Welding process GMAW and it's processeses

Welding

1. Gas Metal Arc Welding (GMAW) Presented by: Daniel Santos, Franscisco Arteaga, Saeed Akhtar.

2. Introduction GMAW is a Welding Process defined as arc welding using a continuously fed consumable electrode and a shielding gas. • GMAW is also known as Metal Inert Gas (MIG) or metal active gas (MAG) welding. • Produces high-quality welds. • Yields high productivity.

3. Equipment To perform Gas Metal Arc Welding, the basic necessary equipment are: • a welding gun. • a wire feed unit. • a welding power supply. • an electrode wire. • a shielding gas supply.

4. Equipment Welding Gun The typical GMAW welding gun has a number of key parts—a control switch, a contact tip, a power cable, a gas nozzle, an electrode conduit and liner, and a gas hose. • The control switch, or trigger, when pressed initiates the wire feed, electric power, and the shielding gas flow, causing an electric arc to be struck Wire Feed Unit. • It supplies the electrode to the work, driving it through the conduit and on to the contact tip. Power Supply. (a constant voltage power supply) • As a result, any change in arc length (which is directly related to voltage) results in a large change in heat input and current.

5. Equipment Electrode Electrode selection greatly influences the mechanical properties of the weld and is a key factor of weld quality. Shielding Gas Purpose of shielding gas is the protect the weld area from the contaminants in the atmosphere. Gas can be Inert, Reactive, or Mixtures of both.

6. (1) Torch handle , (2) Molded phenolic dielectric ( shown in white ) and threaded metal nut insert ( yellow ), (3) Shielding gas diffuser , (4) Contact tip , (5) Nozzle output face

7. Metal Transfer Modes Globular Transfer Welding current and wire speed are increased above maximum for short arc. Welding speeds of up to 110 mm/s (250 in/min). Droplets of metal have a greater diameter than the wire being used Spatter present. It can only be used on ferrous metals. Welding is most effectively done in the flat position when using globular transfer Short Circuit. (Short Arc) Operates at low voltages and welding current. Small fast-freezing weld puddle obtained. Useful in joining thin materials in any position, as well as thick materials in vertical and overhead positions.

8. Metal Transfer Modes Short Circuit (Short Arc) Operates at low voltages and welding current. Small fast-freezing weld puddle obtained. Useful in joining thin materials in any position, as well as thick materials in vertical and overhead positions. The weld process parameters (volts, amps and wire feed rate)- between 100 to 200 amperes at 17 to 22 volts. Metal transfer occurs when an electrical short circuit is established. It can only be used on ferrous metals.

9. Metal Transfer Modes Spray Transfer Occurs when the current and voltage settings are increased higher than that used for Globular Transfer. Used on thick sections of base material, best suited for flat position due to large weld puddle. Spatter is minimal to none. Generally used only on workpieces of thicknesses above about 6.4 mm (0.25 in). The maximum deposition rate is relatively high- about 60 mm/s (150 in/min). Well-suited to welding aluminum and stainless steel.

10. Metal Transfer Modes Pulsed-Spray A variation of the spray transfer mode. Uses a pulsing current to melt the filler wire and allow one small molten droplet to fall with each pulse. The pulse provides a stable arc and no spatter, since no short-circuiting takes place. The smaller weld pool gives the variation greater versatility, making it possible to weld in all positions. Maximum speed (85 mm/s or 200 in/min). Required shielding gas - primarily argon with a low carbon dioxide concentration. Requires a special power source capable of providing current pulses with a frequency between 30 and 400 pulses per second. It requires lower heat input and can be used to weld thin workpieces, as well as nonferrous materials.

11. Metal Transfer Modes

12. Welding Process Groups

13. Comparison ( most common )

14. Advantages High deposition efficiency when used in certain transfer modes. • No Slag to chip as compared to SMAW and FCAW(Flux-core Arc Welding) • The process can be used on thin materials with relative ease if properly set. • Low Hydrogen weld deposit with all electrodes. • High production factor since no slag is required to be removed and uses a continuous electrode. • With the parameters properly set for the application, anyone can weld after a very short amount of practice. • One given electrode size can be used on various thicknesses of materials productively.

15. Disadvantages Requires a Wire Feeder which is difficult to move and can sometimes be a maintenance/repair burden. • Needs Shielding Gas so welding in windy conditions can be difficult. • No slag system so out of position welds are sometimes more difficult. • Increased chance of lack of fusion if parameters and welding technique is not controlled. • The gun is difficult to get into tight places. • Is not suitable for windy conditions and underwater welding.

16. Highlights GMAW process in general, in controlled conditions (inside environment), slag and porosity discontinuities less prevalent than others welding processes with coatings. Fusion is a concern.(suitable for lack of Fusion due welding procedure failure.) Joint fit up, depending of location/position, can be very difficult to reach out some areas. Weld in winding conditions is more critical due externally supplied of gas shield.    Major difference from other welding process is metal transfer mode as machine/arc parameters change.

17. Conclusion Today, GMAW is the most common industrial welding process, preferred for its versatility, speed and the relative ease of adapting the process to robotic automation. It is used extensively by the sheet metal industry and, by extension, the automobile industry.

18. References http://en.wikipedia.org/wiki/Gas_metal_arc_welding  http://www.airgas.com/content/details.aspx?id=7000000000164  http://www.haydencorp.com/content.php?p=manual_welding#gmaw  http://www.trade-equip.co.uk/blog/?p=881