Ballpark, the force will be on the order of tensile or shear strength (yield) times the area affected. So, the perimeter of the area times material thickness. So, 16mm * pi * 1mm * 280MPa = 14kN, or about 1.5 tonne[force]. (Taking a typical 280MPa for mild steel.)

There will be a geometry factor, which I don't know about because I'm not a materials scientist... but this can be looked up. Probably Machinery's Handbook or the like has standard tables??

(Actually rather curious what that geometry factor is, now.)

Also, this amount of force, I think, won't be a big deal to obtain in pulsed form i.e. hammering. May need something bigger than a carpentry hammer but I'd be surprised if more than a 1kg hammer was needed? Doing it by hand of course will require some precision/finesse so it doesn't come out lopsided...

Tim