Laser Welding 304 SS

[Haf]

I would like to laser weld a 304 SS closure disc to a 304 SS cylinder. The ID of the cylinder is 0.25" and the OD is 0.41". The closure disc is 0.02" thick. Pressure in the cylinder could build to as much as 180 kpsi (for just a fraction of a second). I would like the disc to remain attached at this design pressure, although dimpling is acceptable. My question has two parts:

1. Would it be more effective to notch the inside of the cylinder, place the closure disc in the notch and weld from the top or should I just place the closure disc on top of the cylinder and weld from the side?

2. How do I calculate stresses in the laser weld? I assume this involves estimating how much material is joined by the weld (i.e., weld penetration depth)?

I know very little about welding and even less about laser welding. Any help would be appreciated!

Thanks,

Haf

 

[AJohnson]

Haf,

Either design for the welding sounds acceptable, but application details that aren't prvided could change that.

Do you really mean 180 kpsi? Because 180 kpsi in a cylinder with an ID of .25" would mean the 304SS disk would see a pressure of ~720,000 lbs...keeping in mind that annealed 304SS has a typical minimum yield strength of 30-35 kpsi and an ultimate strength of maybe 75-80 kpsi. It is possible to drive the tensile strength of 304SS up to around 200 kpsi, if you cold work it to around 40% or so, but keep in mind the ductility of the metal will drop through the floor, and then when you weld it, you will lose some of the cold work strengthening.

Also, if the cylinder is also 304SS, then you will have to calculate the hoop stress on the cylinder, which is always the limiting factor in an internally pressurized right circular cylinder. Since hoop stress is equal to (internal pressure x radius)/wall thickness, I came up with a hoop stress of 371,250 psi. So I guess the end cap would stay on, and the walls of your cylinder would blow out. Then again, I could be totally wrong. I'm not an ME after all...Anyway, hope this provides some help.
Andy