Best results for stainless?

[davek0974]

I have some stuff to cut from 3mm 304 stainless sheet, never cut the stuff in this thickness before. My machine is a little Hypertherm 30XP and the only stainless I have done so far is 1.2mm which cut very well with the fine-cut consumables at 25A

I did some tests today at 30A and standard consumables, getting extremely hard bottom dross and a small amount of top dross. Book says 2600mm/min (IIRC) but at that speed the bottom dross is very hard and almost like splinters of uncut metal or burrs.

Slowing to 1500mm/min makes things a bit better but nothing like plain steel.

I tried a small 3mm slot and noticed it looked better but that was slowed to about 800mm/min by a sheet cam rule.

Does stainless generally prove harder to cut than mild??

Are there any secrets to cutting 304??

[_Ogre]

304 ss is definitely hard to cut than mild; mild is an plasma burning reaction vs ss is strictly melting the steel away
the thicker the ss the harder it is to cut, also more angularity and dross, 3mm (10ga) and thinner cut fine, i use the book values on them
if your using sheetcam set up rules to slow down and corners and smaller holes

[jimcolt]

The top dross indicates that the torch height is too high. The 30XP with the Finecut consumables wants to almost drag on the material. If you have height control you should maintain the torch to work distance at .020", very close. The dross on the bottom indicates you are cutting too slow.....most do the same thing you did, which is to try to solve the issue by going slower. Faster , closer will produce very nice dross free edges on thin stainless.

Stainless does not oxidize easily (like steel does) so the edge quality is a byproduct of the thermal (melting) capability of the plasma. On steel you get the thermal and exothermic reaction.....due to the oxygen content in air....which makes for a better cut.


Jim Colt Hypertherm

[davek0974]

Thanks Jim,

is 3mm 'thin' ??

I can get great results on 1.2mm and finecuts, but on the 3mm I am using the standard consumables as these tend to fare better on thicker stuff.

I tried 2200mm/m but it barely cut through, i will lower the torch and try again.

[jimcolt]

I consider everything under 6mm (1/4") thin. Your Powermaxx30XP can pierce and cut 6mm and can sever 16 mm.

Remember that you are using a plasma cutter that was developed for hand cutting......so we did not develop the detailed cut charts like all of our larger systems have for mechanized cutting. You will need to develop the best speed for the materials you are cutting based on some trial and error, and from my experience this will need to be done at a fixed torch to work distance of about .5mm on stainless, and I suggest that 3mm is the thickest that you should cut using this height unless your cnc machine has the ability to pierce at twice that height, then index down to the cut height before movement occurs. Stainless needs to have low arc voltage (close torch height) and proper speed....so slow down so that the torch penetrates then incrementally increase speed in small amounts until the dross is at a minimum. You may or may not be able to cut dross free on 3mm with 30 amps. On our larger plasma's we would recommend at least 45 amps for that thickness.

Jim Colt Hypertherm

[davek0974]

Thanks Jim,

yes my setup pierces at 3mm usually then drops to cut height.

When you say torch to work distance of 2mm, are you allowing for the fact that i am using the shielded/drag standard consumables on the hand torch??
If so then that would be considerably higher than i normally cut at which generally equates to around dragging in a standard hand-held usage, but as I modify my shields to reduce the drag feet by 1mm I have an effective clearance of 1mm - this works ok but is obviously out of Hypertherms' comfort zone as I have modified the shield.

I am seriously considering getting the PM45 but am still concerned I will not get the lovely clean, fine detail I do now on 1.2mm stainless with the finecut consumables at 25A.

If only the PM45 took finecuts - is this possible in the future???

[jimcolt]

I corrected my post, I was thinking imperial (.020") and writing metric.....I said 2mm cut height, should have said .5mm. Sorry.

Jim Colt

[davek0974]

Thanks,

thats an issue because maintaining a height of 0.5mm on a warped sheet is pretty difficult even with the good THC (CandCNC) I have.

Its another reason to be looking at a PM45 with machine torch I think.

[jimcolt]

THC's that have faster correction speed and reaction can handle .020" (.5mm) on warped plate with no issues. My Plasmacam THC has no issue whatsoever, and CandCNC's newest Ethernet based THC has no issues with this either.

Jim Colt

[davek0974]

Ok, some help please.

After many hours of messing about, these seem to be the best results I can get. 1500mm/min, 1mm cut height, 30A, standard consumables, 30XP, 304 stainless, 3mm thick. Any faster and there are points where the flame will skip over the metal instead of cutting through. The height of 1mm equates to the 30XP drag-cutting as I modify my shields to give clearance.

The dross is fairly hard but comes off with a grinder mostly, edges will need some serious de-burring though as my stuff is generally arty type cuts with lots of sharp points etc.


Next issue that is baffling me is angularity on one side?

Side A is perfect 90deg cut, side B has around 40deg bevel, top and bottom are good. Consumables nearly new, 20 pierces, a few minutes of cut time.

There is no slack in the movements, this has been baffling me for some time now.
Any ideas???

[davek0974]

I 'might' have found the issue with the angularity.

I was cutting aluminium before this test was made, same consumables so I stripped the torch head apart carefully and found a small fleck of what looked like alu stuck in the small circular gap between the shield and the nozzle.

Presumably this was deflecting or upsetting the air flow that comes through that gap?? This was then not guiding or forming the plasma correctly??

The last test i made after cleaning was much better, I only cut alu occasionally and not made the connection between alu work and poor angularity on the following jobs. Maybe alu is not very good for the little 30XP?

Does the PM45 torch head have bigger gaps to stop this sort of fault??? (still trying to justify buying one )

[jimcolt]

If your pierce height is ALWAYS at the proper height, you will not blowback any material into the area between the shield and the nozzle.

When a piece of material is there you are electrically shorting the shield to the nozzle, this allows double arcing to the material which damages the nozzle orifice and lowers the effective power of the cutting arc (the secondary arc between shield and plate splits some of the current).

The gap and shape of the inside of the shield and the outside of the nozzle on the 30XP, the 45 through 125 systems is based on a technology patent called Conical Flow. It uses the secondary shield gas and the components shape to impinge (squeeze) the arc radially after the arc exits the nozzle orifice, increasing its energy density and cooling the nozzle orifice simultaneously. The increased energy density improves cut angularity and dross as compared to non conical flow.

If the height control is doing its job....there will not be blowback between the shield and nozzle. This is why you see many posts from me stating how important an accurate, repeatable torch height control is.

Jim Colt Hypertherm

[davek0974]

Thanks Jim, an interesting insight into the technology there.

I have faith in my THC, but I am possibly seeing the downside of using a hand only plasma torch in a CNC environment - hand cutting generally uses dragging, especially on the small tools, dragging won't work in CNC so my minor mods to the drag shield allow me some small allowance there, but likewise may also be allowing muck back up into the gap.

Another vote for the PM45 I guess ?



How about the dross - any thoughts or comments there????

[SeanP]

Not the best examples Dave, I haven't done much stainless as well, but these are some dropouts I had left behind, so not really the best side, they are 3mm cut with the powermax 45 at 3000mm/min, I seemed to get quite a bit of edge slope as well.

[davek0974]

Thanks SeanP, I presume that was running at 45A as well??

Those cuts look great, the slope is not an issue for my use, which is oddly very similar stuff to you sample

3000mm/min is way faster than my little XP can go, I'm guessing its just pushing it a little too far on stainless??

Another firm vote for the PM45 then

How do you find fine detail stuff, my main worry is that not having the fine-cut consumables, I will lose some quality on my lettering and numbers that I do a fair bit of???

[SeanP]

Sorry I meant to say it was at 45a.

It's hard to say how the 45 compares to your cuts on finer stuff, send me a file and I will cut some 2 or 3mm to compare if you like.
I haven't tried 30a consumables or done much with lower amps.

Only trouble running faster is then it tests out the mechanics of the table more though.

Sean

Thanks SeanP, I presume that was running at 45A as well??

Those cuts look great, the slope is not an issue for my use, which is oddly very similar stuff to you sample

3000mm/min is way faster than my little XP can go, I'm guessing its just pushing it a little too far on stainless??

Another firm vote for the PM45 then

How do you find fine detail stuff, my main worry is that not having the fine-cut consumables, I will lose some quality on my lettering and numbers that I do a fair bit of???

[davek0974]

Thanks,

I have attached the file/s for the little test job I did earlier in this post.

Speed can be an issue, my machine is home built and I tend to prefer lower cut speeds, up to 2500mm/min, I am sure it will go further but being homebuilt, I guess I could rebuild it with a better design if I had to.

Thanks for the test offer BTW

[SeanP]

Test results here Dave

Not to bad really, 3000 seemed a little fast, it didn't drop out even with a 1mm overcut, so I dropped to 2500mm/min
A bit of clean up and a whack with the mallet should get it to fit

[davek0974]

Thanks for that, much appreciated.

Those results look great, can't see why i would get so much dross, maybe just the extra power and air flow possibly?

Oddly, the 2500 cuts would be lower than the absolute max speed in my manual for this material which was 2600mm/min @ 30A so with yours being 2500mm/min @ 45A there is a considerable difference there, interesting.

I also had a look at your table build and man, that thing is beautiful The motors look similar in size to my ones but i only have one driving the the long axis, that being said, my machine is way smaller and only 625mm x 625mm cut area - I have a small shop and only do small stuff so it was built to fit, it was also built from aluminium section to keep the gantry weight down.

[jakedog]

How do you polish the stainless after?

[Gamelord]

Polishing is a chore depending on how shiny you want to go. For brushed finish, get a burnisher, that is the easiest and quickest way I have found to get the brushed look. The edges I just hit with a flap disk. If you want to go mirror finish then be prepared for some serious work. I start with 200 grit, then 400, then 600, then 800, then 1200 and finish with 1600 grit. Once that is done then I move to the buffer, hit it hard with a spiral pad and then to a buff pad. Afte that I go to the massage parlor and then soak in the hot tub for a few hours. A flawless mirror finish is major work and even more time.