limiting heat distorsion

#1
I do a bit of welding. Mostly learning as I go. Mostly learn what not to do. Still have issues with warping, twisting. I try to not weld in one spot too much. Try to bounce around so as to even the heat buildup. Still get some nasty bows and tweaks. I built a safe door and had to use the one ton truck to get bow out. Redneck engineering at it's best. (lowered the front wheel on the door while the ends were on blocks. Any tricks you guys use?
 
#2
I do a bit of welding. Mostly learning as I go. Mostly learn what not to do. Still have issues with warping, twisting. I try to not weld in one spot too much. Try to bounce around so as to even the heat buildup. Still get some nasty bows and tweaks. I built a safe door and had to use the one ton truck to get bow out. Redneck engineering at it's best. (lowered the front wheel on the door while the ends were on blocks. Any tricks you guys use?
Jim you cant totally stop distortion BUT you can work with it. This NASCAR chassis building class has been a year long lesson in how distortion can be compensated for. When I built my English Wheel frame last week. https://www.oldminibikes.com/forum/welding-and-fabrication/156358-english-wheel-build.html I read the directions and they said to weld the upper arm on first then the lower arm then the legs... then stand it up and weld the truss supports on. I didn't agree with that in my experience. So I had a plan in mind to fit it all up and clamp it down solid and then tack all the joints. So I got it in place like I wanted it, had it clamped down on the Frame Jig table. I then asked the instructor, who has been building race car chassis for most of his life and welding for all of it, how he would weld it. I wanted to add a stiff leg out at the unsupported ends of the arms and he said most definitely. He said weld the horizontal welds on the arms, flip it, clamp it back down and the weld the horizontals on the arms on the other side. Then weld the verticals. Let it cool and then weld the support on the rear of the upright as well as the upper and lower arm braces. BUT only tack the ends of the long braces. Let it cool completely, overnight, and then cut the tacks loose so that the braces could relax and loose any load they might be creating. I cut them the next day and there was a tiny bit of movement when they became free. I then pulled them up tight with a clamp just so they wouldn't move as they were still touching. Welded the horizontals and then the verticals and let that cool. Horizontals and verticals are referring to the position it is in while clamped to the jig table. While waiting I built the legs and had them ready to attach. Picked it up with a engine hoist and got it balanced leveled and tacked the legs on. Everything was good so I welded them solid. I checked the distance between the arms out on the ends and then cut the stiff leg out. It moved 3/16''. That measurement is at a distance of 42 '' out from the upright. I was happy with that. Not perfect but it was not an issue.


The instructor told me that when he was working for Laughlin Racing Products they were having a problem with repeatability on the front of the frame rails. This was 35 years ago. They would tack everything and then weld everything. They figured out that by only tacking the engine bay bars and fully welding everything else, then cutting the tacks on the bay bars before they were welded they got 100 percent repeatability. It removed any pull by doing this.

Others have other tips I hope as I am always interested in reading real world experiences and how to overcome them.

Just remember. Don't weld like a mad man and make everything hot. Work your way around the welds and let it cool before you add more heat to the area. And tack with 4 good tacks, north, south, east and west, before you weld anything solid. Then weld opposite side together. North to west and south to east. I weld right to left if I have the luxury of choice. Thus the pattern. And learn to weld with either hand and in either direction. It makes a huge difference.

And YouTube is a wealth of information on this subject as well.

Doug
 
#3
Also...Depending on the joint design, one could use a copper backing bar. This helps alot to wick away heat, especially with plug welds and other bigger gap joints on flat bar(if you have loose measurement of stock...
 
#4
Also...Depending on the joint design, one could use a copper backing bar. This helps alot to wick away heat, especially with plug welds and other bigger gap joints on flat bar(if you have loose measurement of stock...
When torch welding the hood on my 53 Chevy I used wet rags to make "dam" around where I was welding and seemed to work well on a slit made by a flying fan blade. Sounds like I'm on the right track, tac, clamp, move around, let cool, then cuss when it still moves some.
 
#5
I know a lot of pro shops used to, maybe still do, stress relief, shot peen, or heat in oven to relieve stress from welding. Anything a shade tree welder can do? Wonder if massaging it with an air hammer would help?
 
#6
I know a lot of pro shops used to, maybe still do, stress relief, shot peen, or heat in oven to relieve stress from welding. Anything a shade tree welder can do? Wonder if massaging it with an air hammer would help?
You can heat it with a rosebud on a big torch but if you weld it carefully it wont make a difference. Tack move, tack move, tack move...

Just to see it happen try this. Take 4 pieces of scrap tubing. Cut the ends on 45's if you can. Cut 8 pieces. Tack move, tack move on one and just weld the crap out of the other one. Then lay them on top of one another and see what they tell you.

There is no substitute for time under the hood. But if you have one specific problem like you are then do what I suggested and just see what the difference in a proper thought out pattern is verses just welding it willie nillie.

Quick simple exercise to learn from.
 
#7
We follow FOMOGO’s lead and almost always use clean, polished 1/4” copper plate, bar and angle. Clamped to assure full contact. IDK for sure but excess heat and movement is usually not a big problem. I save all the copper swarf from any lathe work and pack it into exhaust tubing weld points before welding.
Hope this helps, great thread here,
Steve
 
#8
If you are talking about backing a weld I don't back anything except automotive sheet metal. And then only when there is a gap. My sheet metal joints tend to be tight from the start because if I am fabing a custom piece or replacing a piece I overlay the parts and make one clean cut with a Dremel. Yes its a little slow but it always fits like a glove after the cut... If I am welding 1/8'' plate I leave a 1/8'' gap to fill and get proper and complete penetration.

All my exhaust joints are tight and are usually TIG welded.



This inner front fender was built using 2 inners. A right and a left. This is a right side inner. The left was turned around backwards and had been cut through the top bolt holes where it bolts straight up to the outer fender. It was then placed 6 inches inboard as a starting point. Tacked in place and then manipulated until it had the proper profile. It was then through cut with a Dremel and tacked. Then more of the same until we ended up with what you see. A one piece inner that has minimal welding seams and virtually no movement from the welding. I used my Shrinker stretcher to fab the lower edge that clears the suspension. Then the fun began..... We had to make the other side match....

I also like to measure the amount of weld joint in a part that I make. It will surprise you when you do it. There is 161'' of weld joint in the right and 184'' in the left inner fender. Left has more because I had to fabricate a filler piece where the steering box was on the front corner of the fender.





Compare the leading edge on this one and you can see the piece that is missing that I had to make to match the other inner.

 
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