Welding Tips and Tricks

Mig Welding Aluminum with a spool gun
I need some more practice
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My spool gun experience is negligible. I tried one out, bought one, it's still in the box. When I tried it I saw the same thing in Jody's video. Something is happening around and ahead of the puddle. It looks like cathodic cleaning, but I'm told that doesn't happen with spool gun aluminum. What is happening?

I was under the impression that you need around 25-26 volts minimum to get a spray process......in the video jody mentioned 21 volts......what gives?

To answer both questions,

MIG and Spool-gun Aluminum is done "electrode positive". (Jody doesn't emphasize this, but mentions it once in the first segment on spool-gun setup. In EP, you naturally get cathodic cleaning, as the electrons are flying at your gun, and that's exactly what you're seeing in the arc-shots... You'll even notice the soot being blown out of the cleaning zone in that segment with the Hobart with poor shielding issues.

Aluminum also has a much lower melting AND vaporization point than steel, which is why spray-transfer can happen at lower power. That extra stick-out is important, too, as the wire also carries heat back to the tip much faster than a similar-sized steel wire. I've, when careless, heated a tip enough for it to droop from it's own heat before it seized and quit.

Steve S

Then significant cathodic cleaning does take place?

Bill Beauregard wrote:Then significant cathodic cleaning does take place?

That's the way I see it. That's the direction the electrons are travelling, and I think the etching action (and the cleaning of soot) in Jody's video bears this out.

Steve S

Good news, I had heard otherwise from the Miller representative.

Otto Nobedder wrote:To answer both questions,

MIG and Spool-gun Aluminum is done "electrode positive". (Jody doesn't emphasize this, but mentions it once in the first segment on spool-gun setup. In EP, you naturally get cathodic cleaning, as the electrons are flying at your gun, and that's exactly what you're seeing in the arc-shots... You'll even notice the soot being blown out of the cleaning zone in that segment with the Hobart with poor shielding issues.

Aluminum also has a much lower melting AND vaporization point than steel, which is why spray-transfer can happen at lower power. That extra stick-out is important, too, as the wire also carries heat back to the tip much faster than a similar-sized steel wire. I've, when careless, heated a tip enough for it to droop from it's own heat before it seized and quit.

Steve S

Steve, There may be some other science involved that is above my pay grade...but I think you are spot on with your explanation .

Cathodic etching/cleaning does happen when you Mig weld aluminum using dcep and looks very much like the cleaning action you see with TIg Aluminum .

that is if you have a Mig setup that provides a good shielding pattern.

I have used a few spool guns that provide really good shielding and made soot free welds.
but that hobart gave me fits.

and as far as voltage goes, The millerwelds.com weld calculator calls for only 21-22 volts for .035" and 3/64" diameter wire used on 1/8" thick aluminum.
best,

Jody

Everyone thinks AC Equals cleaning.
It's the DCEP side that gets it for you. Speaking tig here.

You know that there is cleaning vs penetration. If you ran full DCEP with tig you would get lots of cleaning but you'd burn your tungsten back.

DCEP is where the cleaning comes from.
So DCEP with mig gets your cleaning, and it burns your wire back, producing spray. If you try mig with DCEN, your wire wont burn back very good.

That's my understanding in layman's terms.

AKweldshop wrote:Everyone thinks AC Equals cleaning.
It's the DCEP side that gets it for you. Speaking tig here.

You know that there is cleaning vs penetration. If you ran full DCEP with tig you would get lots of cleaning but you'd burn your tungsten back.

DCEP is where the cleaning comes from.
So DCEP with mig gets your cleaning, and it burns your wire back, producing spray. If you try mig with DCEN, your wire wont burn back very good.

That's my understanding in layman's terms.

Please excuse my ignorance. Does this mean cleaning could be less thorough with spool gun MIG. I haven't had much call to weld something big like this truck body. It has had LOTS of years to get dirty. I think my only chance would be to grind out a big kerf exposing clean metal but wiping in crud in the process. I had it in mind little cathodic etching happened with MIG. I think the last of the contamination would be like Dr Seuss's pink bathtub ring.

Bill Beauregard wrote:

AKweldshop wrote:Everyone thinks AC Equals cleaning.
It's the DCEP side that gets it for you. Speaking tig here.

You know that there is cleaning vs penetration. If you ran full DCEP with tig you would get lots of cleaning but you'd burn your tungsten back.

DCEP is where the cleaning comes from.
So DCEP with mig gets your cleaning, and it burns your wire back, producing spray. If you try mig with DCEN, your wire wont burn back very good.

That's my understanding in layman's terms.

Please excuse my ignorance. Does this mean cleaning could be less thorough with spool gun MIG. I haven't had much call to weld something big like this truck body. It has had LOTS of years to get dirty. I think my only chance would be to grind out a big kerf exposing clean metal but wiping in crud in the process. I had it in mind little cathodic etching happened with MIG. I think the last of the contamination would be like Dr Seuss's pink bathtub ring.

In theory alum mig should get more cleaning then your average 70/30 tig.
But you have to have the right amount of heat put into the part to get the cleaning action. ( you know this if you've ever tried to add your tig filler to soon before your puddle is fully formed)
Being that you have no heat control with mig, and all your metal pouring in right from the start, it makes it hard to get good cleaning and fusion at the start of a weld.
That's why "hot-start" on these new fancy lincoln/miller pulse machines is so desirable.
In my opinion pulse helps you slow down, get good fusion and give you extra time for cleaning.

Bill Beauregard wrote:Good news, I had heard otherwise from the Miller representative.

He sold coffee at Starbux last week.

He just told you that mig doesn't have cleaning action, just so you'd buy a dynasty.
Looks like it worked too.

[quote="AKweldshop"]He just told you that mig doesn't have cleaning action, just so you'd buy a dynasty.
Looks like it worked too. [/quote

Actually, from him I bought a spool gun. When I tried to buy the Dynasty, Airgas got snotty, I bought that online.