Opinions on DCEP / DCEN

[MichaelV]

Richard, you know I like to have the theory behind it and not take things in just because I am told it is so! I would also say that the rod is not in contact in either DCEP or DCEN with the work piece and that you have an arc in either case, this section in the book is taking about arc welding saying you get a deeper crater with DCEN, to me a deeper crater means more pen.

The analogy to TIG was my own in that, and to my mind, consumable electrode or not, if I had a setting on say 2.5mm steel of 100 amps and was running DCEN the heat is in the metal not the tip as the tip can withstand its own heat build-up with the gas cooling, but if I went DCEP the tip would ball up as now most of the heat is happening at the tungsten.
So I associate the most heat with the most belting, bigger crater and more penetration.

Looking for my Lincoln Tome now to see if it says any different.

Adrian

Also of note when I was having issues with trapped slag in some of my welding a dealer suggested I use DCEN as it gave more pen.

Hi Adrian - a useful, albeit summary explanation here: http://www.twi-global.com/technical...elding-which-electrode-polarity-should-i-use/

Michael

 

[Richard.]

Adrian it is fact that Dcep offers more penetration In welding methods where the electrode is the consumable than DCEN. You can argue your books and webpages forever that's not going to change real welding macros regularly taken from both polarities showing just this.

That TWI page is not making much sense to me or perhaps I'm reading it wrong but it states that
Dcep is reverse polarity with more heat at the workpiece. Am I missing something here?????

 

[AdrianH]

Thanks for that Michael, I have been looking on the TWI site and even though I seem to be logged on I can only ever see the FAQ and not any technical papers.

Yes that link (I can see) says the more pen with DCEP, but does not explain why. But before all pull their hair out, I have seen an explanation that I could accept when it comes to MMA. I will try to put it down here to see if I have got it correct.

DCEP has most heat generated at the electrode or rod, but, this heated metal is propelled by some means to the workface and the heat build up melts the parent metal.

On second thoughts no I still don't get why because using DCEN or DCEP at the electrode the metal is still deposited on the workpiece.

Dam more study.

Adrian

 

[AdrianH]

Adrian it is fact that Dcep offers more penetration In welding methods where the electrode is the consumable than DCEN. You can argue your books and webpages forever that's not going to change real welding macros regularly taken from both polarities showing just this.

Then I would like to learn why it is a fact, what the process is that is causing it, I would like to understand the whys?
Then when I understand the why and if I ever get the chance to do it in a controlled fashion with robotic welding arms with the same 6013 rods in DCEP and DCEN I would like to see the macro's to seal the deal. I just do not like because it is.

Anyhow before we all get niggled about it I have to be up and out early, so good night all fellow welders, from this hobby welder

Adrian

 

[MichaelV]

but does not explain why

Adrian - I think the key phrase in the TWI text is that in the case of MMA, more heat is generated at the cathode. In this context, the cathode is the side of the system from which conventional current departs. So, with DCEP, conventional current leaves the cathode (-ve here), and head over to the anode (+ve here).
Michael

 

[Richard.]

Adrian - I think the key phrase in the TWI text is that in the case of MMA, more heat is generated at the cathode. In this context, the cathode is the side of the system from which conventional current departs. So, with DCEP, conventional current leaves the cathode (-ve here), and head over to the anode (+ve here).
Michael

It won't be a good enough explaination Michael. Id let him find out what he needs to on his own steam.

 

[Farside]

Superficially, it seems to me that directing the flow from electrode to workpiece would counteract the heatsinking effect of the much larger workpiece, too.
There can't be anything new here - whether it's electron flow or the Devil's Own Pixies with their little buckets, somebody has worked it out.

 

[Kent]

Sometimes it's better not to overthink things.
It's like proving god exists dangerous territory lol

 

[wheresmejumper]

I've never seen a good explanation for the penetration stuff.but the puddle is way hotter with more penetration on ep.i read something once about some kinda force propelling the burned off rod particles into the workpiece to satisfy it but can't remember where

 

[daleyd]

I've never seen a good explanation for the penetration stuff.but the puddle is way hotter with more penetration on ep.i read something once about some kinda force propelling the burned off rod particles into the workpiece to satisfy it but can't remember where

You sure you've not just been watching the new star wars film?

 

[Richard.]

Polarity is not difficult to understand why it effects penetration I'm just struggling with how to put it in words.
The thing that Carrys the current is what does the damage is the best way I can see to describe it. If you put live terminals on to something metallic the metal item you connect them to will have a hole or chunk blown out of it but if you make the bench live and lay a shiney spanner across it or even lay your spanner across a car battery it will be the spanner that suffers the most damage so the way I see it the penetration or most damage if you like comes from the item carrying the current.

 

[Richard.]

^^^^^^^
Actually that's a load of s###t because a car battery has a live and Earth like a welder so the spanner has no relevance to it as it simply links them together so disregard the nonsense I'm babbling on about.

 

[daleyd]

^^^^^^^
Actually that's a load of s###t because a car battery has a live and Earth like a welder so the spanner has no relevance to it as it simply links them together so disregard the nonsense I'm babbling on about.

Ha ha, you could have got away with that Richard, you sounded as if you knew what you were on about for a minute....

 

[Richard.]

Ha ha, you could have got away with that Richard, you sounded as if you knew what you were on about for a minute....

No I didn't. I sounded like a sales man that had been well a truly caught out with a badly flawed product and was trying to blag it with a load of bull.
I'm the first to admit when I'm talking dribble.
Only an "effort" badge this time round.

 

[Sarto]

Hi to all.
If you want to dive quite a bit in the theoretical side of welding, you could take a look
to these videos (youtube playlist):

https://www.youtube.com/playlist?list=PLbMVogVj5nJSjLB85-HKhw1aCIBxn3pWj

Keep in mind he is from India (I believe). So his English it's stranger than Doubleboost's
(just joking )

SARTo

 

[BrokenBiker]

yet another interesting and informative thread

 

[TechnicAl]

I hate this subject I can never get it sorted in my head...........anyway here goes

Electrons etc

In TIG welding

With DC- the electrons flow from the tungsten to the workpiece. The electrons evaporating from the W cool it down.

With DC+ the Electrons flow into the W and heat it up plus they also cause resistance heating

So to operate at the same current you need a bigger W with DC+ than you need with DC-........its the current that penetrates

In MMA welding you need the heat in the electrode to melt it so DC+ flows into the rod and it melts.

So the difference is in TIG you dont want to melt the electrode in MMA you do

 

[Kent]

I hate this subject I can never get it sorted in my head...........anyway here goes

Electrons etc

In TIG welding

With DC- the electrons flow from the tungsten to the workpiece. The electrons evaporating from the W cool it down.

With DC+ the Electrons flow into the W and heat it up plus they also cause resistance heating

So to operate at the same current you need a bigger W with DC+ than you need with DC-........its the current that penetrates

In MMA welding you need the heat in the electrode to melt it so DC+ flows into the rod and it melts.

So the difference is in TIG you dont want to melt the electrode in MMA you do

I got the last bit at least

 

[BrokenBiker]

easiest way to explain this is...because science and stuff...

 

[PhillipM]

If some of the heat is contributed to the puddle by the rod coating breaking down and/or resulting ionisation or thermal conductivity changes that would explain the difference with MMA compared to TIG.