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  1. 1. GMAW / Mig Welding Munim Shaukat (Lecturer) Mechanical Engineering Department University of Lahore
  2. 2. Over viewa During this overview, we will discuss the following topics: • Safety • GMAW Basics • Equipment Set-Up • Welding Variables • Process Advantages and Limitations
  3. 3. GMAW Safetya ‘GMAW Safety’ is supplemental and does not replace the information found in ‘Arc Welding Basics’
  4. 4. a Fumes and Gases can be dangerous • Keep your head out of the fumes • Use enough ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing zone and the general area • Local exhaust and mechanical ventilation can be used without reducing weld qualitya Electric Shock can kill – • Do not touch the electrode or metal parts of the electrode holder with skin or wet clothing • Keep dry insulation between your body and the metal being welded or ground • The coil of wire is ‘electrically hot’ so do not touch it.
  5. 5. a REMEMBER – Gas Cylinders require SPECIAL safety precautions • Cylinders must be secured in an upright position • Cylinders should be located in an area away from arc welding, cutting, heat, sparks, and flame
  6. 6. GMAW Principlesa GMAW stands for Gas Metal Arc Weldinga GMAW is commonly referred to as MIG or Metal Inert Gas weldinga During the GMAW process, a solid metal wire is fed through a welding gun and becomes the filler materiala Instead of a flux, a shielding gas is used to protect the molten puddle from the atmosphere which results in a weld without slaga GMAW is the most widely used arca welding process in the United States
  7. 7. GMAW Circuita Three things happen when the GMAW gun trigger is pulled: • The wire electrode begins to feed • The circuit becomes electrically ‘hot• Current flows from the power source through the gun cable, gun, contact tip to the wire and across the arc. On the other side of the arc, current flows through the base metal to the work cable and back to the power source – Shielding gas flows through the gun and out the nozzle
  8. 8. GMAW Componentsa DC or Direct Current power supplya Electrode or wire feed controllera Wire drive roller assemblya Shielding gas source (cylinder) & regulatora Manually held Gun & ground clampsa Wire reel
  9. 9. 1 - Electrodea A GMAW electrode is: • A metal wire • Fed through the gun by the wire feeder • Measured by its diameter
  10. 10. 2 - Arca An electric arc occurs in the gas filled space between the electrode wire and the work piece aElectric arcs cangenerate temperatures up to 10,000°F
  11. 11. 3 - Weld Poola As the wire electrode and work piece heat up and melt, they form a pool of molten material called a weld poola This is what the welder watches and manipulates while welding
  12. 12. 4 - Shielding Gasa GMAW welding requires a shielding gas to protect the weld puddlea Shielding gas is usually CO2, argon, or a mixture of bothaThe gauges on the regulatorshow gas flow rate and bottle pressure
  13. 13. 5 - Solidified Weld Metala The welder “lays a bead” of molten metal that quickly solidifies into a welda The resulting weld is slag free aAn aluminum weld done with the GMAW process
  14. 14. GMAW Equipment Set Up1. Connect work clamp2. Select electrode a. Type b. Diameter3. Select shielding gas4. Turn power supply on5. Adjust machine output a. Wire feed speed b. Voltage6. Adjust gas flow rate
  15. 15. GMAW Process Variablesa Welding variables • Wire Feed Speed (WFS) • Voltagea Operator controlled variables • Travel speed • Gun angles • Contact tip to work distance (CTWD) • Gas flow rate
  16. 16. GMAW component diagram
  17. 17. GMAW Advantages• Welding can be done in all positions• No slag removal required• High efficiency• Less work piece distortion• Large gaps bridged easily ,• High Weld Quality
  18. 18. Typical Setup for voltage• The GMAW machine is a “Constant Voltage” power supply. This is set using the voltage dial• This setting can be monitored by the “Volt” meter on the front panel of the welder• Ideal voltage settings can be found in the wire manufactures data book
  19. 19. Typical Setup for Wire speed• The wire feed rate or speed is set using the dial on the wire controller This setting increases or decreases current or “Heat”. This setting is measured in AMPS or IPM (inches per minute )• Ideal settings can be monitored by the “Amp” meter on the front panel of the welder. Note : Some machines display “Current” (Same as AMPS) or IMP• Ideal settings can be found in the wire manufactures data book for both IPM and Current
  20. 20. Shielding Gas• Air in the welding zone is displaced by inert gas to “Shield” the molten weld pool and prevent it from contamination from Oxygen, Nitrogen and Water present in the atmosphere.• Insufficient gas flow will not displace the atmosphere resulting in “porosity” or voids in the deposited weld.• Flow is measured in CFH (Cubic Feet per Hour).
  21. 21. Insufficient Shielding Gas coverage• Gas not turned on• Flow rate not properly adjusted• Leaks in the hose supplying the shielding gas to the machine• GMAW / MIG Gun loose at wire drive connection• Spatter buildup on gas cup• Windy environment