Dear Vishwanath,

this defect is appearing at a frequency. Hence, one this is sure, this is a parametric issue. It could be due to CNC path planning or may be due to setting in the TIG generator. May be the actuator is moving in a path not exactly circular. It appears like the electrode is not maintaining the exact distance all the time. We do CNC TIG at our lab, and have found this thing appear quite some time.  Can you post a video of the process (close up), also kindly mention the material, TIG equipment, the ignition setting (touch or HF) and the quench setting (ramp down). If you are using frequency, then kindly mention the same.

best of luck.

Dear Mr. Sushanta,

Thank you very much for your reply. Welding takes place in a closed cell.

The welding in done by robot, the material welded is 308 SS of varying thickness. Welding Power source is Fronius with HF.

wire feed - 2.2 m/min ; current 150A, Gas- Argon- 12 LPM.

can you share me what was done at your lab in order to overcome this defect

Pls suggest some improvement that can be done for this defects.

Vishwanath Ji,

Certain things are still not clear, like what is the path taken by the torch tip (is it perfectly circular or is an approximate polygon), how the wire is fed and what are the ramp down settings.

I guess, you are using the famous dip-lift-dip-lift technique of wire feeding, it may work in case of a flat weld, but for fillet weld it may not work. The arc seems to be active through out the contour, with only the filler not being fed at certain interval. If you are using an automatic wire feeder, please try with a fixed wire feed rate and without feedback. Intuition tells me that wire feed is intermittent. You can make some markings on the wire at regular intervals and track the feed rate. Kindly discuss what you find. One more thing, if the plasma is drifting, then also this problem may arise. Please see, if the wire is being grounded somewhere, you may want to insulate it by keeping it on some thermocoal, etc. and check the effect.

In our case, we were feeding Ni powder with an additional Ar stream. It worked in some cases.

best regards.

Dear Mr. Sushanta,

Thank you very much for your valuable inputs. The path taken by the torch is circular. During my observation in this station mostly the wire feeding is continuous and not intermittent. I will again look back on the wire feeding rate as suggested by you and try to collect the details. 

Can you pls tell me something more about Ni powder and Ar stream. How it was used.

Regards,

Vishwanath Kittur