Die cutting packaging foam...

[pointcloud]

No it is PSI on the piston face, caculated via piston size PIE r sqrd X 150 PSI. I can not caculate the out come FORCE.. You will have a fixture with restricting forces that will lessen the total Force.

Plus, Volume will have GREAT effects.. A car tire runs 35 PSI to 60 PSI, where as a REAR Tractor tire will run 10 PSI or 12 PSI.. But both carry almost the same weight.

[peter.blais]

Pressure in PSI is a force spread out over an area, the units will tell you this (pounds per square inch). You can't get from a pressure times an area and end up with PSI still, your units will not work out which is a dead giveaway something is incorrect in your calculation.

force (lbf) = pressure(pounds/in^2) * area (in^2)

--> pounds = pounds * in^2
.....................in^2

Just so we are clear you can find this formula although in a slightly different form- p = f/a on page 442 of "physics for scientists and engineers" by richard wolfson / jay pasachoff.

As you can see it is impossible to perform this calculation and end up with a pressure in psi.

Here's one more quick online source:

"The air pressure is set at 60 psi or pounds per square inch. The diameter of the piston is 10mm, thus it has an effective surface area of 78mm2 or 0.1217in2. With a pressure of 60 psi this means the force can be calculated. Force = (Pressure)*(Area). Thus the pushing force equals 7.3 lbf or 32.5 N. "

Taken from one of their examples. You can see the full deal here:

http://pergatory.mit.edu/2.007/Resou...neumatics.html

[One of Many]

Yes, it would be total force based on the surface area and the PSI of pressure applied to that area. You could try and calculate the linear length of shear to come up with a finite pressure, but that is getting too picky engineering to the low limit.

For the application, I would go big with the cylinder and adjust the PSI accordingly with a regulator. Sure, one cutting die may take less cutting pressure, but undersizing the cylinder may leave you reworking the press later. Your choice. For the record, our clicker is a 2 ton made for leather, rubber, and gasket materials, but we do lots of foam and felt padding. Quite universal really, and very surprising what pressures that last little bit takes to get a clean cut.

A few other suggestions: One is to place stop blocks on the die to limit the depth of pressing the rule dies into the sub plate you cut against. The idea being to cut through the material, but not much(if any) into the sub plate than required for a decent part. Another is that the steel rule dies are trapped in a plywood form, but it is wise to back that up with a sheet of aluminum or other harder material so the rule dies do not press out the back under load. This also helps keep them parallel to the cutting surface sub plate. Assuming that your top platten is also parallel to the sub plate.

DC

[peter.blais]

Yes, the stop blocks are a very good idea- if someone were to tamper with the regulator or something I could see that die easily getting flattened. Like he said above, a 6" diameter piston at 150 psi delivers thousands of pounds- I would think that rule would buckle and fold over on itself under that.

Maybe a couple large bolts in the far edges of the upper carraige that you could simply move the die all the way down to the table and adjust the bolts all the way down to the table- If I used say- 4 large bolts one per corner, that should stop it in its tracks. Something with say a 19mm hex head or around that- Cheap, adjustable, and not requiring a bunch of machine time to make- sounds like right up my alley.

2 ton has been plenty? That would save me some time I could order the cylinder right now rather then waiting to get the die and experiment with it.

I am starting with a regular shop hydraulic press for a frame so I was going to simply plate the two opposing halves so there is a 24 x 12" work surface - or around there- and then set up a table to the correct height so that it is easy to work with a long piece of foam stock.

Backing the die is a good idea- what I was going to do is plate the whole surface under the cylinder and then just either drill and tap a couple holes or figure out some simple clamps to attach it straight to that surface- I kinda thought if you put the load on the back of the plywood die in one spot it would come apart in short time.

I'm excited to get going on this, I need to find a used cylinder on ebay, once I have that I will buy a soliniod and regulator to match the ports on it and I should be on a roll.

This will be great and will give my products a really high end professional look right out of the box.

[One of Many]

If the area of a piston is pi x r^2 then 6" cylinder has 28.27" of surface. The total pressure on that is 4241 lbs@ 150psi. Just over 2 tons. Also that is air which is compressible verses a clicker press which is hydraulic. Secondly, the only useful area is going to be under the cylinder rod, so 12x24" plattens can be problematic. Attempting an off center load will not keep the plattens parallel. That goes along with cutting area and the rigidity of the plattens to remain flat under variable loads across them.

Your material should be in strips such that the stop blocks straddle the strip.

The air solenoid should be a 5 port and the cylinder double acting. Best with probably 3/8" ports for good flow and less restrictions.

DC

[peter.blais]

Yea, I wasn't intending on using the full table to cut patterns, rather I just need a large enough work surface to get decent size pieces of raw material through the press without having to spend a lot of time breaking down large material into material small enough to fit through the press. I thought it would be a lot easier to work with if I just plated the entire width I hvae to work with and then build or find a bench / table of this same height so the long pieces of foam can be slid into and through the press with minimal hassle.

The cylinder I'm bidding on is double acting- but I already purchased a 3 way valve and such thinking that the (quite) stiff springs on the press would return it fast enough on their own. I guess I'll see how that goes and it would be relatively easy to change it over later if need be. I didn't really put that much thought into it- those two springs will accelerate an empty table upwards way way more then fast enough for my needs the question is how quickly my valve system will allow the cylinder to bleed down with the air pressure generated from the force provided by those two springs.

I'm not intending on doing zillions of these nor am I entending on farming out die cut work for anyone else so it really isn't critical that it "flys out of the gate" so to speak, I've got all the time in the world to improve it a bit here, a bit there. I was thinking it would be nice to switch out the tube/ tube guide arraignment for some shafts and bushings which would guide things far more exactly- but for what i'm doing at the moment I can't justify the expense both of $$$ and my time- unless it proves to be neccessary.

The foam, pneumatics stuff, is all in the mail, and the pattern is all drawn up I just need to get final approval from the box printing guys that my dimensions will work then I can send that over to the die shop. Should be making some physical progress on this in the next couple weekends.

This semester we have a large design project in school and it is really killing my free time as far as side projects and stuff go.

[One of Many]

If you desire to cut larger sheets of material then you will need to limit the travel of the cylinder from above the upper platen or make the lower platen adjustable such that the end of the cylinder stroke is where the steel rule die meets the sub plate. If you can keep the steel rule die height and the material thickness common, there would not need to be much adjustment for cutting depth.

The return springs may work for you, depending on how heavy the platen is built, it may just counter balance it, but if low weight, you might still consider flow controls to regulate the speed in both directions either at the exhaust port of your valve or the ports on the cylinder.

I know how these things can be built crude yet functional for temporary. More often than not that becomes permanent and safety complacent. Whatever you do, make it safe first even though crude. Avoid single source activation via one switch or foot peddles.

DC

[mr penguin]

How about using an arbor press? They are really cheap. Go to Walmart and get a white plastic cutting board (made of UHMW or Delrin is the trade name) to use under your steel rule die. Should work like a champ and your arms will look like Popeye's in no time at all. Put your material on top of the Delrin and the die sharp side toward the material and give it the berries. Or... we sometimes turn our die cutting side up on the clicker press and lay the material on top of the die. Lay a piece of material on the die then put Delrin over that and give it some pressure. You may be able to get some scraps of "ejection foam" to glue into the die to pop out the piece. I could mail you a chunk if you need it. Give me a pm if I can help.