Gas Metal Arc Welding (GMAW)

The term Gas Metal Arc Welding is the American Welding Society’s preferred name for this semi-automatic welding process that uses a wire feeder to deliver the filler metal to a hand operated gun to produce the weld.

The process is also widely known by the shop name MIG (Metal Inert Gas). The name Metal Inert Gas was used when the process was first developed to weld Aluminium using an inert (chemically non-reactive) gas supply. The process has evolved to become a favourite choice for welding steel with gases that are not inert.

When compared with Stick welding, the GMAW welding process is faster, easier, and requires little clean-up of welds. This makes GMAW welding cost effective for production welding in fabrication shops. The wire fed welding arc is capable of joining thin sections and bridging gaps in poor fit up situations. Welding is done by using a constant voltage welding machine to supply the power, a wire feed unit with an attached gun to feed the filler wire to the arc, and a gas supply system to shield the weld area.

Figure 1: Illustration of GMAW

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1) To improve the skill of welding especially Gas Metal Arc Welding. 2) To understand the process, the true way of welding and become professional in the welding process. 3) Understand the risk of the welding process and learn the way to weld in the safer way. 4) To born a many professional skill in welding. 5) To obtain good welding results. 6) Applying the project as the Gas Metal Arc Metal Welding subject requirement. 7) Practice and know the machine and tools that use in Gas Metal Arc Welding.

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The voltage, wire speed and gas flow are set by the welder according to recommended ranges for the application before welding. After positioning the gun, the welder pulls and holds the trigger to start the gas flow and the arc. The welder then controls the nozzle distance from the work, the angle of the gun, and rate of travel speed across the joint. At the end of the joint the trigger is released to stop the wire feed, gas flow, and break the arc.

Figure 2: Illustration of Operation of GMAW For most of its applications gas metal arc welding is a fairly simple welding process to learn requiring no more than a week or two to master basic welding technique. Even when welding is performed by well-trained operators weld quality can fluctuate since it depends on a number of external factors. All GMAW is dangerous, though perhaps less so than some other welding methods, such as shielded metal arc welding The basic technique for GMAW is quite simple, since the electrode is fed automatically through the torch (head of tip). By contrast, the welder must handle a welding torch in one hand and a separate filler wire in the other, and in shielded metal arc welding, the operator must frequently chip off slag and change welding electrodes.

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GMAW requires only that the operator guide the welding gun with proper position and orientation along the area being welded. Keeping a consistent contact tip-to-work distance is important, because a long stick out distance can cause the electrode to overheat and also wastes shielding gas. Stick out distance varies for different GMAW weld processes and applications. The orientation of the gun is also important—it should be held so as to bisect the angle between the work pieces; that is, at 45 degrees for a fillet weld and 90 degrees for welding a flat surface. The arc course by; I.

Electric arc forms between a consumable wire electrode and the work piece metal which heats the work piece metal, causing them to melt, and join.

II.

Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from contaminants in the air.

The melting rate of the electrode metal depends on the amount of electric current used.

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Procedure First Stage The project that given is Flat Pad Weld 1) Switched on the main switch and welding machine. 2) Choose the process that you want to use that is Gas Metal Arc Welding 3) Set the parameter on the welding machine. 4) Take filler wire with 1.0 diameter

Second Stage 1) Do some guideline for your beads 2) Start to weld from right to left with 90 degree to 70 degree. 3) Then, weld at the joining both plates and make sure the straightness is accurate.

Third Stage 1) Brush the steel plate with wire brush. 2) make sure the project clean and looks nice without slag and dirty. 3) Turn off the machine and main switch.

Last Stage 1. Do the housekeeping to make sure it can be easily use when anyone want to use it for weld next time. Page 5 of 16

2. Fill up the WPS form and give it to the lecturer.

1. Gloves

Figure 13: Hand Gloves

* To protect our hand from electric, sharp tools, heat and etc. It does also can prevent accident when we weld.

2. Chipping Hammer

Figure 14: Chipping Hammer * Use to remove slag.

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3. Welding Shield

Figures 15: Welding Helmet/Shield * Mask used to protect the eye sand sprinkle face contact with welder. * It also protects the welder from the rays’ ultra violet that can harm the eyes.

4. Hammer

Figures 16: The hammer * Use with chisel to clean slag.

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5. Chisel

Figures 17: Chisel that use with hammer * Use to remove wax and slag of welding.

6. Wire Brush

Figures 18: Wire Brush * To clean the surface of the arc from the iron dust

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7. Pliers

Figures 19: The Big Pliers *To lift or move the hot metal 8. Table vies

Figures 20: Vies Tables

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9. Welding Machine

Figures 22: High Technology Welding Machine * Serves as a key figure in the welding process.

10. Safety Shoes

Figures 23: Safety Shoes * To protect feet from dangerous things and hazard.

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11. Overall

Figures 24: Overall Clothes * To protect body from any harm and hazards.

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There are 3 things that can be discussing about the Gas Metal Arc Welding or in short form GMAW. There are; 1. Technique The basic technique for GMAW is quite simple, since the electrode is fed automatically through the torch (head of tip). By contrast, in gas tungsten arc welding, the welder must handle a welding torch in one hand and a separate filler wire in the other, and in shielded metal arc welding, the operator must frequently chip off slag and change welding electrodes. GMAW requires only that the operator guide the welding gun with proper position and orientation along the area being welded. Keeping a consistent contact tip-to-work distance (the stick out distance) is important, because a long stick out distance can cause the electrode to overheat and also wastes shielding gas. Stick out distance varies for different GMAW weld processes and applications. The orientation of the gun is also important—it should be held so as to bisect the angle between the work pieces; that is, at 45 degrees for a fillet weld and 90 degrees for welding a flat surface. The travel angle, or lead angle, is the angle of the torch with respect to the direction of travel, and it should generally remain approximately vertical. However, the desirable angle changes somewhat depending on the type of shielding gas used—with pure inert gases; the bottom of the torch is often slightly in front of the upper section, while the opposite is true when the welding atmosphere is carbon dioxide. 2. Quality Two of the most prevalent quality problems in GMAW are dross and porosity. If not controlled, they can lead to weaker, less ductile welds. Dross is an especially common problem in aluminium GMAW welds, normally coming from particles of aluminium oxide or aluminium nitride present in the electrode or base materials. Electrodes and work pieces must be brushed with a wire brush or chemically treated to remove oxides on the surface. Any oxygen in contact with the weld pool, whether from the atmosphere or the shielding gas, causes dross as well. As a result, sufficient flow of inert shielding gases is necessary, and welding in volatile air should be avoided. Page 12 of 16

In GMAW the primary cause of porosity is gas entrapment in the weld pool, which occurs when the metal solidifies before the gas escapes. The gas can come from impurities in the shielding gas or on the work piece, as well as from an excessively long or violent arc. Generally, the amount of gas entrapped is directly related to the cooling rate of the weld pool. Because of its higher thermal conductivity, aluminium welds are especially susceptible to greater cooling rates and thus additional porosity. To reduce it, the work piece and electrode should be clean, the welding speed diminished and the current set high enough to provide sufficient heat input and stable metal transfer but low enough that the arc remains steady. Preheating can also help reduce the cooling rate in some cases by reducing the temperature gradient between the weld area and the base material. 3. Safety Gas metal arc welding can be dangerous if proper precautions are not taken. Since GMAW employs an electric arc, welders wear protective clothing, including heavy leather gloves and protective long sleeve jackets, to avoid exposure to extreme heat and flames. In addition, the brightness of the electric arc is a source of the condition known as arc eye, an inflammation of the cornea caused by ultraviolet light and, in prolonged exposure, possible burning of the retina in the eye. Conventional welding helmets contain dark face plates to prevent this exposure. Newer helmet designs feature a liquid crystal-type face plate that self-darken upon exposure to high amounts of UV light. Transparent welding curtains, made of a polyvinyl chloride plastic film, are often used to shield nearby workers and bystanders from exposure to the UV light from the electric arc. Welders are also often exposed to dangerous gases and particulate matter. GMAW produces smoke containing particles of various types of oxides, and the size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, carbon dioxide and ozone gases can prove dangerous if ventilation is inadequate. Furthermore, because the use of compressed gases in GMAW pose an explosion and fire risk, some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.

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All students must share the welding bay because welding bays cannot accommodate all students. Don’t waste the electrode when do the process because electrode is expensive things and should be concerned about other students that want to use those things also. Have to give enough time to student to do practice and task.

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For the conclusion the tasks that give to me have done successfully by working hard by me. For me first, I thought this process was easy but when I do this task I completely wrong. GMAW needs a stable hands skill, hardworking, confident and patience. But thank you to my lecturer En Hazrul Nizam Bin Mohd Taha I can learn the technique and the right way to welding with this process.

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