05Welding processes2 GMAW updated

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05Welding processes2 GMAW updated

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Welding processes2 GMAW updated

Welding Processes – 2. GMAW/MIG/MAG 1. Principle 2. Operating Modes 3. Advantages and Limitations 4. Application and positional capabilities 5. Weld able Metals and Thickness Range 6. Joint Design 7. Welding Circuit and Current 8. Equipment 9. Consumables – Electrodes and Shielding Gases 10. Deposition Rates, Quality Control and Trouble Shooting 11. Weld Schedules Welding Processes – 2. GMAW / MIG / MAG 1.1 Principle Metal inert gas (MIG)/metal active gas (MAG) welding is a fusion welding process that joins metals by melting them with an arc which is formed between a continuous filler wire electrode and the work piece. An externally supplied shielding gas normally provides atmospheric protection of the molten weld pool. MIG/MAG welding is also known as gas-shielded metal arc welding. The MIG/MAG process is often referred to as semiautomatic welding when the torch is hand-held because the consumable wire is fed mechanically and the power source normally regulates the arc length; the only manual control required during welding by the welder for semiautomatic operation are the travel speed, and gun positioning and guidance. The operator is therefore not concerned with controlling the arc length (compared with MMA) and can concentrate on depositing the weld metal in the correct manner. The process can also be mechanised or applied using a robot. Welding Processes – 2. GMAW / MIG / MAG 1.2 Operating Mode – Most popular mode is semiautomatic. Second is the fully automatic. The process can be applied as mechanized. The process can not be used manually. Power supply is normally CV type. Only DC operation (AC not used). DCEP is the normal mode of operation. DCEN rarely used with some specific electrodes. 1.3 Advantages and Limitations Most popular welding process now. High deposition rates, High operator factor, High utilization of filler metals, no slag/flux, less smoke and fumes, lower operator skill level, easy automation etc Position - All positions Limitations include lower accessibility, difficulties with soft electrodes (spool gun feeder), expensive equipment, sensitivity of gas shielding to wind drafts. Welding Processes – 2. GMAW / MIG / MAG 1.4 Common Applications and Positional Capabilities An all position process. Different variations have their own Positional capabilities depending upon electrode size and type of metal transfer. Mainly sheet metal and piping industries. Many other applications such as Aluminium bus bars in electrical industries. Welding Processes – 2. GMAW / MIG / MAG CO2 Welding, Large Electrodes Flat, Horizontal Spray Arc Flat, Horizontal Spray Arc-Small Electrode Vertical, OverHead Short Circuit All Position Pulsed Spray All Position 1.5 Weldable Metals and Thickness Ranges Thickness – Wide thickness ranges (0.13 mm upwards, from thinnest to thickest) Metals – Wide range of metals (most metals can be welded). CO2 welding is restricted to steels. 1.6 Joint Design Similar joint details as SMAW. Smaller groove angle mean better economy and efficiency. 1.7 Welding Circuit and Current The wire feeding system controls the electrode wire feed and welding arc, as well as the flow of shielding gas and cooling water. Self stabilization Characteristics of GMAW Welding Processes – 2. GMAW / MIG / MAG 1.8 Equipment A direct current DC output is normally required. Conventional GMAW power sources have constant voltage (CV) output characteristics. The slope is different according to process requirement. Welding Processes – 2. GMAW / MIG / MAG 1.9 Consumables – Electrodes and Shielding gases Selection of electrode depend upon metal to be welded, thickness and joint design, surface condition, specifications or service conditions. AWS designation system for Solid Wires Selection of shielding gases for MIG/MAG welding is primarily dependent on the material type and metal transfer mode (and hence material thickness). The main gases and gas mixtures used for carbon and low alloy steel welding are CO 2 , Ar-CO2 and Ar-O2. Some mixtures may also contain a proportion of helium in substitution for argon. Welding Processes – 2. GMAW / MIG / MAG 1.10 Deposition Rates , Quality Control and Trouble Shooting Deposition rates are higher for same welding current than for SMAW. The welding procedure, electrode size and CTWD all effect the deposition rate. A low hydrogen process. Quality of welds can be very high. Quality depends on electrodes, cleanliness, procedure, position and skill of welder. Quality also depends on efficiency of shielding envelope Welding Processes – 2. GMAW / MIG / MAG 1.10 Deposition Rates , Quality Control and Trouble Shooting Welding Processes – 2. GMAW / MIG / MAG [...]...Welding Processes – 2 GMAW / MIG / MAG 1.10 Deposition Rates , Quality Control and Trouble Shooting Welding Processes – 2 GMAW / MIG / MAG 1.11 Welding Schedules

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