Welding Process Lecture Notes

Overview of Welding

• Definition of Welding: A permanent joining process of two metals.
  • Permanent joint (unlike temporary joints with screws/bolts).
  • Atomic bonding at the joint.
  • Can join similar or dissimilar metals.
  • Welding can occur with or without pressure.
  • Heat sources can be electric, chemical reaction, or mechanical friction.

Types of Welding

• Types of Welding:
  1. Fusion Welding: Metal parts are melted to join.
     • Includes:
       • Arc Welding:
         • Shielded Metal Arc Welding (SMAW)
         • Metal Inert Gas (MIG) Welding
         • Tungsten Inert Gas (TIG) Welding
       • Gas Welding (Oxyacetylene)
       • Electro Slag Welding
       • Thermit Welding
  2. Solid-State Welding: Metals are joined without complete melting.
     • Includes:
       • Resistance Welding
       • Friction Welding
• Soldering and Brazing: Discussed under the welding chapter but categorized differently.

Shielded Metal Arc Welding (SMAW)

• Electrode: Composed of a core material and an outer flux coating.
• Welding Process:
  • Arc is generated between the electrode and the metal plate to be joined.
  • Electrons flow and create heat in a plasma state.
  • Molten metal from the electrode drops onto the joint area, combining with the base metals to form a weld.
• Flux: Protects the weld area from oxidation by creating gases and forming a slag layer that floats above the weld.
• Current Types:
  • Direct Current Electrode Negative (DCEN) and Direct Current Electrode Positive (DCEP).

MIG Welding

• Definition: Metal Inert Gas Welding (GMAW) uses a thin wire as the electrode.
• Process:
  • Wire is continuously fed through a gun into the weld area.
  • Shielding gas (typically argon and CO2) protects the molten metal from atmospheric contamination.
• Current: Usually direct current (DCEP).

TIG Welding

• Definition: Tungsten Inert Gas Welding (GTAW) utilizes a non-consumable tungsten electrode.
• Process:
  • Arc generated between the tungsten electrode and the base metal.
  • Filler metal can be added separately if needed.
• Shielding Gas: Argon or other inert gases protect the weld area.
• Current: Direct current (DCEN is common).

Gas Welding

• Gases Used: Oxygen (black cylinder) and Acetylene (red cylinder).
• Flame Types:
  • Neutral Flame: Oxygen and acetylene in a stoichiometric ratio (1:1).
  • Carburizing Flame: Excess acetylene (1.5:1).
  • Oxidizing Flame: Excess oxygen (1.5:1).
• Flame Temperatures:
  • Neutral Flame: Inner core ~ 3100°C, outer core ~ 1200°C.
  • Carburizing Flame: Inner core ~ 3300°C.
  • Oxidizing Flame: Higher inner core temperature.

Important Equipment for SMAW

• Electrode Holder: Holds the electrode.
• Workpiece Clamp: Connects to the workpiece.
• Chipping Hammer: Removes slag after welding.
• Wire Brush: Cleans the surface before welding.
• Protective Shield: Protects eyes from UV rays during welding.
• Transformer: Steps down voltage for welding.

Electrode Specification**

• AWS: American Welding Society classification (e.g., E6013, E7018).
  • E: Electrode.
  • 60: Minimum tensile strength (in KSI).
  • 1: Welding position (1 = all positions).
  • Last two digits indicate flux material and current conditions.

Conclusion

• The lecture covered different welding processes and techniques, focusing on practical applications in lab sessions.