Effect of polarity on depth of penetration

[waqasmalik]

Hi all, i am new to welding, i am studying this subject, i have a question regarding effect of polarity on depth of penetration. Any response will be highly acknowledged.


Question is " Why in a consumeable arc welding processes reverse polarity gives more penetration while in non consumeable arc welding straight polarity gives more penetration?


Thanks in advance.

 

[Tmoose]

I believe that quote you provided is based on difference in heat generation at the cathode and anode.

http://www.twi-global.com/technical...elding-which-electrode-polarity-should-i-use/

TWI is pretty smart about such things, but their statement that "Unlike TIG/GTAW welding, more heat is generated at the cathode than the anode' (compared to manual metal arc welding) puzzles me.

 

[Ron]

Confusing at best, but my simple explanation is this....

In order to reverse the natural flow, reversing the polarity causes more heat input, thus melting the base metal quicker and allowing for a more efficient weld process, including penetration.

 

[racookpe1978]

It depends (a little bit) on the polarity.

It depends A LOT on how you set the voltage (the actual current delivered across the gap) and ABSOLUTELY on what method of welding you are using. Thus, in theory, driving the heavier charged ions of the plasma of the filler material into the base metal is going to heat the base metal more than "shooting" far lighter electrons into it.

But, failing to reverse polarity (as you do changing from SMAW (stick) welding to GTAW (TIG) welding on the same weld on the same part using the same machine, gives you a flawed weld that has to be ground out and re-done.

You MUST use the right polarity for the method, then set the current (voltage) for the exposed length of wire (MIG) or the gap length of SMAW or GTAW for the diameter of the filler metal (wire, rod, or filler) and the thickness of the layer being built up.

Start with that.

 

[weldstan]

Arc stability is the primary reason behind polarity requirements for a given electrode classification.