Best Stainless Steel Cut at 800 mm / min ?

03 May 2024 13:12 - 03 May 2024 14:16 #299625 by alangibson
Hello all,

I've done my first cuts on 3mm stainless steel. I'm getting the least dross at 800 mm / min at 45 amps. This seems absurdly slow to me. Can anyone second that?

I've tested about every cut speed/current imaginable by cutting 30x30mm squares. Lag lines are nearly vertical at 800 mm / min but swept back at any higher speeds.

I'm worried that I have a configuration/scaling oddity that's causing me to get odd speed readings. The cut dimensions are spot on though so there shouldn't be any mechanical issues.

Current: 45 amps
Cut speed : 800 mm / min
Standoff: 1.5 mm 
Pierce height: 2 mm
THC: off (cutting 30mm square on flat material, so no need)
Pressure: 55 PSI (set with air flowing)
Torch: IPTM-60
Cutter: Lotos 5500CNC

EDIT: clarifying some points
Last edit: 03 May 2024 14:16 by alangibson.

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03 May 2024 13:46 #299630 by tommylight
What nozzle size?
what pressure?
what torch?
Why THC off?
Unless you have a really flat bed and heat treated metal plates, you must have THC on or the cut quality will vary a lot or be useless.
With normal nozzles, +-0.5mm is the difference between a good and a very bad cut, fine cut ones maybe +-1mm.
And, as a general rule when cutting stainless, more speed and more power = less charring , up to a certain point.
All this is generalized, there are to many variables to account for, so nothing can replace testing, lots and lots of testing and varying just one of the variables at a time.
I make a 100x10mm rectangle and do about 50 to 70 cuts of the same thing while changing gradually THC voltage, air pressure, feed rate, all for the same cut current. Repeat all this for every material, but i limit the current settings to 40-45 and 60A as that is what i have now.
Did all that last two days since i got a new plasma source, cheap china one. Found out it cuts best with 4bar at 45A i had it set at 5.5bar initially! :)
Pressure must be measured and set ONLY while the air is ON.

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03 May 2024 14:15 #299631 by alangibson
Thanks tommylight. I've updated my post to address everything you mentioned. I've got it all covered except I need to check again what my nozzle size is.

My dimensional accuracy is quite good. What I can't figure out is why I get minimal dross and charring at such a low speed. Any higher and I get high speed dross that needs to be ground off.

You gave me an idea that maybe I need to up the air pressure. I'm using the value from my machines cut chart, but it's been wrong on every other value so why not this one too.
The following user(s) said Thank You: tommylight

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03 May 2024 14:29 #299635 by tommylight
Are you in the business of selling car tires? :) That is the only thing in use that has metric and imperial measures for the same thing, so you have everything in metric except pressure :)
Mine says pressure =5kg
no cm2 behind it so that is 5bar, but after testing 4 proved much better at 45A.
30mm square is no good for testing cut parameters, 100-150mm should be minimum. 30mm is not enough to get to cut speed if acceleration is low-ish.

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