Determining weld strength

By Kaynor09 Date 08-31-2005 22:26

Hello. I am new to the welding world and want to determine how many spot welds will be needed before seaming. I have 2 cylindrical components (we'll call it the housing and insert) with a slip fit, max gap of .002" diameter. They are mounted vertically. The Insert is compressing a rubberlike component inside the housing and it takes about 80 lbf to compress it such that the Insert is flush with the Housing. If there is no weld/something holding it down, the rubber component will push the insert back out. How can I determine how many spot welds I will need before removing the holding fixture and going to a seam weld?

Thank you!!!!

By G.S.Crisi (****)

Date 09-01-2005 21:23

Rough, although acceptable, calculation.
1. Multiply 80 lbf by the inside cross sectional area of one cylinder and you'll have the pressure acting inside the cylinder.
If you give the tack welds with an E60xx electrode, 60 means that the ultimate tensile strenght of the welded metal is 60.000 psi at room temperature. If the electrode is an E70xx, then the ultimate tensile would be 70.000 psi.
2. Divide 60.000 (or 70.000) by 3 and you'll have an acceptable safe working strength of the welded metal.
3. If you're going to make, say, 4 tacks, then each one of them will take up one fourth of the total pressure inside the cylinder, already calculated according to 1.
4. Knowing the pressure each tack will take up and their safe working pressure (20.000 psi, if an E60xx electrode is used), you should calculate now the cross sectional area of each tack.
5. As the tack diameter can be quickly estimated, it's easy to calculate now the tack's length.
6.This is just an example. Adapt it to your particular case.
Tell me if it worked.
Giovanni S. Crisi
Sao Paulo - Brazil