Regenerative hydraulic press mod

JTknives

JTknives

Joined
Jun 11, 2006
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So I spent a good chunk of the day driving down and back from Salem’s shop today. This gave me lots of alone time to think which is not allways a good thing. On the way down I had been thinking about the possibility of building a manual drop hammer with big dies just for setting the welds on Damascus stacks. My press is quick enough that it can get away from me and take way to big of a bite on the first weld heat. And with me trying to go fluxless with larger billets I needed a way to gently tap them home quickly. After spending a day down at his shop and getting to run his monster of a hammer I knew I needed somthing similar. But on the way back I started thinking about my press and how I could bump the speed and drop the tonnage to a safe tap,tap tonnage. Not wanting to make it a hammer per say. Just somthing that can get in and out quick and get the welds set. Right now I’m sitting at 1.5”/sec at 24tons. As I’m driving I remember somthing I came across when I was researching my press build called regenerative hydraulics. Basically in a nut shell you connect both A and B ports of the cylinder togather and hit it with the pressure. What you get is a force difference twords the side with the rod.

At my 3000psi this difference is 9425psi. That’s not a bad amount of force to just introduce the hot layers to each other. The way it works is when you pressurize both sides at the same time the oil moves from the rod end to the cylinder end. All you have to do is makeup the difference in volume with the pump. This volume difference is the volume that’s occupied by the 2” rod. At my pumps rated GPM of 6.94 it would move that top die at a rate of 8-8.5”in/sec at the 9425pounds. A selector valve would be built in so I can go from one mode to the other in the fraction of a sec. To give you an idea the kind of speed we are talking about here. If I set the upper limit switch around 1” off the stock it would close that gap in around a tenth of a second. A full cycle rate with the limit switches would be less then a sec. the solonoide switching time is around .1 and down is .125 and up is .5 so that’s .825 total. Even at 1sec that 60 presses per min. I’m not sure about hose diameters and how that’s going to factor into it but if I’m doing short strokes it should not be to much of a problem. Any way enough of my rambling, it’s time for bed.
 
That’s really cool! I think with the right set up, you could really get the best of both worlds, both a very fast, light full time regenerative system and a solinoid switched regenerative system that offers faster ram speed and full pressure! Very cool stuff!
 
Here is a little gif anamation that shows it in a real simple set up. There are a few ways to do it once you see what’s going on and how the fluid moves thorough the circuit.
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That is what I thought you were saying, however, it delivers half force to the dies.

Since a reasonable flow rate pump will provide fast enough ram speed, I don't see why you would trade away half the power of your press for more speed.

My comparison would be:
A 500HP motor is installed in a tractor and a corvette. The vett will reach 150MPH, but won't pull a trailer of hay. The tractor will pull 20 tons of hay easily, but won't go over 30 MPH. If you want a race car, then the corvette route is the way to design the car. If you want to haul hay, then go the tractor route.
 
I'm not really understanding how your press could be so fast that it causes you an issue, unless there's some kind of control problem, causing overshoot. I've run some super fast presses (unless you're running a 23gpm single stage pump, you can't possibly be running as fast), and never had this issue. I do recall you setup some limit switches and such, are you using electronic control that you can't stop on a dime, or run half-open? Do you have a pressure gauge in view so you can see the pressure as it builds once it engages the work? You can typically use that as a guide before you develop a feel for it.

Edit: just realized you're at 1.5 IPS, that shouldn't be remotely too fast, once you get a feel for it, unless you've got some control setup causing overshoot.
 
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Stacy E. Apelt - Bladesmith said:
That is what I thought you were saying, however, it delivers half force to the dies.

Since a reasonable flow rate pump will provide fast enough ram speed, I don't see why you would trade away half the power of your press for more speed.

My comparison would be:
A 500HP motor is installed in a tractor and a corvette. The vett will reach 150MPH, but won't pull a trailer of hay. The tractor will pull 20 tons of hay easily, but won't go over 30 MPH. If you want a race car, then the corvette route is the way to design the car. If you want to haul hay, then go the tractor route.
Click to expand...


Well Stacy, speed is usually more important than tonnage, because of how quick the dies suck heat out of the work with presses, however, this *assumes* that you have fine control over it. When the metal is at welding heat, it moves significantly faster, with significantly less power, overall, doing more work. However, with constant contact of large dies, you can suck a hundred degrees out of the outside of the billet a second. There's a limit with tonnage also, I've run presses that were so powerful, that once the metal would cool past the optimal working temp on the outside, you'd start shearing welds and causing stress fractures on the outside of the billet, because the press had enough power to forge it cold just as easily as hot, without enough feedback in the setup to be able to tell when that was happening. They were pretty much useless for doing damascus work.

Now, is a more powerful press at the same speed better? Up to a point. I'd personally say that 50 tons or so at 2 IPS is optimal for my kind of work.
 
I just want to add though; fast single stage pumps can be tricky at first. It's not a reflection of one's potential, it just takes time to get comfortable with. I've taught a lot of damascus classes with stone-beginners, that have never forged, or even made a knife in some cases, that have no feel for it, and in every class there are at least 1-2 people that even with a dual-stage press, can't stop squishing billets in to pieces.

There's no way I'd be willing to teach those classes with a single stage press, unless it was 0.5" IPS or slower. The press simply doesn't offer as much feedback as a hammer, it's MUCH harder to fly by feel, you have to do it by sight and sound, and each press is different in that regard. The dual-stage pump gives you a moment to think, and offers pretty significant feedback in terms of changing sound and sight, and when you look at the numbers, you'll realize just how damn slow they're actually forging. Any faster, is just too much until you've mastered the press.
 
That is my point. Why would you want 8.5 IPS on a press. 1 IPS is all I would ever want.
 
Stacy E. Apelt - Bladesmith said:
That is my point. Why would you want 8.5 IPS on a press. 1 IPS is all I would ever want.
Click to expand...

You definitely wouldn't want an 8.5 IPS press, or a 200 ton one for making damascus in sizes that can be held with two hands (i.e. without overhead support), either extreme is a recipe for destruction/disaster.


However, for me, a 20 ton 1.5-2 IPS press will work circles around a 50 ton dual stage that's more like 0.3-0.5(plus, more importantly, unloading losses during the stage switch) IPS at high pressure, though my use case is different than JT's.
 
All I was saying is why not having an option for high speed at light tonnage to just set the welds. I’m not talking forging the steel down. Just giving it a light tap tap
 
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