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ransom
ransom Dork
10/25/11 11:43 a.m.

I've found some good resources on how to set stuff up. For instance, here's a fairly clear guide from Miller on setting voltage and wire feed speed: http://www.millerwelds.com/resources/articles/MIG-GMAW-welding-basics

But I'm trying to really make sense of how all the pieces fit together. I keep finding a lot of places that seem to more or less interchange talking about wire feed speed and amperage.

Then there's the basic problem of reconciling my half-baked understanding of electricity with the the idea of setting voltage and current separately... I mean, I would think that if my welder had a current-limiting adjustment, that would essentially be adding resistance, and as a result, lowering the effective voltage at the weld...

Coming to the point, is the relationship between wire feed speed and amperage simply that a lower wire feed speed limits current by dint of the fact that the wire burns back and limits the current which is fed into the weld, and that increasing the feed speed simply facilitates better conductivity?

Seemed like a good topic for my most officially-Dorky post to date...

oldtin
oldtin Dork
10/25/11 12:03 p.m.

Guess this puts me in the category of zen welder - I don't really give a lot of thought to the specific settings - just crank things up till I get good penetration and crank things down if I'm blowing through (or adjust my distance/speed of moving the tip). But yeah, wire speed has an effect on current - also wire diameter - .023 vs .035.... bigger wire = more current carrying capacity = ability to deal with thicker materials.

ransom
ransom Dork
10/25/11 12:18 p.m.

I aspire to a bit more zen (in any number of areas), but for now I feel like I need to understand more about what I'm affecting when I tweak stuff.

One of the things I forgot in my already-wordy post was that not only do some people refer to them interchangeably, a lot of MIG units refer to the one adjustment as adjusting both wire feed speed and current, but they don't make clear whether current is being affected by wire feed speed or whether the unit is doing something else behind the scenes to adjust current along with the wire feed speed...

I'm not so much looking for a mechanistic way of arriving at settings. It seems clear that you have to test and tweak. I need more practice recognizing weld quality and specific issues, but I figure anything that increases my understanding of the process will help.

Giant Purple Snorklewacker
Giant Purple Snorklewacker SuperDork
10/25/11 12:29 p.m.

Think of a MIG welder as a voltage regulator set for whatever you set it for. Assuming a fixed voltage - what happens to current when you vary resistance ( E/IR ) by changing the length of wire between the gun and the work?

The way you get the right amperage for the penetration you need is to vary the feed rate and your hand speed in combination.

Toyman01
Toyman01 SuperDork
10/25/11 12:36 p.m.

More wire = colder. Until the wire speed is so high it won't melt fast enough.

Less wire = hotter. Until there isn't enough wire to maintain an arc.

More voltage = hotter. Until the wire is vaporizing before it gets out of the gun.

Less voltage = colder. Until it won't melt the wire.

To get a good steady arc, you have to play with all of them.

It should sound like a frying egg when you get it right.

ransom
ransom Dork
10/25/11 12:58 p.m.

In reply to Toyman01:
Well, that's just the thing, isn't it?

I have one adjustment for voltage, and one adjustment for wire speed (which in a lot of reading is also observed as the current adjustment), and it sounds like this is pretty normal among MIG units. You have the two items associated with wire speed not only separated, but adjusting opposite of one another...

I'm guessing that in your guideline, you're adjusting amperage by increasing voltage, but it does leave the waters surrounding my question a bit muddy

ransom
ransom Dork
10/25/11 1:00 p.m.

In reply to GPS:
That's consistent with how I've been looking at this. The complete circuit must account for whatever voltage is being applied. It's being reduced by resistance in the welder's voltage adjustment, and then you've got a secondary resistance in the amount of stickout, which provides further voltage adjustment. What I'm wondering about is whether current is effectively being reduced at an effectively near-constant voltage by means of the wire burning back.

I suppose even that is just varying the resistance of the arc itself (up until low wire speed causes the arc to become intermittent and we go all pulse width modulation, kinda...), and current into the metal is just the result of the Welder's power supply voltage, voltage adjustment resistance, cable/gun resistance, stickout resistance, and arc resistance?

ransom
ransom Dork
10/25/11 1:13 p.m.

Typical me; I've really buried my core question in a bunch of rambling:

When you adjust the wire feed/amperage adjustment on a MIG welder, is the machine just changing the wire feed speed, or is it altering anything else to affect current?

Toyman01
Toyman01 SuperDork
10/25/11 1:20 p.m.

You are correct, the voltage switches I always think of as amperage adjustments. That's left over from learning on a stick where amperage was the only adjustment you had. I edited the above post.

I set the Voltage according to what I'm welding. My machine has four settings. Low for sheet metal, high for structural, and so forth.

Then I adjust the wire speed to get the penetration and fill I need or until it sounds/feels right.

My guess is you are over thinking it a little. If it's not welding right, change something. If the problem gets worse, go the other way. If it get better, tweak it some more. You will get to where you know what you need to do just by sound and feel.

You are trying to achieve a balance between available voltage, amperage and wire. Too much wire, not enough voltage, you can actually feel the wire touching the metal. Not enough wire, too much voltage, it won't hold an arc. When you get it right, it's a beautiful thing.

Giant Purple Snorklewacker
Giant Purple Snorklewacker SuperDork
10/25/11 1:20 p.m.
ransom wrote: ...words...

THe part you are missing is that the welding machine is actively maintaining voltage at a constant. You set the voltage by a knob but it isn't some fixed rheostat. You are just telling a a fast acting vReg what to maintain.

You can just assume it as a constant voltage, with the only dynamic resistance being the wire/arc. If voltage is held constant, current rises and falls with the length of wire (r).

ransom
ransom Dork
10/25/11 1:36 p.m.

Thanks, guys!

corytate
corytate HalfDork
10/25/11 1:45 p.m.
Giant Purple Snorklewacker wrote:
ransom wrote: ...words...

THe part you are missing is that the welding machine is actively maintaining voltage at a constant. You set the voltage by a knob but it isn't some fixed rheostat. You are just telling a a fast acting vReg what to maintain.

You can just assume it as a constant voltage, with the only dynamic resistance being the wire/arc. If voltage is held constant, current rises and falls with the length of wire (r).

that's pretty much exactly how I've been learning it, too. Now I just adjust the feed and voltage by sound and it seemed to work out pretty well today. I'm using a small-ish lincoln machine on 24gauge, but the machines at school are "well broken in" aka some are pieces of crap and you cant get em right no matter what..

44Dwarf
44Dwarf Dork
10/25/11 2:19 p.m.

Stop over thinking it when it sounds like bacon in a hot pan you've got it right. DONE

ransom
ransom Dork
10/25/11 2:47 p.m.

In reply to 44Dwarf:

I appreciate the advice, but I'm puzzled about being advised against learning how stuff works.

I may be able to stick metal together just fine on the frying bacon principle, but I prefer to understand the process. In the long run, I figure it'll help with getting set up better and quicker, with troubleshooting, and with not getting caught out when trying something unfamiliar.

FWIW, I'm not having any real issues welding right now, I just have some uncertainty arising from a lack of practice and understanding.

Given the importance of welds in the GRM world, I like caution

Taiden
Taiden Dork
10/25/11 3:39 p.m.

Watch some of the Welding Tips and Tricks mig videos. His youtube channel is very good.

ransom
ransom Dork
10/25/11 4:08 p.m.

In reply to Taiden:

It's true. I subscribe to his RSS feed (though the signal to noise ratio there is lousy, as it contains dumps of posts from site users, many of which are off topic or just "job wanted"...)

motomoron
motomoron HalfDork
10/25/11 4:16 p.m.

For a given power level if the wire feed rate is way too slow it will burn off, breaking the arc until it feeds enough to make contact agin and reestablish the arc. It goes sput-sput-sput-sput, and if you're using wire thicker than say, .023", you'll feel the gun jerking in your hand. If the feed rate is too high, the bead will be oversized and look cold. Penetration will not be optimal.

The Miller GMAW (MIG) book is quite good with regard to actual cause and effect of what the settings change and why.

Eventually you'll gather what needs to be welded, give it 10 seconds of scrutiny and select a power and feed setting on the basis of what gives sufficient penetration and looks nice. If your work falls between power settings, if you're a little over power, turn up the wire feed rate. Conversely, if you need the weld pool a little hotter turn the speed back a little. How fast you run the bead, and whether you "stir" the gun as you pull are factors. Also whether you "pull" or "push" the bead, and whether you're using C25 Co2-argon mix or pure Co2 for shielding gas.

+1 for the Welding Tips and Tricks mig videos. Also the TIG videos when you get one, which is inevitable. As goes autocross/HPDE/TT/road racing, so goes propane/oxy-propane/oxy-acetylene/MIG flux core/MIG w/ gas/TIG...

Streetwiseguy
Streetwiseguy Dork
10/25/11 8:29 p.m.

http://www.welding.org/c-35-blue-gray-posters.aspx

donalson
donalson SuperDork
10/25/11 11:04 p.m.

i'm with the zen guys... had to do some welding the other day... took a few tries to get the right settings and the bacon sizzle sound but once I found it I was amazed at how good it looked lol... started off a little low on the power then bumped it... then found I wasn't feeding enough material so speed up the feed till it had the right sound...

Derick Freese
Derick Freese Dork
10/26/11 12:02 a.m.

I just started really playing with my Lincoln flux core today. This thread is just in time for me. I was also having issues with the guidance that I was being given by my brother who has some welding background. When he left, I started doing exactly the opposite of what he was telling me, and I was starting to lay actual beads. It turned out I had too little power and too little feed speed. I was also moving far too slowly. I had been having trouble laying beads on lawn mower blades to being able to lay decent beads on an old steel RX7 hood I had laying around.

I do feel empowered when I'm welding. Makes me feel like the caveman that invented the hammer.

donalson
donalson SuperDork
10/26/11 12:21 a.m.

tip... pick yourself up an auto-darkening helmet... worth its weight in gold for a newb welder

914Driver
914Driver SuperDork
10/26/11 6:17 a.m.

Ransom, weld two pieces together and then slice it in half. Using the example above, slice the weld horizontally left to right, through the weld. Now look at the weld at the slice.

If the weld is laying on top of the base metal like bird poop on a fence, then the wire is too fast or the heat is too low. (Zenism) On the other hand, if everything is dialed in perfectly and you move your hand too fast across the base metal, it's a bad weld. (more Zenism)

Now splash the sliced weld with a little vinegar and water mix, a light etch. You will see the base metal turn a dark silver or light grey as will the weld metal. Right where the weld metal and base metal meet the metal will turn a darker grey. That's called the heat effected zone. A bigger heat effected zone means better penetration making the base metal and the weld become like one (Zenism).

Oh yeah, practice, practice, practice .....

Welding is like sex, you can read all the books in the world but actually doing it is beyond description.

Welding is like sex, everyone thinks they're good at it until they spend time with a professional.

Welding is like sex because ...... (your turn)

Dan

Giant Purple Snorklewacker
Giant Purple Snorklewacker SuperDork
10/26/11 6:57 a.m.
914Driver wrote: Welding is like sex, you can read all the books in the world but actually doing it is beyond description. Welding is like sex, everyone thinks they're good at it until they spend time with a professional. Welding is like sex because ...... (your turn) Dan

Welding is like sex because it is easier to wave your wand around near the puddle than it is to get good penetration.

Welding is like sex because when you are finished something always burns.

slantvaliant
slantvaliant Dork
10/26/11 7:44 a.m.

Welding is like sex because ...

... lots of people say they're good at it, but few are.

... by the time you find out a welder isn't very good, things have gotten messy.

... I'm usually alone when doing it. (Wait! What?)

Toyman01
Toyman01 SuperDork
10/26/11 7:50 a.m.

Welding is like sex because it always seem like I'm doing it for someone else.

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