Need help with varying tip voltage/ poor cut quality

Hi,

I have a powermax 45 on a cnc table- running Mach3 software/Bladerunner AIO with DTHC. I dry my air with a submicronic paper filter and then a fairly large dessicant dryer.


Yesterday I was cutting a large job in 3/8" plate, and towards the end cut quality completely went away. Long story short, Now I cant get it to cut cleanly again. I've changed my tip/electrode more than once, and "cleaned" the shield cap- I have some on order, but not very confident the shieldcap is causing the problem anyway. I also changed the paper filter- the dessicant is in good shape.

Watching during a cut, after the torch has been on a short bit, the voltage varies alot up and down, causing the DTHC to pulse and create a crappy, saw like cut.

What could be causing my tip voltage to vary? Can this still be a moisture issue?


*EDIT*

I had some time to try a few things out, it looks like the problem is related to the THC/ tip voltage situation. The cuts start relatively clean, and seem to get worse the longer the torch burns. Watching the Mach3 screen, the tip voltage starts out ok- hanging close to its setpoint, but then starts to climb and dive the longer the torch burns.


1. Ground issue? I tried clamping the torch ground directly to the workpiece with no noticable change. I thought possibly moving and banging the heavy 3/8" sheets around on the table cound have changed something. My table is not directly connected to an earth ground/rod.

2. PC related? my PC's are not in the best condition. I actually had a mouse in this one, hanging out on top of the video card- caused it to short out apparently. After replacing the card the PC booted fine and seems to work normal.


Thanks for any and all suggestions

Ben W

The voltage that the THC is looking at is the voltage between the negative electrode and the positive work ground connection. If you are cutting at a constant speed and at a constant height (level plate, THC voltage control off)....then this voltage will remain relatively constant. I suggest that you verify that by doing a straight cut on level plate. You can also check accuracy by measuring the actual voltage at the Raw arc voltage connection with a digital voltmeter and compare that with your digital readout....they should be pretty close to the same.

When the torch is raised (while cutting at a constant speed) you will see the voltage rise....this is because the arc gets longer. So....if you height control is causing the torch to oscilate up and down....expect to see the voltage rising and lowering. I'm sure CandCNC can help you with settings that will eliminate the oscilation....often has to do with gain or z axis speed settings.

Other things that can affect arc voltage (I don't like to call it tip voltage....as 1. Hypertherm plasma systems do not have a part called a tip, and 2. On plasma systems that have a part called a tip....it is the nozzle....which is not where the voltage is measured. The measurement is from the electode to the plate.:

- If there are large amounts of water in the air....it changes the resistance of the plasma arc, which will change the height/voltage relationship. This is unlikely in your case.

- A loose or dirty work clamp connection. Generally if you have clamped directly on the plate you have eliminated this issue.

- Consumables that are at the end of their life will generally cause the voltage to increase....and the torch will dive into the plate , but will not oscillate.


I suggest the problem is with a setting in your software that controls the z axis while in arc voltage control mode.....not in the plasma system.


Jim Colt Hypertherm

Thanks for the reply Jim,

A quick test cut with the THC turned off showed the problem still occurred- arc voltage in the mach3 screen still started to vary up/down and produce a poor cut.


*EDIT*

I solved my issues- I rechecked possible causes today after it didnt seem to be a pc related issue, Found my ground clamp was dirty and apparently not making good contact. I cleaned the jaws up with a file and its cutting cleanly again!


Thanks again for the help Jim

Roughly how much did the voltage vary? And....the torch stayed at a fixed height?


Jim Colt

Quote:

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Originally Posted by binfordw

Thanks for the reply Jim,

A quick test cut with the THC turned off showed the problem still occurred- arc voltage in the mach3 screen still started to vary up/down and produce a poor cut.

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Jim,

The voltage varied around 5-8 volts from setpoint, I.E, set at 117, it would drop down to 112 and as high as 123 or so. When cutting cleanly, its usually with 2 volts.

I actually had trouble with it again today, I cut a full .250" x 4x8' sheet of parts fine, I went to cut a couple small parts and had them mess up. Voltage varied, cut wasn't fully pieced everywhere.


I'm not as certain now as to what the issue is. I rechecked the ground clamp, and looked into possible moisture in air problems. When this issue is happening, it does seem a bit like a moisture issue- although the consumables seem to be holding up very well. The cut starts clean most times, then degrades to a rough cut, with failure to fully piece the sheet in small sections along the part.

Air seems dry. I have had no real issues with moisture since I started using the double filter setup. I purged the machine for several minutes.


I removed the Powermax's cover and looked for issues. I did find a curious situation on the high voltage side of the main board.. what appears to be dirt/dust, light in color, in almost arc-like shapes on the traces on board.

I decided to spray board with a electrical contact cleaner, and it appears theres a film/coating on the board that was peeled/washed away by the spray. The "dust/dirt" didnt seem to wash away easily, so I left it alone.


I retried a cut, and things seemed normal again. At this point Im a bit unsure whats going on- just pleased I was able to finish a few jobs today to stay a bit on schedule.

The internal boards all have a "conformal coating" that is intended to keep dust from shorting components.

I did not get a real good answer from you on the height. There is nothing in the power supply that controls the voltage......voltage is 100% controlled by the resistance of the plasma arc. Things that change the resistance are:

- arc length. If the plate moves away from the torch (warped down) .010"....the arc voltage will change by (increase) about 5 volts. The torch height control is supposed to maintain voltage by monitoring it....and adjusting the z axis (up and down) to maintain the correct voltage. If the z axis has some mechanical slop....or if there is a setting or overshoot issue with the THC electronics....the torch will oscilate up and own a bit, causing the ac voltage to oscilate up and down.

If the Z axis is off....making no up or down corrections....and you still see voltage variation....is the plate moving?

- Slugs of moisture or oil or other contaminants in the air supply will change the chemistry of the "air" being used to develop the plasma arc....this changes the electrical resistance of the arc, causin voltage changes. Usually this will show also as rapid consumable wear and poor cut quality.

- Changes or fluctuation in inlet air pressure (restricted, plugged or "too many" filters can inhibit air flow)....this will also affect voltage of the arc. You should put a pressure gauge after all filters right at the air inlet to the plasma......if it is lower than 90 psi or it fluctuates....then there is a restriction somewhere in the air system....this pressure check neds to be made when air is flowing to the torch.

-Loose or dirty work ground connection will cause varying voltages....with a height control will normally cause the torch to dive into the plate.


Jim Colt

Quote:

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Originally Posted by binfordw

Jim,

The voltage varied around 5-8 volts from setpoint, I.E, set at 117, it would drop down to 112 and as high as 123 or so. When cutting cleanly, its usually with 2 volts.

I actually had trouble with it again today, I cut a full .250" x 4x8' sheet of parts fine, I went to cut a couple small parts and had them mess up. Voltage varied, cut wasn't fully pieced everywhere.


I'm not as certain now as to what the issue is. I rechecked the ground clamp, and looked into possible moisture in air problems. When this issue is happening, it does seem a bit like a moisture issue- although the consumables seem to be holding up very well. The cut starts clean most times, then degrades to a rough cut, with failure to fully piece the sheet in small sections along the part.

Air seems dry. I have had no real issues with moisture since I started using the double filter setup. I purged the machine for several minutes.


I removed the Powermax's cover and looked for issues. I did find a curious situation on the high voltage side of the main board.. what appears to be dirt/dust, light in color, in almost arc-like shapes on the traces on board.

I decided to spray board with a electrical contact cleaner, and it appears theres a film/coating on the board that was peeled/washed away by the spray. The "dust/dirt" didnt seem to wash away easily, so I left it alone.


I retried a cut, and things seemed normal again. At this point Im a bit unsure whats going on- just pleased I was able to finish a few jobs today to stay a bit on schedule.

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Is this the newer DTHCII that uses the direct cable to the 45? I assume it is.

If it continues to happen randomly contact us. We have found some of the THC SENSOR PWM Module cards are sensitive to high humidity and it skews the voltage reading. Usually waht you see is the voltage will start off wrong and slowly correct itself. We will be glad to exchange the module. If that does not correct it it may be something in the 45.

TOMcaudle
www.CandCNC.com

@Tom,

I'm not certain which DTHC I have- id have to look. I dont believe the DTHC is to blame really, as it happens when THC is turned off as well.



Jim,

The voltage varies abruptly during cuts (the cut quality drops drastically and often doesnt fully piece during this voltage change)- even when the THC is off- which means no torch Z axis movement. The plate is also stationary.

This tells me the arc is changing, but I havent been able to confirm exactly why. From what I've seen and what you have posted here, it looks to be either a ground issue or air problems.

My filter setup is about as good as I can do without going to an expensive dryer setup. I have noticed air flow issues in the past, mainly when trying to reuse dried paper elements, I dont believe this is a factor with this current issue.

The plus side is its cutting fine at the moment. I still want to understand better what was happening, to help prevent this from occurring again though.



thanks Guys!

I would mount a pressure gauge right on the inlet to the plasma , after your filters. Monitor it while cutting to see if it drops or fluctuates....either of which will affect arc voltage / height.

It is unlikely that the problem is related to electrical output of the plasma....generally the voltage output is stable....or it will not operate at all.

Jim Colt

Quote:

---

Originally Posted by binfordw

@Tom,

I'm not certain which DTHC I have- id have to look. I dont believe the DTHC is to blame really, as it happens when THC is turned off as well.



Jim,

The voltage varies abruptly during cuts (the cut quality drops drastically and often doesnt fully piece during this voltage change)- even when the THC is off- which means no torch Z axis movement. The plate is also stationary.

This tells me the arc is changing, but I havent been able to confirm exactly why. From what I've seen and what you have posted here, it looks to be either a ground issue or air problems.

My filter setup is about as good as I can do without going to an expensive dryer setup. I have noticed air flow issues in the past, mainly when trying to reuse dried paper elements, I dont believe this is a factor with this current issue.

The plus side is its cutting fine at the moment. I still want to understand better what was happening, to help prevent this from occurring again though.



thanks Guys!

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