They’re different kinds of welding and they can be summed up into a couple of areas but the average homeowner is only going to have the ability to use a stick welder, so that is the primary welding that we are going to talk about in this article.
(The different types of welding being TIG welding, MIG welding, stick welding. There’s also braising which is related to welding but actually it’s not the same thing, it is entirely different. Instead of melting metals together, the melted metal acts like a glue. It is a physical bond, versus a chemical bond. For example some bike frames are braised together because the tubing is soft and cannot handle welding. But we are off-track here….)
First of all, welding is basically melting metals together. It uses an electrical current to melt the metal and then pool it together. It then cools as one unit. The operative word here is an arc or electricity. When large amounts of energy are concentrated at one point on any object they tend to spark. The spark is the form of energy at an excited state.
The energy concentration is so intense that it causes the metal to get into the liquid state or melt. Welding is basically a short-circuit of sorts that concentrates the electricity spark through the electrode into the part that is being welded.
If you remember from circuits, electricity wants to follow a path. Typically an electric circuit such as a light bulb is set up such that the electricity travels from the positive side of the battery, goes through the light bulb and then back into the negative side of the battery. The electricity wants to flow through this circuit. We call this a basic circuit design.
In order for metal to melt a high current is needed. The high current is generated through the welder transformer as it grabs typically 220 V and changes it into a high amperage low-voltage electrical stream. The electrode which is basically metal or steel is melted as the arc is generated across the part and the electrode. It is therefore called a consumable electrode.
The metal from the electrode drips down literally, into the melted pool of the part. Because the metal is solidifying so quickly the metal pools up on the surface of the part, forming a weld seam.
The problem that most welds encounter is that the concentration of the melting is not sufficient inside the part. And so the weld material will melt first and pool upon the surface of the part. The problem that we have however is that the part has not melted sufficiently and so there is a minimal amount of bonding between the weld and the part.
The weld acts as the bonding agent, if you will, between the part surfaces. The part surfaces must be melted equally so that the depth of the melting zone into the parts is sufficient to have good strength.
If you notice on a welding rod it has a crusty material on surrounding it. It almost looks like somebody coated it with clay. Actually that’s not far from it, the clay type substance actually burns and turns into a gas which surrounds the welding arc. It’s hard to believe this, but oxygen can get into the melted part as fast as it melts, oxidize the metal and cause bubbles inside the part. The problem with this is that the weld is all bubbly and weak.
The weld instead of being a strength component now becomes a stress riser where the part will crack especially in the weld area. To prevent the weld from getting bubbly the weld arc must be surrounded by a gas which shields the oxygen from coming in and attacking the metal that is being melted.
On an arc welder there are various ways to shield the metal below from being oxidized. On a MIG welder for example the term MIG stands for Metal Inert Gas Welding. The metal is being fed by a spool of wire which feeds through the gun, however, the weld is surrounded it by an inert gas called argon or nitrogen.
Argon and nitrogen do not react with the metal below and therefore act as good shielding agents. The average homeowner, however, does not need to have such expensive equipment such as a MIG welder. All that is needed is a stick welder.
Downsides To Stick Welding
The downside to a stick welding weld is that the remaining weld is covered with slag. The slag is baked onto the weld and must be chipped away with a hammer. One of the biggest mistakes that a welder can make when using a stick welder is that they become impatient and crisscross the weld. The slag is generated by melting the metal on the welding rod and it literally drips down with the weld material. If you crisscross the weld you cause a stirring action which will mix in the slag and the weld together.
We’ve heard of the man in the book of Daniel (in the Bible) where his feet are mixed iron and clay. As the story goes, the stone crashes into the feet of iron and clay causing the man to topple over. Because the feet are weak, mixed with iron and clay the man tumbles to the ground.
Well the same analogy quite literally can be made with stick welding. You cannot mix clay and iron and get a good result. The natural tendency of trying to rush through a weld and crisscross the weld or weld on top of another weld that was just made is like mixing clay and iron you will have a non-binding or very weak weld.
So keep in mind when you’re welding that you do one pass, let it cool, chip away the slag, re-weld if necessary.
Additionally, the depth of the weld must be sufficient so that part is bonded together and that the weld is not just at the surface. The best way to determine whether or not the weld is penetrating deep enough is to practice on some parts that you anticipate on using. Have a little section of part laid aside so that you can test weld these. Then chip away the slag and do a bend analysis to see if the part cracks or the weld cracks. The part should bend and not crack on the weld.
When welding a part the concentration of the arc is related to the gravity and the drip of the consumable rod into the melted part surfaces. Typically the best type of weld is one that is straight up and down relative to gravity.
So the ideal angle for the rod for example on a 90° joint is to have the rod at a 45° angle. However if you want a better weld you can tilt the part that is at 90° at 45° and you’ll get a better drip into the joint. Upside down joints for example are difficult to do because the melted consumable rod tends to drip away from the part joint and therefore the concentration of weld depth is minimized on the upside down side of a part. Only professional welders understand how to compensate for this when they are welding underneath. It is more ideal for people who don’t weld all the time to try to get the part so that the weld drips into the part surfaces.
A word of note about welding tubing: tubing is very thin and can blow through easily, so care and patience must be taken that you do not get overzealous and concentrate the welding rod in one place for an extended period of time. If the weld does blow through the tube (not to worry however) make sure that you chip away the slag and slowly refill in the hole. A quick method for filling in large gaps is to use nails (as in “carpentry nails”) and lay them on their sides in the gap if there is a large one.
Large gaps in parts can be generated by accidental cutting of the steel and not getting the parts close enough together. A filler material such as a nail or plate is acceptable in this instance. It might not be a bad idea to back up the joint in question with a gusset just to make sure that there is not a stress concentration in this area.
So to recap:
Welding is melting two pieces of metal together with electricity and using a consumable electrode to fill in the gap. Stick welding is the most cost-effective and cheap means of welding available to the homeowner. It however requires that you understand how slag is formed and how slag can actually make a weld weak if you do not address it properly.
The actual depth of the weld is related to the amount of current that is being put into the weld arc. Additionally, the amount of weld depth is related to the relationship of gravity and the consumable rod drip. The part may have to be adjusted accordingly to get the weld to be concentrated properly.
I am a senior in high school and I really enjoy making things with my hands and understanding how things work. How you just explained this is awesome and i appreciate that you describe what is happening as you weld.
I am glad that I could help. There are lots of little things that people have questions about, I know, because I used to ask them myself. And when I got the answers it just helped me visualize where I was going.