I'm looking for information on weld strengths, metal warpage

By Stephan (***)

Date 01-16-2007 11:22

John,

it would be a great honor for me to try to respectfully answer - at least partially - your topic.

But please can you give a little more technical information (materials, range of thickness, welding process...) of what exactly you are interested in?

You may forgive me - and I hope all other colleagues may agree - but the issue is a little tricky and thus not as easy to explain.

Thank you in advance and regards,
Stephan

By jneilson (*)

Date 01-16-2007 14:20

Thanks for the reply. A bit of our work is welding 14 to 16 ga panels (mostly mild steel, some stainless)to 2 x 2x 3/16 tubing. Most times the panels are just welded along the edges, but when we have a piece of tubing that is welded across the middle of the panel we get really bad warping. I would also like something that will tell me how much strength a weld has, like a 3/8 fillet on a 1 x 4 pitch on two pieces of 3/8 plate steel 12 inches long at 90 degrees to each other. Thanks.

By swnorris (****)

Date 01-16-2007 21:31

Weld strength examples based on E70xx:

1/8 fillet weld: weld strength = 1.856 kips per inch of weld.

3/16 fillet weld: weld strength = 2.784 kips per inch of weld.

1/4 fillet weld: weld strength = 3.712 kips per inch of weld.

5/16 fillet weld: weld strength = 4.64 kips per inch of weld.

3/8 fillet weld: weld strength = 5.568 kips per inch of weld.

.928 is the multiplier, which is multiplied by the number of sixteenths in the fillet weld size. For example; a 1/4" fillet weld is .928 x 4 = 3.712.

To determine the fillet weld strength of the length of the weld, for example; a 5/16" fillet weld 6" long, .928 x 5 x 6 = 27.84 kips per each 6" weld. A kip is equal to 1000 pounds, so this weld strength would be 27,840 pounds, if properly welded.

By TimGary (****)

Date 01-17-2007 20:10

You can see by the weld strength info that swnorris gave you that the fillet welds you're placing on the sheet to tubing weldment you described are very strong. The sheet warpage you're experiencing is a direct result of the shrinkage that the fillet weld undergoes while it's cooling, as the thickness of the sheet does not provide enough strength to compete with the stronger / thicker weld. This effect is magnified due to the radius on the corners of the tubing because the gap that the radius creates gives the sheet more room to move.
The best way to reduce the warpage is to change your welding procedure from fillet welds on the edge of the tubing to plug welds or spot welds along the center of the tube. This way the tube acts as a strongback and does not give the sheet room to distort. If you do this, the only warpage you'll still have to fight is a curvature of the tube itself, which is created by welding on only one side. Again, this warpage is caused by weld shrinkage and can be corrected by heat shrinking the opposite tubing wall from which you welded. Another way to fight this warpage is to place your weldment in a fixture that creates a pre-bend in the tubing, opposite the bend direction that the welds will create. If you do this right, after the weldment cools, it will pull itself back straight.
If you can't change your welding procedure, you can try to limit the sheet warpage by placing a heat sink or chill bar on the opposite side of the sheet from which you are welding. This may help limit the warpage as it accelerates the cooling process, but it will not eliminate it.

Tim

By hogan

Date 01-17-2007 20:31

when welding 1/8" plate to one side of a piece of tube steel we will camber the tube in the opposite direction prior to welding