|
What is MIG Welding?
MIG stands for Metal Inert Gas welding, many times called Wire-feed.. Also referred as GMAW (Gas Metal Arc Welding). The "Metal" refers to the wire which is what is used to start the arc. It is shielded by inert gas and the feeding wire also acts as the filler rod. A semi-automatic process, it is fairly easy to learn and use.
What is TIG Welding?
TIG welding produces temperatures up to 35,000 degrees Fahrenheit, yet this concentrated heat can be precisely controlled and directed. When filler metal is required, it can be added manually by feeding welding rod into the puddle, similar to oxy-acetylene welding. In fact, people who have learned to oxy-acetylene weld will usually pick up TIG welding fairly easily.
TIG welding is done with a hand-held torch that holds the slender electrode the welding current passes through. The electrode is surrounded by a ceramic cup which directs the flow of an inert shielding gas (usually argon) that keeps atmospheric oxygen away from the weld zone. Most machines have a control, either foot or hand-operated, that allows you to change the welding current 'on the fly'. These features offer unrivaled control of all aspects of the welding process, and a skilled operator can make a weld that has good penetration with a small, crisply-defined, low-profile weld bead which is quite ductile, or workable. The workability of the weld is an enormous advantage for those doing high-end bodywork, since the best way to repair the distortion caused by welding is to hammer on-dolly on the weld bead! MIG welds, while quite strong, are more brittle than TIG welds, and may crack if they are hammered too much.
Another benefit of the TIG process is that it can be used to weld just about any metal. It's great not only for steel and aluminum, but for stainless, titanium, copper, bronze, and magnesium, to name just a few.
Shielding Gases
Argon
Argon + Hydrogen
Argon/Helium
Helium is generally added to increase heat input (increase welding speed or weld penetration). Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen cracking.
TIG Welding Limitations
Requires greater welder dexterity than MIG or stick welding
Lower deposition rates
More costly for welding thick sections
TIG welding has been around since the 1940's, and although it was considered esoteric at first, now that many people are aware of the advantages offered by TIG welding, the machines have become quite popular and affordable. Most of the better street rod shops (and many serious home builders) utilize TIG welding for both body and chassis work. Once you've become accustomed to the incredible control it offers, and to the beautiful look of a well-formed TIG weld bead, most people get hooked!
The type of TIG machine you should purchase depends on the type and thickness of metal you'll be welding. A TIG welder with a 180 or 200 amperage output, and AC/DC output capabilities will handle most automotive applications. (You need both AC and DC output if you want to weld on steel and aluminum.) For doing bodywork, it's a real advantage to have a machine that will go down to very low settings - starting a weld around 5 or 10 amps is very beneficial sometimes. Some older machines only go down to 25 amps, and it's a bit tricky to do delicate welding on very thin metal with that much amperage.
While TIG welding offers many advantages, learning to make pretty weld beads, which involves coordinating your hands, feet and eyes, takes patience and lots of practice. When you become proficient with TIG welding, the results are very satisfying. Here are a few tips to get you started.
1. Clean everything carefully - including both sides of the base metal and the welding rod. TIG welding is particularly sensitive to any contaminants, which can severely compromise the integrity of the weld.
2. Before you start to weld, get in a comfortable position and relax. Maneuvering a TIG torch is like trying to write neatly in a small space. Brace your arms, move slowly, and focus your attention on the tip of the tungsten electrode - in fact, many people grip the torch like a pencil.
3. Hold the torch at the proper angle. Travel angle is defined as the angle relative to the torch in a perpendicular position. Normal welding conditions call for a travel angle of 15 to 20 degrees. Travel angles beyond this lead to less penetration, poor direction of the weld metal, poor shielding gas coverage, and general arc instability.
4. When TIG welding, always use the push technique - pushing the torch ahead of the weld puddle. Pushing offers you a better view of the weld puddle, provides good gas coverage of the weld, and ensures that oxides have been removed when using alternating current, as you will when welding aluminum.
5. Practice welding on scrap. Start by running a bead on a flat piece of metal - don't try to weld a joint or add filler at first. Experiment with the amperage control to find the right amount of heat. Learn how to control the size and shape of the weld puddle.
6. To start an arc with a machine equipped with high frequency (most good machines are), hold the electrode about 1/8 in. from the work and depress the foot pedal - never touch the electrode to the work during a high frequency start. Many people tilt the torch and rest the gas cup against the work, establish the arc, and then shift the torch into the proper welding position.
7. Maintain consistent arc length - about one electrode diameter from the work. Varying the arc length produces inconsistencies. One common error beginning TIG welders make is lifting the torch or tilting the torch too much to get a better view of the weld puddle. If you need a better view of the weld area, shift the position of your head down and to the side.
8. Maintain a travel speed consistent with the bead shape you desire. Moving the torch very quickly creates a bead that is too narrow, while moving the torch too slowly produces an excessively wide bead. When TIG welding, don't move the torch forward until the weld puddle reaches the desired size. Remember that holding the torch too long in one spot can result in melting a hole through the base metal, especially when welding thin metal.
9. Once the arc is started and you've established a weld puddle of the desired size, you can begin to add filler metal. Hold the filler rod at a 15 to 20 degree angle up from the workpiece, creating a 90-degree angle between the filler rod and the tungsten. Be sure to move the torch and the filler rod progressively so that the weld pool, hot filler rod end and the solidifying weld are covered by the flow of shielding gas. A common mistake is touching the electrode with the filler rod, or touching the weld pool with the electrode. In either case, the tungsten usually becomes contaminated. Always stop and re-sharpen The electrode before you continue.
10. It takes a long time to learn how to combine all the movements TIG welding requires - where to hold the torch, how fast to move the puddle, and how much rod to feed. Have patience, and practice the same moves over and over again - that's the only way you're going to learn to make a good TIG weld. If you need more information on equipment or welding technique, one good on-line source is www.millerwelds.com. You'll find an extensive education section with e-training, tech tips, ask the expert sections and more information to help you get the most from your welding experience.
Weldcraft Tig Torch & Bernard Water Cooler setup
Correct Torch Installation
Torch installation is simple but coolant flow direction is often incorrect. The correct procedure involves:
Supplying coolant water to the water hose of the TIG torch (small left-hand fitting)
Returning the coolant through the power cable (large left-hand fitting)
This procedure directs cooled water to the head of the TIG torch (the heat source), and returns it to the cooler via the power cable. The result is maximum reliability to all components of the torch assembly.
Miller & Weldcraft Tig Torches:
The torch used for GTAW welding may be either water or air cooled. High production or high amperage torches are usually water cooled while lighter duty torches for low amperage applications may be air cooled. The water cooled torch is designed so that water is circulated through the torch cooling it and the power cable. The power cable is contained inside a hose, and the water returning from the torch flows around the power cable, thereby cooling it. In this way the power cable can be relatively small making the entire cable assembly light and easily maneuverable by the operator. When using a water cooled torch a lack of cooling water or no cooling water at all will cause a heat build-up and will probably cause the polyethylene sheath to melt or possibly burn the power cable in two.
A torch manufacturer’s specifications will designate the required amount of cooling water for a specific torch. A safety device known as a “fuse assembly” can be installed in the power cable. This assembly contains a fuse link which is also cooled by the water. If there is no cooling water circulating, the fuse link will melt in two and prevent damage to other more expensive components. The fuse link is easily replaced. When the fuse link is replaced and water flow is maintained, welding can continue.
Air cooled torches are popular for lower amperage applications. They require no additional cooling other than the surrounding air and the flow of the relatively cool shielding gas through the torch. The power cable must be heavier than the cable in a water cooled torch.
The power cable may be wound around the gas carrying hose or inside the gas hose.
Additional Tips
The TIG torch should be connected directly to the cooler as described above.
Do not use the solenoid in the power supply to control water flow. This causes a pressure surge in the torch, and unnecessary wear and heat in the coolant pump.
The solenoid should only be used when connecting to a city water supply. This is not recommended because most city water consists of high mineral content that can cause blockages in the TIG torch, and the pressure should be regulated to prevent damage to the torch.
Water Cooler Setup
Water cooler setup is important and often overlooked. All Miller and Bernard style water coolers, are among the best in the industry. Coolers range from 2 gallons to over a 4 gallon coolant capacity . Always check the cooling capacity of the cooler to the maxium amperage rating of the welding source bring used .
Water coolers should be connected directly into the 110-volt plug available on most TIG power supplies: to ensure the cooler is running when the power supply in on to provide the TIG torch with adequate cooling at all times
Use Miller's Coolant
Bernard & Miller Water Coolers recommend the use of Miller Coolant in their products. Even though you may be tempted to use automotive antifreeze in water coolers, don't do it! Automotive antifreeze includes a stop leak solution designed to plug small leaks. These properties will block the small passages in a TIG torch, eventually completely blocking water flow, causing overheating and failure of the TIG torch. Miller's coolants contain a mixture of distilled water and ethylene glycol to protect against freezing to -37 F or boiling to 227 F . Both coolants contain a compound that resists algae growth
Follow the manufacturers procedures above to improve reliability and extend torch life on your new and existing equipment.
( articles and specs are from Miller Electric , Weldcraft , Bernard , Hobart Welders and ITW .
What is Square Wave?
Square Wave refers to the shape of the voltage cycle in a welding arc. In an AC wave, a typical sinusoidal or sine wave, changes the voltage from positive to negative gradually, although many times a second. This means the voltage will not be consistent and at times will actually go through zero. Square Wave, on the other hand, changes the voltage from positive to negative almost instantly, making for a much smoother and more stable welding arc. This is particularly important when welding aluminum and when considering aspects like cleaning and penetrating action.
What is right for me, MIG or TIG?
For certain type of work TIG is required, like welding chrome moly for some racing organizations. Intricate work, like gunsmithing is also well suited to TIG. TIG is used by many auto restorers who prefer a more precise, perfect finish that requires little to no finish work. TIG is most similar to gas welding in technique, so if you've done oxy-fuel welding, TIG should be a natural transition.
MIG is required by law and by insurance companies in many localities for structural repair of automotive frames. MIG is also much easier to learn and faster to weld. For doing other types of welding, like sheet metal, it can be a matter of personal preference. For an auto body repair shop or a novice welder, a MIG is a good, practical all-around welder.
Flux Cored Welding
Flux Cored Arc Welding (FCAW) is frequently referred to as flux cored welding. Flux cored welding is a commonly used high deposition rate welding process that adds the benefits of flux to the welding simplicity of MIG welding. As in MIG welding wire is continuously fed from a spool. Flux cored welding is therefore referred to as a semiautomatic welding process.
Self shielding flux cored arc welding wires are available or gas shielded welding wires may be used. Flux cored welding is generally more forgiving than MIG welding. Less precleaning may be necessary than MIG welding. However, the condition of the base metal can affect weld quality. Excessive contamination must be eliminated.
Flux cored welding produces a flux that must be removed. Flux cored welding has good weld appearance (smooth, uniform welds having good contour), but leaves more splatter and produces more smoke . Flux welding is not generally used in body work because of the greater prep work after welding and the ability to weld thinner metal is not as good with flux welding . There are some new wires out like "Twenty Gauge" by Harris Welco that has a powered inside for no slag, no cold lap, no splatter and no burn thru on thin sheet metal. Works very well on galvanized metal from 28 gauge to 3/16".
MIG Welding Shielding Gas
The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool. There are three primary metal transfer modes:
Spray transfer
Globular transfer
Short circuiting transfer
The primary shielding gasses used are:
Argon
Argon - 1 to 5% Oxygen
Argon - 3 to 25% CO2
Argon/Helium
CO2 is also used in its pure form in some MIG welding processes. However, in some applications the presence of CO2 in the shielding gas may adversely affect the mechanical properties of the weld.
What is Stick Welding ?
Stick Welding
Shielded Metal Arc Welding (SMAW) is frequently referred to as stick or covered electrode welding. Stick welding is among the most widely used welding processes. The flux covering the electrode melts during welding. This forms the gas and slag to shield the arc and molten weld pool. The slag must be chipped off the weld bead after welding. The flux also provides a method of adding scavengers, deoxidizers, and alloying elements to the weld metals.
What is Plasma?
Plasma - The fourth state of matter following solid, liquid, and gas. Plasma is an ionized (electrified) form of gas. In plasma cutting, a gas such as Nitrogen is sent under pressure through the torch where it begins to swirl and is forced out a small orifice at which point it passes through an electric arc and the gas is ionized. The electricity "excites" the electrons of the gas atoms. Regular air contains enough nitrogen that it is used for most shop size plasma cutters. It results in a very quick, clean cut and imparts little heat into the base metal. Plasma is one step down from a laser.
Why is plasma better than my old oxy-fuel torch? Plasma does not use expensive, hazardous gases, only compressed air in most cases. It imparts much less heat into the piece being cut, warping less. It also leaves a very slim kerf, or cut out area and leaves little to no slag to clean up or grind off. The cost per cutting hour can be less than oxy-fuel since there is no gas cost. It is also much quicker and easier.
Soldering and Brazing
Soldering and Brazing are joining processes where parts are joined without melting the base metals. Soldering filler metals melt below 840 °F. Brazing filler metals melt above 840 °F. Soldering is commonly used for electrical connection or mechanical joints, but brazing is only used for mechanical joints due to the high temperatures involved.
Soldering and Brazing Benefits
Economical for complex assemblies
Joints require little or no finishing
Excellent for joining dissimilar metals
Little distortion, low residual stresses
Metallurgical bond is formed
Sound electrical component connections
What is Duty cycle?
Duty Cycle- The amount of time a machine can be used at a particular output. Expressed as a percentage of a ten minute cycle, a 150 amp machine with a 30% duty cycle set at maximum will allow 3 minutes of use for every ten and a 60% duty cycle would allow 6 minutes of use for every ten. The duty cycle increases as the power setting decreases so if the 150 amp machine were to be used on a 30 amp setting the duty cycle might be 100% allowing it to be used 10 minutes out of every ten.
Keep in mind, however, that the actual total time a machine can be used continuously is not determined by a timer, but typically by a thermostat within the machine which will shut it off if the machine is too hot and needs to cool down before it does more work. Therefore, even a 30% machine can be used more than ten minutes at a stretch. Factors affecting duty cycle include whether or not the machine has an internal fan and ambient temperature of the work area.
What is an Inert gas?
Inert gas - Used to shield the electric arc from outside contaminants and gases which may react with the weld. An inert chemical is one with a full outer shell of electrons which do not normally react with other substances. Inert gases include argon and helium. Some other non-inert gases are used for welding such as CO2.
|
