Welding workshop practice
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Arc welding processes like shielded metal arc welding, gas metal arc welding and gas tungsten arc welding are described. Shielded metal arc welding uses a consumable electrode covered with a flux to shield the weld. Gas metal arc welding employs a continuously fed wire and shielding gas. Gas tungsten arc welding uses a non-consumable tungsten electrode, shielding gas and a separate filler material. The document discusses welding techniques, processes, defects and includes illustrations of welding joints and processes.
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Welding workshop practice
- 1. Welding Workshop Technology Department of Mechanical Engineering College of E&ME, NUST Pakistan
- 2. Contents • Welding Definition • Types of Welding Processes • Types of Major Welding Joints • Arc Welding • Shielded Metal Arc Welding • Gas Metal Arc Welding • Gas Tungsten Arc Welding
- 3. WELDING & ITS TYPES
- 4. Welding • Welding is a fabrication technique that involves joining materials together by heating them to suitable temperatures, by applying heat with or without the use of pressure. • Heating is generated through various sources; electric arc, gas flame, laser, electron beam, friction, current resistance & ultrasound. • Apart from the materials to be welded, an additional “filler” material may be used for welding. The filler material is added to the weld joint. • Welding is used to produce permanent joints unlike bolting and riveting. • Certain literature refer to soldering and brazing as sub-types of welding.
- 5. Types of Welding Arc Welding Shielded Metal Arc Welding Gas Metal Arc Welding Gas Tungsten Arc Welding Gas Welding Oxyacetylene Welding Resistance Welding Resistance Spot Welding Resistance Seam Welding Energy Beam Welding Electron Beam Welding Laser Beam Welding Solid State Welding Ultrasonic Welding Friction Welding
- 6. Weld Joints
- 7. ARC WELDING
- 8. Arc Welding Process • In arc welding, a welding power supply is used to create an arc between the base metals (metals to be welded) and electrode. • Heat is generated in the base metals causing them to melt and fuse together. The electrode can either be consumable or non-consumable. • Filler material may or may not be added to enhance weld quality and protect the welding area from external contamination. • Following are typical arc welding processes: – Shielded Metal Arc Welding (SMAW) – Gas Metal Arc Welding (GMAW) – Gas Tungsten Arc Welding (GTAW)
- 9. Shielded Metal Arc Welding (SMAW) • This process uses a consumable electrode which serves as the filler material as well. • The electrode is covered with a “flux” that gives off vapors to shield the welding area. The core of the electrode melts into the welding area and provides the necessary filler material. • SMAW is the most common and easiest to employ welding technique and is suitable for welding ferrous materials. • Welding electrodes are composed of material compatible with the material(s) being welded.
- 11. Gas Metal Arc Welding (GMAW) • GMAW employs a continuously fed wire that serves both as the electrode and filler material. Shielding gas is flowed around the wire to protect from weld site contamination. • Unlike SMAW, this process is relatively faster since the electrode is fed continuously to the welding area along with inert gas. NO TIME IS WASTED IN REPLACING A CONSUMED ELECTRODE ! • Though GMAW is faster, the separate supply of shielding gas and continuous feeding of wire requires bulky mechanisms. This reduces the ease of use. • GMAW is also referred to as Metal Inert Gas (MIG) Welding.
- 13. Gas Tungsten Arc Welding (GTAW) • A non-consumable tungsten metal electrode is used in this process. The shielding gas and filler material are fed separately into the weld along side the electrode. • GTAW is characterized by high and uniform weld quality however it requires considerable welding operator skill. • GTAW is used to weld thin section of stainless steel and light metals such as aluminum. • GTAW is also know as Tungsten Inert Gas (TIG) Welding.
- 15. Welding Defects • Lack of Fusion: Arises due to little heat input or too rapid motion of the welding electrode. • Cracking: Occurs due to rapid thermal shrinkage as the welded joint cools down. Can be avoided by controlled cooling/heating of the weld. • Excess Penetration: It occurs either due to excessive heat input or too slow motion of the welding electrode. Avoiding it requires a delicate balance between operator speed and welding heat. • Porosity: Arises due to air trapped in the solidified weld metal. • Inclusions: Occurs due to inclusion of slag from various sources such as the flux coating of welding electrode.