A machines rated metal thickness and penetration...how do they figure?

[kris396ss]

This is something I have always wondered. I work for a race car/hot rod speed shop and we do a lot of fabrication work. I am pretty new to it (been a mechanic for a while but only welding for a little over a year now) but I get a lot of experience and training from a very talented fabricator. At work as far as MIG machines go we have a Miller 175 and a Miller 212. I recently bought a Miller 211 for my own use at home. We run them on 50 amp breakers at work and at home I have a dedicated 40 amp for the 211. All these welders are using an Argon/C02 mix for mild steel.

One thing that has always puzzled me, is that for any of these machines when welding metal thicknesses at the end of their rated range (or really just about anything much thicker than 1/8th inch plate) none of these welders would really penetrate completely on a butt weld of two pieces without beveling the edges. If I took two pieces of 1/4 inch or 3/8th's plate, butted them together and cranked my Miller 211 on high, even with a slow hand , pushing the bead up hill and thick wire I don't think I would ever see a weld that would penetrate through the entire thickness of the metal.

This just gets me curious. What exactly DO they consider when rating these machines for particular metal thicknesses?

[Ls2cam]

Good resource>>>

http://www.millerwelds.com/resources...calculator.php

[MR.57]

Good resource>>>

http://www.millerwelds.com/resources...calculator.php

That calculator is awful, especially on the high end. I don't know where they came up with some of the numbers, but they just don't add up in real life.

This is a much better guide.
http://www.millerwelds.com/resources...welding-basics

[kris396ss]

thanks for the links guys, great guides for sure....not to sound like a **** but it doesn't answer my question though.

[engnerdan]

Anything thicker then 1/8 and you need to start putting a bevel on it. You just will not get the penetration you are looking to get. Even with the 211 cranked I think you would be looking at multiple passes with solid wire on 3/8 stock or maybe a single pass with flux core. I have never used a 211, the closest thing I have used is a passport plus at 180 amps. I know that will not do 3/8 in one pass. If I need more heat then that I turn to my Trailblazer and/or flux core wire.

-Dan

[kris396ss]

Thanks, so im not crazy. I know what the guys above were hinting at when they posted the links, obviously the first step towards proper penetration is knowing how to weld. I get that though, and like you said...no matter the technique, most welders simply WONT be able to fully penetrate a butt weld on metals at the end of their rated spectrum without beveling the metal first....

So how DO they rate these welders and figure out what thickness metals they are 'able' to weld? Because they obviously don't rate them as a function of what thickness metals they can fully penetrate in a butt weld...because we all know that wont happen. Maybe i'm wrong, but in my welding experience you aren't going to just blow through 1/4" steel plate for example even on welders that are rated to 1/4" no matter what the technique. Is there a standard bevel angle they rate machines with, or another way I am missing here?

So the question in short, when my Miller 211, or the shops 212 or any welder states on the inside of it's door that it's capable of welding 3/16's, 1/4, 3/8's ect... how do they figure that when it obviously wouldn't get full penetration on a butt weld of that thickness metal?

[Donald Branscom]

This is something I have always wondered. I work for a race car/hot rod speed shop and we do a lot of fabrication work. I am pretty new to it (been a mechanic for a while but only welding for a little over a year now) but I get a lot of experience and training from a very talented fabricator. At work as far as MIG machines go we have a Miller 175 and a Miller 212. I recently bought a Miller 211 for my own use at home. We run them on 50 amp breakers at work and at home I have a dedicated 40 amp for the 211. All these welders are using an Argon/C02 mix for mild steel.

One thing that has always puzzled me, is that for any of these machines when welding metal thicknesses at the end of their rated range (or really just about anything much thicker than 1/8th inch plate) none of these welders would really penetrate completely on a butt weld of two pieces without beveling the edges. If I took two pieces of 1/4 inch or 3/8th's plate, butted them together and cranked my Miller 211 on high, even with a slow hand , pushing the bead up hill and thick wire I don't think I would ever see a weld that would penetrate through the entire thickness of the metal.

This just gets me curious. What exactly DO they consider when rating these machines for particular metal thicknesses?

There have been several posts like yours on this forum lately.
Need to make a distinction about how much current the welding machine draws and how much amperage output the welding machine is set on.


You can look at your instruction manual and look at the graph or other info given to you to determine how much current is being drawn by the welding machine for the amperage you are welding with. Two different things.

A transformer machine is making AC into DC. So there is a conversion factor.
Also transformers can step up the current just like transformers on telephone poles.

As far as what it takes to penetrate a steel plate that is another thing.
No one is trying to penetrate a plate with a welding machine. You are always melting together edges of joints. A fillet weld on a T joint does not usually penetrate the bottom plate. And some T joints are beveled on one side or both on thicker sections.
The reason most weldments are welded on both sides
IS TO GET FULL PENETRATION of the base metal.

In a extreme emergency (rare) you can take a stick electrode like a deep penetrating E6010 rod and blow a hole through a piece of plate, if you do not have a torch available. Old welders secret.

But welding is about welding joints,edges, and gaps. Not penetrating a flat plate.
And the larger the plate the more amps it would take. So it is NOT just the thickness of the plate. Outside air temp is a factor also.

[GilaSlim]

So the question in short, when my Miller 211, or the shops 212 or any welder states on the inside of it's door that it's capable of welding 3/16's, 1/4, 3/8's ect... how do they figure that when it obviously wouldn't get full penetration on a butt weld of that thickness metal?

When the manufacturers publish a thickness rating to a welder, they are assuming the potential buyer/user has sufficient training and experience to apply the required bevel and/or gap to the joint.

In other words, "If you know how to do it, this is what it will do."

[Paul Seaman]

To achieve the max end of a machines capability, you must have more technique. A weave on mig with hang out time on each side of the joint and quick in the middle will help. Also there must be a root opening to achieve max penetration. On 1/4" I use say 1/16"- 1/8". My start will be slightly off cneter and count one,two the fast accross the center, then one, two then back fast accross the center. If you go too far foreward it will look like stiches with lumps. If you don't go far enough you will get humps {overfill** or blow out the back. Practice, practice, practice.

Peace,
Paul