Hydraulic forge press geometry

[John in Oly, WA]

I'm starting to build an H-frame forge press and haven't found this bit of info - Do I set the distance between the cylinder and the bottom die plate so when the cylinder is fully extended, the top and bottom dies just touch? Is there any reason it would be better to set the distance closer? I didn't see this info in Batson's book.

Thanks

[metalanton]

I am currently building an h frame myself and am going to leave extra space between the dies, so that I can just pad that area to make it close completely with drawing dies.  this way if I need more space for punching or fullering operations I have it. my cylinder has a range of 8" so I will probably just add an inch more.  the only factor is that it will change the height of the working area (top die) and overall height of the press, so you will just have to do the calculations and make sure that you are happy with the height.   my press is like the carolina knife press and I plan on just having a removeable die on the bottom plate that will bolster the die holding plate... of course if you go this route you will want the bolster to be very firmly attached because you don't want to add extra play to the mechanism.

[ThomasPowers]

remember that at full extension the system is at it's most vulnerable for kick out

[Kozzy]

The less extended a cylinder is, the less it is susceptible it is to the problems of side thrust.  Not a huge issue in something like a forging press where the cylinder already tends to be fairly short but if you were using a long cylinder, you wouldn't want the working area to be at full extension if there was much side thrust present.  

If I had all the choices in the world (rather than what I can find cheap surplus), I'd choose a cylinder length to try and keep the piston in the bottom third of the cylinder--extending only 1/3 of the possible total extension.  Not a huge deal, especially if the rest of the system can provide rigidity to the extended ram.  More of an issue if the ram and die it carries are free floating.  Some very small forging press adaptations are that way.

I use a similar type of H press (15 ton) for keyway broaches that has a 30" stroke and the free-floating end of the ram is not happy with the side thrusts when it's reaching that end of the travel.  It'll move side to side by enough that it's hurting the seals.

[metalanton]

thanks Kozzy that is a good point that I had not thought about.,. makes me think I should add my bolster to the top die instead so that most of the time the cylinder will not be as fully extended

[John in Oly, WA]

Thanks for the replies. Good things to think about. My cylinder is 5" bore and 8" stroke. I was just concerned that if the dies were set closer than the full travel of the hydraulic piston, there'd be the risk of pressing the press apart.

[Alan Evans]

I find myself at odds with some of the replies. But then I am thinking more basic press versatility than specifically forging press, but some of the principles can apply.

The great thing about hydraulics is that you generate the same push at all points of the stroke...you are not relying on the acceleration of the tools for power like with an air or mechanical hammer. If you are starting from the basis of having sourced a ram then I would design the frame to make the most of the ram stroke and design in a guide system to take care of any lateral thrust. You can always reduce the gap (and therefore any approach delay) by mounting your tooling on spacing blocks or build an adjustable cross bar...but it seems self defeating to have limited yourself by having the tools touch at 60% of the stroke should you then need more clearance for a particular combination of workpiece, process and tools.

Removable sow blocks have been used to vary stroke cycle position on many tools...just need to be built strong enough.

On 21 March 2016 at 4:51 PM, John in Oly, WA said:

Thanks for the replies. Good things to think about. My cylinder is 5" bore and 8" stroke. I was just concerned that if the dies were set closer than the full travel of the hydraulic piston, there'd be the risk of pressing the press apart.

That is bad bad dangerous thinking...you can generate full power at any point in the stroke don't forget.

You will be able to wreck your press if it is not built strong enough at any point of the stroke where the ram meets an obstruction...an obstruction like the workpiece for instance. You are thinking that the cylinder end will be stronger than the press frame and using that for a stop.

The press frame must be strong enough to stall the pump or blow the relief valve well before any risk of frame failure.

Alan

[John in Oly, WA]

Thanks Alan!

The frame is 8" x 8" H-beam with an 8" x 16" I-beam as the top cross member. I tend to overbuild, because I'm not an engineer, and that happened to be the smallest stuff the scrap metal yard had, that was big enough. My dad's an engineer though, and after measuring it and some mental calculations, said, "it's skookum enough"

[John in Oly, WA]

Well, I'm close to having this press finished. Here's some pics showing the sequence of the build.

Now my dad and I are having a debate over the specs of the press. I've been following Jim Batson's booklet and so have purchased a 5hp 3450rpm motor, with a two-stage pump - 11gpm/3.6gpm and a 5" bore x 8" stroke cylinder, which should give me about 24 tons of pressure with a ram speed of 2.16 inches per second (i.p.s.) with no load and about .69 i.p.s. with load. My dad thinks that's way too much horsepower and thinks I (or Jim Batson, as the case may be) has some figures wrong. My dad thinks I could achieve the same results with a 1/4 hp motor. I say that the ram would move too slowly. I'm thinking about metal cooling rates while I wait for the ram to cycle. Dad thinks the ram doesn't need to move so fast.

[Alan Evans]

The faster the better...you can always feather the controls to slow it down. It always comes back to "strike while the iron is hot".

My 30 tonne double acting / two speed pump press has an approach speed up to somewhere between 5-10 tonnes and then flips over to slow. When punching and drifting if I do two heats on 50mm (2") square and keep the metal very hot I can do it all pretty well at the approach speed which has so many advantages....the punch is not in contact for long and so does not get so hot, the pressure is much less so the sliding bolster system can move freely, the workpiece does not chill off so punch withdrawal is easy....

Alan

 

[John in Oly, WA]

And I finished the forge press. I think I need to back off the detent pressure on the valve so it barely engages. Would really like to have a valve that has no detent in either direction. I think that would give me better control with the pedal.

Just testing it to see how it squishes.

https://www.youtube.com/embed/wW11IKcg17s

Definitely need to make a better set of tongs.