Blow Through

[rorie]

Hi folks.

I am very new to welding. I have a cheap 30-135 amp mig welder. I have been practicing my runs and getting on fine. I then took 2mm plate and practiced joining them. I then mounted them vertically and tried that - all was going well.

I then moved out and tried on my car chassis…. After a second day of getting nowhere fast, i am pretty hacked off!

I have it on setting 4 (of 6) but can't get a pool on the go without blowing through, so of course i reduce the power…but i was still blowing through! So i guess my question is: Is too much power the only cause of blow through?

Also, when filling holes i find i blow through even easier! Is there a special technique for this?

As you can see from the photo, although i am blowing through, it doesn't look to be penetrating the parent metal properly!

Thanks!

 

[Welderpaul]

Are you leaving such a big gap between sheets? Close the gap up!

 

[Shedendman]

size of wire your using?
gas or no gas wire?
what type of gas?
Your steel looks very clean indeed,but have you ground it down so thin its like paper as Mrfuzzy said,car body panel are quite thin.
Short runs and step them out a bit ie do a 10mm run then move to another area then another 10mm run let it cool down,then back to the first run,so on and so on

 

[Kent]

Old cars aint so easy as nice sheet, sometimes strike that OFTEN the corrosion is hidden by disguising itself as sound metal. Like others have said its thinner than most usual sheet metal and the gap "fit up" needs to be good. Try shorter runs also back-stepping so you not banging into the hottest spot again.
The photo might actually be a case of over grinding its hard to say. I don't know what and were your welding but that bit looks like a backing and a series of plug welds might help even if it needs a run along the seam after

 

[rorie]

Over grinding….oh yes! I have been welding, grinding, welding and grinding! And getting very frustrated throughout!

I am using 0.8mm wire with gas. I was working on the premiss that the new steel is 2mm, but as you say, the old steel is unlikely to be that thick.

I am guessing the power is indeed too high then for the thickness of steel. I'll try tomorrow with lower settings and report back!

Thanks for the help so far!

 

[Kent]

Over grinding….oh yes! I have been welding, grinding, welding and grinding! And getting very frustrated throughout!

I am using 0.8mm wire with gas. I was working on the premiss that the new steel is 2mm, but as you say, the old steel is unlikely to be that thick.

I am guessing the power is indeed too high then for the thickness of steel. I'll try tomorrow with lower settings and report back!

Thanks for the help so far!

You see you have I think over ground, is it a part you can leave the bead well alone? if so then do this. Just clean it up weld it and let it be. I don't like what I see to be the fit up I should prefer a corner to corner abutment prior to welding or a backer behind the joint plug welded in and then the seam welded. Never expected to learn this in a weekend did you?

 

[Richard.]

What exactly are you reducing. By power do you mean the voltage?
This won't help much. You need to look at reducing the WFS first then adjust the voltage to suit. WFS is your penetration and cause of burn through. As Paul said you need really tight fit up. Gaps make life difficult.

 

[Kent]

What exactly are you reducing. By power do you mean the voltage?
This won't help much. You need to look at reducing the WFS first then adjust the voltage to suit. WFS is your penetration and cause of burn through. As Paul said you need really tight fit up. Gaps make life difficult.

I think it best to say "balance of one 'n t'other" Reducing WFS is likely to make things harder without understanding what the right balance actually looks, welds and sounds like

 

[Richard.]

Which is why I said adjust voltage to suit.

 

[Richard.]

Any how. I've come across this issue many times and the general thought that crosses the welders mind when burning through is s%#t turn down the voltage.
This makes for more problems as the arc width is then reduced further and it actually worsens the problem. A slight reduction in WFS leaving everything thing else the same is a good place to start. More often that not it resolves it if the settings are somewhere near to start with.

 

[Kent]

Richard,
The point I am making is if the OP understood exactly what your saying he wouldn't need help.

 

[Richard.]

Mate I don't follow. He hasn't replied so what makes you think he doesn't understand what I'm saying. WFS (sorry. Wire feed speed).

 

[Kent]

Just thought it a very bold statement to make that's all. Have visions of the guy struggling with implementing it as you might intend and ending up in a right old muddle with his settings (this is why people say "frying bacon" even though my bacon never makes that noise) it simplifies set up, I might say BiZZZZZZZ, BiZZZZZZZZ but someone could take that as spray transfer. What you mean is more towards trimming up right? once your about there and actually not so relevant to the joint at hand which could be done with a fair range of settings well by a guy with plenty experience. Too much wire or too little wire is in short far worse than lack of trimming up just trying to avoid that
I couldn't ever possibly presume to tell someone to do anything with their MIG settings without seeing or hearing it in action personally.

No, getting a good corner to corner fit if possible, backing in place (again if possible), clean sound metal before the welding starts, no challenging gaps and a good return contact are about all that can be said at least to my mind. Oh and don't grind it all down to nothing afterwards

 

[Richard.]

I think your looking to find fault with my comment there Kent. It was pretty simple straight forward and worth a try as it might help.
Turn down the wire speed rather than the voltage and try it. Not much there to muddle really.

 

[Kent]

sorry you feel like that I just tend towards disagreement on the matter of reducing wire feed because of its effect on arc length and stability, especially when your not flat on a bench but twisted under a car. Running a bit too high with a little too much wire than the ideal you can get by pausing and back-stepping even blobbing in. Too little wire is harder than too much in practice and most who struggle will be edge of field settings wise
I am not much of a theory man when it comes to MIG mind and learnt mainly hands on over thousands of hours burn time, indeed for the first two years the college I was released to didn't even have MIG just MMA and OFW. What you hear and what you see takes time to learn (some in my experience never really get it)

 

[Richard.]

Come from a fabrication back ground myself and the theory side of things I have learnt through self funding of overpriced TWI courses and working along side some of the most knowledgable people. And general interest to learn.
Look back to the original post.
" other than reducing the power what else can cause burn through" was his question. My answer was valid. Reducing the power or voltage will make things worse. He needs to know that because he'll be creating more issues. So he's looking at playing with the settings and voltage ain't working so why not change wire speed it's probably the only setting left to change on that so It makes perfect sense than to spout up about sounds and hours under the hood etc. that's only helpful if your standing over the guys shoulder.
Turning WFS down does not make the arc unstable if it's set too high in the first place which it might be.
None of this matters he's not interested in the help as like many fly by members they get what they need and F off.

 

[ms08]

I am very new to this activity and can understand what is being said. My welder has four power settings (switched) and i am working on car bodywork. Whilst i have the wire speed set in the lowest 'band' it is not right at the bottom of that and has been suggested to me on Saab forum to reduce the wire feed to see if my 'blobs' improve. Can't get enough of this at present and was proud of my three small spot welds holding a captive bolt into a plate.....bolt was still bloody hot when i went to pick it up though

 

[Kent]

Richard,
Lets agree to disagree, although I get what your saying I just don't think you can get set up tuned up by the written word past the term "frying bacon etc" .

 

[Richard.]

It's a deal.