MIG Welding FAQs Answered - Bernard and Tregaskiss

1. What drive roll should I use, and how do I set the tension?

The welding wire size and type determines the drive roll to obtain smooth, consistent wire feeding. There are three common choices: V-knurled, U-groove and V-groove.
Pair gas- or self-shielded wires with V-knurled drive rolls. These welding wires are soft due to their tubular design; the teeth on the drive rolls grab the wire and pushes it through the feeder drive. Use U-groove drive rolls for feeding aluminum welding wire. The shape of these drive rolls prevents marring of this soft wire. V-groove drive rolls are the best choice for solid wire.

To set the drive roll tension, first release the drive rolls. Slowly increase the tension while feeding the wire into your gloved hand. Continue until the tension is one half-turn past wire slippage. During the process, keep the gun as straight as possible to avoid kinking the cable, which could lead to poor wire feeding.


Following some key best practices related to welding wire, drive rolls and shielding gas can help ensure good results in the MIG welding process.

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2. How do I get the best results from my MIG welding wire?

MIG welding wires vary in their characteristics and welding parameters. Always check the wire’s spec or data sheet to determine what amperage, voltage and wire feed speed the filler metal manufacturer recommends. Spec sheets are typically shipped with the welding wire, or you can download them from the filler metal manufacturer’s website. These sheets also provide shielding gas requirements, as well as contact-to-work distance (CTWD) and welding wire extension or stickout recommendations.
Stickout is especially important to gaining optimal results. Too long of a stickout creates a colder weld, drops the amperage and reduces joint penetration. A shorter stickout usually provides a more stable arc and better low-voltage penetration. As a rule of thumb, the best stickout length is the shortest one allowed for the application.
Proper welding wire storage and handling is also critical to good MIG welding results. Keep the spool in a dry area, as moisture can damage the wire and potentially lead to hydrogen-induced cracking. Use gloves when handling the wire to protect it from moisture or dirt from your hands. If the wire is on the wire feeder, but not in use, cover the spool or remove it and place it in a clean plastic bag.

3. What contact recess should I use?

Contact tip recess, or the position of the contact tip within the MIG welding nozzle, depends on the welding mode, welding wire, application and shielding gas you are using. Generally, as the current increases, the contact tip recess should also increase. Here are some recommendations.
A 1/8- or 1/4-inch recess works well for welding at greater than 200 amps in spray or high-current pulse welding, when using a metal-cored wire and argon-rich shielding gases. You can use a wire stickout of 1/2 to 3/4 inches in these scenarios.
Keep your contact tip flush with the nozzle when welding less than 200 amps in short circuit or low-current pulse modes. A 1/4- to 1/2-inch wire stickout is recommended. At 1/4-inch stick out in short circuit, specifically, allows you to weld on thinner materials with less risk of burn-through or warping.
When welding hard-to-reach joints and at less than 200 amps, you can extend the contact tip 1/8 inch from the nozzle and use a 1/4-inch stickout. This configuration allows greater access to difficult-to-access joints, and works well for short circuit or low-current pulse modes.
Remember, proper recess is key to reducing the opportunity for porosity, insufficient penetration and burn-through and to minimizing spatter.

The ideal contact tip recess position varies according to the application. A general rule: As the current increases, the recess should also increase.

Recommended article:
Full text of "Sweet's architectural catalogues : for the year 1936

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4. What shielding gas is best for my MIG welding wire?

The shielding gas you choose depends on the wire and the application. CO2 provides good penetration when welding thicker materials, and you can use it on thinner materials since it tends to run cooler, which decreases the risk of burn-through. For even more weld penetration and high productivity, use a 75 percent argon/25 percent CO2 gas mix. This combination also produces less spatter than CO2 so there is less post-weld cleanup.
Use 100 percent CO2 shielding gas or a 75 percent CO2/25 percent argon mix in combination with a carbon steel solid wire. Aluminum welding wire requires argon shielding gas, while stainless steel wire works best with a tri-mix of helium, argon and CO2. Always reference the wire’s spec sheet for recommendations.

5. What is the best way to control my weld puddle?

For all positions, it is best to keep the welding wire directed toward the leading edge of the weld puddle. If you are welding out of position (vertical, horizontal or overhead), keeping the weld puddle small provides the best control. Also use the smallest wire diameter that will still fill the weld joint sufficiently.
You can gauge heat input and travel speed by the weld bead produced and adjust accordingly to gain better control and better results. For example, if you produce a weld bead that is too tall and skinny, it indicates that the heat input is too low and/or your travel speed is too fast. A flat, wide bead suggests too high of heat input and/or too slow of travel speeds. Adjust your parameters and technique accordingly to achieve the ideal weld, which has a slight crown that just touches the metal around it.
These answers to frequently asked questions only touch on a few of the best practices for MIG welding. Always follow your welding procedures to gain optimal results. Also, many welding equipment and wire manufacturers have technical support numbers to contact with questions. They can serve as an excellent resource for you.

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Drunkskunk

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• Jan 11,

• #1

I have a few dumb@ss questions for those who weld MIG.

I'm setting my Welder up for MIG for the first time. Its only been used for Flux core up untill now, and I have almost no experience with MIG. Also I lost the instructions in a flood 7 years ago, and the online instructions from Hobart are only for the newer revisions. Not sure how much applies to what I have. If it helps, this is a 120V Hobart Handler 140.

Whats the right pressure for the Argon tank? I bought a new tank with the welder, and even welded up a cart to hold both, but that was 14 years ago. I never hooked up the valve until now. No clue if it's still full or leaked down. It shows 800lbs

Whats the right flow rate for the gas when welding?

Any tips for practicing welds with MIG? I played with it a little, seems to make cleaner welds but getting good penetration seems harder than Flux-core.

REdiculous

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• Jan 11,

• #2

Our tank has a pressure gauge on the output and we only ever adjust it between 5 and 10psi. Not a guru, but this has worked really well for us.

I couldn't get flux core to do anything useful - tape works better. :lol:

Tench

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• Jan 11,

• #3

Disconect the wire feed so you can place your hand infront of the torch shroud and pull the trigger, set the gas flow so that you can just feel a slight draught on your hand and hear the gas coming out, this will be fine for welding indoors, outdoors will require more due to it being blown away by the wind. Always lead when using mig, point the torch straight at the joint at an equal angle to each of the faces to be welded if they are of equal thickness (bias the torch towards the thicker material if they are different) then lean it back about 10 deg and weld in the direction the torch is pointing with exception of welding vertically down when you would point the torch upwards but move downwards, on thin material anyway.
The actual output pressure setting on your regulator will be dependant on how restrictive the gases passage from the bottle to the torch is so it is best set by feel at the shroud, if you only have a single stage reg the output flow will increase as the bottle pressure goes down, if the reg is getting wet with condensation on the outside you are flowing too much gas.

play with the power and wire feed to find the best setting for the job you are doing on a similar thickness scrap peice, with experience you will be able to set it just about right straight away.
A 140a machine should be quite capable to weld steel upto 4mm thick, much thicker and the heat wont be high enough to cope with the amount being dissipated in the material resulting in poor welds.

That should get you going, now lots of practice!


Cheers Simon.

Drunkskunk

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• Jan 15,

• #4

Thanks for the advice, it got me started, and I've been practicing.

But I'm finding MIG just doesn't have the penetrating power of Fluxcore. I'm practicing on .065" barstock Chrome-moly and I can make some great looking welds that seem to flow well into the base metal, but looking at the back side of the joint, I don't seem to get much penitration even on the highest amp settings.

Am I doing it wrong? Or is MIG just less able to penitrate?

Spicerack

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• Jan 15,

• #5

The lack of penetration may be the gas. Argon is more for Ali and other non ferrous metals. I once used some argon left over from an Ali job and it was not good for steel welds. Migshield is the common gas used here and is a blend of carbon dioxide (around 20%) and argon. Sometimes there are other gases like oxygen added in.

Gordo

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• Jan 15,

• #6

Drunkskunk said: Thanks for the advice, it got me started, and I've been practicing.

But I'm finding MIG just doesn't have the penetrating power of Fluxcore. I'm practicing on .065" barstock Chrome-moly and I can make some great looking welds that seem to flow well into the base metal, but looking at the back side of the joint, I don't seem to get much penitration even on the highest amp settings.

Am I doing it wrong? Or is MIG just less able to penitrate?

I use straight argon for Al or Steel to 3/4" thick, BUT here is some good info.
http://en.wikipedia.org/wiki/Gas_metal_arc_welding

My buddy has 42 welding tickets and is paid $ a day, so he must be good at what he does. He uses straight Argon to TIG (NOT MIG) SS pressure vessels up to 2" thick. After reading the Wiki info on argon/carbon dioxide mix of 90:10 to 75:25, I phoned him to check AGAIN, because I asked him about C02 when he set my system up. 100% Argon does not penetrate as well as the GMAW, but you just turn the heat up a little with MIG or TIG.
I know nothing about the theory of welding, I've just done it all my life until something fails and then go find a guy who knows why. The main reason I have stuck with straight argon is to not have the cost of a 3rd bottle. With O2/propane for cutting and brazing plus the argon, I pay already pay $200 a year for bottle rent, plus the gas used. Enough for a hobby-shop.

Spicerack

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• #7

I'm going to give away my mig gas bottle soon. $200 per bottle just for rent and over $100 for a D size fill, which is not a big tank. We get screwed for this sort of stuff.

I'll keep the O2 for the red'n'black spanners tho.... I use an LPG tank with the oxygen and it is almost as good as Acetylene.

Gordo

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• Jan 15,

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andynogo said: I'm going to give away my mig gas bottle soon. $200 per bottle just for rent and over $100 for a D size fill, which is not a big tank. We get screwed for this sort of stuff.

I'll keep the O2 for the red'n'black spanners tho.... I use an LPG tank with the oxygen and it is almost as good as Acetylene.

Hi Andy,
I am always puzzled about the "almost as good as". I happened to see guys cutting up old steam locomotives when I was a teenager in the 's. 8" thick steel. That is when I bought my first propane cutting setup. Much later, contrary to all current wisdom, I found you can braze very well with it. Where does it come up short?

Drunkskunk

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So CO2 makes it penetrate better? I've got 100% Argon, but from my Beer keggging days I've got a 20LBS bottle of CO2.. I wonder what a valve body for blending them would cost?


Gordo, I'm curious why your friend uses 100%? I was told to go with 100% when I started, but no idea why.

Gordo

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• Jan 15,

• #10

Drunkskunk said: So CO2 makes it penetrate better? I've got 100% Argon, but from my Beer keggging days I've got a 20LBS bottle of CO2.. I wonder what a valve body for blending them would cost?


Gordo, I'm curious why your friend uses 100%? I was told to go with 100% when I started, but no idea why.

Don't know, but I will certainly ask. He is one very studious welder. If he is off work for a month, he puts a full week in the booth at the college before doing pressure vessels. One failure can ruin his career and some lives, if the x-ray misses a void. He is the guy they call when the other guys welds fail. He is always after me to go audit some TIG coarse at the College. Probably to get away from my questions.

CO2
Simple setup. 2 demand regulators with flow meters and a "T" Set the CO2 for 15% of the argon FLOW and fiddle from there. Assuming you have psi of CO2? Look for rebuilt regulators from a service shop. We have a local lady who is a wiz at rebuilds.

Spicerack

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• Jan 16,

• #11

Gordo said:

andynogo said: I'm going to give away my mig gas bottle soon. $200 per bottle just for rent and over $100 for a D size fill, which is not a big tank. We get screwed for this sort of stuff.

I'll keep the O2 for the red'n'black spanners tho.... I use an LPG tank with the oxygen and it is almost as good as Acetylene.

Hi Andy,
I am always puzzled about the "almost as good as". I happened to see guys cutting up old steam locomotives when I was a teenager in the 's. 8" thick steel. That is when I bought my first propane cutting setup. Much later, contrary to all current wisdom, I found you can braze very well with it. Where does it come up short?

Oxy propane (near enough to lpg) burns at celcius. Oxy acetylene burns at celcius. Some jobs- big cutting jobs for example- need the extra heat. For most of us hobbyists, celcius is plenty! Not to mention the cost savings- $0 for bottle rental and $25 for a 9kg refill. Just makes sense. Shame I can't source O2 cheap as well!

Tench

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• Jan 16,

• #12

I always thought that CO2 produces a colder weld than an argon/co2 mix, specific mig welding gas is a mixture of the 2.

http://www.mig-welding.co.uk/welding-gas.htm

JEB

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• Jan 16,

• #13

When I was welding at work, I only had 8 certs. but those were rated as to be able to weld on a atomic sub, not pressure vessels. or pipes. I thought that I forget how to weld SS when the gas supplyer dropped off a new 330cufoot tank where the tank was filled without purging, vacuuming, out the ambent air before filling with argon, used with TIG. The right gas mixture can be important.

Gordo

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• Jan 16,

• #14

Getting off topic.
Steel burns at C. Once it begins to burn, you can shut the other gas off altogether. All the acetylene does over propane is get the steel up to burning temperature quicker. I've never cut anything thicker than 2" so I have never been concerned with speed. Once you get the corner burning, you are away.

I always thought a submarine was a pressure vessel, requiring a pressure ticket?

Chambers

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• Jan 17,

• #15

Drunkskunk said: Any tips for practicing welds with MIG? I played with it a little, seems to make cleaner welds but getting good penetration seems harder than Flux-core.

Hey Drunkskunk,

I'm a welder/fabricator for a living and might be able to help a little

I assume your pushing the weld (correct way with GMAW) rather than pulling it as you would with flux That will make a difference to the peno you will get.
Clean the surface well and make sure your arc length is no more than about 10mm (tip to steel).

You could also try turning your wire speed down a bit and slowing down the weld to build up the heat a bit more. 8)

Of course this could all be irrelevant having not actually seen you weld

Gordo

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• Jan 17,

• #16

Drunkskunk said: I have a few dumb@ss questions for those who weld MIG.

I'm setting my Welder up for MIG for the first time. Its only been used for Flux core up untill now, and I have almost no experience with MIG. Also I lost the instructions in a flood 7 years ago, and the online instructions from Hobart are only for the newer revisions. Not sure how much applies to what I have. If it helps, this is a 120V Hobart Handler 140.

Whats the right pressure for the Argon tank? I bought a new tank with the welder, and even welded up a cart to hold both, but that was 14 years ago. I never hooked up the valve until now. No clue if it's still full or leaked down. It shows 800lbs

Whats the right flow rate for the gas when welding?

Any tips for practicing welds with MIG? I played with it a little, seems to make cleaner welds but getting good penetration seems harder than Flux-core.

Note you change the polarity when you switch from Flux to GMAW;

This video might be helpful?
http://www.weldingtipsandtricks.com/how-to-mig-weld.html

Gordo

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• Jan 18,

• #17

Drunkskunk said: So CO2 makes it penetrate better? I've got 100% Argon, but from my Beer keggging days I've got a 20LBS bottle of CO2.. I wonder what a valve body for blending them would cost?


Gordo, I'm curious why your friend uses 100%? I was told to go with 100% when I started, but no idea why.

I checked and he does use 100% argon for MIG or TIG in their shop. Steel or SS. He has no idea why anyone would claim lack of penetration. He repeated that he welds pipe and pressure vessels, from 5/8" to 2" thick.

Overclocker

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• Jan 18,

• #18

i'm now getting half-decent results w/ flux-core wire but i wanna try MIG. is it that much better?

specifically i'm getting tired of the cleanup needed w/ flux-core. and the smoke

pwd

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• Jan 18,

• #19

Novice MIG welder here (hobby only) but I've been doing my own automotive body work repairs for a few years now. I mostly have been welding on crappy (very thin and corroded) sheet metal (20 GA to 24 GA). The switch to shielding gas from flux core was well worth it for me; it gave me more control and confidence. My welds with flux core were burning through say 70-80% of the time; switching to MIG instantly reduced it to around 30-40% burn through. After about 40-60 more hours experience I've got my sheet metal tac welds only burning through about 10% of the time with MIG.

I imagine the difference would be a bit less dramatic if you are are more experienced welder; also with thicker gauge steel; you wound't run into the same issues I had. Just make sure you select the correct size welding wire and right mix of gas for the job. My little welder came with all the gas fittings so I just had to buy a cylinder of "autoweld" shielding gas and solid core wire; total cost was around $100 CAD.

litespeed

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• Jan 18,

• #20

You still have to clean everything well.....if any smoke, contaminates or oxygen get in your shielding gas it will make your welds porous. Sheilding gas keeps oxygen out to control the weld burn.....add oxygen and just like a cutting torch it will blow holes in it.

Biggest mistake most do going from flux core to mig is forgetting (or not knowing!) to switch the polarity on the ground/wire.

Tom