Bottom of plate from weld.

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How does the penetration on the bottom side look from my previous post?Thanks! Attached Images
Reply:Just looking and remembering from your other thread I'd say that must be .083 thickness. I see blistering and almost complete burn through. That means you are plenty hot and getting good penetration.  Most of the time 'penetration' is what you hear and try for. It also re-inforces the idea that maybe you could focus the arc on the tubing a little more.There are some cases where good fusion is as improtant or more so than penetration. This may be one of those cases. What you'll have here is a very hard weld bead set well down into the plate with the HAZ surrounding it.  In the likely event of extreme forces on the roll bar you could experience "tear out' on that type of weld.  Little less heat and concentrate  more on good fusion and you'll end up with a less dynamic affect on your plate that you'll be bolting down for the roll bar. Fine line between penetration and adequate fusion sometimes and it's a rare case where deep penetration isn't desirable.  Wait for one of the real experts to slap me around and set me straight before you go making a bunch of adjustments based on my comments alone."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:Yes the metal size is .083, sorry.  So then the blistering is not always a good thing.  What should a back side of a weld look like?  How do you know if you are actually getting good penetration?  Thanks!Build a Barstool Racer at BarFlyRacers.com!
Reply:>I was waiting for someone else to weigh in here but they haven't.  Blistering is a good indication that you are right there, and running at max for that metal thickness, just about ready to melt the whole thing down. Your penetration is at near max. However, this melting and freezing is pretty stressfull on the parent metal. It will never be the same as it was before you welded it, maybe harder and more brittle, maybe softer, maybe a combo of both in varying zones throughout the welded area. One problem with thinner gauges, believe it or not, is there is always some movement and flexing. Now you have a hard circle surrounded by safter flexing metal. Cracks may develope slowly or tear out all at once. In this case it is better to keep the impact on the parent metal minimized while obtaining maximum fusion to the base material. The line between the fleixible structure and rigid weldment will be less defined.  Fusion is melting and blending your filler partially into the base material. Much of the strength in this situation is going to come from the thickness of the bead, as well as good fusion.Scary part is with mig it's tuff to tell at a glance whether you've obtained good fusion or just a hot glue job. An occasional blister, okay. Blackened on the back, and a slight raised hump corresponding with the weld bead is good. Take a flap disc and hit it like you're trying to sand it smooth and you'll see this mirror image of the bead on the back side.  Best method is to weld some samples, cut them in half with a band saw and take a look at the cross sections.  Time consuming but well worth it."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:On mild steel heat doesnt tend to hurt much and insures good fusion. At that thickness thats about what I would expect to see on the back.  As Sandy was eluding to there is a difference between penetration and fusion. In many or most cases penetration is a function of joint design, it allows for penetration. Technically this fillet type joint needs no penetration, only a well fused fillet equel to to the thickness of the thinnest piece. Anymore is essentially a waste of material.  These are somewhat generalizations.www.urkafarms.com
Reply:While I am not sure exactly what this product is for, but if you have your heat and wire speeds set, as they are now, and want a better apeearing weld, perhaps trying to rotate your product underneath your gun rather than "walking" around it should produce a smoother, "one piece" weld, provided your material can withstand the continous heat. Instead of three "crescent moons" on the backside, you would see one complete circle with a starting point and a finish point.  Plus on the weld side, you would only have the start/finish point to interrupt the weld.Again, I dont know what this is for, but if there is any need for asthetics on this piece, rotating your product may help.I weld up alot of forklift tilt cylinders and we use 7018 rod, but we chuck our cylinder up in a lathe and turn in (by hand) under the electrode. The low hydrogen rod gives it strength and the continous bead minumizes the chance of future cracks. I know if I weld it without the lathe, it will crack again.Doc.Last edited by NTOLERANSE; 11-01-2004 at 10:20 PM.Some of the things I do would cause a person to get hurt, expelled, arrested, or possibly deported. To put it another way, don't try this at home.Look at the stars whenever your can. That light travelled a long way to get here, dont let it go to waste on some patch of asphalt.
Reply:What I was doing was some test welding to lean to wel rouund tubing.  I am working on intalling a roll cage in a car so I do have the option of rotating it.What makes it so hard to weld is the wire speed for the thick metal.  I find it easier to use FCAW (if I can see through the smoke) because the wire speed is slower.Build a Barstool Racer at BarFlyRacers.com!
Reply:If you are using straight CO2, go to an argon mix and it will cut the heat so you can weld slower and cleaner