What is the importance of depth of weld?

So hear me our, when a weld is done theres a layer of base metal that melts and mixes in with the filler material. Well, why is it important to control that?
Does it matter if its 1 mm or 5 mm thick if its all going to be a continuous metal block?
I know theres some clever reason to design welds with a specific depth but i dont know it. Thats why im asking.

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  1. 2 months ago
    Anonymous

    Take four wooden blocks, lay them out in two sets of two. On one set just smear some glue on the surface and let it dry. On the other, actually properly apply the glue between the boards. It's kinda like that

    • 2 months ago
      Anonymous

      >On one set just smear some glue on the surface and let it dry
      oh the glue analogy, so relevant for a thread on welding.. NO!

      • 2 months ago
        Anonymous

        they say MIG is like hot glue gun dumbass

        • 2 months ago
          Anonymous

          it obviously isnt, welding melts part of the base metal and mixes it with the filler, unlike brazing, soldering or gluing.
          The question is what is the importance of the thickness of this mixed metal layer. It cant just have zero thickness, otherwise it would no different from brazing

          • 2 months ago
            Anonymous

            I can't wait until they show up and laugh at you're ignorence. I bet you aslo don't think TIG is like soldering. LOL.

            • 1 month ago
              Anonymous

              Yeah tig is just like soldering, you jam the electrode against the metal and then touch both with filler wire
              And don't use argon, it's just a waste of money, use grease as flux

            • 1 month ago
              Anonymous

              Just because the process of application is similar doesn't mean the actual method of adhesion is. If you think that a plasma arc melting two pieces of metal together is in any way close to dripping a rubberized glue over two unmelted surfaces, you're a drooling moron.

            • 1 month ago
              Anonymous

              You can tig braze. Just lower the heat. You could probably even braze with a stick welder and a carbon arc if you wanted.

              • 1 month ago
                Anonymous

                This thread is specifically about stick welding mild steel so your inane comment about tig brazing is stupid and unhelpful

            • 1 month ago
              Anonymous

              They say it's a hot glue gun because you press a button and something comes out to connect two pieces. That's it. If you didn't get this, you might be a moron. There is a lot more than just pressing the button. You have to understand the base material, the shape of the join, the thicknesses involved, whether the pieces have, or should have a bevel, surface preparation, filler material, amperage, ac/dc, flux or shielding gas, surface protection, purpose of the join – is it load bearing? Does it need to look good? Does it have to be corrosion resistant? This is all stuff you don't have to worry about with a hot glue gun.

        • 2 months ago
          Anonymous

          >they

    • 1 month ago
      Anonymous

      Fpbp

      they say MIG is like hot glue gun dumbass

      Maybe if you don't know how to use it, bad welds are literally compared to glued together parts

  2. 2 months ago
    Anonymous

    One of my welding teachers was from Nigeria.

    He said;

    >welding is like a good marriage, you need full penetration to keep it together

    • 2 months ago
      Anonymous

      He was also the metallurgy teacher and you need to look up the changes in physical properties of steel based on heat input and the effects of annealing, quenching and normalization.

    • 2 months ago
      Anonymous

      He was also the metallurgy teacher and you need to look up the changes in physical properties of steel based on heat input and the effects of annealing, quenching and normalization.

      ok so how thick should be the region where the base metal mixes with the filler? Does it even matter?

      • 2 months ago
        Anonymous

        It depends on the base material thickness and grain and alloy composition (grade). I do structural and sanitary process stainless GTAW and in the structural your trying to minimize the heat input because you don't want to create to much martensitic grain and that is affected by your heat treatment after. Otherwise it will be brittle in the weld area.

        Sanitary process is autogenous and 304 is austensitic so it's more ductile and it doesn't matter as much and you need a lot of heat to have a full penetration weld on a 1/8" butt joint with no gap.

        What type of welding are you doing?

        • 2 months ago
          Anonymous

          lets say structural, common A36 or similar, fillet or lap welding, 8 mm to 20 mm plate
          My instructor was bothering me regarding the depth of weld, he means the thickness of the zone were base metal and filler mix, i dont understand why that is important as long as its not zero mm since molten steel isnt glue.
          Is all the fuss about grain structure?

          • 2 months ago
            Anonymous

            How is your instructor inspecting the welds? What process?

            Nitric acid after bandsaw cutting would show your penetration. I just passed a 5f pipe to plate cert with that kind of test

            • 2 months ago
              Anonymous

              >How is your instructor inspecting the welds? What process?
              i dont know, i figure its cutting, polishing and acid etch, its done at a lab far away. I have done such etchings at a job i once had
              I get that a weld can be bad if it has porosity, cracks, slag, zones with no actual weld, lack of fusion (where the molten filler just wets the steel but theres no mixing), something something about grain structure
              I dont see why the thickness of the zone where metals mix is relevant. It cant be zero, so what should it be

            • 2 months ago
              Anonymous

              process is arc welding, 6010 and 7018

              • 2 months ago
                Anonymous

                6010 has better base penetration than 7018.

                What position?

              • 2 months ago
                Anonymous

                vertical, i dont see how thats relevant as the question has nothing to do with welding technique and its about the end product.

                >6010 has better base penetration than 7018.
                yes but also sort of not relevant

          • 2 months ago
            Anonymous

            If you are in a welding course he may just want you to add more heat to the weld. If you are say doing pipe welding you space the bevel apart so that you absolutely get 100%+ penetration. The instructor may be looking at your work and just think from experience that you will consistently get a higher quality result if you bias yourself to more heat into the work.

            I am not a welder, but it makes sense if you are a student to try and generate the type of results your instructor is looking for. Ostensibly he knows what is wanted in industry. Later on as you gain experience you can tweak your own technique to what you and your employer wants.

            • 2 months ago
              Anonymous

              >ou bias yourself to more heat into the work.
              this just means a higher current, right? I dont have a "heat" control dial

              • 2 months ago
                Anonymous

                Its been a couple years since I did any stick welding. Yes more current increases the heat. But speed of travel and arc gap have effects.

                https://www.millerwelds.com/resources/article-library/five-steps-to-improving-your-stick-welding-technique

              • 1 month ago
                Anonymous

                In welder vernacular "turn up the heat" means increase the current.

                As stick welders gain experience they often run "fast and hot" and find they get better results.

              • 1 month ago
                Anonymous

                >they often run "fast and hot" and find they get better results.
                So you mean doing higher current, faster material deposition and moving faster?
                I can see this reducing the width of the HAZ.
                Somewhat unrelated, in laser welding the process is very fast and the welds come out very deep and slim. This causes problems with porosity and cracks always near the root. I myself did thousands of such laser welds. I never tested their strength but i'll say that regarding cracks, the welds without root cracks and porosity were W I D E. Reasons: Going slow spreads the heat so the cooling is slow, that gives bubbles time to rise but theres also a hydrodynamic reason where the keyhole of molten metal is hydrodynamically stable only when its wide, a thin and tall tube of molten metal tends to collapse on it self randomly, trapping gas. You can widen the weld not just by going slow, but also by using a wide laser beam, not focused to an ultra small spot.

              • 1 month ago
                Anonymous

                ?si=A2kJgTEMDoCC0VRP
                related, this is what a keyhole looks like, its not like the puddle of arc welding, this "puddle" has a hole in the center were the laser beam is going in. The beam drills fast into the material and walls of molten metal are formed around it. These walls want to close but are held by gas pressures. Turns out that when the hole is shallow and wide like a donut, its harder for it to close on itself.

      • 2 months ago
        Anonymous

        I think the answer is you want to mix as little as possible because to melt more base material directly implies a greater haz. I think the weld nugget and base material are probably stronger than the haz - at least in steels. In tempered aluminum the entire weld and haz is going to be weaker than the base metal. I guess ideally because you want full penetration you probably want to lean toward the side of more heat than necessary - but just stay on the full penetration side of things.

        just my .02

    • 2 months ago
      Anonymous

      >you need full penetration to keep it together

      PrepHole virgin humor folks. It is what brings me here.

      • 1 month ago
        Anonymous

        9 days later but... hey buddy, you got the wrong door, collegehumor is two blocks down.

  3. 1 month ago
    Anonymous

    Kinda hard to tell with 100% certainty what exactly he's after but this is what I think he means. Pic related.

    So take the upper weld, circled in red is the corner of the base material. When you are welding the material you want to see that corner melting. You want to have enough heat to achieve this. Of course when you keep welding you start to 'feel' it's melting, you know it's melting, you don't need to stare at the corner all the time. If it's not melting it's a weld defect called lack of fusion or incomplete fusion. To test this you make a one pass fillet weld, then break the plates apart along the weld seam. You then inspect the break line. If you can see a straight line somewhere in there, i.e. unmelted corner, it's a fail because of lack of fusion. If it's all melted, it's a pass.

    Here's a decent youtube video about the test with a passed weld and a failed weld:

    Another example, take the lower weld, circled in red are all the corners of the base material. If you're welding it in one pass, same thing, you want to actually see all the corners of the base material melt while you're welding.

    • 1 month ago
      Anonymous

      I learned to weld fillets with 6010 for the root pass, then grind it and top it with 7018. I understand intuitively that its a stress point and the first place for a crack to start. However my question was that in "fusion zone" as described by your pic, how deep or thick must that be? I think it needs to be greater than zero mm... but i dont know how big it must be. Because if its too much then its said to cause some kind of metal fatigue due to crystalline whatever. But not enough is lack of fusion, some base metal has to fuse, the weld cant just be molten filler wetting steel

  4. 1 month ago
    Anonymous

    How much Admixture between filler and base metal depends on the application, mostly metalurgical, to much and annealing and or hardening can happen weakening the structure

    • 1 month ago
      Anonymous

      It depends on the way of deposition, short and multi pass stringers on large piece create less stress points as compared to flooding the weld with filler rod in one go

      • 1 month ago
        Anonymous

        Yes

        https://i.imgur.com/vmcyFiG.jpg

        You want the weld beam penetrate in to the middle of the parts, but any more power than that and you just add extra heat, making the HAZ (heat affected zone) larger. HAZ has significant changes in the microstructures of the steel, making grain size larger, and tempering the metal more further away. A larger grain structure has a lower yield stress, according to hall-petch equation, and is more ductile. The larger the HAZ the weaker the seam, especially the more variable the load on it is, because of fatigue. Heat treatment after welding can help, but is often expensive and time-consuming. Also in a non professional setting it can be difficult to get the temperatures right, and end up making the whole part weaker. Enough power that the weld seam goes all the way through the part, or halfway if you seam both sides, and not a bit more. Thats the perfect balance youre looking for. Lazers are much better welders because the keyhole puddle they create is much higher concentration of energy, making them much deeper penetration with less HAZ.

        And yes
        I had an argument with quality control once about having to do stringers on a part that was going to be fully heat treated, was i the butthole for saying since it was going past the curie point the grain structure gets normalized as if it was never welded granted some slight composition diferences?

    • 1 month ago
      Anonymous

      >l, to much and annealing and or hardening can happen weakening the structure
      Any way to fix this structure with heat treatment? Hardening i could fix just by heating and slowly cooling, no?

  5. 1 month ago
    Anonymous

    You want the weld beam penetrate in to the middle of the parts, but any more power than that and you just add extra heat, making the HAZ (heat affected zone) larger. HAZ has significant changes in the microstructures of the steel, making grain size larger, and tempering the metal more further away. A larger grain structure has a lower yield stress, according to hall-petch equation, and is more ductile. The larger the HAZ the weaker the seam, especially the more variable the load on it is, because of fatigue. Heat treatment after welding can help, but is often expensive and time-consuming. Also in a non professional setting it can be difficult to get the temperatures right, and end up making the whole part weaker. Enough power that the weld seam goes all the way through the part, or halfway if you seam both sides, and not a bit more. Thats the perfect balance youre looking for. Lazers are much better welders because the keyhole puddle they create is much higher concentration of energy, making them much deeper penetration with less HAZ.

    • 1 month ago
      Anonymous

      >HAZ has significant changes in the microstructures of the steel, making grain size larger, and tempering the metal more further away. A larger grain structure has a lower yield stress, according to hall-petch equation, and is more ductile. The larger the HAZ the weaker the seam,
      So if the HAZ is weaker than the base metal plate but the weld itself is stronger than the base metal, then the HAZ should be the weakest spot in the plate?
      This means one ought to design a structure with steel that is extra thick in the HAZ region as a form to compensate. Am i right? Because otherwise it will break there, its as if the whole thing is built from HAZ

      • 1 month ago
        Anonymous

        It's more brittle, as in less tolerant to dynamic stress, welded cast iron is an extreme example of this as it can crack during cooling without even being touched, the base metal is really hard to begin with.
        > extra thick in the HAZ region
        There's 2 problems:
        Thicker meral needs higher current to be welded effectively, or longer time which results in a larger HAZ, this effect is evident if you've ever welded stainless steel
        Second issue: the weld failure occurs on the weakest part of the metal structure like everything else. In this case that part would be exactly in the transition area between the thick and regular thickness of the part. It's also harder to fabricate and adds weight.
        You fight HAZ with increased deposition speed, intermittent welds and multiple narrow beads.

        • 1 month ago
          Anonymous

          >You fight HAZ with increased deposition speed, intermittent welds and multiple narrow beads.
          Ok but in principle are you saying that welded metal structures will always be weaker than the base metal?
          Basically, if one were to do some butt weld between two steel strips and put them in these test machines that pull them apart, they would snap at a lower tension than a continuous steel strip?

          • 1 month ago
            Anonymous

            >Ok but in principle are you saying that welded metal structures will always be weaker than the base metal?

            Virtually any discontinuity of any type in any material will be weaker than a homogeneous solid of the same material. Stress risers alone ensure that. The effects of heat on steel are just icing on the cake.

            There's a reason some steels (like 1018 or A36) are categorized as "weldable" and others (like the majority of hardenable steels) aren't. Weldable steels generally low carbon/low alloy types, because they don't respond readily to the normal heat/quench cycle that's used to harden other steel types. A hot weld bead takes that same cycle to pretty significant extremes locally, resulting in a spot that is extremely hard and brittle (which happens to any hardenable steel), has metallurgy significantly different than the parent material (like stainless alloys becoming no longer stainless) or both.

            For weldable steels, you just live with it. A good weld might be weaker than no weld at all, but not by much. You might want some kind of heat treat afterward, like stress relieving, depending on the alloy and application. For the steels that aren't readily weldable, like medium-carbon stuff (1045, 1060), you can usually get away with it by using pre/post heat, and/or doing the regular heat treat of the part afterward. Anything else, you're looking at either some more exotic process (like forge or laser welding) or just designing around a part that can't be welded.

  6. 1 month ago
    Anonymous

    looking good does not mean weld strength. also this is not a subject for debate, this is long established facts. a lot of amateur welders actually are terrible and don't know it.

    • 1 month ago
      Anonymous

      Some amateur welders are alright due to the fact that they make actual welds as compared to the shit you see on youtube, "cold" welding and series of tacks with SMAW we all know.
      Good looking welds are a misunderstood rule of thumb, good looking doesn't mean technologically correct but ugly usually does mean bad, porous and full of undercut. My instructor taught me to make welds that are slightly uglier than the ones from Instagram, which is a misleading analogy but the point is to focus on doing the job correctly

  7. 1 month ago
    Anonymous

    Go read your wps and stop asking questions

  8. 1 month ago
    Anonymous

    [...]

    Another way to blow minds is appropriate use of torch brazing, which we used on steel rule fabric cutting dies for easy frequent repair. (They're like big cookie cutters for fabric and driven by mechanical presses.)

    Brazing joins dissimilar materials nicely and repair is cake.

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