Ironworker hydraulic system question

Hi everyone I am on that quest to build a hydraulic system for a machine that is similar to a hydraulic ironworker. It's going to be a simple tandem Center system with one 12 volt solenoid spool so oil will be continuously be sent through the system by a fixed displacement gear pump. When the system is initiated the the spool is energized and the double acting cylinder extends and does the work. The spool is brought to neutral and the cylinder self retracts. I could run a simple single acting cylinder with a huge spring to retract the cylinder however I don’t like the idea that the rod seals would not be lubricated plus having the spring as a possible item to break is not a smart idea. I know about hydraulic kick out valves that are used in log splitters but was not planning to use them in the design. I have used ironworkers in the past but don't own one. Anyone knows how they work ? What kind of valves or spool used? I tried to look online for owner manuals for various brands of ironworkers but no luck. Thanks in advance.

Another reason you have to have hydraulic power on the retract is that you have to pull the punch back out of the hole while the stripper holds the work piece down. You should also have a "jog" feature that allows you to stop the punch at any position so that you can easily align the punch on the layout mark. That means you spool valve need a real neutral where oil is bypassed allowing the piston to remain stationary.
I have fiddled with many hydraulic units but only as an operator. You also need micro switches linked to the piston stroke to limit the end position of the piston as many punch and die sets vary in dimensions. You also need to adjust stroke to allow for thickness. You can waste a lot of time making full strokes when you are punching hundreds of 1/8th thick pieces.

so the idea is to have the constant return leg with a t to the return stroke side of the cylinder and the power stroke would get full flow? you need a flow valve on the return leg so to regulate the amount of flow to the return stroke, plus a relief valve to allow the cylinder to stall but still allow the pump to pump. this is in addition to limit switches per above.
make sure you do not build in any features that store energy, ie so that when the unit is shut off there is enough spring force in the structure or potential energy from say a dropping punch. this is a safety no no. so say you have a punch that is only held up by hydraulic pressure and when you turn off the pump it continues to stay up but can slowly drop down due the the oil draining. this could cause you to be injured when changing tooling.

My old Scotchman has a big spring. Seems perfectly workable design to me.


metalmagpie

Why in the world would you not want your hydraulic ram double acting???? (powered both ways) You could add very simple mechanical limits to control stroke if you like.

Because on the up stroke it punches at the front. On the down strike it shears plate or runs a small brake die on the top side


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Exactly, if your punching on the up stroke, your powering up. And if your shearing/pressing on the down stroke, your powering down.
Just what a double acting ram does, powers both directions.
On a single acting ram you will only have hydraulic power one direction and the opposite side of the ram will be vented to your tank or in some cases just vented to atmosphere, but will require some form of mechanical energy to return the stroke of the cylinder piston back.