1. Welding Workshop Technology
Mansoor Ghazi, 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.
CHECK SOLDERING & BRAZING

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
Friction Welding is considered a forging process however it is common to be referred to as 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. (CHECK THE EFFECTS OF AC & DC POWER SOURCE ON WELDING)
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.

10. SMAW - Illustrated

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.

12. GMAW - Illustrated

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.
CHECK GAS WELDING (OXYACETYLENE WELDING)

14. GTAW - Illustrated

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.

16. That’s it ! For now Learn more stuff in the welding shop