Plasma cut quality

[ajclay]

I can see the end of my cnc plasma project. Cut my first part a few days ago. That was a happy day! I'm trying to optimize the cut quality looking for some guide lines on what to adjust. Amps, arc voltage/height, and air pressure.

I'm running a Hypertherm 1650 air machine. The manual gives suggested guide lines on the variables, but not on how to tweek them to make better. There aren't any good or bad examples in the manual, just a set up chart.

Can you guys give some "rule of thumbs" on cause and effect of cut quality.

Thanks for the suggestions.

AJ

[WSS]

AJ,
I am going to tag along here. I am about a month away from cutting some parts with a CNC, however I do have a 1650 hooked up and ready to run on a mag shape cutter. I have a project for next week and am a bit nervous. It is cutting holes in our customers 3/4" thick parts. I noticed today half the parts are painted and the other half are super rusty. Should make for a fun trial run!

Tommy

[ajclay]

Tommy,
Nothing like just jumping into the fire cutting 3/4 plate... I know in the end what's going to happen.. It just like everything else, we'll just have to pay our dues and spend the time.... Take notes.

I was hoping here in the ZONE where everybody knows everything, someone would have an example chart of photos or examples of what happens when one perameter is way off. To much, to little speed, wrong amprage, torch height to high to low and so on.

Maybe there's not just one answer for each problem, but I'm going to keep looking and asking. Stay in touch about your machine and results.. email if you like. ajclay@cox.net

[lowpull]

I had found a doc that discussed one thing and that was the super hard dross, Turned out that my speed was too high. I slowed my speed down about 10 percent and it turned back to flaky dross.

[Edwardo]

The settings in the manual are pretty close to what i cut at, i found that speed is 1 of the most important aspects of a clean cut, to slow and you get alot of dross... clean dry air is also important... once you are up and running and get used to your machine it is easier to make adjustments, i have crashed my torched a few times playing with the settings so its basically trial by error for me....lol

EDD

[jimcolt]

Rules of thumb for best plasma cut quality...

1. If you have a Hypertherm system...follow the "optimal" cut speed charts exactly as listed in the manual. The cut charts in the manual show two cut speeds, optimal and maximum....optimal is what you should use for mechanized cutting for the best combination of edge squareness and dross.
2. Follow the torch stand off distances exactly as specified in the manual....there is a pierce height, and there is a cut height. Pierce height is critical....otherwise the nozzle will be damaged from blowback on the first pierce...and cut quality will be affected.
3. There is a pierce delay time for each material and thickness....the torch must remain at the pierce height for the entire pierce delay time (with no x or y movement)...this allows the torch to fully penetrate the plate. As soon as the pierce time is over...the THC should index the torch to the cut height...and start x and y motion.
4. Cut height should stay at a fixed height until the x and y motion achieves at least 80% of the optimal cut speed (from the Hypertherm manual)....then the THC should begin monitoring arc voltage and adjusting the height during the cut. The cnc control or PC should be monitoring ct speed...and if the speed ever drops below 80% of optimal speed..the the z axis should be frozen untill the speed again exceeds 80%. If this is not done...then the arc voltage height control will dive the torch during corner slowdown.
5. Adjust the arc voltage if the torch is not maintaining the physical standoff that the manual recomends....if the torch is running too close, increase the arc voltage approximately 2.5 volts to raise the torch .010" higher. The recomended voltage settings are also listed in the Hypertherm cut charts....however physical height is more important than the voltage.
6. If there is light, difficult to remove dross....you are probably cutting too fast. If there is heavy, easy to remove dross..you may be cutting too slow. Usually (depending on the plasma systems and the metalurgy of the material being cut...you will find a "dross free zone" between too fast and too slow. Better plasma systems (industrial oxygen or High Definition plasmas) will have a wider dross free zone. Air plasma systems often have a narrow...or non-existant dross free zone.
7. Use the consumables as suggested by the operators manual for each material thickness. Lower power consumables will produce better edgae quality, hole quality, and edge squareness...but at lower speeds as compared to high power consumables. If you use an 80 am p process to cut 1/8" steel....expect high cut speeds, dross free cuts, and seriously tapered edges as well as distorted holes. If you use the fine cut consumables (at the Hypertherm recomended power levels) you will see dramatically better edge quality...but at a lower speed.

Not all plasma manufacturers publish accurate cut parameters.....Hypertherm does. The published parameters will work with very little tweaking.....and the tweaking is due to various carbon and silicon content in the material, as well as with different cutting machine and height control accuracies and acceleration characteristics.

Hopefully this will help you get started....the most important think is pierce height and cut height..

Good Luck, Jim Colt

[WSS]

Aside from durability, this is why I purchased a Hypertherm! Jim, thanks for the clear, descriptive help. I will post some before and after pics of cut quality after I finish next week.

[ajclay]

Jim,
Good deal. In other words just go by the book. Really that's what I wanted to hear. But the further in-depth info you gave was what I was looking for.

Yesterday I ordered the fine cut parts for the torch so I sould have all the right pieces and parts.

It will take a few days for me to finish up a couple of loose ends on the machine and then I'm going to bare down on cutting some material.

I will post some photos and I'm going to give a movie a try.

Thanks again! AJ

[WSS]

Some good news to report with the 1650. I had a chance to do some cuts today and I was impressed by the way it "just" worked! I was nervous about settings and PSI and nozzles and amperage, well I made 24 cuts, each one with a different setting and all were more than acceptable. I went CW, CCW, fiddled with air pressure and amperage. I was ready in the back of my mind to default to my oxy/fuel set-up (which was close by, just switch the torches). It had two bad pierces, but the lead in was long enough. I don't have a clue why, but they were both in a row. I unscrewed the assembly and cleaned/brushed the pieces and re-assembled according to the manual, and back to .5 second pierces! Here are a few pics

[ajclay]

WSS
Those cuts do look good for the thickness. You pulled the setting out the manual like Jim was talking about? Looks like your cutting table is heavy enough :-))

[WSS]

Originally Posted by ajclay WSS Those cuts do look good for the thickness. You pulled the setting out the manual like Jim was talking about? Looks like your cutting table is heavy enough :-))

AJ, I have to be honest, I copied/pasted/printed Jim's post #6 and started at 80amps, and worked until I had "dross free" cuts as Jim recommended. I am not sure of the speed, as I am using an old pantograph with a vari-stat to control the speed, it turns from 0-100. The oxy could not cut above 50 (it would lose the cut in the corners) and the plasma sailed dross free at 65, but would cut at 75 with a little dross. I would estimate the speed to be about 25ipm, I have another 80 or so cuts to do on Wed. and I will time them and measure the cut to be accurate.

The table is an old acorn/platen lay-out table that is about 3" thick. It will be transformed back to a lay-out table when our Dynatorch is finished. It is kind of like a pair of shoes that don't fit, it will last forever!