Constant Force Air Cylinder System

Use a spring.

The questions you asked indicate that an air cylinder will never work for you.

It is much more expensive both initially and during the life of the device to use an air cylinder.

Unfortunately a spring will not provide a constant clamping force, and the change over a 1.5" of stroke will be considerable. This is the reason I am looking for alternative solutions.

If the air pressure is to be the same both sides of the piston in an air cylinder, then the cylinder and the piston are redundant; one can get rid of them without affecting the operation of the equipment.

"Spring is in the air."

Why don't you simply add a sleeve with an internal spring that rides below the punch by. 1/4/inch. Sleeve contacta ts workpiece first, the punch hits and sleeve strips sheet off punch as retracts.

"Hope springs eternal."?

This sounds like it may be a good application for an Air Over Hydraulic Cylinder:

http://www.milwaukeecylinder.com/pdfs/mc_hydraulic-pneumatic_devices.pdf

Okay this material is 1.5 thick. At that thickness how flexible is it?

With a 1.5 inch working stroke for your pressure pad, I agree that springs are not practical. This sounds like a drawing or forming operation. where you need the maximum clamping force at the start of the working stroke. I have done this many times with this type of tool using air or nitrogen cylinders (depending on the clamping force required)

Connect the cylinders in parallel to a relieving pressure regulator. The regulator should be sized to allow sufficient flow through the relief port to keep the pressure in the cylinders constant throughout the stroke.

You need to check with the Rube Goldberg Division of LynDoor™Industries for a solution.

You are making this far too complicated for a simple punch. A spring loaded ring that rides with the punch will be much simpler unless you have unlimited time and money to support the failures I see in your future.

KISS!

Since you have not told.us what you are punching it's impossible to give meaning ful help.

Also your level of experience is important.

KISS

Good advice.

This is a standard, commonly used design for press tooling, one that I have used successfully many times. Do you realize that the springs required to do this would have to be about 20 inches long in order to provide sufficient initial clamping force without producing excessive force at the bottom of the stroke.

Material is NOT 1.5" thick, but I need to push the punched-out peace and tack it onto another part. The system is tacking segments of friction material around a transmission/clutch disc and I am doing this on both sides of the disc concomitantly. The friction material itself is between .030" and .150". The cylinder idea was counting on the different area of the active piston since on one side you subtract the rod. Transferring the air from one side to the other was meant to reduce the volume of air evacuated through the muffler/pressure valve. It is common in hydraulic applications where you need speed.

This is air, not hydraulics. You don't need the extra complications of a regen circuit. In the end you gain nothing, just a bigger cylinder to provide the same force as a smaller cylinder.

That sounds better, I was wondering how you were punching through 1 1/2" thickness of any material.

A common alternative to the usual spring system is to use urethane blocks. They do not last as long as springs, depending of course on how much deformation you induce into them.

It's kind of difficult for us to offer you a solution when we can't see your process can you send a picture?

Gringogreg, you give me hope! That's not to say that I reject kisses.

KISS is an acronym. It stands for Keep It Simple, Stupid.

I would have to say that in almost every instance where we were punching something we would use a sprung stripper plate. I understand where you are going with the air cylinder idea but you will have better success with a CCR spring.

There are springs that are manufactured to be a Constant Compression Rate.

Look for die springs. HERE is a list from this sites Product and supplier page.

Take a look at these suppliers!

These springs are not appropriate to this application. They are generally used in counterbalance applications.

If the material is only .03" to .150" then a spring is perfect for the application.

There is something that I don't completely understand.

• Are you punching the material and then manually applying them to the plate or are you doing this in one operation?
• Are you punching the material and in the completion of the cylinder stroke applying it to the plate?

I'm a bit confused. Please explain.

The apply is a continuation of the punch. The punch doesn't stop after cutting the material, drives the material through the die on the disc. I have a mirrored punch-die...doing the same thing from the opposite side so upon indexing the disc 360 deg. I have a complete disc with friction material on both sides. Parts have variable thickness, that's what drove the stroke up to 1.5".

Ok, I understand now.

You're punching the material and applying it in one 1.5" stroke. Now I can wrap my head around it.

Truly without seeing the machine it will be difficult to offer a solution.

Is there room on the table or behind the punch to add a finger clamping device that holds the material down when the punch cycles? It possibly can be controlled by your existing air supply and controls.

And once again......

Truly without seeing the machine it will be difficult to offer a solution.

I know exactly what you are doing. I've been there and done that using air cylinders (but I never got the t-shirt) and It worked.

Have you ever herd of a die cushion, used for deep draw dies. This is exactly how they function.

That is one thing I didn't think of. I guess it works a little bit like an air suspension on a truck.

Watch the action of a sewing machine, in particular, the presser foot.

When you use your cylinder add a large pressure vessel to the pressurised side, at the same pressure as the cylinder. And make it large so that the increase in volume as the clamp is pushed up, (relatively speaking), is a small proportion of the whole, making the pressure increase similarly small. This will satisfy your stated need to keep pressure ( nearly ) constant. Do you have room for a cylinder or could you use a pressurised bellows around the punch?

Jim

Good idea. I've used that method with nitrogen springs (cylinders)

Gentlemen, I congratulate myself for joining this forum; that is to say that you are all great. I'll Google die-cushions, I'll see how and if cylinders will fit the existing design and also try to find a picture or drawing of a sewing machine (didn't feel like taking my wife's sewing machine apart last night). And, I guess, I'll have to decide what do I make part of the machine and what part of the tooling/die. Obviously I will have a variety of geometries to punch. I designed and built quite a few machines, some (record) big, but this time I have to do the tooling for a machine somebody else is designing. Thank you all very much.

A die cushion is just a very large diameter air (or nitrogen) cylinder mounted underneath the bed of a punch press for operating the blank holder of a draw die. They are a standard accessory for most presses. You may want to investigate draw die designs for ideas.

Did looked it up this morning. Hard to incorporate in a back-to-back press operation. I have two mirrored punches. However, the sewing machine pressure bar looks promising; keep the clamp "ON" and only release when punch retract to feed material. Now my spring stroke is a bit more than my material thickness difference. Why is it that all the very old concept/ideas are ultimately the most reliable? Simplicity I guess?

I think a few replies were referring to KISS

• Keep
• It
• Simple
• Sir (or Stupid as it is commonly referred to)