WELDING Notes
1. Introduction to Welding
Welding is a fabrication process that joins metals by melting and fusing them using heat and sometimes filler materials. It is widely used in industries like automotive, aerospace, shipbuilding, and construction.
2. Common Welding Processes
(A) Arc Welding (Electric Welding)
- Uses electric arc to generate heat (above 3000°C).
- Common types:
- Shielded Metal Arc Welding (SMAW) / Stick Welding
- Gas Metal Arc Welding (GMAW) / MIG Welding
- Gas Tungsten Arc Welding (GTAW) / TIG Welding
- Flux-Cored Arc Welding (FCAW)
- Applications: Construction, pipelines, shipbuilding, structural steelwork.
(B) Oxy-Fuel Gas Welding
- Uses a flame produced by burning a fuel gas with oxygen.
- Common types:
- Oxy-Acetylene Welding (OAW) – Uses acetylene and oxygen (Temperature: 3200°C).
- Oxy-LPG Welding – Uses liquefied petroleum gas (LPG) and oxygen (Lower temperature than acetylene).
- Applications: Sheet metal fabrication, automobile repairs, light structural work.
(C) Brazing
- Uses filler metal with a melting point above 450°C but below base metal melting temperature.
- Stronger than soldering, but weaker than welding.
- Common methods: Torch brazing, furnace brazing, induction brazing.
- Applications: HVAC, pipe fittings, jewelry making, electrical contacts.
3. Welding Tools & Equipment
| Tool/Equipment | Use & Specification |
|---|---|
| Welding Machine | Supplies power for arc welding (AC/DC types). |
| Electrodes | Used in arc welding to form a strong joint. |
| Welding Torch | Used in gas welding to mix and ignite gases. |
| Filler Rods | Added material to strengthen the weld. |
| Gas Cylinders | Stores oxygen, acetylene, or LPG for gas welding. |
| Regulators | Controls gas pressure for welding flames. |
| Welding Helmet | Protects eyes and face from sparks and UV rays. |
4. Safety Methods in Welding
✔ Wear fire-resistant clothing and gloves.
✔ Use welding goggles and helmets for eye protection.
✔ Work in a well-ventilated area to avoid gas poisoning.
✔ Store gas cylinders upright and secure.
✔ Keep a fire extinguisher nearby for emergencies.
5. Gas Welding Methods & Flame Adjustment
(A) Types of Flames in Gas Welding
- Neutral Flame – Equal oxygen and acetylene (Used for welding most metals).
- Carburizing Flame – Excess acetylene (Used for welding aluminum, high-carbon steel).
- Oxidizing Flame – Excess oxygen (Used for welding copper, brass, zinc).
(B) Gases Used in Welding & Cutting
- Oxygen (O₂) – Supports combustion in all gas welding processes.
- Acetylene (C₂H₂) – Produces the hottest flame (3200°C), used for gas welding.
- LPG (Liquefied Petroleum Gas) – Cheaper alternative to acetylene, used in low-cost welding and brazing.
- Compressed Air – Used with LPG for low-temperature soldering and brazing.
6. Difference Between Soldering and Brazing
| Factor | Soldering | Brazing |
|---|---|---|
| Temperature | Below 450°C | Above 450°C |
| Filler Material | Soft solder (Tin-lead, Tin-silver) | Brass, Silver, Copper alloys |
| Joint Strength | Weaker, used for electrical work | Stronger, used for mechanical joints |
| Application | Circuit boards, plumbing | HVAC, pipe fittings, tools |
7. Use of Oxy-Acetylene, Oxy-LPG & Air-LPG for Brazing/Soldering
| Gas Combination | Usage |
|---|---|
| Oxy-Acetylene | High-temperature welding and brazing of steel and alloys. |
| Oxy-LPG | Cost-effective alternative for welding and brazing, used in HVAC and plumbing. |
| Air-LPG | Used in low-temperature brazing and soldering, ideal for refrigeration pipes and small metal repairs. |
Conclusion
Welding is a critical process in metal fabrication. Understanding different welding methods, safety precautions, flame settings, and the difference between brazing and soldering ensures strong, durable joints in various applications.
