Q1. Name any 3 common welding processes?
i- Gas Metal Arc Welding (GMAW)
ii- Gas Tungsten Arc Welding (GTAW)
iii- Shielded Metal Arc Welding (SMAW)
Q2. Describe any one of the 3 welding process above?
Ø The gas metal-arc welding process (GMAW), often called MIG, has revolutionized arc welding. In the GMAW process have 4 type of welding, flux cored arc welding (FCAW).metal inner welding (MIG), metal active gas (MAG), and co2 welding.
Ø Gmaw is a process where a continuously fed metal electrode (Wire) contacts the base metal and produces heat. The arc is shielded by an inert gas or external gas (Argon, helium, CO2, argon + Oxygen or other gas mixtures).
Ø In this process, a consumable electrode (in the form of wire) is fed from a spool through the torch (welding gun) at a preset controlled speed. As the wire passes through the contact tube of the gun, it picks up the welding current.
Ø The consumable wire electrode serves two functions: it maintains the arc and provides filler metal to the joint. The method of delivery of the filler metal allows GMAW welding to be basically a one-handed operation which does not require the same degree of skill as GTAW.
Ø GMAW offers many of the advantages of GTAW. Since there is no flux, GMAW welds are clean and there is no slag to remove. GMAW enables you to produce sound welds in all positions quickly
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GAS METAL ARC WELDING PRINCIPLES
Ø The GMAW process is performed using DCEP ( Direct Current Electrode Positive)
Ø Alternating current is never used for GMAW
Ø DCEN is used only for a specialized process using emissive electrodes.
The American Welding Society uses an alphanumerical system for GMAW wire classification. For example, a solid wire electrode may have the AWS classification ER70S-3, sometimes referred to as an S-3 wire. Each letter and number represents a specific defining characteristic.
The "E" stands for electrode, the current carrying device.
The "R" stands for rod, meaning that the electrode can also be used as a filler rod for GTAW applications.
The number "70" indicates the minimum as-welded tensile strength measure in thousands of pounds per square inch (ksi).
The "S" refers to a solid electrode wire.
The "3" refers to the level of specific alloy, deoxidizer(s) that makes up the carbon steel electrodes chemical composition.
Basically, there are five major factors that influence the choice of filler wire for GMAW welding.
1. Base plate chemical composition
2. Base plate mechanical properties
3. Shielding gas employed
4. Type of service or applicable specification requirements
5. Type of weld joint design.
MODES OF TRANSFER
1) Short Circuit Transfer
Short Circuit Transfer Short circuit transfer refers to the welding wire actually “short circuiting” (touching) the base metal between 90 - 200 times per second. With short circuit transfer, wire feed speeds, voltages, and deposition rates are usually lower than with other types of metal transfer such as spray transfer. This makes short circuit transfer very versatile allowing the welder to weld on thin or thick metals in any position. Limitations of short circuit transfer:
- A relatively low deposition rate
- Lack of fusion on thicker metals
- More spatter
2) Globular Transfer
Globular transfer refers to the state of transfer between short-circuiting and spray arc transfer. Large globs of wire are expelled off the end of the electrode wire and enter the weld puddle. Globular transfer can result when welding parameters such as voltage, amperage and wire feed speed are somewhat higher than the settings for short circuit transfer.
3) Spray Arc Transfer
Spray Arc Transfer Spray arc transfer “sprays” a stream of tiny molten droplets across the arc, from the electrode wire to the base metal. Spray arc transfer uses relatively high voltage, wire feed speed and amperage values, compared to short circuit transfer.
Q3. Differentiation between the advantages and disadvantages three of the selected welding process above?
| Types of Welding | Advantages | Disadvantages |
| Shielded Metal Arc Welding-(SMAW) | Ø Very portable, welder needs only to carry leads anywhere the weld needs to be done. Ø Equipment is affordable. Ø Can be used in all positions, and be used indoors our outside as wind doesn’t usually affect weld pool. | Ø Only a few inches at a time can be welded before another electrode is needed. Ø Electrode ends (butts) are wasted. Ø High level of skill needed to produce sound welds. Ø Many electrodes have low penetration. Ø Arc blow can occur with direct current. |
| Gas Metal Arc Welding-(GMAW) | Ø Welding can be done in all positions Ø No slag removal required Ø High efficiency Ø Less work piece distortion Ø Large gaps bridged easily , Good for poor fitup Ø High Weld Quality | Ø Increased risk of porosity due to the loss in gas shield. Ø The welding plant requires more maintenance. Ø High risk of lack of fusion, in the dip transfer mode. Ø The cost of the welding plant. Ø Portability. |
| Gas Tungsten Arc Welding-(GTAW) | Ø Produces good quality welds and generally free of defects. Ø Free of the spatter or slag, sparks and smoke which occurs with other welding process. Ø Can be used with or without filler metal as required for the specification. Ø Used inexpensive power supplies. Ø Used to weld almost all metals, including dissimilar metal joints. Ø Good for welding thin material. Ø Allows for welding in all positions. | Ø The is difficulty in shielding the weld zone properly in environments. Ø Slower travel speeds than other processes. Ø Lower filler metal deposition rates. Ø Hand-eye coordination is a required skill. Ø Brighter UV rays than other processes. Ø Equipment costs can be higher than other processes. Ø Requires high level of operator skill. |
