Contents:

• Classification of welding processes - Principles of Oxy-acetylene gas welding

• A.C metal arc welding, resistance welding, submerged arc welding

• Tungsten inert gas welding, metal inert gas welding, plasma arc welding, thermit welding,  defects in welding

• Soldering and brazing. 

Plasma arc welding (PAW) is an advanced fusion welding process that utilizes a constricted, high-temperature plasma arc to join metals. It's similar to TIG welding in that it employs a non-consumable tungsten electrode, but PAW separates the electrode from the shielding gas envelope, enabling more precise control over the arc and weld pool.

A PAW torch comprises a tungsten electrode positioned within a water-cooled copper nozzle. An inert gas, typically argon or helium, flows through the torch, constricting the arc and creating a highly concentrated plasma stream. This intense plasma arc, reaching temperatures exceeding 20,000°C (36,000°F), melts the base material, forming a deep, narrow weld.

PAW offers several advantages over other welding methods:

1. High Precision and Weld Quality: The constricted plasma arc produces a focused heat source, resulting in narrow, deep welds with minimal distortion. This precision makes PAW ideal for welding thin materials and applications demanding high-quality welds.

2. Versatility: PAW can weld a wide range of metals, including aluminium, stainless steel, titanium, and exotic alloys. It's particularly effective for welding reactive metals that tend to oxidize during welding.

3. Deep Weld Penetration: The high energy density of the plasma arc allows for deep weld penetration, making PAW suitable for welding thicker materials in a single pass.

4. High Welding Speed: Plasma arc welding can achieve faster welding speeds compared to TIG welding, particularly for thicker materials. This increased speed enhances productivity and reduces overall welding time.

5. Reduced Heat Input: The focused plasma arc minimises heat input into the surrounding material, reducing distortion and residual stresses. This is particularly beneficial for welding thin materials or components that are sensitive to heat.

6. Ease of Automation: PAW is well-suited for automation due to its stable arc and consistent weld quality. This automation capability further improves productivity and reduces welding costs.

PAW finds applications in various industries, including:

1. Aerospace: PAW is extensively used in the aerospace industry for welding aircraft components, particularly for lightweight alloys like aluminum and titanium.

2. Automotive: PAW is employed in the automotive industry for welding automotive components, including engine parts, exhaust systems, and body panels.

3. Chemical Processing: PAW is utilized in the chemical processing industry for welding piping, vessels, and other equipment that handles corrosive chemicals.

4. Food and Beverage: PAW is used in the food and beverage industry for welding stainless steel tanks, pipes, and other equipment that must meet strict hygiene standards.

5. Medical Devices: PAW is employed in the medical device industry for welding implants, surgical instruments, and other medical components that require high precision and biocompatibility.

6. Nuclear Power: PAW is utilized in the nuclear power industry for welding reactor components, piping, and other critical structures that must withstand extreme conditions.

7. Semiconductor: PAW is used in the semiconductor industry for welding delicate electronic components and interconnects that require high precision and minimal contamination.

Thermit welding, also known as exothermic welding or thermit bonding, is a fusion welding process that utilizes an exothermic reaction to generate molten metal, creating a strong metallurgical bond between the materials being joined. This process is particularly effective for welding large steel sections, such as rails, pipes, and structural components.

Mechanism of Thermit Welding:

Thermit welding involves the ignition of a thermite mixture, typically composed of aluminum powder and a metal oxide, such as iron oxide. This reaction produces a superheated molten metal, typically reaching temperatures around 3000°C (5432°F), which melts the base metals, forming a weld pool. As the molten metal cools and solidifies, it fuses with the base metals, creating a strong, continuous joint.