Liquid Nitrogen... for freezing... anyone have any thoughts?

[Dadnatron]

I would like to mechanically 'machine' some open cell foam. I am looking to build customized pillows. I've been building/forming them by hand, and this isn't a reasonable way to go about making them. Each is different, specifically designed for my patient's shape and needs, so a mold will not work. Right now, I just want to see if I can find a bit that will remotely work, before I invest more heavily in machinery. I have about 20 different bits that I want to test, however, given the extremely limited nature of what I am doing, I am not getting any decent 'cutting' results, because the foam is catching on the blade.

I think that freezing it might allow me to do it better, so I thought I'd use Liquid Nitrogen.


What I'd like to do... buy about 5gal of liquid nitrogen and freeze samples of foam then test them with my router. If I can get anything which even remotely seems like it will work, I'll feel better about moving to the next step. There is a chance that I can get a bit/machine/foam combination which will work without freezing, but at this moment, I am not there.

I called Praxair, and they will sell me the liquid nitrogen, no problem, but I have to have a dewar. Dewars of the size I envision are well over $1000 and up as far as I can tell. I don't 'know' that I need 5 gal. I just suspected that would allow me to spend a Saturday afternoon, freezing, cutting, and cussing enough to test the bits I have available to me.

Any thoughts on getting liquid nitrogen for such a task?

 

[coldsteelva]

Have you considered an electric heat knife? They are designed specifically for cutting (melting/sealing) through foam. 13 Watt Heavy Duty Hot Knife

 

[Ford850]

Depending on the size and shape of the foam, a band saw can work well too. It doesn't catch like you'd think it would, and produces relatively clean cuts.

 

[Dadnatron]

A hot knife won't work on this foam. But I appreciate your thoughts.

Its not that I can't cut it, its that I need to be able to design the pillow shape in a CAD program and have a machine 'mill' it out. I have to find some other way than me, a tape measure, and a knife. By the time I have evaluated the patient, obtained a 3D file to use for measurement and shape, etc, examined MR and physical findings... a final product made with a carving knife just isn't going to cut it as a business model. A hot knife won't work any better.

 

[Dadnatron]

These pillows are customized specifically to fit the patient. They aren't rectangles of foam and although a bandsaw might help with sizing the overall shape, it won't do what I need. These are 3D shapes that only a 4D or 5D mill could do.

Depending on patient needs, they hold the head in an optimal position to relieve certain types of pain from specific problems. I build ridges, depressions, shapes for shoulders, neck, etc into each pillow. And they all have to be specific for that patient.

While one patient might have issues with a herniation on the right, weigh 300lbs and have a short neck, the next patient might have a nerve compression on the left, weigh 90lbs, have scoliosis, and have a thin neck. Those pillows won't look any more alike than a dachshund and a basset hound. similar... but very different.

 

[Ford850]

A hot knife won't work on this foam. But I appreciate your thoughts.

Its not that I can't cut it, its that I need to be able to design the pillow shape in a CAD program and have a machine 'mill' it out. I have to find some other way than me, a tape measure, and a knife. By the time I have evaluated the patient, obtained a 3D file to use for measurement and shape, etc, examined MR and physical findings... a final product made with a carving knife just isn't going to cut it as a business model. A hot knife won't work any better.

Ok, that makes more sense.

 

[/pine]

Methinks you are going to need a much smaller bit...something small enough that will cut/remove but not catch...it will take a lot of passes and leave very small foam refuse...

I don't see how it would be practical to try to exotically freeze (and keep frozen long enough) to achieve what you're wanting to do...JMO...Good Luck...

 

[SPYDERLK]

Have you tried dry ice? Conceivably, porous foam could be impregnated w/o damage and just outgas as you machine. It would definitely stay cold. Because of the double phase change latent heat is huge. CO2 sublimes at atmospheric pressure holding at about -75C.

 

[Kyle_in_Tex]

I first thought hot wire knife too, made out of nickel chrome.

I have a Fanuc Robodrill 5 axis machine at work. I also have vertical mills (3 axis). Before investing much, I'd freeze a small piece and try to cut it.

We also have large amounts of Nitrogen at work. You will need what is called a Dewar to handle it. It is the cheapest way to get and store it. Not sure how you would keep an entire pillow sized piece frozen. Ice quickly attracts to where you spray the LN.

I see open cell foam with scallops and other shapes, so I know somehow it is getting cut or molded. Maybe you should try to make a mold by machining, and then make the pillow. What ever you do don't buy machineable foam.. that stuff is nasty, gets all over the place and sticks to everything. I won't let anyone cut it anymore in our shop.

 

[jpolcyn]

Delille Oxygen in Columbus ohio has a small dewar they let people borrow. You obviously have to put a deposit down of a couple hundred dollars i believe. I used to work at a welding/gas supply house and people would come in with coolers to get them filled as well. That is at your own risk obviously.