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Introduction To MIG Welding - Electricity, Electronics, & Robotics Introduction To Gmaw Welding

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Introduction to MIG Welding - Electricity, Electronics, & Robotics

Introduction to MIG Welding - Electricity, Electronics, & Robotics introduction to gmaw welding

Introduction to MIG Welding

Ch. 10 GMAW Equipment, Setup, and Operation

(GMAW) Gas Metal Arc Welding:

Introduction to MIG Welding - Electricity, Electronics, & Robotics introduction to gmaw welding
  • Gas Metal Arc Welding is the American Welding Society's official name, but in the field (GMAW) is commonly called by some other names.
  1. MIG- Metal Inert Gas Welding
  2. MAG- Metal Active Gas Welding
  3. Wire Welding

  • GMAW can be performed as a semi-automatic, or a fully automatic.
  • Robotic welders often employ GMAW because of its adaptability for various positions.
  • Today wire exceeds 50% of the total tonnage of filler material produced and used.
  • This large increase is due to an improved quality in GMAW welds.
  • This improvement is due to: increased reliability of the wire feed systems, improvements in the filler metal, smaller wire sizes, faster welding speed, higher weld deposition rates, less expensive shielding gases,and improved welding techniques.

Metal Transfer:

  1. Axial Spray Metal Transfer:
  • Very small metal drops are directed from the tip to the work piece at a high rate of speed. There are hundreds of drops per second.
  • This projection of drops allows welding in vertical and overhead positions.
  • Spray transfer process requires 3 conditions: argon shielding, DCEP polarity, and a current level above a critical amount called the transition current.

  1. Globular Transfer:
  • This method is very rarely intentionally used.
  • The transfer of larger globs of metal is usually only desirable when combined with pulsed spray transfer.
  • The large globs will fall from the electrode when they are big enough that gravity overcomes their natural cohesion properties.

  1. Pulsed-arc Metal Transfer:
  • This method uses the large globs associated with globular transfer, but uses interrupted pulses to keep the glob better controlled. The amp range flirts with the globular transfer voltage continually moving back and forth to that threshold. This will keep the glob more uniform and easier to work with.

  1. Buried-arc Transfer:
  • In this method, argon is used as a shielding gas to help control weld splatter.

  • This method also uses large globs of transfer metal, but this method forces the electrode under the surface of the molten weld pool.
  • This is beneficial because it creates a much nicer looking weld with much less spatter.
  • This method is highly used in fully automated welding processes on thin material.

  1. Short-circuiting Transfer GMAW-S:
  • Low currents allow the liquid metal at the electrode tip to be transferred by direct contact with the weld pool.
  • To start this process, the wire is in direct contact with the molten weld pool.
  • Once the electrode touches the molten weld pool, the arc and its resistance are removed.
  • Without the arc resistance, the welding amperage quickly rises as it begins to flow freely through the tip of the wire into the molten weld pool.
  • The temperature rises quickly which increases the resistance. This rise in temperature and the high current flow causes the electrode to turn molten rapidly.
  • This high heat causes a small explosion. This small explosion has sufficient force to cause deeper penetration. 
  • This is a relatively low heat process. Because of this, GMAW is a very widely used welding process.

Filler Metal Specifications:

Introduction to MIG Welding - Electricity, Electronics, & Robotics introduction to gmaw welding
  1. GMA welding filler metals are available for a variety of metals.
  2. The most common are for carbon steel and stainless steel.
  3. The filler metals are available in diameter sizes ranging from 0.023 inches to 1/8th inch diameter.

Wire Melting and Deposition Rates:

  • Wire Melting Rate: measured in inches per minute. or pounds per hour.
  • Deposition Rate: This is the rate at which the full weight of the wire is deposited onto the weld material. Not all of the wire will be deposited. Some is lost as slag, spatter, or fume. Deposition rates can vary between 80% with cored wires to 98% while using solid wires.

Welding Power Supplies:

Introduction to MIG Welding - Electricity, Electronics, & Robotics introduction to gmaw welding
  1. Voltage: is a measurement of electrical pressure.
  2. Electrical Potential: means the same thing as voltage and is usually expressed by using the term potential (P).
  3. Amperage or amp: Is the measurement of the total number of electrons flowing, in the same way that gallons is a measurement of the amount of water flowing.
  4. Electrical Current: Means the same thing as amperage and is usually expressed by using the term current (C). 
  • GMAW power supplies are the constant-voltage, constant-potential (CV, CP) type machines.
  • The relationship between current and voltage with different combinations of arc length or wire-feed speeds are called volt-amperage characteristics.
  • To maintain a constant arc length while increasing current, it is necessary to increase voltage.

  • Current increases come from increasing the wire feed rate.

Speed of the Wire Electrode:

  • The speed is usually recommended by the welder manufacturer.
  • The speed is rated in inches per minute (IPM)
  • There is an adjustment knob on the welder which controls wire feed speed.
  • The feed rate can be adjusted to compensate for the welder's skill in controlling the weld puddle.

Molten Weld Pool Control:

  1. Shielding Gas:
  • Shielding gas has an effect on the weld produced.
  • Affects: method of metal transfer, welding speed, weld contour, arc cleaning effect, and fluidity of the molten weld pool.
  • Some metals require an inert gas such as argon or helium.
  • Other metals prefer reactive gases like carbon dioxide.
  • Most common combos are:
  1. 75% argon + 25% CO2
  2. Argon + 1%-5% oxygen
  3. Carbon Dioxide (CO2)

  1. Power Settings:
  • Welder is looking for a careful balance between volts and amps. If either or both are set too high or too low, the weld penetration can decrease.
  • Amperage is adjusted by changing the wire feed speed.
  • Faster wire speed results in a higher amperage since more amperage is needed to keep the electrode melting at the faster speed.
  • This will not increase penetration and is very likely to decrease penetration significantly.

  1. Weave Pattern:
  • Most of the standard weave patterns will work with GMAW.
  • The key is to always keep the electrode in the welding puddle.
  • Each time the welder leaves the pool, a loud pop will indicate that the arc had to be reestablished.
  1. Travel Speed:
  • The electrode must remain in the pool so the welding speed can not go faster than the ability of the welder to melt the metal.
  • If the welder moves too quickly, the weld may have poor adhesion to the base metal.

  1. Electrode Extension: 
  • This is the distance from the contact tube to the arc measured along the wire.
  • Adjustments in this distance cause a change in the wire resistance.
  • This affects the weld bead.
  • As the length away from the work increases, the voltage goes up.

  • Since the voltage goes up, the amperage must go down.
  • This results in a reduction in weld heat, penetration, and fusion.

  1. Gun Angle:
  • This is the angle to which the gun is held against the work piece.

  1. Backhand Welding:
  • Backhand welding means that the gun precedes the welding action.

  • It is also called a dragging action.
  • This motion results in deeper penetration.

  1. Forehand Welding:
  • Forehand welding means that the welding action precedes the gun.
  • It is also called a pushing action.
  • This motion results in a wider puddle with less penetration.

Push Type Feed System:

  • This type of system pushes the electrode through the gun.

  • The spool resides in the welder and the push system is right in front of the spool.

Pull Type Feed System:

  • This type of system pulls the wire.
  • The pulling mechanism is usually located in the gun and pulls the electrode from the welding spool.
  • This system can move even small wires over long distances.

Push/Pull-type feed Machine:

  • Use a synchronized system with feed rollers at both ends of the electrode conduit.
  • This is a good system for moving even small wire over long distances.
  • This system costs more than a single feed system.

Linear Electrode Feed System:

  • Does not have gears or conventional rollers.
  • Uses a small motor with a hollow armature shaft.
  • Motor continually spins at its peak operating speed.
  • The roller pitch is what changes.

Spool Gun:

  • This is a compact self contained system at the welding gun.
  • Contains the wire and driving mechanism in the gun.
  • Often used for small or soft wire.

Spot Welding:

  • GMAW can produce high quality spot welds.
  • GMAW spot welding has some advantages over conventional spot welding.
  • Welds can be made thin to thick material.
  • The weld can be made even though the welder only has access to one side of the work piece.
  • The weld can be made when there is paint on the interfacing surfaces.


Introduction to MIG Welding - Electricity, Electronics, & Robotics

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