Die Design for Pipe Punching

Make the die as a shoe and place it on a rod to travel the distance in to the pipe to the area the works to be done. On the shoe use spring plungers to have it hold contact with the surface to be punched. The rod holding the shoe can be held with a ball joint allowing it to float in the tube.

Use a "U" type bar with the die inside, and alignment reference on top, when in place put a forked wedge in from the other end to take punch loading, the angle under the die should be designed so as not to displace the wedge under load. Just a thought.

You did not mention the wall thickness of the pipe, or the shape of the holes. If relatively thin mild steel, could you fill the pipe with water and freeze it? Then, a tapered knife edged punch could punch the hole without any die at all on the inside.

Just a crazy idea, but might work, depending upon the unmentioned variables.

I suggest you can use laser cutting instead of Punching...Punching stroke can deform the pipe if not clamped...as you hinting it will be moved...you may be thinking of multiple punches...it will sure deform & weaken the pipe....also as the Punch hole will have some burr...it will hinder free movement of die....so you may try laser cutting...its clean...it gives little burr...HAZ is very samll...quick changes in shape possible...only limitation would be a setup...

Another solution would be C lamp type punch & Die ...Die floating inside with a magnetic clamp...swichoff magnet while moveing....just a wild thought!

Guruprasad.K, Mumbai

Cost is a factor to be concerned about here. Laser cutting i think is out of our budget. Also i have seen videos of such dies working, without any deformation in pipe. But i am unable to locate the way die is held inside.