Bore of Tube shrinking during weld
Bore of Tube shrinking during weld
(OP)
I have a tube with a pre drilled hole in it and a collar slid over that. I am then fitting a 1.125" outside diameter tube into this as per the illustration. The tube obviously shrinks during welding which means we need to ream it out afterwards as another tube slides inside it. What is best practice to reduce the shrinking.
At the moment we place collapsable bungs up the tube to help reduce it.
At the moment we place collapsable bungs up the tube to help reduce it.





RE: Bore of Tube shrinking during weld
RE: Bore of Tube shrinking during weld
But, you probably won’t completely eliminate that kind of deformation and shrinkage caused by the welding. It’s the nature of the beast when you are welding. So you better resign yourself to having to do some final machining or reaming of the bore. If you do a hundred of them and measure them all, very carefully, you might determine that you can over-bore them a bit in the first place, and minimize the reaming after the welding. But then you’ll probably have a single or a couple slight high spots in the bore.
RE: Bore of Tube shrinking during weld
RE: Bore of Tube shrinking during weld
If I were to measure the distortion would it be proportional in the sense that I could counterbore the tubes before welding to take that into account or would they still distort maybe more because of a slightly reduced wall thickness.
Also, The expandable collets we use now are made from brass, would copper act as a better heat sink?
RE: Bore of Tube shrinking during weld
I suggest that you build a fixture or guide to assist with reaming after the weld. I don't think that you will be able to compensate by pre-counter-boaring unless you are willing for this section to be loose.
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P.E. Metallurgy, Plymouth Tube
RE: Bore of Tube shrinking during weld
I don’t understand how finely that fit is intended to be, and you haven’t chosen to tell us. If the next pipe just has to fit in the i.d. easily and it is o.k. that it ride on a couple high spots or high ridges on the i.d., then you could probably do some of them, measure the change in the i.d., and finally learn what the oversize bore has to be. During this learning process you would ream them to make them work, after measuring. Finally, you might be able to avoid the reaming operation from what you’ve learned. I don’t think it’s a heat sink (cooling) issue. The welding operation is inducing a circumferential residual stress which is squeezing the pipe to slightly smaller dia., and the more so the nearer you are to the weld, and you can’t find a mandrel strong enough to prevent this. You could expand the pipe, putting it in circumferential tension to counteract this shrinkage from the welding. That expansion dimension should be about what I’m telling you to measure, but you are measuring the shrinkage you want to overbore to compensate for. This shrinkage will depend on the heat input during welding, the pipe dia. and wall thickness, and the configuration of the weld. So, a thicker pipe with all else being the same, will shrink less. A lighter, less heat input, weld will cause less shrinkage, all else being the same. This is kinda like the material movements during a shrink-fitting operation.
RE: Bore of Tube shrinking during weld
RE: Bore of Tube shrinking during weld
RE: Bore of Tube shrinking during weld
Is your tube shrinking, or is it warping?
Could you heat everything up before you weld? Weld warping is caused by differential cooling.
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JHG
RE: Bore of Tube shrinking during weld
Drawoh it is mainly shrinkage after welding, there is some distortion which is minimal.
RE: Bore of Tube shrinking during weld