Unstable Pilot Arc

By plasmapilot Date 08-08-2011 10:02 Edited 08-09-2011 14:11

On our welding machine using plasma welding process, unstable pilot arc behaviour occurred. In a difficult to be determined time and condition the pilot arc starts to “flicker” .It can happen directly after starting the arc, after some time (2 – 3 hours) of arc burning or just after using higher amperage (during welding). When the flickering of the arc occurs the deterioration of the weld quality is observed. With no parameter changed in the program it is visible that the flow and melting of the material is differ-ent.
In case of leakages, dirty installation etc., we have tried a lot, but we haven't found the root yet. I hope that someone has an idea what the root of the problem could be.

Now an additional questions: On the two attached pictures you can see two different colours of the welding line. What could cause this?

Attachment: Aktionlist.pdf - What we have done so far (23k)

Attachment: Checklist.pdf - What we have checked or changed so far (16k)

Attachment: normalcolour.JPG - normal colour of the welding line (58k)

Attachment: unusualcolour.JPG - Unusual Colour of the welding line (66k)

By Lawrence (*****)

Date 08-08-2011 11:44

Welcome to the Forum.

I'm confused about your terminology.

Is your plasma arc welding operation a "non-transferred" arc type?

If the flicker is during the "pilot arc" it can't have an effect on the weld quality because a pilot arc does not weld.

If your "transferred arc" is flickering, the first thing to check is your work clamps and electrical connections. More consultants collect fees for reminding folks to clean up ground and work lead connnections than you might imagine.. A simple corroded or loose copper connection will disrupt a plasma arc... They are quite sensitive.

By plasmapilot Date 08-09-2011 10:03

Thank you for your answer. I am sorry if it is a little bit confusing. I will try to upload a video where you can see the problem as soon as possible.

To your questions and suggestions: It is a "transferred" arc type. And the flicker is during pilot arc and transferred arc.
We have already checked all electrical connections and work clamps and cleaned everything (also the pipelines, valves, etc.). We have also checked the electrodes, power supply, gas quality, gas pressure, but found nothing. So we really run out of ideas...

Maybe one additional note: We have two automatic welding machines from two different manufacturer. Both worked without any problems and then out of a sudden the same described problem occurred on both machines.

By 99205

Date 08-09-2011 14:45

The problem could be in your Arc Control circuitry. The intermittent nature of this problem suggests a control board is nearing failure. I would also have a tech look at the machines main capacitators to see if they are starting to fail. Might also be a good idea to check your high frequency contacts for carbon build up and proper gap, if your machine has them. I've experienced intermittent problems on plasma machines before and it can be a nightmare to figure out. The best way to find the problem is to start with the simplest fix first and work your way up to the more expensive repairs.

By 99205

Date 08-10-2011 17:33

I would say you're about to have an expensive repair bill.

By Metarinka (****)

Date 08-14-2011 16:13

I hate diagnosing plasma and tig arc gremlins. If you've inspected your gas and found no issues then there's that. I've seen small holes in cables that only open up when the gantry was in a certain position (seen that one). You can check for that by making a Tee off of your gas supply just upstream of the welding head and using a trace gas analyzer.

As mentioned I would also look into the power condition of the building. Might be something going off phase or in a different area that's causing the power supply to get wonky.

I had a very similar issue drive me crazy, it was bad ground on our rotating pipe fixture. The machine had 2 grounds, one to the machine and one the building. Well if the electrical path switches between the 2 paths, the weld box goes crazy because it's not seeing anything in it's feedback loop.

I would look at electrical issues, maybe hook up a calibrated shunt and check voltage or current at different places. and mentioned switch out ground leads, or clean them up and try different locations / more.