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This was an interesting thread a while back on a different forum. What are some of the tricks we are using to control heat warp and weld pull? I think most of us do the usual and clamp it up good to control it, but as most of you know that aint enough in a lot of cases. I had mentioned a buddy whos flat trailer nearly was a beaver tail after he got done welding new spring perch's on it. I had one guy tell me he would have heated the opposite side with a torch to keep that from happening. I never tried this and in many case's that may not be an option. When I was asked I said I would have tried to counter the weld pulling by welding a piece on the opposite side to get a little pull in that direction, then tried to stress relieve it before I cut that back off. It worked in the past. Now a trailer is a pretty forgiving piece of work. I am doing a job this week that has 4 by 4 by 3/8" angle welded to the bottom of a piece of 2 by 2 by 1/4" tube, after welding the angle has to run no more then .010 out 4" from the welded area. That square tube is going to want to move about three times that if not done correctly. What would you guys do. You can ask me what I am going to do but I cant tell you until next week. I have not decided yet. I like to set up my machine and run a test first just to see how its going to react. You know how temperature, welder settings, and material can change the effect, so I like to see where I will be at first.Dan.Repair Specialties LLC
Reply:Hopfully you are making more than one?? If you are then tack welding the lengths back to back sometimes helps. If the shrinkage is extreme then back to back with a space block between in the middle to give a prebend.
Reply:I am doing 8 of these. The space block idea will be used for sure. I use a milled 2" piece and then add steel shim to get what I need. After I do my test pieces I will determine if I am going to preheat and put a slight counter in it prior to welding. A thought-- I have never tried this for controlling warp or pull, but I wonder if a bit of preheat just before welding does much, even if so , how much could you actually control it for holding a tolorance ? I that to have to go in and machine it after welding, but sometimes that is the best solution to holding really true tolorances. The problem with this project is that all pieces have to hold tolorances and machining one doesnt solve the other which will be the pull on the tube,these are going to be some pretty sizable welds so that tube is going to want to pull pretty good. Gotta love this stuff, if it were easy , everyone would be doing it and we wouldnt have jobs.Dan.Repair Specialties LLC
Reply:Weld shrinkage is caused by the difference in temperature between locations. The expansion stresses increase as the difference in temperature increase. Preheat can help but in this case with a long thin piece it is not very practical unless you have a helper chasing the welder with a torch spot heating. The biggest problem with angle is that shrinkage will pull about the neutral axis. That imaginary centerline is in the air between the angle legs. As a result angle often distorts in more than one direction. You end up with a bow in the horizontal and also in the vertical. To control distortion you can clamp, prebend, use a sequence such as back stepping or skip welding, preheat, and lay down your welds small and as fast a possible to reduce total heating (multiple passes is the worst scenario). You mention machining afterward. It can be very frustrating for the machinist because he can clamp the unit as it sits, machine it off flat but when he removes it from the planer or milling machine it will spring out of shape. By machining he has removed some material that was helping to restrain the material and as a result it chooses a new shape. The answer of course is to normalize in a furnace then machine afterward. it doesn't sound practical in this case. How long is this tube/angle assembly???
Reply:something out .010 at the start is out 3/8" after 4 feet..best thing to do is make everything square from the start..tacks in the corners and one every 1/2 inch all the way around (going opposite of each other) as fast as you can..do a filler pass on one side (listen for popping tacks..pop! stop and fix)then a filler on the opposite side etc..keep the first pass small and when its done while its hot go over it again but this time dont stop if you dont have too..You can ask me what I am going to do but I cant tell you until next week.
Reply:I follow you 100% on that. And even thou the 2 sq. material is thin (1/4 wall) that the 3/8 thick angle is being welded to, it is still fairly stout but when laying two good welds two inches apart 90 degrees across it, its going to pull. My drawing is at the shop and its my rare day off away from there. But I will tell you what this part looks like. Basically it is a 2 long piece of 2*2*1/4 Sq. Tube with two 4*4*3/8 pieces 2 wide welded 2.010 apart to the bottom of it so that it, then has a piece is 2*2* 3/8 dead center on the top over the 4*4 angles. Auto cad this isnt, but the pic gives the idea here. Machining the space is not an option because the tube also has to hold less the .020 from each end. Normally I do machine these types of projects back to spec providing it is allowed, on thicker material warp-age from machining isnt too challenging provided you are just dusting things off. My thought as of this minute today is to tac the top piece in pretty well and let it pull slightly, then tack in the bottom and see where I am at, then hopefully if it goes as imagined I can lay my welds strategically and keep it close enough to spec to fixture it and stress relieve under fixture pressure. If you study my crappy paint shop drawing you will see that there will be a very slight amount of machining that could be done at the bottom of those 4*4s due to the top could fall into spec and the 4*4s would not and I could take a couple thou out and not challenge the structural integrity. This is all Mondays challenge. Cant wait for Tuesday! Attached ImagesDan.Repair Specialties LLC
Reply:One word. Pre-stress.
Reply:Is that two words ? , I agree, pre stress is a good idea. I read something once in a very old welding book about using a torch to heat and pre stress the material, again it showed doing this on the opposite side of the the area to be welded. The problem there was trying to control the amount and problem 2 is keeping the twist out. I never got to the welding end of this project yesterday, there is much more to it then just this piece so I spent the day-half on the phone (Monday) and the other half cutting,grinding, and milling. Hopefully after a morning of drilling and tapping I will finally get to have some fun and strike and arc.Dan.Repair Specialties LLC |
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发表于 2021-9-1 00:13:16