Dished end diameter before forming.

[Jay_]

Hello all,
As a steel fabricator company, we sometimes are required to do all kinds of dished ends (Flanged and dished or dished ends only), and it’s sometimes for tanks or decorations or even for the food industry. The routine is that the customer gives us the outer diameter after forming, thickness as well as maximum depth of the dished end (and in case of flange we assume a length). Now it’s our job to determine the diameter of the cut so after forming we can get the required outer diameter.
Throughout years of fabrication, we managed to collect a huge data for this issue that depends on material grade, thickness, outer diameter and depth and it’s now somewhat easy for us to do it faster, but it was only the result of years of experience.
When i first started at this job i thought this operation was easy and i also thought that the diameter of the cut piece is somehow equal to the blank diameter but that was totally wrong.
You see the material is under plastic deformation so the required piece diameter will always be less than the blank diameter by some fraction. In our factory we have 10 models to do this kind of job, called 1 through 10, and they are enough for our work. I could never understand the science behind it so i could empirically make some equation that relate the initial diameter to the after forming diameter (practically and not theoretically). If anyone have any reference that i could look at, that would be very helpful.
Regards,

Detailing is a hobby,

 

[saplanti]

Jay,

Nothing fancy about it. It is the geometry that everybody can manage. Additionally you need to consider mistakes in manufacture (during cold/hot forming), skirt length (if needed/available) and machining extension (mostly required for weld chamfer machining). I would not rely on any platicity on the plate to reduce the blank diameter. So as a manufacturer you should know all these to provide the final product geometry in addition to the required material properties.

I trust this is sufficient.

 

[r6155]

You need to calculate the neutral axis of the plate after forming. See Roark's stress and strain

Regards