Weld porosity
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Senior User
Joined: Nov 2003
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From: WA
Weld porosity
I am currently fabricating a front bumper with 10" channel iron and I am using a lincoln model 200 MIG welder. If I remember right it was set on F with a wire speed of about 325-350. Once I finished welding a 3 foot long stretch of material I had a bead width of about 1/4"-3/8" and it actually looked pretty good. However, when I started to grind it smooth I noticed all sorts of small tiny pits in the weld. The wierd thing was that before I ground it down there was no pits visible at all. Was I moving too fast? what do you guys think it was caused by? Is there a way to prevent this from happening again? Also, what is the proper movement technique when welding with a MIG? I was moving in a "C" pattern.
Thanks.
Thanks.
Senior User
Joined: Nov 2004
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A few things could have caused it to happen. 1- too much heat, 2- travel speed (with your hand) too fast 3- poor metal quality.
As long as the weld is solid I would use some surfacer, sand & paint. I have spent hours welding, grinding & rewelding TRYING to get it "just right" only to find out it was a problem with the metal. Greg
As long as the weld is solid I would use some surfacer, sand & paint. I have spent hours welding, grinding & rewelding TRYING to get it "just right" only to find out it was a problem with the metal. Greg
Tuned
Joined: Feb 2004
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From: Missouri
Originally Posted by gbadgley
A few things could have caused it to happen. 1- too much heat, 2- travel speed (with your hand) too fast 3- poor metal quality.
As long as the weld is solid I would use some surfacer, sand & paint. I have spent hours welding, grinding & rewelding TRYING to get it "just right" only to find out it was a problem with the metal. Greg
As long as the weld is solid I would use some surfacer, sand & paint. I have spent hours welding, grinding & rewelding TRYING to get it "just right" only to find out it was a problem with the metal. Greg
Posting Guru
Joined: Apr 2005
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From: Edgerton, WI
It really depends how bad the porosity is too. If its very small pits that are fairly spread out, I wouldnt even give it a second thought.
However, if the pits are fairly large and not spread out, Id grind it out and try again.
With MIG welding you need to metal to be as clean as possible. MIG doesnt work well if the metal has oil or paint on it.
Octane
However, if the pits are fairly large and not spread out, Id grind it out and try again.
With MIG welding you need to metal to be as clean as possible. MIG doesnt work well if the metal has oil or paint on it.
Octane
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Joined: Mar 2005
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From: Summit, MS
Highboy,
I'm gonna guess you had one or more of these: 1) dirty/rusty/oily metal 2) wind 3) poor gas flow. If the weld looks like styrofoam on the inside, then it is not just a cosmetic issue. That weld is no good and needs to be ground out, problem fixed and rewelded. Let me know if I can help you figure it out.
I'm gonna guess you had one or more of these: 1) dirty/rusty/oily metal 2) wind 3) poor gas flow. If the weld looks like styrofoam on the inside, then it is not just a cosmetic issue. That weld is no good and needs to be ground out, problem fixed and rewelded. Let me know if I can help you figure it out.
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Hotshot
Joined: Feb 2004
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From: Marengo, Iowa
It could be as simple as the tank was low, making the flow not adequate. It sounds to me to be a gas issue, if the whole weld was this way. I've gotten away with welding right through oil, just turned the gun such that the flame went ahead of the weld, burning the oil off before the weld got there. When you weld for production numbers, and the company is too cheap to prewash the parts, you do what you have to to get the numbers. But back to the task, if you had a fan blowing on you whilke you were welding, either turn it off, hold the gun closer to the weld, or turn up the gas flow. It is possible you were holding the gun too far away from the weld to get adequate sheilding. You need to be as close as you can get without catching the nozzle on the weld. Watch out for slag buildu too, inside the nozzle, it will cut your sheilding gas flow, on the end it will catch in the weld and make a mess too.
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Joined: May 2005
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I agree with fellro86, the two main reasons for weld porosity is not enough cover gas and metal prep. You need to grind away all mill scale, rust, and grime. Get down to the good metal. Good cover gas is the most important. You should be running about 30 on your regulator. Make sure there is no breeze blowing your gas away. If there is porosity in your weld grind it all out and run another bead. I've been mig/stick welding for 20 years, my best advice is to take your time and do it right the first time. PM me if you have anymore questions.
Senior User
Joined: Mar 2005
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From: Summit, MS
You can get away with welding thru oil if it is light and only on the surface, but that's about it. Paint, plastic residue, grease, bondo, etc. will all outgas when they get hot and cause porosity, even if they are on the underside of the bead. Clean metal, plenty of cover gas gives good weld. Otherwise, not so good weld. Could be your hold-off is too long like fellro86 said, again a gas problem.
Hotshot
Joined: Feb 2004
Posts: 11,697
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From: Marengo, Iowa
Yeah, I don't recommend trying to go through the crud as I had stated, it was a heavy forming oil, but I would have rather not have had to do it. Clean materials make life easier, and things like bondo and bugs don't weld well... The bugs thing is from when I have welded and wasps kept flying into the flame, messing up my welds... tends to make a nice gas bubble...
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Hey, Welders out there - What about the angle of the gun? Should highboy 74's direction of gun always be pointed back into, or at the weld? If the sheilding gas (nozzle) is directed away from the puddle, where is the sheild? MIG welding is great in many applications, but in an inexperienced situation such as this one, I would reccomend a SMAW.
I have had to deal with this very same problem several times on the job (Pipefitter), fabbing in shop with an inexperienced MIG welder. Gun angle in relationship to the 'puddle' is critical.
I have had to deal with this very same problem several times on the job (Pipefitter), fabbing in shop with an inexperienced MIG welder. Gun angle in relationship to the 'puddle' is critical.
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From: WA
I believe the gas regulator was set at 20 psi with 50 PSI left in the bottle. The weld is porous only through the top 1/32". The holes are round and spherical about the size of the tip of a pen or smaller. It was on a butt weld that mated two pieces about 1/4"-5/16" thick and the porous pits are only in certain areas and not over the entire weld. I do believe there could have been an ever so slight breeze when I welded that day. The structural ridgity of my weld is far from compromised and has no structural bearing on the bumper, it is purely cosmetic. I just need to prep it for the finish coat. I also wonder which way my gun should be aimed and what distance it should be from the work. I have both melted my nozzle (2 or 3 as a matter of fact) for being too close and also spattered terribly from being too far away. Any and all comments are greatly appreciated. I need all the advice I can get and would love to make perfect welds in the future.