GasMetalArcWelding

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Gas Metal Arc Welding (GMAW) Tech Connect Welding

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GMAW Safety Precautions Electrical Safety Make sure all electrical equipment has an earth ground. Keep electrical connections tight, clean, and dry. Keep work area, equipment, and clothing dry.

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GMAW Safety Precautions (continued) Electrical Safety (continued) Never dip a GMAW gun in water. Never touch hot parts of the electrode holders. Disconnect and lock out all electrical power sources before doing any work on electrical equipment.

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GMAW Safety Precautions (continued) Electrical Safety (continued) Keep welding cables as close to the work area as possible. Do not connect cables to the building framework. Always check the work area for any electrical hazards before starting a project.

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GMAW Safety Precautions (continued) Handling cables, gas hoses, and coolant hoses Never pull a welding cable to force it over an obstruction. Never drag a welding cable through dirt or oil. Only use clean, dry rags to clean a welding cable. Properly store welding cables when not in use.

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GMAW Safety Precautions (continued) Handling cables, gas hoses, and coolant hoses (continued) Never interchange gas and water hoses. Disconnect and remove electrode holders and cables after each use. Keep cables off any metal tables or any grounding surfaces. Make sure that water-cooled systems have the water turned off when shutting down. Use welding cable covers

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GMAW Safety Precautions (continued) Handling hollow castings and containers Vent hollow castings before beginning any heating, cutting, or welding activities. Do not heat, cut, or weld any tanks, drums, or containers until they have been carefully cleared of any flammable materials.

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GMAW Safety Precautions (continued) Working with arc rays Wear appropriate personal protective equipment to protect your eyes and skin. Shield work areas to prevent an arc flash from injuring nearby workers.

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GMAW Safety Precautions (continued) Environmental concerns Make sure the work area is properly ventilated. Wear a respirator when necessary to protect from breathing dangerous fumes. Wear earplugs during periods of continuous loud noise. Make sure the lighting is bright and free of glare.

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GMAW Safety Precautions (continued) Working with electrodes Always wear safety glasses when working with electrodes. Make sure that you have the correct spool or coil before leading and cutting tie wires. Position the coils close to the reel before lifting and then lift with your legs, not your back.

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GMAW Safety Precautions (continued) Working with electrodes (continued) Never look into a gun while you are feeding wire into it. Never point a gun at anyone else. Never place your finger or hand over the contact tip to verify if the wire is feeding properly.

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Personal Protective Equipment for GMAW Hoods

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Personal Protective Equipment for GMAW (continued) Hoods (continued)

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Personal Protective Equipment for GMAW (continued) Lenses Electrode size and amperage determine the level of lens protection. Use the lens manufacturer’s selection chart to select the appropriate shade.

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Personal Protective Equipment for GMAW (continued) Protective clothing

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Principles of GMAW Usually operates on direct current electrode positive (DCEP) or direct current reverse polarity (DCRP). A wire is used as an electrode and a welding arc is struck between the electrode and the base metal. The electrode melts and becomes part of the weld. The process is controlled by a constant voltage, which is set by the welder.

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Advantages and Disadvantages of GMAW Advantages An easy process for beginners to learn. Electrodes never need to be changed during the process. Reduces the chances of distortion in base metals. The arc is always visible to the welder, which allows for better welds.

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Advantages and Disadvantages of GMAW Advantages (continued) Efficiently deposits the welding wire into the joint. Can be used in any position. Can be used on both light and heavy gauge metals. Can be used on both ferrous and nonferrous metals.

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Advantages and Disadvantages of GMAW Advantages (continued) Can be adapted to either automatic or semiautomatic operation. Requires no cleanup because no slag and very little splatter are causes.

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Advantages and Disadvantages of GMAW Disadvantages Cannot be used in a windy environment. Electrical components must be carefully setup. Equipment is more expensive. Some weld joints can be hard to reach with the welding gun.

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Benefits of Learning GMAW Enables you to learn and understand the uses of consumable electrodes and shielding gases. Introduces you to electrical concepts and electrical controls not used by other processes. Allows you better visibility of the arc, electrode, and weld zone than other processes. Enables you to acquire additional skills that are useful in a competitive job market.

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Different Methods of Metal Transfer Short circuiting transfer Also known as “short arc.” Uses a low electrical current, low voltage, and a small-diameter electrode. Metal is transferred when the electrode touches the base metal and the molten metal from the heated electrode enters into the weld pool. Used to join thin sheet metal and parts that have large gaps.

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Different Methods of Metal Transfer (continued) Short circuiting transfer (continued) How it works: The welding machine maintains a constant voltage. The voltage drops to zero when the wire “short circuits” the base metal. The electrical current rapidly increases, which forces the end of the electrode to separate from the base metal.

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Different Methods of Metal Transfer (continued) Short circuiting transfer (continued) How it works (continued) : The arc reignites and the steps are repeated.

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Different Methods of Metal Transfer (continued) Globular transfer Uses a higher electrical current and high voltage than used for short circuiting transfer. How it works: An arc is created that melts the end of the electrode and the base metal. The globule increases in size until it falls off the end of the electrode.

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Different Methods of Metal Transfer (continued) Spray transfer Uses a higher electrical current and higher voltage than used for globular transfer. Produces good penetration and very little splatter. Commonly used in the flat position or for horizontal fillet welding. Requires a shielding mixture of at least 90% argon.

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Different Methods of Metal Transfer (continued) Spray transfer (continued) The current setting must be set above the transition current. How it works: Hundreds of metal droplets are formed every second and travel directly into the weld.

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Different Methods of Metal Transfer (continued) Pulsed spray transfer Similar to spray transfer except it uses two different currents: background current and peak current. Background current and peak current alternate. Allows for good penetration. Can be applied in all positions.

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Different Methods of Metal Transfer (continued) Pulsed spray transfer (continued) How it works: Background current is applied to the electrode, causing a shielding gas to form. Droplets of molten metal form at the tip of the electrode. Peak current is applied. Droplets of molten metal form at a constant rate and are transferred through the arc to the base metal.

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GMAW Equipment Welding machines Types of machines: Inverter welding machine Transformer-rectifier welding machine

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GMAW Equipment (continued) Characteristics of a GMAW welding machine Provides a constant voltage power supply. A crank knob can be used to adjust the voltage. Automatically adjusts to the welding position.

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GMAW Equipment (continued) Wire feeder Feeds the electrode wire to the welding gun. The inch switch causes the electrode to feed out as long as the switch is pressed. The purge switch enables the welder to control the shielding gas flow.

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GMAW Equipment (continued) Welding gun Includes a switch to start and stop the welding process. Controls the electrode wire, shielding gas, and coolant. Available in a variety of shapes.

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GMAW Equipment (continued) Types of welding guns

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GMAW Equipment (continued) Parts of a gun tip

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GMAW Equipment (continued) Gun maintenance

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GMAW Equipment (continued) Electrode wire Use an electrode wire that has a composition that matches the composition of the base metal. Use a 0.020” to 0.045” diameter wire for short circuiting transfer. Use a 0.035” to 0.045” diameter wire for pulsed spray transfer.

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GMAW Equipment (continued) Electrode wire (continued) Use a 0.045: to 0.125” diameter wire for spray transfer.

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GMAW Equipment (continued) Common GMAW electrode wires

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GMAW Equipment (continued) Electrode extension Allows the welder to control the amperage and voltage to correct for spatter, penetration, and bead width. Allowing too much electrode extension decreases the amperage and increases the voltage. Allowing too little electrode extension increases the amperage and decreases the voltage.

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GMAW Equipment (continued) Electrode extension (continued) Recommended extension lengths: Short circuiting transfer – ¼” to ½” Spray transfer – ½” to 1” Pulse spray transfer – ½” to ¾”

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GMAW Equipment (continued) Shielding gases Mainly uses argon and carbon dioxide (CO2). Can also include mixtures that contain helium and oxygen. Normally consists of argon with 1% to 5% oxygen or argon with 3% to 50% carbon dioxide. The type of shielding gas determines the level of penetration.

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Causes and Corrective Actions for Common GMAW Problems

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Causes and Corrective Actions for Common GMAW Problems (continued)

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Causes and Corrective Actions for Common GMAW Problems (continued)

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Troubleshooting Techniques

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Troubleshooting Techniques (continued)

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Troubleshooting Techniques (continued)

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Troubleshooting Techniques (continued)

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Troubleshooting Techniques (continued)

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Troubleshooting Techniques (continued)

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Troubleshooting Techniques (continued)

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GMAW Application Techniques Forehand welding Also called the “push angle.” The electrode points in the direction of travel. Decreases penetration and gives a wider, flatter bead. Used mainly on thicker metals.

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GMAW Application Techniques (continued) Backhand welding Also called a “drag angle.” The electrode points in the opposite direction of travel. Increases penetration and gives a more convex, narrower bead. Provides a more stable arc. Leaves less splatter on the workpiece. Used mainly on thinner metals.

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GMAW Application Techniques (continued) Steps for properly ending a weld Procedure 1: Release the gun trigger as the bead reaches the end of the weld. Hold the gun in place for a few seconds to keep the molten puddle covered with the shielding gas until it cools. Slowly pull the gun away.

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GMAW Application Techniques (continued) Steps for properly ending a weld Procedure 2: As the bead reaches the end of the weld, reverse the travel of direction. Break the arc. Hold the gun in place for a few seconds to keep the molten puddle covered with the shielding gas until it cools. Slowly pull the gun away.

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Welding Techniques and Their Correct Positions

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© 2008 Oklahoma Department of Career and Technology Education