High Pressure Nitrogen 2

[FabproHelp]

What exactly is the trick to getting high pressure to work correctly. I can't seem to get my pressure any higher than 1.05 mega pascals. The book calls for a 3.0 nozzle but I can't get anywhere close to the pressure required with that nozzle(book calls for roughly 1.5 MpA). I have to switch down to a 1.4 nozzle in order to get as high as the book says. Do I need to adjust the HP regulator coming in to the laser?


I am currently making an attempt at 3/8 SS. Running an Amada FO-3015 with a 160i control

 

[AndreCarneiro]

Hello FabproHelp,

I'm having the same problem has you, but i don't even get a cut straight. Always with tons of gross. But i'm using a 2,5mm with 1,5 MPa.

I have a 3kw Rosin Laser and with Percitec laser

What is the Focus you are using?

 

[FabproHelp]

Well I have yet to find something that actually works out well. The last attempt I was at -.200 in. The dross is terrible on mine as well. From what I was reading online it looks as though I have my focus set to deep. At the moment I don't have enough time to keep playing with it. Thursday I will be back into the material with ample time to play around. It is weird because the book makes it look as though the laser should easily be able to get to that pressure.

 

[AndreCarneiro]

The situation is equal to me, if you can i've started a thread with SS 10mm steel take a look, i will do more experiments tomorrow then post the results. I'll keep in touch trying to help you helping me too!

I've found this

https://books.google.pt/books?id=pR...epage&q=how to laser cut guide amada&f=false,

give it a look too, it seems a good book.

 

[jjl1210]

If you want a good cut on 3/8 stainless you will need a 3.0 nozzle but I need some more information first. What is your nozzle gap? because you can find some pressure when you lower it. Also what do you have for your gas supply? is it a big bulk tank or a small tank you roll up to the laser. You need to build up the pressure in the tank before you can get 10 kg so on the small tanks it may not keep up with the pressure.

 

[FabproHelp]

How far away should your nozzle gap be? When thinking about the pressure I had never imagined the nozzle gap would increase it. I use 180 Liter tanks @350 psi. Machine regulator maxes out at about 280 psi

 

[jjl1210]

This is a good start.

 

[FabproHelp]

What condition are you using? I'm just cutting a small rectangle and use E4 for my conditions.

 

[SGAFFNEY]

jjl1210. Respectfully, it looks like you have an error in the cut condition you posted. The only focal position used by Amada lasers (assuming the laser has NC focus) is on cut condition line 1. The condition you posted shows -0.051 inch which is way to high. I recommend that once you find what works well that you set all the same to avoid confusion. This will also be affected by the accuracy of the focal point base setting.

Regarding gas settings and nozzle. Keep in mind that both gas pressure AND volume have to be considered. Larger nozzles equal less pressure and more volume. Think of a garden hose.... no restriction on end of hose equals high volume (gallons/minute flow rate) but low pressure and velocity. The water will only go a few inches out the end of the hose. Put a nozzle with a smaller opening on the end of the hose and the volume or flow rate will decrease but the pressure and velocity will increase shooting the water several feet. The nitrogen reacts in a similar fashion.
Also consider the diameter of the nozzle in relation to kerf (cut width). 3.0mm (0.12 inches) vs. 0.3mm (0.012 inches. This is why the pressure will increase as you reduce the nozzle gap creating a back pressure. The smaller the nozzle gap the more concentrated the gas flow will be into the kerf. I have cut 0.375 stainless nicely with a 2.5mm nozzle but think that the 3.0mm nozzle would be better if you have pressure and volume needed.

The liquid nitrogen tanks that you are using can also be an issue. Are you drawing off the gas outlet? Are you turning on the ppressure building valve? Have someone watch the regulator while you are trying to cut to see just how much pressure is available while cutting not just when no gas is being used.

Good luck! Hopefully this will help you understand the process. Attached is a cutting condition from Amada for your review.

 

[jjl1210]

Look at the focus on condition 2. We used this material to etch a tube so in order for us to remember where the focus was we copy it to condition 2. One of the first things I teach them is the only focus line that is used is the first so use the others so you can keep track of your changes. The focus was never put back because I use the photo to show them how to keep track of what the focus was before it was changed.

 

[krugtech]

When cutting with N2, most of the time the problem is the system feeding the machine, not the machine. The volume of N2 needed usually means going to liquid N2. I've seen many mistakes over the years. Here's a few things I've learned-

1. the gas companies do not maintain their liquid dewars and many have trouble building pressure

2. you need high pressure dewars that put out at least 300psi

3. don't use a regulator, the dewar controls the delivery pressure, a regulator is just an unnecessary flow restriction. Protect the machine with blow off valves, not regulators.

4. you need to take liquid from the dewar, not gas. Run the liquid into an evaporator. Don't size the evaporator for your worst case cut scenario, size it for your worst case failure scenario. If an N2 leak develops you can draw a lot more than what a specific nozzle size and specific pressure will draw. Just like the blow off vale, the evaporator is key to protecting the machine.

5. run a large diameter line from the evaporator to the machine. I don't care what size the inlet is into the machine, run a fat line. The machines have a pressure drop through them, don't add to it.

6. If you go to a bulk tank, the same rules apply.

Chris

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[meps11]

When you are centering your laser on low and you get it centered switch to high and see if centering is the same this get rid of the dross

 

[drossfree]

Most often when cutting 3/8 ss I use a 4 mm nozzle on my fo3015 my gas pressure goes down to about 1.7 MPa and my focus is between -3 and -4.5 mm however the critical part is the speed of the cut. If you go too slow the bottom of your cut burns and you get large hard dross. If you increase your speed you should get better results I cut 3/8 ss at 28 to 32 IPM

 

[drossfree]

Are you using a double nozzle? I use only double nozzles with the 7.5" head they increase pressure and reduce gas consumption. However double nozzles cannot be used with the 5" head because the focused beam will hit the inside of the double nozzle and melt it closed which can be quite dangerous for your lense