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  #11  
Old 12-25-2005, 10:08 PM
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Default Re: metal thickness and mig welding

Most of the 175 model machines I have used will do 1/4 no problem. I have welded 1" with min, Beveled the pieces and make multiple passes, When I was done do a filler pass slow and plenty of wire speed and it has yet to fail as a hinge point on a piece of farm machienery. If you have a quality welder properly set up it is up to you to make the weld proper. As said before Practice,,,
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  #12  
Old 12-27-2005, 01:01 AM
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Default Re: metal thickness and mig welding

we have a hobart handler 145 here at work and i have yet to find something i cannot weld with it--does well on mild or stainless--only thing i have yet to try is aluminum--but i would normally just TIG aluminum anyways

my personal view on flux core wire cannot be displayed in this "family" environment [img]/ubbthreads/images/graemlins/grin.gif[/img] even though i'm sure there are times when nothing else will work--i just cant stand it,[img]/ubbthreads/images/graemlins/mad.gif[/img] if i wanted to clean up a mess i'd just stick weld it ya know?

i have literally made fixtures out of 1/2" plate steel with nary an issue--with good preparation all things are possible
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  #13  
Old 12-27-2005, 01:53 AM
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Default Re: metal thickness and mig welding

"""""Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, but sometimes pressure is used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces."""""

Sure, you can "weld" something 10 feet thick with a tiny welder - with enough passes. But would it be Strong?

Welding is melting the base material together, then adding a little filler material to fill the void created.

Without enough heat, all that happens is the filler melts a tiny layer of the base material to stick to.

Cut across the weld with a grinder or chopsaw. Soak it in acid a few minutes - you'll see how well it "melted" into the base material.


Ever try to cook a pizza with a propane torch?
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  #14  
Old 12-27-2005, 08:02 AM
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Default Re: metal thickness and mig welding

[ QUOTE ]
Sure, you can "weld" something 10 feet thick with a tiny welder - with enough passes. But would it be Strong?

[/ QUOTE ]

Yes. A friend who is a union ironworker worked on Lock and Dam 26 at Alton. One of the projects he worked on was one of the lock gates that is a huge curved plate mounted on arms that swing the gate down to the bottom of the lock chamber so that tows can pass above it. I think that it is called a Tanner Gate.

It was assembled in place and he and several other ironworkers spent many days, in shifts around the clock, welding the arms to the gate. It was summer, but they used heating blankets constantly to keep the steel warm, and tents to keep the wind off.

They would spend an entire shift laying in pass after pass. Then at the start of the next shift an engineer crew would come in and X-ray the weld. If there were any flaws they were gouged out with an air-arc. Then the next crew would start laying in weld.

It's been ten years or more and I don't remember a lot of the details, but I think the welding went on for several weeks. And I believe that when they were finished with the welding they spent several more days, if not weeks, with the heating blankets slowly cooling the assembly.

The Corps of Engineers is happy, and the welds haven't broken. So yes, multiple pass welds can be strong. I believe the consideration in multi-pass welds is 'wetting', which says that if the new weld bead wets, or melts into the surface, it is bonded. The surface is as strong as what's under it, so there's no need to penetrate a great distance into the base metal.

Of course, they didn't use a 110 volt inverter to weld it, they used BIG welders so that they could burn lots of BIG wire into the puddle, and do it hour after hour without stopping. Their progress was discussed in terms of pounds per shift. But the principals should hold for a smaller weld with a smaller machine and smaller wire; it's all in the joint design, preparation and technique. If they're right you will have a good weld.

Where penetration really becomes critical is in a joint where the pieces aren't V'd out. If you butt the square edges of two quarter-inch plates together, your machine better be capable of melting a puddle a quarter inch deep.
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  #15  
Old 12-27-2005, 11:49 AM
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Default Re: metal thickness and mig welding

I can confirm that your welder will do a good single pass weld on 3/16 butt joint (gapped and beveled), having tested the welds by hammering them over with a sledge hammer. I'd suggest that after you get your technique looking good, make some sample joints of the type you plan on doing for your project and do some destructive testing. After you get the metal to break, note where it breaks off. The weld bead should be slightly thicker than the metal itself, so it shouldn't break, nor should it tear away from the base metal without ripping apart, showing incomplete fusion, as Rich has refered to. You may have penetration, but you don't want a cold lap that looks like fusion but isn't. That is the real problem with mig welds that "look" good but really are not. You see this sometimes when you tack weld something in position, then snap it apart to reposition it. Not enough heat and what looked like a weld was really more like glue.

You will love that SP-175. But its important to know its limits.
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  #16  
Old 12-27-2005, 11:58 AM
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Default Re: metal thickness and mig welding

When doing multiple passes the idea is to make the filler melt into the base material deep on the first pass. The second pass has to melt deep into the first pass's bead.
The third and subsequent passes have to do the same.
On each pass the filler "becomes" the base material.

A little welder not much more powerful than a hair dryer just doesn't have the ability to not only melt the wire, but melt the part it's trying to attach to, plus compensate for the heat sink effect of the rest of the material surrounding it.

Sure, it can be "stuck together" but it's not near as strong as if it was done properly.

Properly engineered - over engineered - and done by professionals sometimes is necessary. Most home welders don't have the skill or a hot enough welder to make it as strong as it should be, nor do they have the ability to keep it hot - like the heat blanket. And they certainly don't have the ability to x-ray it. It can be very dangerous!

Ever see a tow hook come off? A bumper when you were winching from it? How 'bout a shackle mount?
That's why I'm against advising folks to do multiple passes -- especially when they are first learning.


Comical when it happened, fortunatly it wasn't a tragedy -
Saw a guy winching his friend out of sand - the entire bumper, winch and all, pulled right off! The remote control stuck "on" - till the wires pulled loose. The guy panicked when it started to pull loose, but the solenoid stuck and he couldn't stop it. He was jumping around screaming - really funny to watch. But it could have been a real problem if he'd been winching up a hill or something critical.

It was done with a 110 volt welder with multiple passes. And the welds looked very good! But looking at the broken welds afterwards it was obvious it all went on cold - barely any penetration at all. I hope he never tests his roll cage - which he welded himself too!

That's the biggest problem with MIG - you can make it look pretty without strength or penetration - it can easily fool you.
Stick's harder to do that. Usually if it looks good, it is.

When practicing every once in a while cut across the weld - preferably with a chop saw. Soak the cut in acid till it shows the grain. You can see the penetration - how deep it actually melds into the base material.

Try breaking the weld - the break should be as far away from the bead as possible, showing penetration. Use acid on that broken weld - you can see the stress risers!

Penetration is not only getting the filler deep in the joint, but deep into the base material too. Neophytes often judge by how far it got into the crack.

Hmmm, that explains it - my ex had stress risers on her legs! I guess she wasn't welded right.
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  #17  
Old 12-27-2005, 04:29 PM
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Default Re: metal thickness and mig welding

I'm with you 100%. Probably should have put more emphasis on design, prep and technique. All three must be at levels no beginner will have. And if the joint is critical, non-destructive testing.
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