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Welding Tech



In a repair shop, welding equipment may be needed to replace or patch sheetmetal on a vehicle body, to install a trailer hitch, to fabricate or install engine mounts, to make chassis or suspension modifications, to install or remove exhaust components, to repair cracked or broken stampings and castings, to fix a broken hinge or support, to remove broken fasteners, to separate rusty parts, or to do any of a wide variety of different repair jobs that require the ability to heat, melt or join metal. If you are good with a welder, it will be a big plus when you're looking for employment at a shop. Your school may offer a welding program or your automotive class just might have a welder sitting around in the corner. Whenever you get the chance, practice with the welder. It's the only way one can get good at it. Welding Precautions Before we go any further, there are a couple of points you need to keep in mind about welding. The first is that welding isn't as easy as it looks. You need some basic training in welding techniques otherwise you're going to be very frustrated with your initial attempts to weld metal. Producing good quality, high-strength welds requires a certain amount of skill and a thorough knowledge of your welding equipment. Second, welding produces extremely bright light, as well as ultraviolet (UV) radiation, that can burn your eyes. Approved eye protection is always required when welding (the amount of shading will depend on the type of welding equipment being used). Bystanders should also be warned not to stare at the welding arc or flame. Shaded goggles or a full face mask with a shaded viewing slot should always be worn while welding. Auto-darkening welding helmets ($125 to $400 price range) are even better because the glass doesn't darken until you start to weld. Ordinary welding goggles and masks can be difficult to see through until the flame or arc is lit. Third, welding is a potentially dangerous process that must be treated with respect and common sense. You must wear heavy leather gloves and protective clothing to minimize the risk of being burned by molten metal dripping or splattering from the work surface. Arms should be covered and pant legs should extend over the tops of your work boots. Welding also gives off toxic fumes, so avoid breathing the vapors and work in a well-ventilated area. Also, the arc or open flame must be kept away from fuel lines, the fuel tank and other nearby materials that are flammable and may be ignited by the heat (carpeting, upholstery, wires, brake lines, rubber and plastic parts, etc.). Finally, surface preparation is extremely important to achieve good quality welds - especially on aluminum. Oil, grease, paint, dirt, rust, oxide and anodized coatings are all contaminates that can weaken a weld. Surfaces to be welded must be clean and dry. Aluminum surfaces should be cleaned with a stainless steel brush (the brush should be used on aluminum only, otherwise it may pick up contaminants). Gas Welding Oxyacetylene welding uses a mixture of acetylene gas and oxygen fed through a torch to create flame temperatures of about 6,000 F. Each gas is stored in its own high pressure cylinder and is fed through a pressure regulator to a hand-held torch. Knob adjustments on the torch allow the user to change the gas mixture to create different flames for different purposes. Interchangeable torch tips with different lengths are available for different welding applications. Oxyacetylene welding is used primarily to weld heavier gauge steel components, but it can also be used to cut metal when the flame is fed extra oxygen (an "oxidizing" flame). Special "cutting torches" are also available for this purpose. Gas welding generates a lot of heat so it is not suitable for thin sheetmetal or for high-strength steels that lose strength if they get too hot. When the flame is adjusted to produce less heat, a gas welding torch can also be used for "brazing" (joining metal by melting brass filler rod to fill the gap) and for heating and loosening rusty and frozen parts. Use caution when heating heat-treated parts such as springs, steering knuckles and other suspension components because too much heat can weaken and damage the metal. For this type of heating, a propane torch is much safer. Oxyacetylene welding is a very versatile process and requires only a torch, regulator set (the gas bottles are usually rented) and mask or goggles for eye protection. A basic torch set may cost only a few hundred dollars. The main consumables are the bottles of gas, flux (used to clean and prepare the weld area) and filler rod when used to fill in joints. Arc Welding Arc welding uses a high amperage electrical current to create temperatures of more than 7,500 F. Arc welding is used primarily for welding heavier gauge steel. It uses a consumable electrode rod and a high amperage current generator. The generator has two leads, a negative one that is clamped to the workpiece and a positive one that the operator uses to hold the electrode. When the electrode is touched to the surface of the metal, it sparks and forms an intense arc. The rod must then be held at a certain distance from the surface of the metal to maintain the arc while welding. Rods are coated with flux to keep the weld area clean, and different types of rods are required for different alloys of steel. Arc welding cast iron is possible but is very difficult because cast iron is brittle and tends to crack as it cools and shrinks after it has been welded. Furnace welding (preheating a casting to high temperature in an oven and welding it while it is still hot, then keeping it warm while it slow cools for a period of many hours) is about the only welding technique that works well on cast iron. Arc welding equipment is available in various amp ratings, with the higher amp units (200 amps and up) typically requiring a 220-volt outlet. These typically sell for several hundred dollars and up and are required for welding heavier gauge steel. Smaller capacity 90 to 130 amp arc welders are also available that can be plugged into an ordinary 115-volt outlet. Some of these sell for $100 or less, but are only suitable for light work on metal up to about 3/16" thick. The only consumables are the electrodes, which come in various diameters ranging from 1/16" to 5/32". The cost of the electrodes varies depending on the type of metal, but is typically $10 to $25 for a 5-lb. bundle. MIG Welding Metal Inert Gas (MIG) welding (also called Gas Metal Arc Welding or GMAW) is a versatile and popular method for welding light sheetmetal and thin-gauge steel. It is also the recommended method for repairing or joining structural components and body panels made of high-strength steel and high-strength low alloy steel. Also called "wire feed" welding, MIG welding uses a high amperage electrical current to create a high temperature arc. But instead of using a consumable rod like an arc welder, a MIG welding uses a thin wire that is fed through the nozzle in the handle. This makes it much easier to maintain the arc and also limits the heat to a very concentrated area. The on-off cycling of the arc, which happens about 20 to 200 times a second depending on the voltage setting, also reduces the heat required to make the weld and minimizes heating of the surrounding metal. MIG welding can be used for continuous welding, stitch welding or spot welding with or without gas. When gas is used to shield the weld area (either carbon dioxide or a mixture of 75% argon and 25% CO2), it prevents oxides from forming on the metal that interfere with the strength of the weld and also helps cool the surrounding area. Gas shielding is necessary when welding aluminum (pure argon is recommended, but an argon/CO2 mixture also works) and so is aluminum wire (ER4043 or ER5356). The gas may be supplied from a bottle or from special flux core wire that generates its own gas when it melts. The depth to which a MIG welder can penetrate depends on the amperage as well as polarity. Most MIG welders use "reverse" polarity with the wire being positive and the metal work piece being negative. This setup gives the greatest penetration with the fewest amps. Weld penetration is also greatest when CO2 gas is used. But CO2 also gives a more unstable arc, which encourages spatter. For thin materials where less penetration is needed, an argon/CO2 gas mixture works best. For extremely thin gauge metal, straight polarity (wire negative) is recommended. This puts more heat into the wire rather than the metal, which leaves behind a higher bead. But at the same time, it lessens the likelihood of burning through the metal. When MIG welding high-strength steel, AWS ER-70S-6 wire is usually recommended. Some body repairmen use a silicone-bronze wire for MIG "brazing" cosmetic repairs on exterior panels because it grinds off easily. But because this kind of wire isn't as strong, it should not be used for structural welds. A 150 to 200 amp MIG welder can handle most common jobs in an automotive repair shop. These units typically sell for $700 to $2,500 or more depending on the features and amperage. Less expensive light-duty 115-volt MIG welders, which sell for as little as $300 to $600, are also available for jobs that don't require more than 70 amps. Most of these are the "gasless" MIG welders that use the special flux core wire to eliminate the need for bottle gas. Consumables include spools of wire ($10 to $120 depending on the gauge, length and type of wire) and gas (if used with solid core wire). TIG Welding TIG welding is a special type of arc welding that is used mostly to repair heavier gauge aluminum components and aluminum castings such as cylinder heads, engine blocks and transmission housings. Aluminum is trickier to weld than steel because oxide forms quickly on the bare metal. This creates a barrier that protects the metal against further corrosion, but also interferes with welding by increasing the current required to break through the layer. Therefore, the metal must be shielded by gas (pure argon is recommended) while it is being welded so the oxide can't form. Aluminum melts at around 1,200 F compared to 2,500 F for steel. Although it takes less heat to melt the metal, the heat must be more concentrated in the weld area because the metal conducts heat away so quickly. That's where TIG welding comes in. TIG welding is essentially arc welding with a shielding gas and a nonconsumable tungsten electrode. The TIG process creates extremely high temperatures in a concentrated region while the shielding gas protects the weld from contamination. No flux is used, so there is no slag to cause problems. Nor does the process itself produce smoke or toxic fumes, making it a clean welding process. There is no transfer of metal across the arc in TIG welding so there are no globules of spatter to contend with. There are also no sparks if the metal is free from contaminants. This can be an advantage in situations where spatter might create problems around the weld area or on adjoining parts. If filler metal is needed, it can be added manually using an aluminum alloy filler rod. The technique is the same as when using a filler rod and oxyacetylene torch. The alloy of the filler rod must be compatible with the base alloy. ER4043 filler rod is one of the most commonly used rods for TIG welding aluminum-silicon alloy castings. For high magnesium alloy castings (which can be identified by chemical tests), a ER5356 filler rod is recommended. TIG welding equipment consists of an arc welder power unit with a tungsten electrode gun and shielding gas supply. High-amperage guns are often water-cooled, but low-amperage guns can be air-cooled. TIG welding can be done using direct current of either straight or reverse polarity, or alternating current. When alternating current is applied to the surface of the metal, it heats the metal during one-half the voltage cycle (electrode negative) and cooks off the oxide during the reverse portion of the cycle (electrode positive). This back-and-forth heating/cooking action keeps the weld free from contamination and makes for a strong weld. Using direct current with straight polarity (DCSP - electrode negative) can produce more heat at the work surface, but it doesn't do as good a job of cleaning the metal. Using direct current with reverse polarity (DCRP - electrode positive) does a fine job of cleaning the surface, but it doesn't produce as much heat. So high frequency alternating current works best when TIG welding aluminum. There are a variety of different electrodes that can be used with a TIG welder. Most experts say tungsten thorium (color coded green) electrodes work best with aluminum. Zirconium tungsten electrodes perform even better, but cost five times as much and are hard to find. Crack Welding When welding a cracked aluminum casting, it's very important to determine the full extent of the damage so the crack can be completely ground out. Extend the grinding a short distance beyond the visible ends of the crack to make sure you've eliminated all damage. The area can then be cleaned up by bead blasting or brushing prior to welding. Aluminum is nonmagnetic so magnetic crack detection equipment is no help in finding cracks. You have to use penetrating dye instead. To find cracks with dye, all dirt and oil must first be cleaned from the surface. The dye is then sprayed on and allowed to dry. Wipe the excess dye dust off then spray on the developer. Any cracks will then appear as dark lines on the metal. If you're welding a casting (such as a cylinder head, manifold or other part that's subject to thermal stress in normal use), preheat the casting to 200 to 300 F with a propane torch or by placing it in a baking oven (use a temperature crayon or very accurate thermometer to prevent overheating). The heat helps cook out oil and grease that might contaminate the weld while reducing the chance of cracking once the weld cools. After welding, the part should be allowed to cool slowly. This can be done by placing it back in the oven or wrapping it with an insulating blanket. Welding Safety: Welding can be dangerous if you are not paying attention. The first rule of welding safety is Eliminate any Horseplay! Other safety issues that should be addressed are:
  • Ventilation: It is important to use enough ventilation to keep the fumes and gases from your breathing zone. For occasional welding in a large room with good cross-ventilation, natural ventilation may be adequate if you keep your head out of the welding fumes. However, be aware that strong drafts directed at the welding arc may blow away the shielding gas and affect the quality of your weld.
  • Electric Shock: Remember, electric shock can kill. Wear dry, hole-free leather gloves when you weld. Never touch the electrode or work with bare hands when the welder is on. Be sure you are properly insulated from live electrical parts, such as the electrode and the welding table when the work clamp is attached. Be sure you and your work area stay dry; never weld when you or your clothing is wet. Be sure your welding equipment is turned off when not in use.
  • Arc Rays: It is essential that your eyes are protected from the welding arc. Infrared radiation has been known to cause retinal burning. Even brief unprotected exposure can cause eye burn known as welder's flash. Normally, welder's flash is temporary, but it can cause extreme discomfort. Prolonged exposure can lead to permanent injury.
  • Watch your workspace: Before you get started on any welding project, it is important that you make sure your work area is free of trash, sawdust, paint, aerosol cans and any other flammable materials. A minimum 5' radius around the arc, free of flammable liquids or other materials, is recommended.
  • Gas Cylinders: Cylinders can explode if damaged. Always keep your shielding gas cylinder upright and secured. Never allow the welding electrode to touch the cylinder.
A fire extinguisher should also be on hand during any welding. Finally, see the instruction manual for your welder for added safety information. You can also visit www.lincolnelectric.com/community/safety for added information on safety. Information provided courtesy of Lincoln Electric, Cleveland, OH.

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