Hello, I'm a 3rd year M.E. student with a side business doing parts for watercooled volkswagens. Anyways, I have a few high end products and I'm looking to really convey that in the packaging, by packing them in die cut foam inserts.

Traditionally this wouldn't be economically feasible do to the cost of the tooling and the low quantities i'm doing, but I happen to be lucky enough to have a little bridgeport series 1 cnc, so my next thought was hell it wouldn't be that hard to make a punch / die to cut these out myself, using a cheap automotive press frame and I had planned to ditch the bottle jack in favor of a much faster pneumatic ram.

Anyways, the problem I run into is I have no idea what kind of force it will take in practice to shear the cheap low density charcoal packaging foam I planned on using.

I figured I may be able to save a lot of messing around by checking to see if there was anyone on here with any experiance stamping / cutting such soft material- and how tightly you fit up your punch / die (I was thinking a few thou would be fine for this? ), as well as what materials you used for each.

I'm on a budget (who isn't?) but I would like to get at least 1000 pieces through this contraption without repairing or replacing the punch or die. I was thinking aluminum would be more then strong enough, and sortof hoping to use a plastic female, but really I know nothing on punching this stuff.

This is basically what I'm shooting for:

http://www.foamexpress1.com/Packaging/PackagingSample.jpg

Any help?

An easier and cheaper way would be to get a gasket or seal shop to make you a cutting die. They use a piece of plywood that has strips of sharpened steel stuck into a router grove in the shape of your cuts. They are pretty damn cheap usually under $100, and work like hot damn. We have used them to cut sheets of rubber and its the only way to go for stuff like this.

An aluminum die with a plastic punch would probably leave a pretty sloppy, unprofessional looking cut.

hmmm, yes thats a pretty good idea. I actually saw something ~ similar on "how its made" the other day- they were using a press and a die similar to what you mention to cut foam for hockey goalie pads.

I'll call around and see if there is a gasket /seal shop that can do it, if not I can always fool with making that myself- I do have the stuff to do it, I'm just sure they would get it done much much faster. I am fortunate enough to be in salt lake city which is a pretty industrial town so there is usually somebody with what you need. :)

Just out of curiousity, the steel "blades" if you will- what kind of thickness is usually used there? If worst comes to worst I'm thinking I could brew that up myself, I've never milled wood before but I'm sure it can be done, just slow compared to a router i'm sure. Wouldn't kill me though for a one time / only once in a while job.

Get some old broken bandsaw blades grind them sharp, well if you only have to make one or two... You can cut (jig saw) some 3/4" plywood and screw it to the outside...

Also EPS foam is CHEAP, and you can have it fit whatever for pennies... I use it all the time, they do all the cutting for me... The most expecive I use is like $0.25..

I did this once myself. Used a stainless steel razor edged blade I found at the local saw sharpening shop. Sheared it up into the proper lengths. Found out that using gloves to handle them was important;)

hth

sorry, should have been a little more clear... these were bandsaw blades used by the meat packing industry. No teeth, just a razor edge.

Just out of curiosity, the steel "blades" if you will- what kind of thickness is usually used there? If worst comes to worst I'm thinking I could brew that up myself, I've never milled wood before but I'm sure it can be done, just slow compared to a router I'm sure. Wouldn't kill me though for a one time / only once in a while job.

The blades are about .035 - .050 thick, I think the ones they use come with a sharp edge. You could use band saw or hacksaw blades like pointcloud suggested. Milling wood is a cake walk, you could easily make them yourself. You just need a torch to heat up the bends and a little bit of your own time.

I usually see them being used on a "clicker press", but you can use a small press or even do it by hand.

Just use a cheap air cyclinder (spe??ing)... ebay.. regulator, 110v valve and a light switch.

Any steel rule die fabricator in your area can help you out. Once you see how they are made, you should be able to produce your own if you can locate the materials. Benders and notchers for the steel rule materials will be the bigger expense. Using dense silicon foam rubber inside and around the outside works great for die strippers. We do tons of this stuff on clicker and punch presses yearly.

This will take a fairly large air cylinder. Maybe 4-6"? Don't forget to install speed controls on the valve or flow controls on the cylinder. Dual palm buttons are a must and technically should incorporate an ant-tie down circuit!

DC

I was going to stick my load cell inline with the press / die and measure the force the bottle jack is putting out to get it done, then calculate the air cylinder needed from that.

I'll see what I can find in terms of steel rule / blades / whatever. I have some old bandsaw blades I'm just afraid I wouldn't get them ground exactly even- may end up with little tabs you have to tear where there is a low spot on the blade from some sketchy grinding work.

i made some of these dies and punched out model airplane kits for a customer.some of the material i cut was 1/8 ply. i used my hyd. press and a piece of nylon to cut against. it worked real well.
good luck Dar

A very small cyclinder will work with this foam you are useing.. No need for a 6" diameter... A 6" at 150psi has over 4200 psi on the piston face?

A 1" will have almost 120 psi, what is WAY more than you will need to cut this foam...

Your bottle jack will cut it with it's own weight..

All of the above is assuming sharpness of the balde is at it's best..

Pounds of force, not psi ;) And yea your numbers are spot on- thats the kind of force I would expect if I was going to try to shear it with a punch / die arraingement, although even then, this is pretty soft stuff.

4230 lbs I think would flatten one of these dies.

Thats what I was hoping to hear, makes my life cheaper and easier. I just need to call around on tuesday for a diemaker locally. There are lots of internet guys too but local would be nice.

Sounds like I'm on the right track now, I probably just need to modify this press a bit so that I have a larger flat work surface to make my life easy- need to punch about 250 of these, plus another 500 thin rectangles for the top / bottom of the box.

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.

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/Resources/machine/pneumatics/pneumatics.html

:cool:

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

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. :wee:

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

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. :)

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