New tutorial: Welding 101, theory and practice.
 

In my teaching basic MIG welding classes and reading questions here, I find there are a number of misconceptions and misinformation that can lead to making the process much more difficult than it actually is. I have answered some of the same questions and corrected misconceptions many times in other threads, but then they get buried in the original threads. I am starting this topic so there can be one thread concerned only with welding. The emphasis will be on MIG welding the thinner metals typically needed on our trucks. If anyone else would like to add their own expertise, I welcome such posts, but please let's try to keep the information factual more than opinion and try not to get carried away with debating the preferred equipment brands etc.. If I bring up a particular manufacturer or source, it is because I am personally familiar with it and I think it has significant enough differences from other choices to make it stand out, or simply to exemplify a typical product. I am rather frugal myself, so I will sometimes suggest less expensive functional equivalents and DIY constructions.
Now let's get started!

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I am as well. Enjoy reading your posts Ax. Very informative!!!

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Ok, I'll throw my latest challenge up for comments, suggestions. The short RBs on my '56 F350 are in pretty bad shape. A PO had scabbed heavy diamond plate over top the RBs which compounded any rust problems that already existed. So by time they came out of my E tank, they looked like swiss cheese on the step surfaces.
So I picked up a set of RBs from an F600. These boards I picked up appear to be reasonably solid. We'll see when they come out of the E tank.:-X16
The ribs are essentially the same dimensions but the F600 has four ribs instead of three and are several inches wider. I plan to cut my original boards back to solid metal which will be just about to the perimeter frame and then cut what I need from the donor RBs. Wish me luck.
Oh, yeah, I have a Lincoln 175 with gas and have put in a few patch panels. ...Still learning. Most of my experience has been stick. Wish me luck.

The Guru has stepped up again! Thanks AX will be reading and learning! Maybe a video down the road?

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Lesson 1 is currently being proofed. Will be posted shortly.

AX, thank you. Subscribe

Gil

LESSON 1: WHAT IS WELDING?
The difficulties start with not really understanding what happens when we make a weld, so let's start there.

Welding is basically the joining of two pieces of material of the same composition together by apply sufficient heat to the juncture to cause both pieces to reach their melting temperature at the same time so that the molten material flows across the juncture and combines together, then allowing the juncture to cool and solidify into one piece. Keep this definition in mind throughout the following discussion.

Note that there is nothing said in the definition about adding anything besides a heat source capable of melting the material, and that the material being welded does not necessarily have to be metal. For example, many plastics can also be welded to themselves.
The heat source is not specified except that it needs to be able to bring the material to it's melting point and be controllable and localized enough to not just melt the entire thing.
When welding steel the heat source used is typically a gas burning torch or an electric arc (continuous spark), but other heat sources can be used such as electrical resistance (spot welding), a thermite rod used for welding underwater, explosive force, or a forge and hammer such as employed by a blacksmith.

How steel reacts:
Steel has certain physical and chemical properties that affect it's weldability that need to be considered and addressed to weld it successfully.

First is it's physical properties:
Steel when heated enough to become molten (liquify) has a high surface tension. That means it wants to pull itself together to occupy the least amount of space it can. If you heat a small piece of steel until it melts completely it will pull together into a ball. If you heat just the edge enough to start to melt it will shrink back and thicken. If you heat a small spot in the center of a piece of thin steel to just below it's melting point the metal will start to pull in on itself at the point of highest temperature, the basis of both heat shrinking and warpage. To accomplish a successful weld you must bring both sides of the juncture to its melting temperature at the same time so the molten metal mixes and pulls together across the juncture rather than melting separately and pulling away from the juncture. The puddle formed must be small enough to solidify before gravity causes the molten metal to drip, "blowing" a hole. The metal needs to become molten from top to bottom of the juncture so the mixing can take place completely thru the juncture forming one solid piece. This complete melting and mixing is what welders call "full penetration". full penetration is achieved when there is a slight rippling or barely raised area along the length of the seam on the back side. There should not be large lumps (too much penetration) or should you be able to see the line of the original edges of the seam (too little penetration). It is difficult to control the heat well enough to always get perfect full weld penetration when welding thin sheet since it almost instantly goes from red heat to molten for a ways back from the junction compared to the metal thickness. You can help control and localize the heat by placing a non ferrous heat conductor against the back side of the seam at the point of heating such as a plate of copper or aluminum (molten steel will not stick to either of these metals, but they need to make intimate contact with the steel for at least an inch or two around the weld to be effective). I split a 12" or so long piece of 3/4" copper water pipe down one side for 5 or 6", pry it open with a pair of pliers and hammer it flat on a dolly or anvil to form a spatula shaped tool using the unsplit portion of the pipe like a handle. A 2x3" or so piece of 1/8-1/4" thick aluminum plate or T extrusion also works well.
If you start to get large buildup or lumps on the back side of your seam, stop and grind them near flush so you can get good contact with your heat dissipator tool. Practice on pieces of the same thickness steel until you can produce a seam with continuous full penetration.
Warpage occurs when the metal is heated unevenly either front to back or side to side. Uneven front to back heating will cause the metal to want to curl. Uneven side to side heating will cause the metal to warp away from the hotter edge. Even heating along a weld seam will cause the metal to shrink in along the seam (when viewed from the front) in a cross section similar to the simple flying bird shape we all learned to draw as kids.
To reduce warpage and/or shrinkage there a several steps that can be taken. First lock the piece down by either clamping it in place with welding clamps placed so that they hold the two pieces together directly on top the seam to reduce curling, and/or tack the pieces together at intervals, starting with each end then ~ 6" apart starting at the center then reduce the space between tacks by bisecting the distance, working alternately towards the ends. after each round of tacks, adjust and realign the fit with light application of hammer and dolly. Once the tacks start getting closer than 6" apart skip around and allow them all to cool completely to room temp between tack series. If the gap between the two pieces grows to more than the diameter of your filler wire slip a thin strip of sheet edgewise into the gap until it protrudes ~ 1/16" on the front and weld over it with slightly larger diameter tacks, catching both original pieces evenly. The slight front protrusion will melt into the seam. grind off any that protrudes from the back side.
We will learn how to correct seam shrinkage in a later lesson.

So far we have welded with just heat such as with a Oxy-Acet torch, TIG torch, or spot welder, we have not added any extra metal. If we examine a spot weld, one we did or a factory one, we can see a depression in the center and a slightly 'proud" or higher rim around the edge. The depression id where the metal melted, the rim is where it pulled back and thickened before freezing. You could picture a heat only weld seam like a continuous spot weld. You would have a trough along the juncture with a mound along either side. Assuming full penetration the juncture would be physically as strong as the two pieces of steel being welded, since they are now all one piece of the same material, just as if they were one piece to begin with. Structurally the juncture would be weaker though, simply because it is thinner and therefore would concentrate any forces acting on the joint at that point. That concentration of stress would result in the metal work hardening and subsequently failing along that line. To reduce and spread the stress beyond the juncture, we can melt in some additional "filler" metal into the molten weld puddle, building up the seam thickness. Since the molten puddle will always be lower in the center, we add enough filler metal to slightly overfill the puddle, resulting in the build up along the juncture we call the "weld bead". We can leave the bead proud to add the additional strength of the thicker metal, or we can grind it down flush without reducing the strength or concentrating the stress along a narrow line. When welding with a gas or TIG torch the filler metal is added by dipping the end of a piece of filler rod into the molten puddle when it forms to melt in then withdrawing it when enough metal has been added. This when done with enough practice and coordination results in the characteristic "flattened line of dimes" bead shape.
However this requires the operator to "rub his/her belly while patting his head and keep time with his foot all at the same time", it can be done after a steep learning curve and lengthy practice.
Unlike the gas or electric arc torch, the MIG welder uses resistance heating, somewhat like the spot welder, of the electrified filler wire short circuited to the metal being welded at the contact point to simultaneously produce enough heat to melt the juncture and automatically feed in the desired amount of filler metal while maintaining the instantaneous short circuit needed to continue melting the juncture. This makes MIG welding semi-automatic, able to be done one handed, and easy to learn to do successfully. Once the machine is adjusted, the operator only has to guide the "stinger" along the juncture at a steady rate to produce a successful weld.
Two notes to finish this lesson:
First, the MIG machine does not use an electric arc. It uses an electrical short circuit of the electrified resistive filler wire to produce the welding heat, so the wire must make contact to start the weld and continue to make contact as it melts into the bead. We will discuss this in more detail in a later lesson.
Second The wire fed out of the contact tip of the MIG stinger is NOT WELDING WIRE!!! The wire is doing no welding. The heat produced by the high amperage electrical current being short circuited through the resistant steel wire is doing the welding. Please call that wire by what it functionally is, the FILLER WIRE. By calling the filler wire by it's proper name, it will remind you of it's purpose and help you understand how a MIG welder works.

Next lesson: the chemical properties of molten steel and the function of flux and shielding gas in welding.

Before jumping in please read my posts in "the hood, the bad and the ugly" and "welding patch panels" topics.

I'm on the edge of my seat! More! More!:-X22

Subscribing. Since I am near the end of the mechanical repairs to my '52 I am closer to starting the body work. I am afraid, very afraid.

Subscribed! AX, we need to get you some kind of award for helping everyone with stuff like this!

Since I don't have any children or SO, my 2 brothers know as much or more than I do since we grew up working on race cars and hotrods together, I really don't have anyone else to teach what I've learned to. I am a teacher at heart and by education (MS in education) so I have a passion for teaching.