Welding Tips and Tricks

I don't have the best welding education, as money and time are a factor. but I would have to say it was very limited in my 6 week intro course at the local trades school. as far as my booklets could tell me my amps are controlled directly by a ratio through my wire feed speed, and are not directly displayed on my machine. and are also modified through my distance from my workpiece and contact tip.

Now when I see specifications about welders in catalogs and online they give duty cycle ratings in ***Amps/**% I don't really know what my amps are when i am working and haven't had it properly explained to the me. I know its V up and Amps down the further you move away from the work, but what the heck are my amps really at?

this a Loaded question? like asking where babies come from? or how big is the universe?

I'd rather tell you where babies come from...'

Regardless, the total amps gives you a guide to the machine's capability, in a manner you can compare to a stick machine.

The amps through a MIG arc are affected primarily through wire speed. You set a voltage, and adjust wire speed to match. When you hit the wall for wire speed, you've hit the upper limit for amps on than machine at that voltage. At maximum voltage available, when you hit that wall, that's all the amps the machine will carry.

This lets you compare the machine (say 250A) for performance against a similar 250A stick machine. You can expect similar weld capabilities.

As for babies... I remember going to a picnic with dad, and coming home with mom. That was a good day.

Steve S

@ Otto - leaving the baby thing out of this !

I've always thought that Mig / Stick welders were not strictly comparable on amps - as the voltage & therefore total heat / KW power used were not that similar.
For your 250amp example - now that's a big(ish) stick welder for most people - does anyone here routinely weld at that current & what size rod would that be ?

A 250 amp Mig on the other hand is only at the top end of hobby welders - most shop welders are at least 350 ( where I've worked 400 >500amp was normal ) & they are bought for duty cycle !! to allow around the 250amp range to be used without overheating so it would seem you need proportionately more amps for mig than experience tells you is normal for stick - I think it's hard when someone asks about size of Mig welder required to give a good answer - other than the biggest you can afford or have power to run.
( not trying to offend you here - maybe a separate post on duty cycle is in order as it seems to be generally a mis-understood area )

The only thing that I know about babies, is that the 'Stork' brings them, and the 'Swallow' takes them away.

Otto Nobedder wrote:I'd rather tell you where babies come from...' Steve S

Also your wire size will affect the amp carrying capabilities. For example a 1/16" wire will have more surface area than the standard .035" wire so it will carry more amps. Wire speeds will be slower with larger wire and deposition rates will obviously be much higher with the larger wire. Aluminum is much more sensitive to wire size and speed than steel. Flux cored wires can be quite touchy as well in this regard. Your machines manual may give a guesstimation of where the amps are at a certain speed with a certain size of wire but that's as close as it will typically get without getting a DC meter to read it while you are welding. Hope this helps.

@ noddybrian,

As you said, the numbers do not compare directly. Re-reading my answer, I was even more vague than I was trying to be .

I suppose a more applicable way to say it would be: You can expect to be able to do with a 250A MIG any weld you would NORMALLY do on, say, a Miller Bobcat 225. If you run the 225 wide open (3/8" or 7/32" 7024 jet-rod comes to mind), you'll hit duty-cycle issues, but you can do 1/8" 7018 all day long, and do the same welds with the 250A MIG all day.

I suppose the easiest part of Ohm's law to apply to the power at the weld would be P=I^2/R, as changing wire size and/or speed directly affects the resistance at the arc. Stick-out also affects resistance to a smaller degree.

Biggest rod I ever stick-welded was 1/4" 7024. 270A DCEN (!) on a 500A machine (duty-cycle & long leads). 7024 is a 1G only rod, but it makes tracks! You can lay a 3/4" bead in 3/8" plate like 1/16" dual-shield. If not for rod changes, It would be nearly as fast, and the slag peels up in long curls leaving a bead that looks like F/C.

Steve S

Two questions, please.

First, is it accurate to say that in the voltage range 15 V to 32V, the ratio of amps to volts to get the sizzle in MIG welding (12mm stickout) is 6:1?

"Between 15 and 32 load volts, the ideal ratio between amps and volts is 6:1 -- for every one volt of load, six amps are needed to burn off the wire properly. For example, if you set the machine for 20 volts, multiply that number by 6 for the correct amperage: 20 x 6 = 120 amps. There is a fair amount of leeway in setting the machine, but this 6:1 ratio will get you close to the correct settings from the start." Page 142 Todd Bridigum How To Weld MotorBooks 2008

One of my MIG welders is a Ross, a handyman machine with four rocker settings that select from taps on the power source. The four rocker settings are 15.5 V, 15.7 V, 16.5 V and 19.7 V (from manual supplied with welder). I can only calculate the amperage from wire speed and burn off values (7.6 metres per second, 0.9 wire with burn factor of 4 cm per amp = 170 amps). Now I have to set the wire speed to deliver the required amps. All well and good. Works in practice. But it doesn't match the 6:1 theory.

I've also tested the 6:1 theory against the Miller calculator. FCAW 0.9 mm wire, 4.8 mm mild steel (3/16"), 190 - 220 amps and 15 - 16 volts. The ratio doesn't work for me. Am I missing something? (I have no doubt that Todd Bridigum can weld very well.)

Second, the wire burn off factor of 4 cm per amp for 0.9 mm wire I obtained from Tips and Tricks site. Does it apply to all makes of wire? Is it a result of the physics of the metal in the wire? Is it the same for solid wire and cored wire? Where does this number come from?

Thanks for any help.

Here is the link to that wire burn off stuff I mentioned.

http://www.weldingtipsandtricks.com/Mig ... -tips.html

I've had to convert it to metric, and my last posting didn't give all the steps in the calcs but anyone can rework these for themselves (in fact, will need to, starting with their own wire speeds for their specific welders).

This stuff really helps in conversations, "lessons", with beginners, for whom words like "bacon sizzling" and "watch your stickout" are covered in mystery when they first look at sparks and smoke and spatter. (Yairs, TIG welders, some of us do have sparks and smoke and spatter. Even fumes and slag.)

But back to the issue: where does this "wire burn off" value come from?

WerkSpace wrote:The only thing that I know about babies, is that the 'Stork' brings them, and the 'Swallow' takes them away.

Otto Nobedder wrote:I'd rather tell you where babies come from...' Steve S

I love this forum!

AnvilJack wrote: I've also tested the 6:1 theory against the Miller calculator. FCAW 0.9 mm wire, 4.8 mm mild steel (3/16"), 190 - 220 amps and 15 - 16 volts. The ratio doesn't work for me. Am I missing something? (I have no doubt that Todd Bridigum can weld very well.)

Just a little, maybe meaningless input - Flux-core in that dimension is rare (or maybe they are normal, for gasless-welding?) - Most industry flux-core requires gas, and start from 1,2 mm and up.

Anyway, 0,8 or 1,0 mm solid wire with 190-220 amps you will run on at least 25V. I can take a note of wirefeed speed and volts tomorrow at work. Most of my day was ~ 13 m/min, 31-32V, 275A with solid 1,0 mm wire. Which gives a ratio of about 8-9:1 - Do notice, this in spray-mode. Dip-transfer may be different.