Welding, Soldering and Brazing

• Soldering: Uses low heat and filler metal without melting the base metal;
  • Temperature – Below 450°C
  • Base Metal Fusion – Base metals do not melt
  • Filler Material – Required (low-melting alloys like tin-lead or silver)
  • Strength – Weakest joint, used for electrical and delicate work
  • Applications –  Electronics, circuit boards, jewelry, plumbing
  • Heat Source – Soldering iron or torch
• Brazing: Uses moderate heat and filler metal to bond without melting the base metal;
  • Temperature – Above 450°C but below the melting point of base metals
  • Base Metal Fusion– Base metals do not melt
  • Filler Material – Required (brass, copper, silver alloys)
  • Strength – Stronger than soldering but weaker than welding
  • Applications – Pipe fittings, HVAC, jewelry, automotive
  • Heat Source –  Torch, furnace, induction heating
• Welding: Melts and fuses base metals;
  • Temperature – Above 4500°C (depends on metal type)
  • Base Metal Fusion– Base metals melt and fuse together
  • Filler Material – Optional (may or may not use filler material)
  • Strength – Strongest joint, often as strong as base metal
  • Applications – Heavy-duty fabrication, construction, pipelines, automotive, aerospace
  • Heat Source – Arc, gas flame, laser, electron beam, resistance

• Fusion welding –
• Gas Welding –  joining metals by melting the workpieces and a filler material (if needed) using a flame generated by burning fuel gas with oxygen or air.
  • Oxy-Acetylene Welding (OAW)- mixture of oxygen and acetylene to produce a high-temperature flame.
  • Gas Cylinders
    • Oxygen Cylinder (Color: Black )
      Stores oxygen at high pressure (around 150–200 bar).
    • Acetylene Cylinder (Color: Maroon )
      Stores acetylene at around 15 bar pressure.
  • Pressure Regulators- Regulate gas pressure from cylinders to the required working pressure.
    • Single-stage regulators: Reduce pressure in one step.
    • Two-stage regulators: Reduce pressure in two steps for better control.
  • Hoses and Connectors– Flexible rubber hoses transport gases from cylinders to the torch.
    Color-coded for safety:
    • Red hose: Acetylene
    • Blue hose: Oxygen
  • Welding Torch (Blowpipe)- Mixes oxygen and acetylene in proper proportions to generate the flame.
    • Has control valves to adjust gas flow.
  • Nozzles and Tips
    • Attached to the torch to direct the flame.
    • Different sizes for different welding tasks.
  • Spark Lighter – Used to ignite the flame safely.
  • Flashback Arrestors– Prevents flame from traveling back into the cylinder, avoiding explosions.
•  Types of Flames in Gas Welding
  • Neutral Flame (Equal oxygen and acetylene –  1 : 1)
    • Temperature: ~3200°C
    • Used for mild steel, stainless steel, aluminum, and copper.
  • Carburizing Flame (Excess acetylene)
    • Low-temperature flame (~3000°C) with a yellowish tip.
    • Used for welding high-carbon steel and certain non-ferrous metals.
  • Oxidizing Flame (Excess oxygen)
    • High-temperature flame (~3500°C) with a shorter, bluish-white inner cone.
    • Used for welding brass and copper.
• Advantages of Gas Welding
  • Portable and cost-effective.
  • Can weld a variety of metals, including thin sheets.
  • Provides good control over heat input.
• Disadvantages of Gas Welding
  • Slower than other welding methods (e.g., arc welding).
  • Not suitable for very thick materials.
  • Fire hazard due to flammable gases.
• Arc welding – uses an electric arc to generate intense heat (up to 6000°C) to melt and join metals. The molten metal solidifies to form a strong weld.
  • An electrode carries electric current to create an arc between the electrode and the workpiece.
  • A shielding gas or flux coating protects the weld from contamination.
• Types of Arc Welding Processes
  1. Shielded Metal Arc Welding (SMAW) / Stick Welding
  2.  Gas Metal Arc Welding (GMAW) / MIG Welding
  3. Gas Tungsten Arc Welding (GTAW) / TIG Welding
  4. Submerged Arc Welding (SAW)
  5. Plasma Arc Welding (PAW)
  6. Stud welding
  7. Thermit welding
• Shielded Metal Arc Welding (SMAW) / Stick Welding
  • Uses a coated electrode that melts and provides both filler material and shielding.
  • The flux coating creates a protective gas and slag.
•  Gas Metal Arc Welding (GMAW) / MIG Welding
  • Uses a consumable continuous wire electrode and an inert gas (like Argon or CO₂) for shielding.
• Gas Tungsten Arc Welding (GTAW) / TIG Welding
  • Uses a non-consumable tungsten electrode with inert gas shielding (Argon or Helium).
  • Filler metal is added separately if needed.
• Submerged Arc Welding (SAW)
  • Uses a continuous wire electrode and a granular flux blanket over the weld area.
  • No visible arc as it is submerged under the flux.
• Plasma Arc Welding (PAW)
  • Similar to TIG but uses a constricted plasma arc for more concentrated heat.
• Stud welding is a process that joins a metal stud (or bolt) to a workpiece by generating heat through an electric arc or capacitor discharge.

Comparison of Arc Welding Processes

• Thermit welding (also known as exothermic welding) is a process where metal is melted using the heat generated from a chemical reaction between aluminum powder and metal oxide (usually iron oxide).
  • Thermit mixture (Al + Fe₂O₃) is ignited at 2500-3000°C.
    • Fe2​O3​+2Al→2Fe+Al2​O3​+Heat
  • The reaction produces molten iron and slag.
  • The molten iron flows into the joint, welding the metals together.
    
  • No need for external power.
  • Applications: Railway track welding, pipelines, electrical connections, heavy-duty steel structures.

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