Metal Joining Processes

Arc welding is a versatile method for joining metals using an electrical arc to heat and melt the metal, allowing it to fuse together. Here are some key points
about arc welding:
Process Overview:
o An electrode is held close to the metal to be joined.
o An electrical voltage creates an arc between the electrode and the workpiece.
o The intense heat generated by the arc melts the metals, allowing them to fuse together.
Types of Arc Welding:
o Stick Welding (SMAW): Uses a consumable electrode (stick) with flux coating.
o TIG Welding (GTAW): Uses a non-consumable tungsten electrode and inert gas.
o MIG Welding (GMAW): Uses a consumable wire electrode and shielding gas.
o Flux Cored Arc Welding (FCAW): Uses a tubular wire electrode with flux.
o Submerged Arc Welding (SAW): Uses a granular flux and submerged electrode.
Advantages of Arc Welding:
o Produces high-quality, strong welds.
o Accommodates imprecise fitment of components.
o Portable and suitable for field use.
o Can be adjusted for manual or automated techniques.
Applications:
o Automotive manufacturing
o Industrial piping
o Shipbuilding
o Structural steel erection
Remember, arc welding has a rich history and continues to play a crucial role in various industries
 Shielded Metal Arc Welding (SMAW)

Principle:
o SMAW, also known as “stick welding,” uses an electric arc between a consumable electrode and the base material
to create coalescence.
o The electrode is coated with flux, which disintegrates during welding, producing shielding gases and molten slag.
o The slag protects the weld area from atmospheric contamination.
Working:
o To strike the arc, the electrode lightly touches the workpiece and is then pulled back slightly.
o Droplets of the electrode pass into the weld pool.
o The flux coating disintegrates, creating shielding gases and slag.
o Slag floats on the weld pool, protecting it from contamination.
o Once solidified, the slag is chipped away to reveal the finished weld.
Advantages:
o Versatile: Suitable for various metals.
o Affordable: Simple equipment.
o Outdoor Use: Ideal for outdoor applications.
Disadvantages:
o Discontinuous: Electrode replacement interrupts the process.
o Fumes: Difficult to control.
o Slag Inclusions: Welds may contain slag.
 DC Welding:
AC (Alternating Current) and DC (Direct Current) are two o Arc Polarity:
different types of electric current used in welding. Let’s explore ▪ DCEN (Direct Current Electrode Negative):
their differences: ▪ Ground clamp is positive, electrode is negative.
AC Welding: ▪ Concentrates heat on the workpiece (good for
o Arc Polarity: Alternates between positive and negative. penetration).
o Applications: ▪ DCEP (Direct Current Electrode Positive):
▪ Commonly used for down-hand heavy plate welds. ▪ Ground clamp is negative, electrode is positive.
▪ Suitable for welding aluminum and similar metals. ▪ Concentrates heat on the electrode.
o Advantages: o Applications:
▪ Penetrates deeper. ▪ Suitable for all arc welding processes.
▪ Works well for magnetic materials. ▪ Better for welding thinner metals.
▪ Eliminates arc blow. o Advantages:
o Disadvantages: ▪ Stable arc.
▪ Less stable arc. ▪ High penetration.
▪ More weld spatter. ▪ Less weld spatter.
▪ Lower filler metal deposition rates. o Disadvantages:
▪ Requires correct polarity for specific welding processes.
In summary, AC welding is ideal for aluminum, while DC welding provides
stable arcs and quality welds on most metals. Understanding the right polarity
and its impact on welding quality is crucial for successful welding operations!
Fusion Welding:
o Definition: Fusion welding involves joining two or more materials by heating them to their melting point, allowing them to fuse together.
o Process: During fusion welding, the base metal and, if needed, a filler material melt and solidify to form a weld joint.
o Examples: Common fusion welding processes include shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc
welding (GMAW), flux-cored arc welding (FCAW), submerged arc welding (SAW), and plasma cutting/arc cutting 12.
Solid-State Welding:
o Definition: Unlike fusion welding, solid-state welding does not involve melting the base metal. Instead, it relies on heat and pressure to create a
bond between materials.
o Examples: Solid-state welding methods include friction welding, ultrasonic welding, explosive welding, and diffusion bonding.
Weld Bead:
o The deposited material formed during welding. It results from the melted base metal and filler material solidifying as the weld cools.
Heat-Affected Zone (HAZ):
o The region around the weld joint where the base metal experiences temperature changes due to welding heat. It can affect material properties.
Weld Pool:
o The molten metal area created during welding. It forms at the joint interface and solidifies to create the weld bead.
Penetration:
o The depth to which the weld metal fuses into the base metal. Proper penetration ensures a strong joint.
Weld Joint Types:
o Butt Joint: Two pieces meet edge-to-edge.
o Lap Joint: One piece overlaps the other.
o T-Joint: Forms a “T” shape.
o Corner Joint: Joins two pieces at a right angle.
Remember, understanding these terms is crucial for successful welding operations!
Tungsten Inert Gas Welding (TIG)
Principle:
o TIG welding, also known as gas tungsten arc welding (GTAW), uses a non-consumable tungsten electrode.
o An electric arc is created between the tungsten electrode and the workpiece.
o Inert gases (such as argon, argon-hydrogen, or argon-helium) shield the weld pool from atmospheric contamination.
o TIG welding produces high-quality welds suitable for critical applications.
Operation:
o The tungsten electrode is held in a TIG torch.
o The arc is struck by touching the electrode to the workpiece and then retracting slightly.
o The heat generated melts the base metal and filler material (if needed).
o Inert gas flows through the torch to protect the weld pool.
o The weld solidifies, forming a strong joint.
Advantages:
o Excellent control: Precise heat input and arc stability.
o High-quality welds: Suitable for thin materials and critical applications.
o Clear visibility: No flux coating, easy to operate.
Applications:
o Welding sheet metals.
o Joining stainless steel, magnesium alloys, and copper base alloys.
o Aircraft industry, rocket motor fabrication.
Limitations:
o Slow process: Requires additional filler rod.
o Tungsten contamination: Tungsten can contaminate the weld, making it hard and brittle.
o Shield contamination: Shield gas can cause contamination if not controlled.
o High equipment cost.
Plasma Arc Welding (PAW)
Principle:
o PAW uses a non-consumable tungsten electrode to create an electric arc.
o The arc generates a plasma—a gaseous mixture of positive ions, electrons, and neutral gas molecules.
o Plasma jets with high energy density are produced (transferred arc process) for high-speed welding and cutting.
o Non-transferred arc process creates a plasma of relatively low energy density for welding and plasma spraying.
Working Principle:
o Energy provided to inert gas releases electrons, creating a hot ionized state (fourth state of matter).
o Non-consumable tungsten electrode generates the arc.
o Plasma forms, producing high temperatures used to join two plates.
o Similar to TIG welding but with a non-consumable electrode.
Equipment:
o Plasma Arc Torch: Contains tungsten electrode, collets, inner and outer nozzles.
o Shielding and Plasma Gas Supply: Inert gases (argon, helium) protect the weld area.
o Filler Metal: Optional; feeds directly into the weld zone.
Advantages:
o Precise control and high-quality welds.
o Suitable for critical applications.
o Clear visibility due to no flux coating.
Limitations:
o Slow process: Requires filler rod.
o Tungsten contamination: Can make welds hard and brittle.
o Shield contamination: Must control shielding gases.
o High equipment cost.
 Operation of SAW
Submerged Arc Welding (SAW): A • Continuous Process: Electrode
continuously fed.
Comprehensive Overview • Position: Primarily horizontal welding.
1. Principle of Submerged Arc Welding (SAW) • Current Range: 300 A to 2000 A.
• Definition: Submerged arc welding (SAW) involves creating an electric arc between a
continuously fed electrode and the workpiece.
• Electrode Types: Solid, cored, or strip.
• Electrode: Non-consumable tungsten electrode. 4. Applications of SAW
• Flux: Granular fusible flux (lime, silica, manganese oxide, calcium fluoride, etc.) covers
the molten weld and arc, preventing atmospheric contamination. • Long Continuous Welds: Ideal for large
• Process: The flux becomes conductive in its molten state, providing a path for current pieces of metal.
flow. It also shields the arc and molten metal. • Structural Steel Fabrication: Bridges,
• Advantages:
o High deposition rate (about 45 kg/h). buildings, pipelines.
o Deep weld penetration. • Shipbuilding: Hulls, decks, bulkheads.
o Minimal welding fume and arc light. • Pressure Vessels: High-quality welds.
o Suitable for both indoor and outdoor applications.
o Low distortion. • Railway Industry: Rails, tracks, switches.
o Strong, uniform, ductile, and corrosion-resistant welds. 5. Limitations of SAW
2. Equipment for SAW • Slow Process: Requires filler rod.
• Submerged Arc Welder: Inverter-based or conventional.
• Flux Hopper: Holds granular flux. • Tungsten Contamination: Can make welds
• Power Source: Constant voltage welding power supply (AC or DC). hard and brittle.
• Wire Feeder: Feeds the consumable electrode.
• Shield Contamination: Must control
• Welding Torch: Delivers the arc to the workpiece.
3. shielding gases.
• High Equipment Cost.