Nozzle Size vs Gas Pressure vs Standoff etc.

[RPosty]

I have always just fixed machines and never had to worry too much about application because where I used to work had a lot of highly skilled machine operators with many years of experience. So As long as I could get the Machines running, they could take it from there. Now I work at a very small job shop with very little expertise that have been just doing the same way they have always been and I see them struggle everyday.

Machines: PRC2200 & PRC1500 with Turbo Upgrade, Facuc C2000 and Amada F03015 with 4000w Fanuc resonator. We also have a couple old Lumonics/Photon machines, V505 and a V1200.

So here is today's big question:

For The PRC's which both have contact heads and followers, What size Nozzles should we be using for Stainless (thin and thick), what nozzle standoff distance, Gas Pressure and Focus do you find beneficial?

Currently they pretty much use full power with full pressure coming out a .120" nozzle just barely off the material. They only vary feedrate, duty cycle and frequency to compensate for material thickness.

this seems crazy to me. We tend to go through a lot of Output Couplers. They used to go through a lot of external optics until I replaced the 1/4 wave silicon with a copper version and replaced the Zero Phase Silicons with the used internal folds which believe it or not increased the up time of these machines. The Optics Manufacturer kept trying to convince me the copper isn't any better, but I haven't had one fail yet.

They also use the uncoated windows to protect the lenses.

"I am stuck on Band-Aid brand, 'cause they are stuck on me"

 

[Chally72]

Yikes! Sounds like they need a day or two with a proper tech.

More knowledgeable individuals than me will soon step in, but...when cutting Stainless, I use a 0.080" single nozzle up to 0.140" material, and an 0.100" beyond that. Gas pressure varies from 8-13 bar as thickness goes up. I don't like varying feedrate...I target a feedrate and vary my power, duty cycles, pressure, etc.. to make good cuts at that speed. Otherwise, how can you quote things with consistency if you're constantly screwing with the feedrate on all the programs! If you choose one variable to remain fixed, that should be it.

 

[SGAFFNEY]

The questions are too generalized to get specific answers. I am guessing that you are talking about "clean cutting" with hi pressure nitrogen. In my experience you would not use the same size nozzle across the board. In thin material 20-18 ga I sometimes used a 1.5mm (.060 inch) dia nozzle. I didn't get to a 3.0mm (0.120 inch) dia nozzle until I got to thicker materials 3/16 - 1/4 inch range. Nozzle geometry is also important. Molten SS is very viscous (thick) thus requiring hi pressure to expel it from the narrow kerf. Think of nozzle dia like a nozzle on the end of a garden hose. No nozzle = lg volume and low velocity, small nozle = smaller volume and higher velocity. The other thing to consider with nozzle dia is focal point. Focal point is usually set to aprox 75-85% thru the material so the thicker the material the further out the nozzle the focused beam has to travel. The beam will be in a V shape as it focused from the cutting lens so if you use to small of a nozzle on thicker material the beam can actually "clip" the nozzle and cause serious problems. When you say "barely off the sheet" regarding stand off distance, I am not sure what that means. They may be trying to concentrate the gas flow into the kerf to compensate for using such a large nozzle, especially in thinner materials. This gets fairly involved as you can see. I agree that they need someone to come in and teach the operators how to cut. It always amazes me that management doesn't see how that will pay for itself in a short time. The additional cost of scraped parts, deburr cost, reprogramming due to scrap part, extra material cost, production/scheduling delays.....etc have a cost as well, not to mention the frustration for everyone involved. Don't forget all of your laser should have had cut conditions supplied by the manufacturers. While these are never bullet proof, they can be a good place to start and they should not charge you resupply you with that information.

 

[RPosty]

Thanks, generalized is what I am looking for anyway. I like to hear as many different ways to skin a cat as I can. I find even diametrically opposed approaches to anything still has an educational value to me. The Shop I am working for now is very set in their ways and very resistant to change, but a good group of people nonetheless. So What I am trying to do is learn what I have never needed to learn so that I can get good at what they do and slowly bring them around. This has already worked in different area's with them. The owner is never around anymore, maybe once a week or two and pretty much handed everything over to this younger guy who is very hard working but inexperienced He has worked here since he was in High School.

So your input is very appreciated, and I will be doing a lot of on the fly educating of myself. I am really looking forward to learning all this anyway. I do have the basic cutting info from the manufacturers like PRC, but I really like to know what veterans think.

How about Nozzle Tip shapes? They use flat knurled nozzle tips shaped like plates. where I used to work used bullet shaped nozzles for the co2 machines and tapered for our ND/Yag cutters.

"I am stuck on Band-Aid brand, 'cause they are stuck on me"

 

[JeanFreli]

Well I agree with Chally72. Me I'm the first one at the shop to break the ice with a fiberlaser 2kw and since only three months I operate that machine.I learn it hardway and stil a lot to go.
The first thing I see is the feederate.I find an average and stuck on it. For my little experience I never been more in trouble until I'll start to change it. For example, .125 mm (11ga) 130 in<min. Clean cut but I"ll try faster to see. The guy from Ermaksan came today and that's what he set. The thing I find the pressure very high compare to you guys. For that 11 ga 18 bar and nozzle stand off...easy they said always .0394 in (1mm). Power always maximum...2000. And nozzle size 3mm.
And yet for ss .187mm (7ga) and .250mm he had burrs and leave me with that to go take his plane for Turky. I'm telling you all what I know and not shy of it because I have to start somewhere. And it is true they have basic parameters in the machine but don't work in thick pieces. They go to 22 bar pressure for .250 at 38 in;min. You should see how fast the gaz is going down from the tank.
On that a big thanks to you RPosty for that post.

 

[Chally72]

Jean, those sound like incredibly high pressures. For me, the benefit of lower pressures, in addition to keeping nitrogen consumption low, is to reduce the tip-ups of adjacent pieces caused by the nitrogen, especially on thin pieces. I've lowered my gas pressure on thin stainless and varied other parameters to keep a clean cut. This has lowered the scrap rate I get from whacking a piece that flies up into the path of the nozzle because I ran a cut right next to it with high pressure purge. I can nest my pieces closer together, utilize more of the sheet, reduce scrap rate, and reduce my gas costs all at once...

 

[JeanFreli]

Well Chally sound good to hear that. I found it high too. Today I start the change slowly. The things is the cut is very nice but you are very right to say the benefits of closing your pieces. The other things (with too high pressure) is the vibration of the sheet (especially thin materiel) when you cut. If it keep cutting you have a cut like a saw. Anyway I first change the size of the nozzle. I saw somewhere in the forum nozzle 3mm starting at 7ga. I hesitate for size 2.5mm and 2mm.Finally went for 2mm. My first piece wasn't nice but easily adjusted after. My goal is going to 12 or 13 bar for .125ss. Nozzle stand off is going good for everything at 1mm (.o394 in).
Since they change all the head it going very easy to adjust. The collimator was contaminated. I asked what can cause that but no answer. He undercover let me know that he prefer the CO2 machine because less sensitive. Except today for the first time I cut .048 ss and let me tell you it is fast. Feedrate 800 in.min. I had a film burning before. The film burning was a little bit slower than the real cut. Pretty amazing to see that. When the head come back home after she finish the program it's like receiving a bird in your windshield car . The speed is 3G.
Tomorrow I'll work on the 7ga. Still dross. I tried the rule of the thumb for the focal but don't really work. They said 2/3 of the thickness. I do .187 by .66666 egal .12466 divised by .0394 and result 3.1 mm focal. But still working on that.

 

[RPosty]

Okay Next week I am going to try PRC Laser's recommended settings for 11 Guage 304SS (3.0mm/.120") for Our PRC 2200. They suggest:

1500 watts CW @ 71 inches per minute
or 2200 watts CW @ 106 inches per Minute
195 PSI/13 Bar
2mm Nozzle (.080")
Focus -2mm into the material (5" FL Lens)
Nozzle Standoff 0.8mm (.032")

Not sure our tables can do 71 inches per minute because lead screws and ways are old and worn. I believe 50 inches per minute is our max. So any suggestions what to alter to compensate for slower speed? Sould I increase or decrease Assist Gas Pressure?

I think they pierce with oxygen, then cut with N2. What do you prefer to pierce with?

"I am stuck on Band-Aid brand, 'cause they are stuck on me"

 

[JeanFreli]

Well Rposty your set is very closed of what I run for .125mm ss. Stainless series 200
2000 watts at 130 in.min
Nozzle 2mm Focal -2
Standoff .0394 Pressure 18 bar
I thought to put the pressure down but the cuts are perfects with absolutely no dross. Can pass my finger on the side and no cutting my finger.
71 in,min is closer to the speed of .187mm (7ga).
Me today I had problem with my sensing. Error; body touched received. Body touch fault. I'm stuck on that. I just start working to adjust the 7ga when it happen.
Opposite to plasma laser are very sensitive, fiber laser at least. I don't know about CO2. But that's the joy of getting a great piece cut. You look at it and you can say you work for it. The welder are very happy too.

 

[RPosty]

I have some experience with capacitance head issues, I imagine most work the same. First make sure your Sensor cable is attached good and snug, any play at all can cause all kinds of issues. Does it get worse when assist gas is on? if it does then it is probably the connection at the nozzle. on some heads (laser Mech for example) the smt connector has an extra long center conductor that is attached to the nozzle with a set screw in copper which can come loose over time with heat at the nozzle. On our Amada machines, the smt push on connectors fail over time hen i have to solder a nw=ew one on (like $10 out of allied, newarks or digikey).

"I am stuck on Band-Aid brand, 'cause they are stuck on me"