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  1. #1
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    Default Different welding processes compared for heat input

    One thing that I have wondered about is how you can compare the different welding processes..

    In the past I have come across people telling me how crap MIG is for penetration and strong welds.... Their basis for this statement was when they had fans in a crushing plant fabricated, but they kept exploding in use... the welds were coming apart... It was mig welded...

    I have been doing a bit of heavier welding using 7018 rods and about 170 amps.... It runs a nice bead, seems to penetrate well...

    I grab my 240V 250amp MIG.. Crank it right up with 0.9mm wire and it simply does not seem to put the same heat into the weld that the stick does...

    So what would be a comparable MIG sized machined compared to a stick machine, to get the same amount of heat input into the weld and penetration.. I realize MIG has a lot more variables to choose from...

    I would like to get a mig comparable to what say a 300 amp stick welder can do...
    Gold, the colour of choice for the discerning person.

  2. #2
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    MIG penetration is heavily influenced by a number of variables. See: http://www.weldingtipsandtricks.com/...rocedures.html for more.
    I use stick welding for heavier stuff, 3mm thick and up.

  3. #3
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    I think there is more to penetration than the total amount of heat put into the job.

    One of the major benifits of MIG is that it is more efficient with the amount of heat going into the job.

    As I understand it MIG is less likley to cause distortion in the job than stick because there is less waste heat.

    from my own experience I get better and more reliable penetration with mig than I do with stick.


    one of the big advantages to MIG is that you can run closer to the blow thru point than you can with stick...because you can see exavtly what the weld is doing and if it starts to look like it wants to blow thru you can either stop, slow down or speed up depending on what is appropriate....and you can restart immediately.
    Also because you can see the actual weld as it is laid, you can make fine adjustments to the wire feed and current.

    You have much finer and more consistent control of the welding process with MIG.

    While MIG is way easier to get a good weld than stick...there is still the need to apply "craft and understanding" when welding critically loaded joints........I think maybe MIG is somtimes too easy and people forget.



    cheers
    Any thing with sharp teeth eats meat.
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  4. #4
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    just another thaught.

    One critical difference between MIG and stick is the diameter of the electrode.....MIG is considerably thinner than stick for a given thickness weld.

    This influences a great many things.

    because the current is chaneled thru a smaller area..

    less current is needed to achive melting point of the metal
    The melded area is smaller in area
    thus less heat is wasted

    It can also be argued that less current is required to achieve a given penetration.

    cheers
    Any thing with sharp teeth eats meat.
    Most powertools have sharp teeth.
    People are made of meat.
    Abrasives can be just as dangerous as a blade.....and 10 times more painfull.

  5. #5
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    Quote Originally Posted by .RC. View Post
    In the past I have come across people telling me how crap MIG is for penetration and strong welds.... Their basis for this statement was when they had fans in a crushing plant fabricated, but they kept exploding in use... the welds were coming apart... It was mig welded...
    Seems fairly simplistic. What about investigating the design? Maybe that was the failure.

    On the topic of heat, Jody had a good video a while back that some of you would have seen where he did a number of test runs on lap test joints with tig, doing nothing but varying heat and travel speed. The purpose of the video was to show the HAZ around the weld and how the hottest, fastest weld put the least total heat in. He didn't cut up the samples to test penetration but you could see they were all good.

    OK, quick search and here's the video:

    https://www.youtube.com/watch?v=DmVCLi6cxok

  6. #6
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    It is very easy to lay an acceptable looking bead with a mig, not so easy to lay one that actually performs as well as it looks.
    Many people make the mistake of trying to run a big bead in one pass with a mig. The wire MUST be at the leading edge of the puddle at all times to prevent over roll and the voltage/wire relationship must be maintained. You definitely DO NOT turn the volts up to increase penetration. Next comes choice of gas. CO2 has a much better penetration profile, more like stick actually. Argoshield has a much narrower profile, which means that the bulk of your penetration could easily miss the joint. Mig is less tolerant of contamination than stick.
    Set up and used correctly, mig will out penetrate stick. To be honest though, neither one penetrates as much as most believe and amperage dos not make as big a difference as one may think.
    A 180-200A mig will run right along side a 300A stick welder.

  7. #7
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    Quote Originally Posted by soundman View Post

    It can also be argued that less current is required to achieve a given penetration.

    cheers
    You have never trained as a welder have you?
    CHRIS

  8. #8
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    Thanks everyone... You have convinced me that for the bigger stuff I will stick with stick welding, and just use my MIG for the small stuff...
    Gold, the colour of choice for the discerning person.

  9. #9
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    Quote Originally Posted by .RC. View Post
    Thanks everyone... You have convinced me that for the bigger stuff I will stick with stick welding, and just use my MIG for the small stuff...
    Done properly MIG can be used for bigger stuff but that depends on so many things and the ability and training of the welder is paramount to doing it properly. I suppose the same can be said about any stick welding, even more so than MIG. I would urge anyone who has not done so to do a couple of courses at TAFE and actually get some good training, it will open your eyes to how complicated the process can be.
    CHRIS

  10. #10
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    Quote Originally Posted by .RC. View Post
    Thanks everyone... You have convinced me that for the bigger stuff I will stick with stick welding, and just use my MIG for the small stuff...
    I would probably rethink that conclusion. I love stick welders and regularly use them, however Mig welders will also weld heavy sections just as well as a stick welder. Provided of course you know how to use both welders.
    Let's talk heavy sections.
    AD45B.jpg
    The entire center hitch of these trucks are welded with .9 and 1.2mm solid wire mig. Thicknesses vary from 16mm to 100mm. The chassis, subframes and in fact nearly every other piece of the truck is welded with solid wire mig.
    With a 180A mig, you can confidently lay down 12mm fillets, (3 pass), to WTIA Cert8G standard which stipulates 100% penetration and no over roll among other things.
    It really gets up my nose when I hear the story that migs are no good above 3mm etc. When migs first came on the scene, not a million years ago either, tradesmen were doing things such as 10mm vertical down fillets that were abject failures, that is where the myth that migs would not penetrate and were only good sub 3mm started. Wrong technique, poor result.
    Here's a little test that the doubters can try for themselves. Take a 4 100X10 plates say 200 long. Weld 2 in a tee fillet joint with stick, weld only one side of the joint, a 10-12mm 3 run fillet will do nicely. Now do the exact same with a mig welder in the hands of someone competent. Now, try and break them. The mig welded joint will take substantially more to break than one welded with rutile electrodes and a little more than one welded with E48XX (E70XX) electrodes. Penetration will be 100% on both joints and the plates will have actually bent before the welds finally succumb.
    Migs are a damn good tool, one that unfortunately most never seem to have learned to use correctly. Manufacturers propaganda has not helped either. I laugh when I see a welder rated to run a 15mm fillet in one pass for example. No mig or stick will run that in one pass, 6mm, maybe 8mm in one pass is probably the limit. Any more and penetration and fusion rapidly suffer.

  11. #11
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    Quote Originally Posted by Karl Robbers View Post
    Now do the exact same with a mig welder in the hands of someone competent.
    That's the key isn't it Karl?

    I regard myself as a competent TIG and Stick welder and thought that these skills would be pretty quickly transferable to MIG when I bought that machine. Of course it helped, but I have to say that I found the learning curve for MIG welding quite a challenge and it took quite a while to get heavy welds that I regarded as acceptable. Given that MIG welds are more likely to look good even if they're not, it's important to have a good critical look at every one of your MIG welds to make sure they're doing what you think they are.
    Last edited by WelderMick; 24th Sep 2014 at 10:20 PM. Reason: fixed a typo

  12. #12
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    I shudder when I see a post that says.....I have just bought a welder and need some advice to get started. I can recall being advised when MIG first came into the TAFE system that it could not be used for out of position work, that sure has changed.
    CHRIS

  13. #13
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    Quote Originally Posted by WelderMick View Post
    That's the key isn't it Karl?

    I regard myself as a competent TIG and Stick welder and thought that these skills would be pretty quickly transferable to MIG when I bought that machine. Of course it helped, but I have to say that I found the learning curve for MIG welding quite a challenge and it took quite a while to get heavy welds that I regarded as acceptable. Given that MIG welds are more likely to look good even if they're not, it's important to have a good critical look at every one of your welds MIG to make sure they're doing what you think they are.
    Definitely agree, the most accessible form of weld test is a visual inspection. Every weld, by every welder should receive a critical eye as gas may run out or settings alter with little warning.
    Stick welding has the advantage that much of the adjustment is taken away from the operator. Set the amps, strike an arc and away you go. Migs add several variables that must be understood in order to get the best results. This understanding is rarely if ever gained from an instruction manual.
    Many tradesmen will gladly help out a new starter, but sadly a great many myths are still present within the trade and manufacturers often distort facts to suit the product they are selling. Tafe is probably the most sure way to learn the basics.

  14. #14
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    Quote Originally Posted by Karl Robbers View Post
    Stick welding has the advantage that much of the adjustment is taken away from the operator. Set the amps, strike an arc and away you go.
    Until it is broken open and inclusions, cold starts etc are found in the weld but I know what you mean. MIG appears to be simple but in reality it has not so obvious problems. Welding, any welding is a complicated process and there are some dead people who will atest to that because someone with no training thought they could weld. There was an instance some years ago now where a loaded deck broke away from the house and it collapsed due to poor welding and design and people died. My TAFE teacher used to investigate things like this as a job and the photos weren't nice.

    I will get off my soapbox now but people who think they know how to weld frighten me.
    CHRIS

  15. #15
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    Quote Originally Posted by Karl Robbers View Post
    I would probably rethink that conclusion. I love stick welders and regularly use them, however Mig welders will also weld heavy sections just as well as a stick welder. Provided of course you know how to use both welders.
    Let's talk heavy sections.

    The entire center hitch of these trucks are welded with .9 and 1.2mm solid wire mig. Thicknesses vary from 16mm to 100mm. The chassis, subframes and in fact nearly every other piece of the truck is welded with solid wire mig.
    What size welders do they use for such things? 400/500 amp ones?

    I was looking at my transmig 250SE and it has two tables on the back...

    One table for the factory fitted 15 amp plug.. it says 180 amp output..

    Then it has another table for a 30 amp plug.... 250 amp output..

    I have a 40 amp 240v line in the shed, supplying the phase converter.... I wonder...
    Gold, the colour of choice for the discerning person.

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