Piercing 1" plate with Powermax 105

[humanzee99]

I am in a bind at work. I am trying to find a good setting for a Powermax 105 to pierce 1" steel plate. I have started at .270 height and 1.5sec delay, 21ipm. The first cut turned out great, but after that I had issues. I used the same height and set the delay for 2 sec just in case. A few inches in after pierce the torch would rise and fail to cut the material, producing a lot of molten slag shooting out. Unfortunately the THC goes nuts when cutting 1" at 105amps and wants to climb up to 0.3-0.4" for no apparent reason. The last cut I made I had to sit there during the cut and manually decrease the voltage from 160 amps to 150 as the small piece is cut out to maintain the cut height of around .125, it varied form between .110-.138. The cut was ok with one of four sides being vertical, the others being off by about 5 degrees but still usable. The last piece I cut out I turned the auto sampling off, and the z axis reading was about the same, between .105-.130 and the piece was usable. With auto sampling on the pieces are scrap. If I could I would simply tell the Z to stay at .125 after pierce but I do not have that option.

I may be having software issues. The interpretation of voltage to true height seems to be getting misinterpreted. The THC of the software I cannot seem to correct. On the older plasmacam software I was able to control more variables. With the current software I cannot. In general, when running at 105 amps for 1" plate, the THC gets worse and worse with each piece. The pieces are only 4" wide by 5.5" tall for now, and does not exceed the duty cycle of 80% @105amps.

I was originally trained on a Samson 510 basic table using a Hypertherm 65. I encountered many problems but was able to fix them. The current table is giving me a headache with the THC. I cannot manually set certain variables that I could on the original Plasmacam software.

[Rodw]

At a guess, the voltage is autosampled too early before the voltage has stabilised after piercing.
I published a plot of arc voltage (in green) here
http://linuxcnc.org/docs/devel/html/pla ... _thc_delay

The blue line at the bottom is a higher resolution plot of the arc voltage error between cutting chart voltage and actual voltage. It shows exactly where the THC was enabled and the voltage sampled. You can see before this point the voltage is naturally stable once the pierce subsides..

If the voltage is sampled too early before the voltage subsides to the natural level, the THC will increase the height to get the voltage back to that artificially high start point.

If the torch is too high then rooster tails would be inevitable.

The thickest I have cut is 16mm and I did not really see any appreciable increase in the required sampling delay vs 3mm so by pushing out to 2 seconds was the right thing to do but maybe it was not enough.

I think on balance given the thickness of the material, I would cut with the THC disabled unless you are getting a lot of warping. You might also consider slowing the cut speed.

[mdwalker]

The nozzle is probably being damaged after the first pierce causing some of your issues. This could be from the pierce itself or possibly from dragging through the slag pool after the pierce. The best thing is to edge start if possible. If that isn't possible try making all of your pierces first then come back and cut. I have had good success with this method. I will make the pierce and then stop immediately after the pierce and move to next pierce. After making all of the pierces I will knock off any slag puddles on top of the material and check the nozzle to be sure it doesn't have slag sticking to it. Then I will continue with my cuts.

[djreiswig]

Does PlasmaCam have the ability to ramp pierce? I've had good luck on thicker material using a ramp with plunge rate the same as feed rate and no pierce delay.

[humanzee99]

Thank you all for the quick responses. I do not have the ability to ramp pierce.

The shield is still ok. After a few rounds I checked the consumable nozzle and there some some junk in there, but the nozzle consumable was acceptable. The slag pools during pierce would get worse and worse until after the 5th attempted shape to be cut out the pierce height to cut height would not establish and the shape would not cut.

[humanzee99]

One last thing, the torch wants to dive all the time as well, the thicker the material the more it wants to dive. When it dives, more often than not the Z caution appears because the torch hits the work and the z has to be manually adjusted up and then "ok".

[weldguy]

Like MD said edge start whenever you can or you can drill a start hole for interior cuts.

THC can be off on 1" plate, not really going to warp and that solves that nasty problem. Just pierce high and have the torch lower to a specified work height during the lead in so its at the proper cut height by the time it gets to the profile your cutting.