[Goldhunter_2]

CNC zone has so many forums I am never sure if I am posting something in the right one or not but figured since the end result (hopefully) will be a metal working machine this section will do.

OK I have some understand but have some questions for someone more knowledgeable about Pneumatic Air Cylinder

*What I know is I need is a 5" to 8" stroke , a mounting celvies (sp?) on one or both ends, air powered, Rod must also retract and support 1/6th of the attached die.

* Now what I don't understand or comprehend is the maximum outward extended pressure a Pneumatic Air Cylinder What determines why one cylinder is stronger (provides more force) then another one? is it the amount of air psi provided to the cylinder or does it have something to do with the overall diameter of the cylinder it self (some are narrow some are wide)


I'm not sure if it matters but here is a little extra info about intended use in case it has any clarification for the cylinders . I plan to use four to six cylinders on a two adjustable slider rail to attach to dies and press/stamp light sheet metal mostly 22-20 gauge maybe some 16 gauge and every now and then maybe as heavy as 14 gauge but not often.
I am in the middle of another project right now so I not in a huge rush but would like to find out the info about the Pneumatic Air Cylinders so I could start watching for a good deal on some used Cylinders.

[Geof]

It depends on the air pressure, which is force per square inch and the diameter of the piston inside the cylinder which determines the area on which the pressure acts.

A cylinder with an inside diameter of 3" has an area of 7.07" square inches and if this is used with air at a pressure of 100 pounds per square inch the force acting on the cyliner rod is 707 pounds. Actually it is a tiny bit less due to friction inside the cylinder.

With a double acting cylinder the retract force is slightly less because the piston rod occupies some of the cylinder area. A 5/8" diameter rod has an area of about 0.31 square inches so the retract force is reduced by about 31 pounds.

For your bending plans it is very likely air cylinders will not have enough force without being unmanageably large. Hydraulic cylinders which work at pressures ten to thirty times high than air cylinders would probably be needed especially for the larger thickness material.

[Al_The_Man]

*a mounting celvies (sp?) die.

* Now what I don't understand or comprehend is the maximum outward extended pressure a Pneumatic Air Cylinder What determines why one cylinder is stronger (provides more force) then another one? is it the amount of air psi provided to the cylinder or does it have something to do with the overall diameter of the cylinder it self (some are narrow some are wide)

.

Clevis?

You maybe need to take a look at basic fluid power, which is basically the same as pneumatics when it comes to understanding cylinder operation.
e.g. The force exerted by a cylinder would be the area of the cylinder x the pressure, e.g. a cylinder of 4" dia has a piston surface area of 12.57sq", if operated with a pressure of 80bls, 12.57x80 = 1000lb pressure.
Al.

[Goldhunter_2]

Al,
yes that is probably the correct spelling for Clevis

I am really trying to avoid Hyd system if possible just because it would be more involved and expensive in set up.


Quote " a cylinder of 4" dia has a piston surface area of 12.57sq", if operated with a pressure of 80bls, 12.57x80 = 1000lb pressure."

in your example compared to Geof's you decrease the air psi but increased the diameter of cylinder so basically increase either or both diameter and PSI would gain force. even in your example 6000lbs of force is allot

[Goldhunter_2]

Geof,

Ok so if I am understanding correctly the answer is two part first part the wider the diameter of the cylinder the more surface area and more force applied and vs versa a narrow cylinder would have less surface area thus apply less force. Second is the more PSI of air applied will increase the force the cylinder ram puts out ie: 50,100,150psi is more PSI = more output force

I'm trying to get away with using air pressure form my larger air unit it is 10hp elec, 120 gallon tank and current have to set at 190psi this is what I have set up running my other stuff and figured it cheaper and easier to use what I have.

So your thinking that six air cylinders over a 4'x6' table area spaced roughly 1.5' apart both lengthwise and side to side would not have sufficient force to stamp that thin steel with ?

[Al_The_Man]

I am really trying to avoid Hyd system if possible just because it would be more involved and expensive in set up.


Quote " a cylinder of 4" dia has a piston surface area of 12.57sq", if operated with a pressure of 80bls, 12.57x80 = 1000lb pressure."

in your example compared to Geof's you decrease the air psi but increased the diameter of cylinder so basically increase either or both diameter and PSI would gain force. even in your example 6000lbs of force is allot

Not sure where you get the 6000lbs?
I think Geof made an error in the area, a 3" dia cyclinder has an area of 9.42sq" according to my calc?
I never intended that you should get into hydraulics, just most of the principles are the same.
Al.

[Geof]

..... So your thinking that six air cylinders over a 4'x6' table area spaced roughly 1.5' apart both lengthwise and side to side would not have sufficient force to stamp that thin steel with ?

It depends how thin "thin" is and how complex the shape is. What you need to remember is that you are working with two areas: Your cylinders which generate the stamping force and the area of your work piece that is being stamped. Imagine you wanted to emboss a pattern into a sheet of metal the same size as your table. The table area is 3456 square inches and if you used six 6" diameter cylinders at 190psi you have a total force of 32,233 pounds. This sounds a lot but divided by the table area it works out at 9.34 pounds per square inch. So you can do an experiment on a small scale. Make a die that replicates an area of 20 square inches of the pattern you want to emboss and you will need about 180 pounds. So stand on the die. If you do not weigh enough pick up a 50 lb bag of sand and stand on the die.

I used to find it surprising how much force is needed to emboss simple shapes into fairly thin aluminum sheet but not any more having made many setups to form dimples for countsunk screws in thin aluminum. It is easy to form the material around large radius curves but as soon as you want to get sharp corners and fine detail the required force increases dramatically.

If you don't want to get into full hydraulic systems do some searching on pneumatic-hydraulic amplifiers. This is where you have a large diameter air cylinder pushing on a small diameter hydraulic cylinder. If the difference in diameters is a little more than threefold; 6" air cylinder 1-1/2" hydraulic cylinder, the hydraulic pressure obtained is about ten times the air pressure so if this is now driving six hydraulic cylinders on your table you are getting over 300,000 pounds over the table area or more than 90 pounds per square inch of table surface. This would be enough to do something in thin material.

Of course your table and all the structure to support the cylinders will have to be very rigid but as soon as you get into wanting to form metals you have no choice; things have to be rigid, heavy and powerful.

[Goldhunter_2]

Not sure where you get the 6000lbs?

used your example of 1000lbs force for each cylinder and multiple buy all six cylinders I was planing to use 1000 x 6 = 6000

[Geof]

.. I think Geof made an error in the area, a 3" dia cyclinder has an area of 9.42sq" according to my calc?....Al.

Area of circle is pi x r x r; 3.1416 x 1.5 x 1.5 = 7.0686

I have, and do, made/make mistakes but not this time.

[Al_The_Man]

Area of circle is pi x r x r; 3.1416 x 1.5 x 1.5 = 7.0686

Yeah.. plugged in the wrong numbers.. it is getting late here, at least that is my excuse. :devious:
Al.

[Geof]

...... even in your example 6000lbs of force is allot

This discussion is interesting and I hope instructive.

6000 lbs is a lot, sometimes, but on the other hand sometimes it is not a lot. My truck fully laden is about 6000 lbs but it is supported by the tires on a total area of about 150 square inches so the road only experiences about 40 pounds per square inch. 140 pounds is not a lot but when it is a woman walking in high heeled sho the road can experience 714 pounds per square inch. The woman would probably be highly indignant if the road told her she weighed more than my truck.

[Goldhunter_2]

Geof,

That's funny you say stand on it, that is actual how I have done .125 aluminum several times before....... and no I don't weight enough I throw on anything heavy I have nearby then get on there an jump up and down (now you know why I want to build this ...lol


ok thanks I'll do some searching on pneumatic-hydraulic amplifiers

The 6" cylinder would probably be getting out of reach I been looking at 1.5", 2.5", 3.25" and 4" diameters

[Goldhunter_2]

This discussion is interesting and I hope instructive.
140 pounds is not a lot but when it is a woman walking in high heeled sho the road can experience 714 pounds per square inch. The woman would probably be highly indignant if the road told her she weighed more than my truck.

I wouldn't want to be the one that had to tell the lady that :stickpoke

Yes instructive

[Geof]

...... jump up and down.....

Ah, impact forces; you need to do some other experiments.

Find a weigh scale that goes up to something like 1000 pounds and try jumping on it; I think you will be surprised how much impact force you exert.

Alternatively consider a hammer driving a nail compared with how much force you need to exert to pull the nail out. A typical claw hammer gives you a mechanical advantage of about ten to one; a pull of 80 pounds on the handle exerts 800 lbs on the nail.

Obviously if it takes 800 pounds of force to extract the nail it must take a similar amount or more to drive it in. So an 8oz (half pound) hammer is exerting a force of 800 pounds when it impacts the nail. When you jump onto something from a height of 1 foot you can easily exert an impact force of several humdred pounds.

I just Googled and found a link that suggests a person weighing about 150 pounds will exert a force of about 400 pounds just by jumping a few centimeters. It did not specify how many ' a few' was nor whether it was a stiff legged landing or flexed knees.

You can crudely calculate how much force you exert when jumping onto something. If you jump from a height of four feet and flex your knees about six inches on landing the landing force is about 8 times your weight.

I don't recommend it but you can try a stiff-legged, locked knee landing and you will exert a force much, much higher than eight times your weight. You may also be a candidate for a trip to the emergency ward due to fractured heel bones because of course the force you exert on what you land on is also exerted on your feet.

[Al_The_Man]

when it is a woman walking in high heeled sho the road can experience 714 pounds per square inch.

They were talking of banning them on aircraft at one point, Stiletto's, not Women, after a heel of one punched a hole in the cabin floor. :boxing:
Al.

[Geof]

I think you are showing your age Al.

[kawazuki]

And don't forget air is relatively inefficient in high pressure situations as it can be compressed which produces heat so the duty cycle of the machine reduces as cooling periods are required. Oil on the other hand doesn't compress and unless you get to stupidly high psi numbers or cycles doesn't require cooling. I think industry uses hydraulics for stamping and pressing for good reasons.

[Goldhunter_2]

I have been looking up those amplifiers last night and this morning and there pretty pricy so I think that pushes the choice back to either just air or just Hyd. I looked around the shop this morning I have a two handle hyd control lever , probably most of the fittings but not four way splited blocks I would also need to buy six hyd cylinders and a 110v Hyd pump with resovior so my out of pocket expenses will be about four times as high if I go Hyd compared to air:violin:


On a positive note during my search I saw a guy (ebay) that had a three cyl hyd press doing exactly what I want to do and he said he uses both wood and metal dies. His press uses a spreader bar under the hyd cylinder going all the way to the out side of his dies opposed to what I was planing of have a Cylinder towards the outside of each of those spreader bars for larger one piece stamps.

[Goldhunter_2]

And don't forget air is relatively inefficient in high pressure situations as it can be compressed which produces heat so the duty cycle of the machine reduces as cooling periods are required. Oil on the other hand doesn't compress and unless you get to stupidly high psi numbers or cycles doesn't require cooling. I think industry uses hydraulics for stamping and pressing for good reasons.

The duty cycle would be more related to the compressor ability then the air cylinders wouldn't it ? there would plenty of cooling time since the set up of dies and material would take me hours probably (at my pace anyway) then a single part stamp and hours again to change out dies.

well to me I think there is a difference between " industry use" and "Hobbyist use" Hyd maybe a better choice I am looking back at that now but it also will cost quite a bit more money and something I have to consider

[Al_The_Man]

I think you are showing your age Al.

Hey, I'm a dedicated follower of fashion..
Al.