How does welding metal work?

[spidey07]

I've always been impressed with good welding (like the beauty used on a bicycle frame). It seems there are so many different kinds/types.

But how does it really work/perform? One would assume that the weld is always the weakest point, but maybe you can make the weld stronger then the pices it's joining.

 

[FoBoT]

no, the weld isn't stronger that the rest, anytime you have a joint, it is a flaw/weakness in the metal

 

[drinkmorejava]

I haven't done a whole lot of welding, but using thinner pieces (1/8 inch), the weld is definitely structurally stronger than the material in many cases.

 

[spidey07]

Originally posted by: FoBoT
no, the weld isn't stronger that the rest, anytime you have a joint, it is a flaw/weakness in the metal

So under stress, the flaw in the metal will fail before the weld?

Really?

 

[Kelvrick]

Originally posted by: spidey07

Originally posted by: FoBoT
no, the weld isn't stronger that the rest, anytime you have a joint, it is a flaw/weakness in the metal

So under stress, the flaw in the metal will fail before the weld?

Really?

Umm, from what I'm reading, he's saying weld= flaw.

 

[FoBoT]

MIT has a course on Welding and Joining Processes

Course Description
Discusses a wide variety of processes and materials from the viewpoint of their fundamental physical and chemical properties. Specific topics: cold welding, adhesive bonding, diffusion bonding, soldering, brazing, flames, arcs, high-energy density heat sources, solidification, cracking resistance, shielding methods, and electric contacts. Emphasis on underlying science of a given process rather than a detailed description of the technique or equipment.

http://ocw.mit.edu/OcwWeb/Materials-Sci...g-ProcessesFall2002/Syllabus/index.htm

 

[dartworth]

Originally posted by: FoBoT
no, the weld isn't stronger that the rest, anytime you have a joint, it is a flaw/weakness in the metal

negative...the filler metal is as strong or stronger...

 

[lupi]

It also depends on the original metal, the type of welding done and materials used.

 

[FoBoT]

not the filler, the joint

 

[dartworth]

the same goes for the joint...

 

[GagHalfrunt]

A GOOD weld can easily be stronger than the surrounding metal. A bad weld can be a serious flaw that's much weaker than the surrounding areas. It all depends on the quality.

 

[FoBoT]

http://www.gowelding.com/weld/failure/failure.htm

 

[Jeff7]

Originally posted by: spidey07

Originally posted by: FoBoT
no, the weld isn't stronger that the rest, anytime you have a joint, it is a flaw/weakness in the metal

So under stress, the flaw in the metal will fail before the weld?

Really?

If it's a good weld, yes. One of my classes has us doing welding for a few class periods. One of the welds we're testing is a butt weld between two pieces of strap steel 1/8" thick and 3/4" wide. The samples are then subjected to a tensile test. Ideally, the weld will hold and the material will yield first. I have thus far done 3 samples each of stick, MIG, and TIG welding. One weld, a TIG weld, was good - the steel strap stretched and then broke, with the weld still perfectly intact.
The rest of my welds came apart like I was using taffy. Those welds adhered to the metal on both sides, but the weld material itself was pulled apart.

 

[spidey07]

Originally posted by: FoBoT
http://www.gowelding.com/weld/failure/failure.htm

Good info! Thanks!

Uncle Spec was a master welder and let me play from time to time.

I'll never forget grabbing a hold of something I was welding while standing in some water, quite shocking. I don't know what kind of welding that was - but you clamped one lead on the piece and the other clamp held a "stick".

-edit-

This topic comes from a History Channel "great engineering" show. They were talking about how hard it was to weld "hardened steel" and the knowledge of metalergy/experience needed. Something about the carbon in the iron mad it flake.

 

[Squisher]

What usually fails with a good weld is the old metal just beyond the end of the weld. That metal was not manufactured with the notion that it's going to be super heated then air cooled and as such it experiences some detrimental effects.

I have seen many good welders and a few great welders. We've got one guy at work that worked in a pertoleum refinery. He had to weld on pipe that was full of gasoline. You don't want to burn through on that one.:shocked:

 

[NikolaeVarius]

A good weld should be structurally stronger than the material surrounding it.

I heard somewhere that a good weld looks like a toppled stack of coins. Not sure if this is true though.

 

[Injury]

I worked at an iron foundry for a while... they had an entire sheet metal department that did some really large scale work. I was third shift and they were there bright and early in the morning. If I ever got done early I would go watch them work.

A couple of the guys in my department knew how to do it quite well to daily repairs to all the crap that would break down and such, and they always said they would teach me a little bit, but never did.

I picked up on the basic idea just helping them out, but never got to learn how to do it.

Definately something I would take a class on if I had the money to spend on the equipment to do my own work at home and enough projects to justify it. Mostly I think it would be fun for a couple of sculpture projects here and there.

 

[dartworth]

Originally posted by: Squisher
What usually fails with a good weld is the old metal just beyond the end of the weld. That metal was not manufactured with the notion that it's going to be super heated then air cooled and as such it experiences some detrimental effects.

I have seen many good welders and a few great welders. We've got one guy at work that worked in a pertoleum refinery. He had to weld on pipe that was full of gasoline. You don't want to burn through on that one.:shocked:

Yeah it is kind of nerve racking...I've welded on similar lines in a few refineries...

 

[Rubycon]

Originally posted by: tenshodo13
A good weld should be structurally stronger than the material surrounding it.

I heard somewhere that a good weld looks like a toppled stack of coins. Not sure if this is true though.

Take a roll of dimes and lay 'em over. That's what a good fillet looks like. If you can do that overhead, you're good.

 

[freebee]

I just successfully soldered an entire 20 pin power supply connector by hand (including shrink wrap tubing). Each wire had to be done individually and matched by color!!!

Soldering is like welding for nerds.

 

[NogginBoink]

Originally posted by: spidey07


I'll never forget grabbing a hold of something I was welding while standing in some water, quite shocking. I don't know what kind of welding that was - but you clamped one lead on the piece and the other clamp held a "stick".

That type of welding is commonly (though not technically) known as, believe it or not, "stick welding."

Really.

 

[TitanDiddly]

I am a Materials Joining Engineering Technology major. (AKA welding)
-Properly made welds can be stronger than the surrounding metal.
-There are almost as many different types of welding as there are needs for welding.

There are three kinds of welding you're likely to see in a basic welding class:

Stick (SMAW- Shielded Metal Arc Welding) - The second kind of welding ever. Essentially, a steel rod covered in a ceramic-like material called flux is connected to the positive connection, the workpiece to ground. An arc is established between the electrode(steel rod) and the workpiece. This creates intense heat that melts both the steel rod, the workpiece, and the flux. The flux creates a gas pocket as it melts, and also slag. The gas protects the molten weld metal from the atmosphere and stabilizes the arc. The slag creates a hard ceramic coating on the weld which protects it as it cools. This is later chipped off, leaving a clean steel weld 'bead'.

MIG - (GMAW - Gas Metal Arc Welding) This is completely different from stick. In this process, a bottled shielding gas and a spool of wire is used. Both the gas and the wire are fed through a hose to the welding gun. The gas shields the weld and stabilizes the arc, just like in stick. The wire carries the electrical current. With low current, the wire will short circuit to the metal and melt in. Higher currents cause a constant arc, and the end of the wire melts off in fairly large drops, and into the weld pool. In even higher currents, tiny droplets form on the end of the wire at a high rate, and are propelled into the weld by the electromagnetism created by the current. There is no slag in GMAW, but a similar type of welding exists called FCAW(Flux-cored arc welding), wherein a flux powder is carried in the core of the wire. This does the same thing as flux in arc welding, and does form slag.

TIG (GTAW - Gas Tungsten Arc Welding) In GTAW, the arc and filler metal come from different places. The welder holds the electrode, which is made of Tungsten. Tungsten can withstand extremely high heat without melting, and also is a very good conductor at high temperatures(thermionic). The arc is initiated between the workpiece and the tungsten electrode, and a weld pool of molten metal is established. Then, the welder feeds in a welding rod, which is just a plain rod of metal of similar composition to the base metal- it may contain alloying elements to make a stronger weld, or just be plain metal like the base metal. GTAW also uses shielding gas from a bottle. GTAW may be DC electrode positive or negative, or also AC.

There are about a bazillion more. If you want to know more about any of them, feel free to ask.

 

[Jeff7]

Originally posted by: freebee
I just successfully soldered an entire 20 pin power supply connector by hand (including shrink wrap tubing). Each wire had to be done individually and matched by color!!!

Soldering is like welding for nerds.

Except that you're only melting lead or tin, not steel, there's no UV emitted, no sparks flying all over the place, and no risk of electrocution. When I was doing some TIG welding, the entire area around the weld was glowing orange. In TIG welding, the base metal is melted by a powerful electrical arc, and filler metal is melted into the pool of liquified metal.

Welding makes me just a wee bit nervous, not only for the reasons I mentioned, but with gas welding, you're dealing with very flammable gas. My instructor said that one time he was trying to multitask a bit, went to hang up his welding torch, but missed. It fell down right beside his foot, instantly cutting through his sneaker. He says that he has a scar in a line where the torch went. The sneaker was melted partly into the wound.

My high school physics teacher also did some welding. His detailing of the parts that suck: regular exams for skin cancer due to exposure to UV radiation, and having hot sparks fall on his shoe, which would then burn right through to his foot.


For other details, it appears TitanDiddly is one of our resident welding experts.

 

[Rubycon]

Originally posted by: Jeff7

My high school physics teacher also did some welding. His detailing of the parts that suck: regular exams for skin cancer due to exposure to UV radiation, and having hot sparks fall on his shoe, which would then burn right through to his foot.

You forgot the part where the smokers forget and leave their butane lighter in a pocket and a spark nails it - BOOM! :Q

 

[xXped0thugXx]

Originally posted by: GagHalfrunt
A GOOD weld can easily be stronger than the surrounding metal. A bad weld can be a serious flaw that's much weaker than the surrounding areas. It all depends on the quality.

like he said it depends what material youre welding with. i've been an ironworker for years if you appropriately weld the material to the steel or what have you it will be stronger than the piece you are welding together.