I'll be paying special attention to this article. Rust removal and rehabilitation is coming up soon. Besides that, you write a great piece...

 

Great information - thanks.

 

I'm like that dog in the you tube video...."yeah?, yeah?, uhuh?" .....I kind of look like him too!
Good stuff Ax,
Thanks!

 

thanks. very helpful.

 

Anyone who finds this interesting, learns something, just click on the rep button. Give the man his reps.

 

Subscribed, Repped, Thanks AX.

 

Ditto on recognition and admiration.

Thanks for putting this up for us.

 

Subscribed! Definately not a pro and always open and willing to learn new tips/tricks and ideas as well as learn more theory. Let'er rippp Ax.

 

Ax, if I may reinforce a point in your last paragraph, and then my reason for doing so.
The molten metal flowing together in the puddle is the actual weld. As stated, without filler wire we still have a weld if the metal flows together. With a mig, the wire provides the means to heat the metal to melting while adding some filler material. The wire is NOT the weld. Many great looking mig welds are simply nicely applied filler wire on top of cold metal that never puddled together, never became welded. The first part of your article provides the key. The base metal must melt together or you don't have a weld. I've heard folks refer to a mig as a hot melt glue gun for metal. Weak welds result from that ignorance. It's all about the puddle.
Great start, can't wait to see the rest.

 

Two questions.
Will there be any pop quizzes?
What is the tuition cost?

 

Thanks for the reinforcement, that point cannot be emphasized too often or too strongly! That's why I forbid my students from calling the filler wire "welding wire". The heat does the welding, the wire is just a poor electrical conductor and adds extra metal to the bead. I will go over this point again when I talk about the mechanics of MIG welding and examining the weld bead penetration.

 

Subscribed, The knowlage is very much appreceiated. Thank you

 

Great job AX, keep it coming!

 

LESSON 2: WHAT IS WELDING? (Cont.)

So far we have learned what is required physically to produce a weld, we must melt the metal at a junction so it can flow and mix across that junction then when the heat is removed, freeze, forming a continuous mass. A very simple concept, right? What could possibly go wrong??? Well unfortunately it's not exactly falling off a log simple, the molten metal itself and it's surroundings have some chemical properties that can throw a monkey wrench into the works.

Chemical properties of molten steel:
We all know that steel is composed primarily of the element iron. We also know that iron is chemically reactive (which means that it is not in it's most stable chemical form but wants to be), it has a pretty strong desire to "mate" with oxygen and settle down. When it does, the two marry and become iron oxide, which we commonly know as the nemesis of old truck enthusiasts, namely RUST (cue the ominous villain music...)
But rust isn't just the reason we have to weld in patches in the first place, but it is also a problem when making those welds. Iron oxide is much weaker than steel (that's why it crumbles when we touch it) so it has no business in our welds. In addition to the hot and bothered iron molecules wanting to mate with the surrounding oxygen, there are other contaminant oxides and gases that can be entrapped in the weld as well, carbon dioxide and monoxide from the carbon in the steel, burnt dirt, paint, etc. The gases will form bubbles that get trapped in the freezing molten steel, making the weld into steel swiss cheese, weakening the joint.
The easiest first step is to remove any outside contaminants. old rust, paint, bondo, undercoating, etc., should be removed by mechanical means for at least an inch or more to each side of the joint, on both the front and back of the pieces. We want to weld only clean solid metal. Remember new bare metal often has an oil or clear coating applied to keep it from rusting in storage.
Next we need to try and prevent the molten metal from coming in contact with the oxygen in the air so it can't mate until the metal refreezes and becomes more chemically stable. The best way to do this is to use a “chaperone” or a “chastity belt” to keep the iron and oxygen apart. The chaperone of choice in welding is to bathe the area of the weld with an inert (chemically inactive) shielding gas cloud to push the oxygen away long enough for the molten metal to mix and solidify. For MIG welding steel we use a 75% -25% mix of argon and carbon dioxide, or pure carbon dioxide gas fed from a storage tank, thru the welding hose and out the stinger around the contact tip. The gas is concentrated at the fusion point by the gas concentrator cup. The gas starts flowing automatically when you squeeze the trigger, and continues flowing for a brief instant after you release it.
Some MIG welders do not have provision for the use of shielding gas (those machines should be called wire feed welders, NOT MIG. MIG stands for Metal Inert Gas process, therefore if inert shielding gas is not used, it is not MIG.
Wire feed welding as well as Oxy-Acet welding uses a “chastity belt” rather than a chaperone to prevent the oxygen from reaching the molten metal. That “chastity belt” is called FLUX. Flux is a mix of chemicals that melts at a slightly lower temperature than the melting point of the metal and forms a molten glass-like material that floats on and covers the surface of the molten metal, shielding it from the oxygen in the surrounding air. It also has what chemists call a reducing agent in the mix that will kick out any oxygen atoms that might sneak through a break in the flux coating before any permanent harm is done. The flux then hardens on the surface of the weld as the weld freezes.
In wire feed welding the flux is supplied in a special filler wire called FLUX CORE WIRE. This wire is actually a tiny tube filled with flux. As this type filler rod melts, the necessary quantity of flux is also supplied. In gas torch welding the flux is applied as either a paste brushed over the weld joint or the heated filler rod is dipped into a container of powdered flux then applied to the weld.
OK, if flux works to keep the weld oxide free, why use gas? There are several reasons using shielding gas is preferable to using flux: First, the wire size of flux core wire is limited by how small a tube can be made and filled with flux, so flux core wire is always 0.030 or larger (see future lesson on choosing wire size). Second, the reducing agents in the flux as they work, plus any moisture in the flux, air, or on the metal surface will boil and cause spattering of the molten metal. This spatter needs to be ground off to clean up the weld and the surrounding area, and may clog and short out the gas cup to the contact tip. The hot spatter may also end up on your arms, lap and/or in your shoes, where it's uncomfortable at best. Third, the hardened flux will soon combine with moisture in the air, melting into a corrosive liquid.
Therefore the flux residue must be removed completely by chipping off the brittle glass form, with sanding or abrasive brushing, or by melting away with hot water. If any is left behind it will eat into the metal and any paint that is applied over it.
With shielding gas the spatter is reduced to nearly none, and there is no additional cleaning of the weld needed. The smallest sizes of solid filler wire can also be used. Only a small amount of shielding gas is used since it only flows when actually welding and it helps cool the weld quicker, so it is the preferred method for welding thinner metals, especially where appearance is important.

Next lesson: The equipment and accessories needed for MIG welding.

 

Great work AX, this is awesome. I learned how to mig and tig weld long ago when I had a construction job, but I have very little background knowledge on the subject. I look forward to reading more!