Welding
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[edit] Introduction
Welding. One of the most important trades of the world in which we live. Welding is defined as 'the fusing of two or more pieces of metal or plastic'. It binds the office buildings in which we work, the malls where we hang out, and in every car that we will ever drive. Welding is a 'skilled trade', which means that not everyone can pick up a welding torch and build something, it must be learned. Because of this, welders are often paid well or above average wages. Interested? It actually doesn't take too long to learn, in some cases a journey person status can be reached in as little as 3 years. The skilled welder has a steady hand, good hand-eye coordination, and good working ethics.
[edit] Safety
Safety is a key player in all types of welding. The human body is mostly made up of water, and water and metal don't usually go together well. Make proper use of safety goggles/glasses, gloves, leather clothing, work boots and welding helmets. Welding is HOT, so keep around a metal pail of cooling oil or water, and, just in case, a can of instant-freeze for yourself. Wear earplugs if you are sensitive to loud noise, as it can get pretty loud while welding and grinding. Make proper use of and KNOW the tools you are using, if you don't know what something is or does, ask... it may save a limb or even a life. Be wary of sparks and weld flashing, eyes are extremely sensitive, and if extreme or prolonged enough, damage can lead to permanent blindness.
[edit] History
Welding has been around in some form or another ever since people realized that metal could be useful. One of the oldest methods of welding was actually forging. A metal ore would be retrieved by mining, smelted in a hot fire, collected into a large quantity of almost pure metal, and hammered into shape by using different fire techniques. Different methods of kindling, stocking and airing a fire could control the heat that it would produce. For example, to forge a sword a fire would need to heat the metal (likely copper or bronze), to a red-orange glow. Eventually, mixed metals (alloys) were used for higher strength and a range of new uses.
[edit] Processes
[edit] SMAW
There are several different ways in which to weld. The most common in industrial workplaces is 'SMAW', or "Shielded Metal Arc Welding". The 'stick' or 'rod' is placed into a 'stick holder' (gun or clamp style) which is then scraped or tapped onto the grounded weld piece to produce an 'electric arc', which produces enough heat to melt the 'rod' and form it into the weld piece. This process utilizes electricity to push out a "glob" of molten metal onto a plate(s) of metal, the 'workpiece'. Pipeline and structural welders use this method the most because of its deep 'penetration' (how much it digs into the base metal), and pressure handling capabilities.
[edit] MIG/MAG
The next most common method of welding is MIG or MAG welding (MIG- Metal Inert Gas and MAG- Metal Active Gas), MIG welding utilizes the same principal as SMAW, but the consumable is not a 'rod', but a wire on a spool, which is fed through a 'gun'. The welder may prefer this method because of its ability to travel along the weld surface faster, and has a similar outcome in quality of the weld. However, spools of wire can be expensive, and the use of a 'shielding gas' is needed to keep the weld free of contaminants (oxidization, particles, bubbles, etc.). A similar method of MIG/MAG is available, simply called 'flux core welding'. The only difference with this method is that there is no 'shield gas', but the wire is either coated or filled with a 'flux' material, which burns off and produces its own shield gas. The welder must chip this flux off the face of the weld, as it stays on the cooled metal surface once the weld is completed.
The reader should note that the processes talked about in this chapter are the most commonly used methods that a welder may use. There are however, other methods that will be discussed in a later chapter.
[edit] Oxy-Fuel Cutting and Welding
OxyFuel cutting and welding is a skill all in itself. The terms, oxy- (standing for oxygen,) and fuel (the assortment of gases that produce combustion) speak for themselves. Oxy-Acetylene welding is the most common fuel to use, but others can include natural gas, propane, MAPP gas, gasoline or any number of 'hot' gases.
Generally, the principal for oxy-fuel welding or cutting is the same. Oxygen is supplied in ratio to the fuel gas, and is then lit by a sparking lighter. Valves on the torch handle control the flame (more oxygen to make an oxidizing flame, or more gas to make a carbonizing flame, or in between to make a neutral flame). Welding with oxy-fuel usually desires a 'neutral flame', with no 'feather'. A 'feather' is cooler then the 'cone', the flame at the very tip of the torch. 'Feathers' can be used to determine how carbonizing a flame is. A slightly carbonizing flame is desirable when welding with brass rod, or 'brazing', thus, the 'feather' should be present, but only slightly above the 'cone', about a half of an inch. For direct welding of steel and mild steels, no 'feather' should be present, but use of a hot 'cone' is efficient. For steel, the welder may desire to apply the use of a 'filler rod', or a long, skinny rod of metal similar to the base metal. This helps to build up a weld face and strengthen the joint. This is done by heating the base metal into a molten puddle at the base of the joint, and then 'dipping' or adding the filler rod directly to the puddle.
Cutting involves the same principal, but requires (in most cases) a special torch handle and head. In a regular torch head, there is only one 'orifice', or hole, for which the gas and oxygen can pass through. In a cutting torch, however, there is the one 'orifice' in the center, and a circle of orifices around it. The purpose for this is simple. The torch is lit regularly, and adjusted to a hot neutral flame. The flame is wider, more forceful and louder (although not much). The torch handle has a lever on it that allows the welder to have an extra "burst" of oxygen when he or she desires. This burst blows the hot metal out of the way, allowing a gap to be created, thus the cut is formed. This burst of oxygen is easier to be applied if there is more room to push the oxygen through, thus the extra orifices are essential.
[edit] TIG (GTAW) Welding
TIG welding is a form of arc welding, with the same principal to that of MIG/MAG or SMAW. An electric current is supplied, and is fed through a handle. TIG stands for 'tungsten inert gas' and GTAW for 'Gas Tungsten Arc Welding', both meaning the same thing. Tungsten is used as an 'electrode', which is semi-permanent in the torch. It carries the electric current and is used to establish and keep an arc. Tungsten is used because of its conductivity, versatility and high melting temperature. The electrode will become contaminated, however, if accidentally dipped into the weld pool. TIG is preferred by many because of its ability to weld "almost any metal". As long as a filler material (rod) is available, that particular type of metal can be welded with TIG. TIG welding is achieved by operating the torch in a similar manner to oxy-fuel welding, but the operator controls the heat by means of electricity. There are 'remotes' that the welder can use for this task, or it can be set directly on some machines, so it will not fluctuate. Fluctuation is desired in some cases, where the base metal must be cooled sufficiently at regular intervals so as to not burn a hole.
For other, more advanced welding techniques, see the Wikipedia.org "Welding" article.
[edit] SMAW
[edit] Introductory arc welding
Stick Metal Arc Welding is often the first welding technique that a welder learns. A machine supplies a negative electrical circuit to the work-piece via a clip and a welding rod is attached to the positive end of the circuit. When the rod is brought close to the work-piece the current connects creating sparks and heat which melts the metal and the rod together. It requires a very steady hand and patience. It is possibly the oldest electrical welding technique still in use. Pre-electrical techniques included 'soldering', 'forging' and 'oxy-acetylene (flammable gas) welding'. It is difficult at first to weld solid bonds without creating bubbles and SMAW is important for this skill as it is easier to feel what the weld is doing (welding is only possible when the eyes are protected by darkened glass so feeling is important). SMAW is preferred in high-strength structure welding, such as construction or pipeline. It generally takes more time and patience to stick weld than it does to MIG or gas weld. SMAW should be the method spent the most time on learning for a beginner welder. Welding practice should begin with an 'E6013' 3mm rod. This is a simple rod to manipulate, and has a medium heat range, with a medium penetration. Amperage for this rod should be set in AC current, working around 85-95 amps. This is an all position rod, suitable for many general applications.
To practice as a beginner, start with a 1/4 inch thickness metal plate around 1ft x 1ft. Do not forget to wear gloves and welders eye protection. If you are right handed start on your left, working to the right, and vis-versa for left handed (MIG welding goes the opposite direction). Try to weld straight lines across your one foot metal plate until it is covered in stripes. Chip off the black residue (slag) with a Chipping Hammer and use a wire brush for any smaller pieces of residue. If you allow the plate to cool down (try keeping a container of water nearby to dip your hot work-piece in), you can use both sides of the same plate repeatedly until you are comfortable and steady with the rod. You should learn to hold the tip of the rod around 2mm or less from the work piece and at a 45 degree angle. It is also nessecary to change rods in the middle of a weld without affecting its quality but this should become easy when you get your pace and angle comfortably. The rod will stick to the work-piece a lot at first. You will soon find that arc welding is like blowing hot liquid from a straw in the dark. You need to learn to make straight, smooth lines (beads).
When you are convinced that your welds are smooth and can maintain the tip of the rod at 2mm from the work-piece, move on to joints. The basic welding joints are T-joints (in the shape of a T, also known as fillet-joints) and lap-joints (overlapping edges, one resting on top of the other). To practice, use metal strips, 1/4 inch thickness, 2 inches wide and 8 - 12 inches long. Place two metal strips together in a T shape or overlapping and 'spot' weld at each end to keep them in place. Now weld from one side of the joint to the other in a careful, small circle motion of the rod, with an angle of 45-65 degrees (in both the up-down direction and left-right direction) keeping a distance of 1-2mm between the rod and the work-peiece. It is important to hold the tip of the rod so close to the joint as a good weld will melt and fuse the edges of the original work-piece. The finished weld should look almost smooth and the slag should break off effortlessly (will take at least a few hours practice for most people). The most important part of the weld is inside. Break your finished welds open with a hammer and a vice. Be careful. A good weld is not easy to open and fingers are easily removed against a piece of steel. Try weakening the spot welds with a hacksaw on difficult pieces. A good weld will have decently fused the original edges together. The bead should not cut a groove into the face of the work-piece or leave bubbles and gaps in the weld (the bond should be complete inside leaving no visible straight edge under the weld). This is the requirement to pass a welding examintaion. Note that a welded piece will lean toward the joint as it cools. Although enough heat is required to fuse the work pieces together, too much heat will make the whole piece red hot, worsening the distortion when it cools so practice is important.
Slightly more difficult to weld correctly without warping is the end-to-end-joint (two pieces beside each other end to end or side by side). This is only slightly more difficult than the previous joints. Practice on two 1/4 inch strips as before but this time take the edges off the strips with a file or rasp so that you are welding into a V-shape. Place together at the edges and weld along the gap. The weld should be done in a careful, small circle motion of the rod, at a slightly more raised angle than before around 60-80 degrees. The finished weld should look like a "stack of dimes" or evenly spaced ripples in the weld. The sides of the weld should be evenly flushed with the base plate raising to a bump in the middle. If the weld looks "stretched", the travel speed should be slower and the tip closer. There will be significant 'slag' and 'spatter' on the sides of the weld, and will be just generally ugly looking. If the build up of the finished weld is higher than about an sixth of an inch, the travel speed was likely too slow. Slightly mor difficult than this is the corner-joint (end to end in a V or L shape). The requiremets for these welds are the same, properly fused without any bubbles or gaps.
Once these welds have been mastered, play around with welding a plate in a vertical position. Weld vertical beads going up, not down. This is significantly more difficult than a flat position, and can be frustrating to learn, but patience is important. Use a counter-clockwise circle motion, spiraling upwards, pausing at the top of each motion. It may feel more comfortable to pause at the bottom of this motion, but this will cause bad 'undercut', where the sides are not filled in with weld material.
Once this has been mastered, one may choose to continue in SMAW, or move into oxy-fuel welding for a time.
- Remember that most arc welds shouldn't be cooled in water or cooling oil, but by allowing air access around the whole joint. Cooling, in most cases, changes the way the metal atoms retract and can weaken the weld.
[edit] 6010 and 6011 Rods
E6010 Rods are the most preferred rod for deep 'root' passes, or where a lot of penetration is required. Often, this root pass is covered with two hot passes and a cap or 'face' pass with E7018 rods. This rod has been said to be one of the hardest rods to use, due to the constant attention to rod manipulation, travel speed, and 'arc length'. E6010 is a 'fast-freeze' rod, meaning it is suitable for use in all positions. It is best used with the positive polarity on the rod, or 'reverse polarity', (DC-) with amperage from 75 to 95 being the best (depending on the application). Practice using this rod by cutting (or buying) two 1/4 inch plates with about a 35.5 degree bevel on either side. The bottom of the bevel should be a sharp edge, which will be ground down to about a 3/16 of an inch lands, with either a 3/16 inch gap or 3/32, which ever is more comfortable. Start by simply running a bead down a plain 1/4 inch scrap plate to get the feel of the rod. The flux is cellulose, and is ugly looking at the end; use a wire brush and chipping hammer to clean off. Once comfortable manipulating a straight bead, place the two beveled plates together with the lands facing each other. Make sure that they are perfectly even, as this will cause less grief for the root pass. Use 80 or 85 amps to run the root pass, and start with tacking the two plates together. Weld the root with a 'backhand' motion, (pushing the rod from the base of the weld to the top). Once the root is finished, flip the plate over and wire brush off the bottom; the weld should have fallen through the gap and sealed along both sides evenly if done correctly. If this looks shallow or pitted, turn the amperage up by 5 (but to no more than 90 amps,) and try again, pitching the rod into a sharp 85 to 90 degree angle to the plates. While welding, try to 'dig' the rod into the sides of the bevel, pausing on the sides. If done right, a loud crackling-hissing noise will be heard. This is simply the 'wind' as the weld falls through the bottom of the root. Remember to keep a short arc length with this rod, no longer than the thickness of the rod itself. Otherwise, the weld will be weak, insufficient and contain excessive spatter. Also, consistently weave the rod back and forth, pausing slightly off center, both sides. Once cleaned off, the root pass should be shiny and smooth on the face side, and evenly deep on the bottom. Continue to practice the root weld until it comes naturally and comfortably, as this is a main strength of the whole weld.
Next, a weld will be placed over top the root; a 'hot pass'. Turn the amperage up to 90 or 95 amps (+10% comparing to the root amperage). Weld over top of the root, digging into the sides of the bevel by weaving and pausing on each side momentarily. Minor undercut is normal in this case, and will be filled in by a second hot pass.
The second hot pass should be conducted the same as the first, but the welder may choose to turn the heat down by 5 amps, depending on the joint to be produced. After this, finish with a 'cap' or 'face weld', which must have no undercut on either side. This pass should be done around 85 amps. Use a weaving motion, something like upside down "U's", pausing on either side to allow filler metal to fill in any undercutting. The 6011 rod is essentially the same as a 6010, but is used in AC instead.
[edit] 6010 and 7018
The next thing to practice is a 6010 root pass, with 7018 hot and face passes. This is a common method used often in pipeline and boiler welding. The 6010 will dig into the root pass and cause it to have a higher tensile strength. The 7018 will add more strength to the top than would a 6010 alone. It also has a lesser chance of undercutting the side, which would cause a weaker weld. For the most part, a 7018 rod is easy to manipulate, and deposits nicely. Use DC straight (DC-) polarity around 105 to 115 amps. The flux on this rod is strange in how it reacts to moisture and humidity. A 'rod oven' is essential if these rods are going to be used in large quantities. The flux must be thoroughly dried out to be used properly, otherwise it will not protect well enough and the weld may look sloppy and weak. If only being used for a personal project, find an old baking sheet, turn up the kitchen oven to around 350 degrees, and bake the required amount of rods for about fifteen minutes. This is far cheaper than a rod oven. To practice with this rod, simply run several beads in the flat, vertical and horizontal position. If control of the 6010 rod has been achieved already, this will not be a big problem. Remember to make small cursive 's' motions on the horizontal weld, pausing at the top, and continuing through quickly on the lower area. Vertical welds should be done in a sort of 'z' motion, pausing on either side, and going quickly over the middle, zigzagging upwards. Once this has been accomplished, practice some more on the 1/4 inch plates in all these positions, welding the root with the 6010. Don't forget to grind lands into the beveled sides (about 3/16 of an inch). Once the root has been cleaned and satisfactory, use the 7018 at 105 amps DC-. For the third pass, turn it up to 115 amps DC-, and finally, for the cap weld use 105 amps again. Remember to clean between each pass, otherwise strength will be decreased. Cool slowly by leaning it somewhere that is not affected by a draft, but where room temperature is stable. Make sure that air has access to the whole plate. You can test these bevel welds by cutting each one down the middle, crossing the weld path. Grind each edge smooth, and the welds should be ground flush to the rest of the plate; both root and face sides. Place in a 50 or 25 ton press, pressing slowly into 'U' shapes. To test the root pass, place the face weld upwards. To test the face weld, simply face the root weld upwards. If there is more than a quarter inch of cracking anywhere on either weld, the weld should be retried.
