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An introduction to welding


Author: NJR Steel
Article Views:13022
Categories: Manufacturing, DIY

The following article will provide a basic introduction to welding principles and practice, focusing on stick and MIG welding applications.

Different welding methods/machines

Shielded metal arc welders (SMAW) / Stick welders

An example of a stick welder
An example of a stick welder


SMAW welding makes use of stick welders, so named because the coated wire welding electrode resembles a stick you might pick up from your lawn. Electric stick welders cost less than other welding systems, but require more practice and skill to master. People who want to begin welding are often short on cash, and may well choose to begin with a stick welder before possibly moving up to a wire feed welder after a few years.

Application

A stick welder is more limited in its applications, but never needs a refill for gas bottles. Just plug in a stick welder, flip its switch, and it will be ready to weld. It also remains ready to go until the next time you use it. Just keep some welding rod stored in dry, low humidity conditions and you will be ready to weld at any time. If yours is a 120 volt welder, you can take it with you to a job almost anywhere, even though it may be limited in welding power. (Actually, a stick welder can cut steel. A small diameter rod is used at high amperage in a sawing motion through the steel. A bed of sand is usually placed below to catch all of the globules of molten metal.)

Stick welding uses an electrode or welding rod. Electrodes have different numbers to describe them. Some weldors like 6013 electrodes; others prefer 7018; and 6011 electrodes are also widely used. Each has different characteristics which make it more suitable for certain applications and less suitable for others. The numbers provide details on the characteristics of each type of electrode, but those details are beyond the scope of this article.

Gas metal arc welders (GMAAW) / MIG (metal, inert gas)

An example of a MIG/wire feed welder
An example of a MIG/wire feed welder


MIG welders were invented to increase production rates by removing the need to stop and replace a burned electrode. For the beginning, occasional welder; a MIG welder makes learning to weld much easier.

MIG welders, also known as wire feed welders, use a continuous wire electrode on a spool. Rollers in the welder are driven by a motor and feed the wire at a steady rate through an electrode holder, usually called a gun. The fresh weld is protected from the oxygen in the air by being continuously covered with an inert gas. If oxygen comes into contact with the hot, fresh weld; the weld becomes porous and is weakened.

MIG is generally preferred and more expensive than flux core wire feed welding. MIG-capable welders are more costly than flux core welders because they include a gauge for regulating the shielding gas flow, a tube around the gun liner for carrying the gas to the gun, and a solenoid valve to start and stop the gas flow when the arc begins and stops. There is also the cost of the gas and a steel bottle to contain it. MIG welders can be used with flux core wire, but flux core welders cannot be outfitted as MIG welders. The advantage of MIG welders is that the welds have a better appearance and better penetration. There is also less cleanup after welding. But, in windy conditions, the gas that shields MIG welds can be blown away before it does its job.

Application

Turn on your wire feed welder and let it run for a minute or so before beginning to weld. You may either push or pull the gun.

Much of what applies to stick welding practices also applies to welding with a wire feed unit. A steady hand, the correct angle of the electrode holder (stinger or gun), the correct heat setting, the correct travel speed, etc., are all necessary in both processes. However, in stick welding, attention is given to the length of the arc; whereas with wire feed welders, the amount of wire sticking out of the end of the copper welding tip at the end of the welding gun becomes important. See the manual for your welder.

Wire feed welders are also much easier to use than stick welders. They do not require the same skill level and amount of practice as stick welding. Some say laying a bead with a wire feed welder is like putting down a bead of toothpaste on a countertop; almost anyone can do that. The catch is that it is much more difficult to see where you are welding with a wire feed welder.

It is not uncommon to wander off of the joint while welding with a wire feed welder. This can be overcome by looking under the gun ahead of where it is welding, as there is enough light from the arc to see a bit of the unwelded joint to use as a guide for the moving gun. That works unless the sun is coming from over the weldor’s shoulder. In that case, the inside of the helmet is bright and one has great difficulty seeing even the arc. An auto-darkening helmet is a tremendous help, and well worth the cost.

In order to be sure your weld has good penetration and is not a “cold weld” (weld material laid over the parent metal without any real bonding), look for blue discolorations in the parent metal on both the left and right sides of the weld as a sign of good penetration.

When it is time to stop welding with a stick welder, the weldor simply pulls the electrode away from the steel and the arc stops. When using a MIG welder, those who are used to stick welders need to learn to release the trigger on the gun before pulling the gun up and away from the steel. Failure to do this results in a couple of inches of wasted electrode wire sticking out of the gun. This must be trimmed before beginning to weld again.

There are some good videos on YouTube for how to do MIG welding.

When to replace the wire feed’s tip

In time, the hole in the tip wears and exactly where the wire will strike the metal when the trigger is pulled becomes less predictable. When you notice this unpredictability, it is time to replace the copper tip.

Flux cored arc welders (FCAW)

Flux cored welders use a thin wire electrode that has a chemical powder in its center. This powder melts and flows over the weld to protect the fresh weld from oxygen. This hardened coating is called slag. After the weld cools, you can chip or brush it off, depending on how thick it is. With a flux core welder, one can sometimes begin a new weld without trimming the burned end, but there are other times when an arc will not begin without first trimming the wire to make a fresh new end.

Whereas MIG welding requires very clean steel, flux core welders can dig through some surface impurities to make a good weld. Flux core welders can also be used in windy conditions with no problems.

Gas tungsten arc welding (GTAW) / TIG (tungsten inert gas) welding

TIG welders use a torch with a sharp tungsten tip to make a pool of molten metal with an arc. The operator dabs metal from a thin wire rod into the pool. At the same time, the operator increases or decreases current to the arc with a foot pedal control.

TIG welding makes beautiful welds on aluminum and various special metals. It requires much skill and practice to master.

Gas welders

Oxy-acetylene (gas) welders use two tanks, one filled with oxygen and the other with acetylene. Both gases flow through hoses at controlled pressures to mix and burn with a very hot pointed flame in a torch. A gas welder can cut steel, heat steel for bending as if it were a piece of soft wire, and weld or braze.

Handy terminology

Penetration

Penetration means the welder did not merely lay a bead of welding material over the top of a joint, but some of the parent metal melted and fused together below the weld, too.

Weaving

Weaving is moving the arc from one side of the joint to the other in order to make certain the weld penetrates into both sides of the joint. A weaving pattern is also used to prevent sag when welding in an upward direction on a vertical joint.

Sag

Sag is molten metal that flows out of the joint while welding due to the effects of gravity. This can be a problem when the weld is vertical, overhead, or horizontally along the side of a vertical surface. Avoiding excess heat, using electrodes designed to harden quickly, fixing the angle at which the arc is directed, and general manipulation of the arc may be used to counteract sag.

Welder vs. weldor

Technically, a welder is the equipment used to make welds, i.e. the welding machine. A weldor is the individual who uses a welder to make welds. Often “welder” is used for both.

Educational resources

If you buy a new welder, it will come with a thin manual that covers safety, some mechanical information about the welder, and a few basic welding procedures to get you started.

If you buy a used welder without a manual, you can probably download a manual for it, or a manual for a similar machine. There are many aids available for the person who wants to learn to weld. Some are in text (either electronic or on paper), while others are videos. There are numerous video tutorials on all aspects of welding on YouTube. Some are done well; others are rather poor.

Safety

Ventilation

Electric welding rods produce toxic fumes. Have a fan nearby, and stand near the open garage door. Galvanised steel also makes fumes you do not want to breathe. Grind the zinc coating away before welding and use good ventilation.

UV burns

Cover your exposed skin. Arc welding generates UV rays linked to skin cancers. Resist the temptation to peak out from under the welding helmet in order to see while striking the arc. Instead, use a piece of carbon rod.

UV burns from welding
UV burns from unprotected welding


Spatter burns

Cover up all exposed skin with thick, durable materials such as leather to protect yourself from burns caused by globules of molten metal.

Preparation for welding

Getting a good ground

A good ground connection is necessary to making a good weld. Ground clamps that come with welders from the factory are often barely adequate, and they usually deteriorate over time. Making a better ground can really boost the performance of any welder.

If the finish on the parent metal is not something very special, it is possible to grind away a bare area and attach the ground clamp there. A simple way to get a good ground through heavily painted or plastic coated surfaces without grinding and unnecessarily marring them is to attach a Vise-Grip locking plier very tightly and then connect the ground clamp to the pliers rather than to the work piece.

Preheating

An example of a gas torch for preheating metal
A gas torch for preheating metal


Preheating the joints with a MAPP gas torch before welding will give your welder a boost beyond its normal capabilities. Preheating is also useful when joining two pieces of steel of different thicknesses. Pre-heat the thicker piece to make it easier to get a good weld.

Practice

It is a good idea to make some practice welds before you weld anything that needs to be done properly.

The welding process

How to stand

Sometimes you will need to weld while kneeling or crouching. Most of the time, you will be standing. You want a steady hand. When possible, you may want to grasp the hand holding the gun or stinger (electrode holder) with the other hand to steady yourself. Since you do not want to fight the heavy cables when you are stick welding, hang the cable over something, even your arm or shoulder, so there is a short, very flexible hanging loop that does not restrict the movement of your arm or hand.

Use a fairly square stance with your feet separated to give more stability. If you are near a bench, you can rest your hip against it to steady yourself. Or, if it is convenient, rest your elbow on a flat surface while welding. All of this results in more control.

Striking the arc

We naturally jump back when sparks begin to fly and we hear electrical popping noises. One of the hardest things at first is to remain steady when the arc first strikes. This is true whether you are using a wire feed welder or a stick welder.

Striking an arc with a stick welder has been described as being like striking a match. The danger is that the end of the rod sticks on the metal without making an arc. Then the machine begins to growl very unpleasantly. That happens to everyone quite a few times. Quickly jerk your wrist side to side to break the rod loose from the steel. When that happens, it usually means you need to increase the amperage a bit on the welder’s output. On the other hand, higher amperage can produce too much spatter. The trick is to find the right heat (amperage) for the metal being welded and the rod being used. In theory, you very lightly scratch the end of the rod on the steel as if it were a match. Think of the pressure you use with your fingernail to scrape a piece of lint from your sleeve. That is about the right amount of pressure when striking an arc. Then you immediately pull the rod away from the metal just a little. Adjust the length of the arc so that you hear the sizzle of bacon frying.

Because the rod burns away as you weld, you will need to continuously and gradually lower the electrode holder (stinger) nearer and nearer to the metal to maintain the proper length of the arc. If you find yourself frustrated because the rod frequently sticks when you are trying to strike an arc, use a carbon rod to help get the arc started. This technique is especially helpful when you have stuck a rod once or twice and the coating is beginning to come off of the end of the rod.

Some general guidelines on heat settings

Your welder’s manual will include a chart for setting the heat (amperage) range for the thickness of the metal you are welding. If you are using a wire feed welder, this chart will also suggest a wire speed setting. You may need to make minor adjustments for the best possible weld bead. Some new welders automatically make the proper heat and wire speed settings once the operator dials in the thickness of the metal. If you are using a stick welder, the size of the rod in thousandths of an inch is about equal to a workable welding current for that rod. All of these usually have a range of current that extends from below to above these numbers. So:

  • 3/16 inch rod = 0.187 inch = 190 amps
  • 5/32 inch rod = 0.155 inch = 150 amps
  • 1/8 inch rod = 0.125 inch = 125 amps
  • 3/32 inch rod = 0.094 inch = 90 amps
  • 5/64 inch rod = 0.078 inch = 75 amps
  • 1/16 inch rod = 0.062 inch = 60 amps

You may find that your actual settings would be a little lower than these suggestions. But, it is still a neat correspondence that the rod diameter in thousandths of an inch is very near to the correct amperage setting.

Stick, flux core, and MIG welding: Do not move too fast

Hold the electrode (rod) at about a 75 degree angle to the work surface. A very common error is to travel or move the arc along the length of the joint too rapidly. This results in a poor and incomplete weld. When you are moving forward along the joint at the right speed, a crescent of light, like an eighth moon will appear at the front edge of the bead near its top. Go too fast and you will not see the eighth moon crescent of light. With a little practice you can distinguish this crescent of light from the brilliant flash generated by the arc. Welding is not just laying down a bead of welding rod material over the joint, but it is also melting the parent metal below the surface so it fuses together, too. That is called penetration.

Penetration

In order to achieve better penetration in your welds, do not butt the two pieces tightly against each other. Instead, leave a small gap between them. That allows the arc to get down between the two pieces and make for a better weld. How much gap depends on the thickness of the metal, the thickness of the rod, and the amperage setting used on the welder’s output. This gap should not be too large. Good fit up is also needed. That means there are no large gaps that a weld bead cannot bridge in one pass.

Position

The best choice is never to weld “out of position.” That means you always hope to weld with the joint below you on a work surface facing upward. “Out of position” welding happens when the joint is above you, or vertical, or along the side of something like a wall. Special techniques are required for each of these to prevent “sag,” which is molten metal flowing away from the joint before it can cool enough to harden.

While you are learning, you can put practice welds into a vise and pound on them with a very large hammer to bend them sharply. You want a weld that does not break, or if it does, it breaks next to the joint in the parent metal, but not in the joint.

The hot side is the short side

Always take heat distortion into account.
Always take heat distortion into account.


Heat distortion is always a problem with welding. You are laying down hot, molten steel. When it cools, it contracts. One of the most difficult tasks is to weld two pieces to make a 90 degree corner and have the corner measure 90 degrees when finished. The hot side is the short side. Whatever was hot more recently will pull together the most in the end.

There are several things you can do as preventive or corrective measures. You can plan the order and the direction in which you weld the pieces together to minimise the shrinkage effect. You can tack weld the sides of a joint and check the setup before going further. Hopefully, the tack welds will restrict the shrinkage.

You can guess how much shrinkage there will be and open the placement of the setup, assuming you are welding from the outer part of the corner toward the inner part, so that the pieces will be positioned properly when the welds cool; but this is almost like forecasting winning numbers for the lottery. Still, make a guess on opening the joint. Take measurements. Open the joint an extra 1/16 inch over 12 inches for 1/8 inch thick angle iron 1 inch in size. Weld and measure the finished product when it has cooled. Cut the joint open and adjust the amount the joint is opened for compensation. Weld again and check.

You can clamp the pieces to something solid before welding and pound on them while cooling to relieve stresses in the hope that the pieces do not move during their cooling. You can check the pieces after they have cooled, heat them, and bend them back to their desired position. In general, avoid excess welding heat and avoid more passes than necessary.

Hot steel will always contract when it cools, and welding involves hot steel. Do some planning and build in a way to leave an open door for making corrections.

A note of caution: Welding across a load bearing member creates a weakened area prone to breakage. Welds to a load bearing member should always be parallel to the length of the member.

Staying on the joint line

Most often practice and more practice is advised to learn to keep the arc on the joint line.

Welding helmets come with clear lenses over the tinted lenses. These become dirty and pitted, even discolored. All of those things affect visibility. Periodically clean or replace the clear lenses.

You can also clamp down a guide for your hand to follow. This might be a piece of board about 1 inch thick. The heel of one hand can ride against it to give a straight line guide for following the seam to be welded.

A weldor uses a piece of timber to guide their hand.
A weldor uses a piece of timber to guide their hand.

Hurry up and wait

Actual welding takes very little time. It is the getting ready to weld that takes the time. You can probably get away with welding pieces of 1/8 inch steel together without making a chamfer on the edges to be joined. Even 1/8 inch stock should be welded from both sides for penetration and strength. An old adage is to weld a little and cool a lot. After welding, pounding on the welded joint with a chipping hammer reduces stresses in the weld.

There is also the matter of duty cycle. Every welder has a duty cycle. That means it will overheat and stop welding if used continuously. The duty cycle is often 20/80. That means after welding for 2 minutes (20 percent) you must let the welder cool for 8 minutes (80 percent). Often a weld can be completed in less than 2 minutes and you will need more than 8 minutes to get ready for the next weld, anyway, so it all works out.

Cast iron

Occasionally one encounters something made of cast iron. Its molecular structure is quite different from steel. When welding cast iron, the weld will bind with one side of the joint, but will be very brittle at the other side, and the joint will soon separate, forming a new break. This can be puzzling and frustrating, but there are ways around the problem. The easiest is to pound moderately, but not too hard, with a hammer on both sides of the weld, and do this continuously until the weld has cooled enough so that you can hold it with your hand. Another strategy is to preheat the joint before welding and then cover it with heated sand so that it cools very slowly.

Weld a little in one spot, and then move on several inches to another, and another, and so on. Eventually, weld a little more on the first bead and then the next and the next. Keep this rotation going until you finish. The idea is to avoid heating any one spot excessively.

You can insert partially used electrodes so the burned end is near the mouth of the keeper. That way you’ll find them easily and use them before you start a new rod.

Helpful accessories

An auto-darkening helmet is a tremendous help, and well worth the cost.

A keeper restricts exposure to humidity by the electrodes or rods. Commercial keepers are available for a very reasonable price.
A carbon arc torch is a very useful accessory for a 230 volt stick welder. It allows heating steel for easy bending.

A piece of aluminium angle, about 18 inches, long will come in handy, as steel does not stick to aluminum, so there is no danger that you will weld something to the aluminum. It makes a handy accessory to put into your vise. You can clamp things to it before welding. It is a help when welding thin materials that might burn through easily. The aluminium acts as a backing plate to absorb extra heat and to prevent blowing holes in the thin steel. Still, you must weld in short bursts with your wire feed welder or you could still burn a hole. You can even turn it over so it is like a “V”, and then lay two pieces of rod into the “V” for welding them end-to-end while keeping them aligned.

The day will come when a friend brings something to be welded by you, and the friend needs eye protection. An inexpensive extra welding mask is good to have.

Source: Instructables


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