|
|
Just a question. I watched one of Jody's videos (weldingtipsandtricks.com) talking about downhill mig and lack of penetration. I also read that if the material is too thick for the machine, a "good" weld can be made with multiple passes. So my question is this, why would multiple passes help if there is little to no penetration? Wouldn't the filler metal just pile up and sit on top? I'm just curious. Looking at Jody's video and seeing the weld profile after etching just made me wonder. Then again, he was talking about downhill mig. Mike
Reply:Hello Mike, the main thing about downhill welding is that the puddle can often out-run the actual penetration/fusion portion of the arc and thus doesn't allow for a bond between the welding bead and the parent metal (think the effects of gravity). This will occur when improper technique is used or the abilities/settings of the welding machine/power source/process utilized aren't properly applied. When you are welding on something that is thick and that particular welding combination isn't rated to weld in a single pass, multiple passes can be used. These multi-pass applications simply require good fusion between the passes/layers in order to provide a sound weld when applied to materials thicker than say, a smaller mig welder can weld in a single pass.If fusion exists and cold-lap isn't present or voids aren't included in the welding process you can weld many items that seem overly heavy for a particular machine combination. That's the key in a nutshell. Good luck and best regards, Allanaevald
Reply:I know one thing don't try a bend test using 1/2" plate running a down hill MIG .035 wire. Open root Double V Groove test, weld root on one side, back gouge the other side with the grinder, put a root in that side. Then cap it out. It failed every time except once. The one I welded still showed signs of tearing on the corner, but that can be disregarded if there is no sign of inclusion from where it started. We switched to 3/8" plate and all of them passed much more easily. I think the weld metal itself on 1/2" just cant stretch enough in a bend.Last edited by AndrewDavenport89; 04-23-2015 at 03:10 PM.
Reply:Good penetration to me means abundant base metal dilution into the weld resulting in generous tie in to the root, but could result in "cold lap" at the toes. A good weld IMO does not need generous tie-in, but adequate tie-in, and "good" wetting at the toes.Sometimes a giant single pass weld is worse than smaller multiple passes.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Originally Posted by Hambone2004Just a question. I watched one of Jody's videos (weldingtipsandtricks.com) talking about downhill mig and lack of penetration. I also read that if the material is too thick for the machine, a "good" weld can be made with multiple passes. So my question is this, why would multiple passes help if there is little to no penetration? Wouldn't the filler metal just pile up and sit on top? I'm just curious. Looking at Jody's video and seeing the weld profile after etching just made me wonder. Then again, he was talking about downhill mig. Mike
Reply:Originally Posted by shovelonSometimes a giant single pass weld is worse than smaller multiple passes.
Reply:Originally Posted by aevaldHello Mike, the main thing about downhill welding is that the puddle can often out-run the actual penetration/fusion portion of the arc and thus doesn't allow for a bond between the welding bead and the parent metal (think the effects of gravity). This will occur when improper technique is used or the abilities/settings of the welding machine/power source/process utilized aren't properly applied. When you are welding on something that is thick and that particular welding combination isn't rated to weld in a single pass, multiple passes can be used. These multi-pass applications simply require good fusion between the passes/layers in order to provide a sound weld when applied to materials thicker than say, a smaller mig welder can weld in a single pass.If fusion exists and cold-lap isn't present or voids aren't included in the welding process you can weld many items that seem overly heavy for a particular machine combination. That's the key in a nutshell. Good luck and best regards, Allan
Reply:Originally Posted by ZTFabHe also used Hot Rolled material with no surface prep. That weld was destined to fail from the start as he set it up to.
Reply:Originally Posted by AndrewDavenport89I know one thing don't try a bend test using 1/2" plate running a down hill MIG .035 wire. Open root Double V Groove test, weld root on one side, back gouge the other side with the grinder, put a root in that side. Then cap it out. It failed every time except once. The one I welded still showed signs of tearing on the corner, but that can be disregarded if there is no sign of inclusion from where it started. We switched to 3/8" plate and all of them passed much more easily. I think the weld metal itself on 1/2" just cant stretch enough in a bend.
Reply:Well I might have went a different direction with your question haha.
Reply:Automatic pipeline welding with MIG I believe is done downhill with short circuit transfer.
Reply:Originally Posted by Welder DaveAutomatic pipeline welding with MIG I believe is done downhill with short circuit transfer. |
|
发表于 2021-8-31 22:38:24