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tapwelder
10-14-2007, 02:21 PM
I want to make a hydraulic metal punch. I want to about 10 ton cylinder. Most cylinders are rated in psi. How could I figure the number of tons? surely 10 tons require a a 20,000 psi cylinder???

Could anybody suggest some books to read? I have never dealt with hydraulics.

Thanks

denrep
10-14-2007, 02:40 PM
PSI of the hydraulic pressure x the actual piston surface area.

"actual piston surface area" is without the rod. Subtract area of rod, for rod end piston area.

Fluid power pocket book, probably free at the supply house.

Pi X Radius squared = piston area

subtract - Pi X Radius squared of rod, from piston area; for surface are of rod end of piston.

denrep
10-14-2007, 02:50 PM
... I want to about 10 ton cylinder...

4" cylinder rated for 2000psi working pressure, would be real close for you.

You probably want to build a simple, low pressure open center system.


What are we punching?
How much cylinder stroke?
What kind of duty cycle?
Do you have a pump/motor package in mind?

triptester
10-15-2007, 08:38 AM
Here is a site that will have free calculators.


http://www.baumhydraulics.com/calculators/cyl_calc.htm

tapwelder
10-15-2007, 10:10 AM
Thanks guys.

Denrep

What is "low pressure open center"?

I want to punch 9/16" sq hole into 1/8".

4" stroke would be safe. If I could find it then 2" would work.

Hadn't considered duty cycle.

Still looking for motor/pump. Any suggestions? Looking at electric stuff.

I don't want this thing to be too physically large. Not so concerned about weight.

tapwelder
10-15-2007, 10:18 AM
To calculate tons from lbs do you use 2000 lbs/ton or 2240lbs/ton. What is the difference between short ton and long ton?







Alright scratch this question. I looked it up. I was searching yesterday and sombody had used a long ton as a conversions factor.

denrep
10-15-2007, 11:27 AM
Thanks guys.

Denrep

What is "low pressure open center"?

I want to punch 9/16" sq hole into 1/8".

4" stroke would be safe. If I could find it then 2" would work.

Hadn't considered duty cycle.

Still looking for motor/pump. Any suggestions? Looking at electric stuff.



Low pressure is in the range you're considering, maybe a relief pressure of 2200psi and working pressure 1600 - 2000. Open center is a simple system where the fluid simply circulates in an "open" circuit. Fluid is pumped at a fixed rate, any fluid not used to move the cylinder, would simply return to the reservoir.

If you have the die, I would set up a porta-power to make a test punch. Plumb a pressure gauge into the line and calculate how much pressure it takes to punch the job. From here you can do a little math and be sure you're working with good numbers.

Right now I notice that there are lots of newer yet obsolete forklifts coming down the scrap pike. These are loaded with premium hydraulics, valves, strong short stroke tilt cylinders, and even 12v - 36v DC pump and motor combos. You can probably pilfer top quality components at just over scrap prices.

You could use any length cylinder and "short stroke" it or install mechanical stop spacers over the rod.

Industrial power units, complete with motor and controls, tank, valve, relief, filter and pump are readily available. Your size, is easy to buy good used for 500.00 or less, tougher to find single phase.

Here's some rough math: With a 5" forklift tilt cylinder, you need about 80 cubic inches of oil per punch cycle. Fluid is 231 cu in per gallon. So a 10 GPM pump delivers about 2300 cu in per minute. That would be around 28 punches per minute or a punch cycle in about 2 seconds. A smaller pump capacity of 5 GPM would be about 4 seconds per cycle.

For an AC power unit, look for a deal on a 3 to 10 GPM size, maybe from a trash compactor or bailer, these usually have had an easy life, compared to production machines. Higher GPM pump flows can be reduced with a flow control valve. Thus tailoring the flow to your job. No significant extra power is used, or heat generated, by diverting the unused pump capacity back to the tank.

Good Luck

David R
10-15-2007, 08:31 PM
Alfred E. Newman :) said it all. Be careful with the porta power. Some develop 10,000 Psi instead of 2 or 3K. I have no idea how much it takes to punch the hole you need. The only punches I have seen are punch presses with the BIG flywheel.

Sounds like a cool project. I have been a forklift mechanic most of my life. Those pump motors are nice, but the duty cycle is not there. Use em 100% and the brushes go away real fast. 36 volts DC @ 100 amps takes a lot of battery and charger. AC motor driven would be much better. You may have to cool the oil if you are going to use it a lot.

David

Tinbasher
10-15-2007, 08:39 PM
To punch that size hole in 1/8 material...I'd forget hydraulics and set it up mechanically...like a fly press or with a compound action on a handle like a roper whitney punch...just my opinion.

tapwelder
10-15-2007, 11:15 PM
DavidR,

According to roper whitney site 8 tons should do it. I think I will make a 20 ton setup. I assume with motor efficiency of 85%, I will get 17 ton. Is that correct?

Been thinking about it for a couple of years.


Tinbasher,

I have a roper whitney 20 ton c-punch. It will to 1/2 in through 1/2in material if you have the back and support to do it. I have done 450 holes with it before, got old after about 10 holes.

I motorized that c-punch, but the worm drive was the wrong size and it took nearly 2 min for a cycle, though it did work. I'll try that again in the future, I got a worm drive out of a bandsaw recently.

Anyway, the hydraulic punch would probably turn into a small ironworker, with a shear and possibly notcher, unless I can find some really small cylinders. My goal is a relatively small, shop made tool.

Thanks again guys.

denrep
10-16-2007, 04:21 AM
According to roper whitney site 8 tons should do it. I think I will make a 20 ton setup. I assume with motor efficiency of 85%, I will get 17 ton. Is that correct?


No measurable efficiency loss to be concerned with.
All fluid power calculations can be made at 100%.

20sq inches X 2000 psi = 40,000 lbs
5" cylinder piston = 20sq inches of surface area
20sq inches @ 2000psi = 40,000
20sq inches @ 1500psi = 30,000
20sq inches @ 1000psi = 20,000

If 8 tons will do it, this would make a nice "lazy" press.
Hydraulic system components will not be maxed out due to high pressure and the associated heat.

If you need to keep it light, a 3.5" cylinder, would deliver 9 ton.

CarterKraft
03-04-2008, 12:14 AM
wouldn't a lever work really good for this?

I was thinking of doing the same thing but use a lever and a frame to multiply the force.

Hammack_Welding
03-04-2008, 07:31 PM
wouldn't a lever work really good for this?

I was thinking of doing the same thing but use a lever and a frame to multiply the force.

To answer your question yes, it will. I built a press brake several years ago, and that was exactly how I got my require force I needed. I wanted to bend 8' of 1/4" plate. I couldn't do it feasibly with a single cylinder, and I didn't want to try multiplie. So I basically attached a cylinder to a lever to force the brake down. Worked like a charm. Only problem I had was, like the fool I am, I sold it with the intentions to build a bigger better brake, but still haven't gotten around to it.

Tapwelder, Not sure of your design, but have you thought of using an Air operated Hydraulic jack? You could build a frame and have it so the jack forces down the punch. Would be light enough to move, and you can use your jack for other things if need be. Would be pretty simple, and alot cheaper than buying a pump, motor, cylinder, and running wires. Post some pictures as you progress. I'd love to see it.

TSOR
03-04-2008, 10:27 PM
I have this 4 ton Heinrich punch.

It will punch 1/2" holes in 1/8" steel all day. I believe you can get a 9/16" punch and die set for it also. Square and round are available and maybe other shapes.

About $350 new considerably cheaper used. The punch and die sets you can get from MSC for about $20 a set.

oldhousehugger
03-05-2008, 04:47 PM
From the days when I was a tooling designer, the first thing you must do when figuring force required to punch any metal is to look up the sheer strength of the material you are punching. Once you find that you figure the actual wall surface area of the sheered hole. For example a one inch round hole in 1 inch thick material would give you (PI) x dia x thickness = about 3 x 1 x 1 = about 3 square inches of material to sheer in order to punch it.
If your shear strength was say 20,000 lbs /square inch then you would need 60,000 lbs force and then some to punch the hole. Add to that the condition of your tooling and the friction inside the barrel of the die and you get some idea of the forces required to punch. Then go back and figure your cylinder force requirements.
Of course if you've been doing this for a while you already know all this stuff and can go right to the hydraulic questions.
Hope this helps

comp
03-06-2008, 10:26 AM
lurking for updates :)