and stiff) and then just run right along the HAZ on the backside of the welds with a torch. Get it just orange at first. Then see how close you are. If you need more, do it again.

x2 this would be my suggestion as well, but if you have a thick enough welding table you could stitch the angle down to it and it may help a bit, but will also require more time.

That piece would be super easy to flame straighten, probably less time then stitching the angle to the table and then cutting it off and cleaning off the welds...

 

[tominboise]

Would you guys worry about preheating the joints at all prior to welding?

 

[LopezBart]

To straighten things, you don't need a torch; a weld whose shrinkage will be in opposition to the first weld will help a lot, since it will pull it the other way. Now in this case, after tacking all four corners, you're pretty much set. And I'd v-out the welds, and stick weld that w/ 7018. You'd be done pdq. Of course, I don't have a tig machine (yet) .

 

[readhead]

What is this for? How much warp is acceptable? When we did a lot of production welding taking the time to figure out the required fixture was time well spent rather than trying to straighten weldments after the fact.

LopezBart is correct with the idea of running beads on the opposite sides to bring things back into shape. Let them cool and sand the beads off slowly. For only two parts that may make the most sense.

Weld deformation is a science all by itself. When I was teaching structural welding there was a pipe welding class running in the same shop. It was fascinating to watch those guys make up pipes with mating flanges and if the flanges didn’t match up perfectly the instructor would run some cover beads in the right place and pull that flange right into place.

 

[Jswain]

Would you guys worry about preheating the joints at all prior to welding?

Depends how big your welder is. If you V out the plate and get everything spotless and have a decent size tig welder you shouldn't need to

 

[Chris_Hamilton]

To straighten things, you don't need a torch; a weld whose shrinkage will be in opposition to the first weld will help a lot, since it will pull it the other way. Now in this case, after tacking all four corners, you're pretty much set. And I'd v-out the welds, and stick weld that w/ 7018. You'd be done pdq. Of course, I don't have a tig machine (yet) .

Agreed. With that material thickness that is all you need. Tack the corners and proceed. If the plate starts to pull (much more likely than actual warpage) lay a stitch down on the opposite side of the last weld made, provided that's when the plate started to move. Better yet, tack a corner, if the plate moves, hammer back in place. Tack again, and hammer again if necessary. Once you have all the corners tacked you are not going to get significant warpage.
You are going to want to put a real good bevel (1/2 thickness or so) on it (1/2 piece) as welding 1/4 to 1/2 is a sizable difference in thickness.
As for preheat, only if your equipment doesn't have the amps to comfortably do the welds. At the absolute bare minimum you need a 200 amp TIG IMO if you are going to lay down good welds on that material. 250 amps would be better. If all I had was a 180-200 amp welder I would probably preheat it some. Just warm the metal. Don't worry about getting it any shade of cherry. Just get it "hot". Then hustle and lay down your tack. Do the same when you lay a bead down in either direction (across, up/down)

 

[tominboise]

Agreed. With that material thickness that is all you need. Tack the corners and proceed. If the plate starts to pull (much more likely than actual warpage) lay a stitch down on the opposite side of the last weld made, provided that's when the plate started to move. Better yet, tack a corner, if the plate moves, hammer back in place. Tack again, and hammer again if necessary. Once you have all the corners tacked you are not going to get significant warpage.
You are going to want to put a real good bevel (1/2 thickness or so) on it (1/2 piece) as welding 1/4 to 1/2 is a sizable difference in thickness.
As for preheat, only if your equipment doesn't have the amps to comfortably do the welds. At the absolute bare minimum you need a 200 amp TIG IMO if you are going to lay down good welds on that material. 250 amps would be better. If all I had was a 180-200 amp welder I would probably preheat it some. Just warm the metal. Don't worry about getting it any shade of cherry. Just get it "hot". Then hustle and lay down your tack. Do the same when you lay a bead down in either direction (across, up/down)

I have a Primeweld 225A TIG machine, so I will heat it some prior to tacking and welding. It's cold in the shop and the steel has a lot of heat capacity.

 

[tominboise]

What is this for? How much warp is acceptable? When we did a lot of production welding taking the time to figure out the required fixture was time well spent rather than trying to straighten weldments after the fact.

LopezBart is correct with the idea of running beads on the opposite sides to bring things back into shape. Let them cool and sand the beads off slowly. For only two parts that may make the most sense.

Weld deformation is a science all by itself. When I was teaching structural welding there was a pipe welding class running in the same shop. It was fascinating to watch those guys make up pipes with mating flanges and if the flanges didn’t match up perfectly the instructor would run some cover beads in the right place and pull that flange right into place.

I am building a Finger brake and the long angle piece is the main bed, so as flat as possible. I am only building one of these, I hope, so taking some time to get it as correct as possible is OK.

 

[Jswain]

Instead of fully welding the middle piece I think I would just give it 2x 1/2" stitch welds on each flat section so 8 total. No preheat, no bevelling, should keep it from warping too bad. Sounds like it more just needs to be held there to keep the angle stiff.

Put one stitch weld on each flat section then let it cool/work on your end pieces and then do the other 4

 

[tominboise]

I don't have a water cooled torch on this machine, so I will be limited to short stitch welds anyway. I need to buy a water cooled torch and rig up a cooling system loop.
I could just stick weld it, I suppose, but prefer the looks of the TIG welds when completed.

 

[Monza Harry]

Tom I interpreted your pre heat question to mean: "if I preheat this will it warp?" If I read that right, the answer is maybe. However a little pre heating and maybe even some post heating can minimize the shrinkage from welding one side. I don't think you will need to preheat to weld with enough "Vee" prior to welding. Preheating will definitely help with the weld pull though. You need to remember though, heating shrinking is a skill unto itself. Harry