Earlier, Max Krippler wrote:

Can anybody tell me what are the typical pressures required to dimple
a skin and also to compress a flush rivet?

Forming the shop head will require the same pressure regardless of
whether the other end is universal or flush.

My experience with using a small hydraulic ram to squeeze MS20470AD4-6
for HP-18 wing box spars is that it took about 3500 psi behind a 1"
diameter piston. Given that the area of the piston is (.5")^2*pi =
..785 in^2, the force would have been .785 * 3500 or around 2750 lbs.
It might have been a bit less, but I'm pretty sure that's what the
neighborhood was.

For AD3 rivets, I imagine that the force would be proportionally
smaller according to the area of the finished shop head.

As for dimpling, I never measured the pressure, but I believe that
it's substantially less than required for riveting.

I hope that helps some.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com