Fundamentals of Welding Summary

Necessity: Required when manufacturing a single piece is impossible or uneconomical, for easier transportation, or for maintenance disassembly.
Joining vs. Assembly: Joining (welding, brazing, soldering, adhesive bonding) creates permanent joints. Assembly typically involves mechanical fastening methods, some of which allow disassembly.

Definition: A process joining two or more parts at contacting surfaces using heat and/or pressure; filler material may be added.
Importance: Provides permanent, economical joints and allows fabrication "in the field."
Drawbacks: High labor costs (manual), high energy/danger, difficult disassembly, and defects that are hard to detect.
Safety Hazards: Molten metal temperatures, flammable fuels (e.g., acetylene), and electrical shock.

Joint Types: Five basic types: (a) Butt, (b) Corner, (c) Lap, (d) Tee, and (e) Edge.
Weld Types: * Fillet Weld: Used in corner, lap, and tee joints; shaped like a right triangle; requires minimal edge preparation. * Groove Weld: Associated with butt joints; requires edge preparation (e.g., square, V, U, J shapes). * Plug and Slot Welds: Used for joining flat plates. * Spot and Seam Welds: Used for lap joints; associated with resistance welding.

Definition: Coalescence via melting base metals. Autogenous welds use no filler metal.
Arc Welding (AW): Uses an electric arc ( $10,000\,^{\circ}F$ / $5500\,^{\circ}C$ ) between an electrode and work.
Resistance Welding (RW): Fusion via heat from electrical resistance and pressure.
Oxyfuel Gas Welding (OFW): Fusion via burning fuels (like acetylene) with oxygen.

Electrodes: * Consumable: Rods (sticks) or continuously fed wire that provide filler metal. * Nonconsumable: Tungsten electrodes that resist melting; filler metal is added separately.
Shielding: Protects reactive hot metal from air using flux or shielding gases (Argon, Helium, $CO_2$ ).
Processes: * SMAW (Stick): Coated consumable electrode; common but limited by stick length and slag removal. * GMAW (MIG): Continuous bare wire with gas shielding; higher productivity/arc time than SMAW. * GTAW (TIG): Nonconsumable tungsten electrode; high quality, no spatter, but slower. * PAW (Plasma): Constricted plasma arc ( $28,000\,^{\circ}C$ / $50,000\,^{\circ}F$ ) for high energy density and penetration.

Resistance Spot Welding (RSW): Widely used in mass production (e.g., $10,000$ welds in a car body).
Resistance Seam Welding (RSEW): Uses rotating wheels for air-tight overlapping welds (e.g., fuel tanks).
Oxyacetylene Welding (OAW): Employs $C_2H_2$ and $O_2$ . * Safety: Acetylene is unstable above $15\,lb/in^2$ ; stored in cylinders with porous filler and acetone ( $CH_3COCH_3$ ).

Definition: Joining via pressure or heat/pressure without melting base metals or adding filler.
Key Processes: * Diffusion Welding (DFW): Solid state fusion at elevated temperature and pressure. * Friction Welding (FRW): Coalescence via heat of friction between surfaces. * Ultrasonic Welding (USW): Coalescence via moderate pressure and ultrasonic oscillating motion (> 20\,kHz).