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Thread: MIG Questions

  1. #1
    Join Date
    Jun 2007
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    21

    Default MIG Questions

    I am taking my second class in GMAW/MIG at a local junior college. Up until now, Ive been working, for the most part, with sheet metal. This week I started with plate (each piece is approximately 8 x 8), and Im having difficulty making the second and third passes.

    Keep the following in mind: Im using a Miller CP-302 welding machine, so power is not an issue. The voltage and wire speed are appropriate: the arc is stable, theres litter spatter, and it sounds like bacon frying. Im using CO2 as the shielding gas.

    The plate is prepared with a Victor oxyacetylene cutting machine with a 30-degree bevel on each piece. The bevel is finished lightly with a hand grinder; a root face of approximately 3/32 is placed on each piece. The two pieces are tack welded at the back. Im welding in the vertical position, moving up.

    Im doing ok making the root pass; the penetration is not what Id like, but I think that will improve with practice. As my instructor suggests, I make the root pass with a small u shape and that seems to work well. As stated above, my difficulty is with the following passes.

    Id like to know the following:

    1. What pattern do you recommend for the second and third passes? (My instructor recommends what I think of as a ladder-type pattern, pausing slightly at the sides.)

    2. Given the size of the 1/2 plates and the other details provided above, what is the appropriate root opening I should maintain after tack welding the two pieces.

    Thank you for your time.

  2. #2
    Join Date
    May 2007
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    Grande Prairie, Alberta Canada
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    729

    Default

    Given your information, I would have a 3/32" to 1/8" gap.

    Pay very close attention to your root pass - you need to get this right, or you'll fail a bend test every time. Your fill & cap passes are useless without proper fusion on your root pass.

    Now, your root pass can be Vertical Up, or Vertical Down, either will work, as long as you are working with a keyhole and are ensuring good fusion to both sides.

    Fill Pass: Box weave. Kind of hard to explain but stay with me here. The basic motion will be a "U" shape that is laid on it's side, with the open ends facing towards you, and the bottom of the "U" facing the root pass. When you get the hang of it, this will give you a full, level, weld deposit that is very easy to stack another fill pass, or cap pass on top of. Start on one side of the bevel, follow bevel into root, cross over root, follow bevel back out. Repeat. Each time that you cross through the center, try to raise up 1/2 the diameter of the electrode. It will seem a little wierd at first but keep with it...Eventually, following the bevels will feel more natural, and you won't have to concentrate on the sideways "U" motion - then you will be able to concentrate on keeping your upward steps small, and having a nice tight pattern.

    Cap pass: Straight weave. Side to side motion, pausing slightly at edges as needed to ensure proper blending out of the toes of the weld. Again, each time you pass through the center, try to raise up slightly, about 1/2 the electrode diameter. Yes, it will feel like you are welding over top of the previous pass, but when you get the hang of it, your speed will actually increase because you will deposit less each time across the joint. When you are doing it correctly, you will end up with flat looking, tightly stacked weld beads, with very slight reinforcement.

    You never stated what size of wire or what setting you are using, but when I use ER70S-6 wire, .035" and I have a joint like this, a basic setting I use is 16.5 Volts and 175 IPM or so. Of course, it can be done much faster at higher settings, but for a beginner to learn, this is where I set the machine.

    Hope it helps.

    Later,
    Jason

  3. #3
    Join Date
    Aug 2007
    Location
    New Orleans, LA
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    161

    Default

    He just told you everything you need to know to do it right. Uphill with the MIG using either straight wire or fluxcored I do it exactly the same as I run 7018 uphill, and his explanation is as good as any I can give. I think he did leave out the key words though, heheh, PRACTICE, PRACTICE, PRACTICE!

    I turned my machine down to 16 volts just to see what it was like. I quickly got bored with it. I'm used to running from about 19 to 25, mostly around 23 on anything from 12 gauge on up (I do the light stuff downhill) using NR211-MP. Can't tell you the wire speed because it doesn't tell me, lol.
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  4. #4
    Join Date
    Nov 2007
    Location
    Southern Louisiana
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    421

    Default welding technique

    It has been my experience that we as welders will typically apply a technique that works well for one process to other processes. Sometimes we get away with it and it is OK and other times we won't. What we need to remember is the deposition rates for wire feed welding are different that other processes. due to this fact we need to be concerned about lack of fusion. So running a weave pass with MIG is more difficult to get correct than just running stringer beads. Yes the weave will fill the joint faster but the lack of fusion issue is problematic. Typically if you run destructive testing on a weave pass with MIG it will crack out in the toes. Travel speed or the speed of linear movement is critical with wire feed. This is not to say that there aren't times when a weave of some size isn't appropriate. the key is applying it when it is needed and knowing when that is and what the variables are. As you go through school for welding and on through your career, practice, practice and then practice some more. I am sorry to say that technology changes and advances so quickly that sometimes the dissemination of information isn't really all that solid. We see manufacturers develop some new item and they work with it for months before the public sees it. They then try to share the information with their distribution people and that is typically a day or two if they are lucky. Then the educators will get the opportunity to see the new technology and work with it for a day or so and then off they go. The understanding of the intricacies doesn't get from the development lab to the educator as it should. It is a fact of our society today, I need the information but I only have 15 minutes to consider it before I am off to something else. To help with this there are opportunities such as the Miller roadshow where they drag that big truck around and let people try the machines and teach them how to use it. They even have classes inside that trailer to help understand it. That puts the responsibility back on the welder to take a day off of making money to go learn how to use the machine correctly. My advice is to take the time, I know it is money but inefficient operation is money also. So off the soap box, we as welders need to understand our processes to a degree where we know the ability of the process, not just the machine or the gas or the wire but how they all work together to get it right.

  5. #5

    Default MIG Questions

    I hope I'm not the only one here that takes exception to the statement about what works for one job will work for the next.... and that's what we do???

    SJMiller

  6. #6
    Join Date
    Aug 2007
    Location
    So. Cal
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    335

    Default Well??

    Quote Originally Posted by sjmiller View Post
    I hope I'm not the only one here that takes exception to the statement about what works for one job will work for the next.... and that's what we do???

    SJMiller
    Not sure if I would say it raises to the point of "takes exception", but I would say and/or agree that each job is different. Not just the job description, but everything. Variables in electricity, differing steel properties, weather, steel temp, etc., etc. all play in the wonderful world of variables inherent to welding. This tends to be a "experience" education rather than text book. However, logging your techniques, settings and other parameters have always proven to be the best "start point" for the next similar project.

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  7. #7
    Join Date
    Mar 2007
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    Deltaville, VA
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    Default

    I think that a couple of posters missed the point diamondback was trying to make. What I read was that many of us who used stick for a long time are trying to apply the same techniques to Mig. The material disposition rates are quite different between the two processes, consequently, what may be the best procedure for stick, will not be the best procedure for Mig.

    I, like many of you, I'm sure, still follow the same basic patterns/movement that I used with stick. With Mig, I tend to move faster from shoulder to shoulder (less time in the middle) than I did with stick. Seems to have worked so far, but I guess that what diamondback is saying is that there may be a whole different procedure which will give better results.

    Guess it's never too late to teach old dogs new tricks.

  8. #8
    Join Date
    May 2007
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    Grande Prairie, Alberta Canada
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    Default

    I have read diamondbacks post, and everyone is entitled to their opinion. I disagree with some of the statements made, and do not believe that the post in that much detail was warranted in response to the question, but that is MY OPINION.

    My post was in direct response to the OP's questions. When the coupons are fed through the rollers on a guided bend test, if the root weld is poor, the coupon cracks & tears & the weld fails. The OP asked for suggestions, and received them. I'll agree with Jolly Roger that the settings I outlined can be "slow" to an experienced welder, but for a newcomer learning the techniques, slower IS better. There is A LOT to concentrate on when you are just starting out. Learn the technique correctly, and the speed WILL come.

    If you want to follow diamondbacks suggestions and just run stringers go ahead. I have had no issues with running vertical up GMAW, FCAW-SS, or FCAW-DS welds using a weave pattern. I can pass NDT (X-ray & magnaflux) and guided bend tests without lack of fusion. Others experiences may vary.

    What I will read into diamondbacks post is an overall concern that with GMAW is very easy to have good appearing but structurally poor welds. I would agree strongly with that concern. I have commented to that effect numerous times on this forum.

    Sorry if I misunderstood the post. Run on sentences without paragraphing like ideas together really derails my train of thought.

    Later,
    Jason
    Last edited by Black Wolf; 12-09-2007 at 01:50 AM.

  9. #9
    Join Date
    Mar 2007
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    Deltaville, VA
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    Default

    Hey Jason,

    Agree with your posting 100%. Also agree the the OP's question regarding technique was answered quite well.

    Don't know if you caught it in a previous post, but seems that diamondback has just recently been hired by Miller. I think what you are seeing in his post is a degree of frustration with how information/procedures relative to new equipment is/is not getting to the field. An example would be a guy who's stick welded for 20+ years may not be taking full advantage of some of the new Mig equipment available (ie pulsing).

    As has been discussed in detail in other posts, few tig welders (KB excepted) are really taking advantage of say the advanced features of the Dynasty 350. Most are just trying to duplicate the results they were getting with previous equipment. Some of this, I'm sure, is the result of workplace pressure to produce results (results being a billable product). Too few employers see "messing around with machine settings to see what they do" as a productive venture.

    The auto industry is a prime example of the absolute requirement for "continuing education". The old shade tree mechanic with his dwell meter and timing light and little else is lost in today's computerized and fuel injected vehicles. Without a computer and an ECM reader he's operating in the blind. In the marine field, companies such as Brunswick have requirements for continuing education for your mechanics or you loose your certification as a recognized shop.

    For the continued development of the welding field, I feel it's incumbent on the major manufacturers (Miller, Lincoln, Hobart, etc) to provide a means of getting new information to the field in a timely and cost effective manner. In this vein, the use of interactive tutorials and better owner's manuals may be more "cost effective" than a one or two day workshop scattered around the country.

    Just my thoughts. Comments?

  10. #10
    Join Date
    Mar 2006
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    Queens NY
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    Default

    I'm not nearly qualified to comment on the techniques explained above, but i would like to add that if Miller would produce a few short "How To" videos for their web site SHOWING actual techniques and equipment features (basic to advanced) it would greatly help most of their customers. (Not animations!). As an amature who knows no one who is a professional welder, they few instances of actual welding i have seen has helped me greatly. I was suffering with aluminum TIG, then i saw a Lincoln rep at englishtown run a but weld and it helped me immensly.

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