Joining Processes

Joining Processes

1. Fasteners

   • Velcro
   • Rivets
     • Used instead of welding to prevent crack propagation
     • Difficult to weld Al alloys
     • Heating would reduce strength of age hardened alloy used
   • Nuts and Bolts
   • No seal
     • Potential for Galvanic Corrosion

2. Brazing + Soldering

   • Brazing
     • Brass
     • T > 450˚C
   • Molten braze/solder fills gap by capillary action
   • Can join metals with different Tmelt
   • Can be reopened
   • Little metallurgic effect on parent metals
   • Requires good preparation of the surfacee
   • Solder
     • 40%PB;60%Sn
   • Limited strength

3. Welding

   • Non-Arc Welding
     • Forge
       • Force surfaces together at above recrystallisation temperature
     • Friction
       • 2 dissimilar metals with common axis of symmetry
       • Rotate one metal (100-200RPM)
         • Press against other metal (50-200MPa)
     • Friction stir welding
       • Works well with Al alloys
       • Softens the plastic
     • Resistance (spot) Welding
       • Force + Current >1000A
   • Arc Welding
     • Manual Metal Arc
       • Welding Rod
         • One Electrode
         • Consumable or non-consumable
         • The magnetic field created helps transfer the electrode metal to the workpiece
       • Arc produces temperatures >5000˚C
       • Gaseous shield prevents oxidation - weak and brittle joints
         • Ferromanganese
     • Submerged arc
       • Automated MMA
       • Flux poured ahead
       • Uncovered electrode
       • Arc submerged in flux
     • Tungsten Inert Gas
       • Externally applied filler
       • No flux, slag or post weld cleaning
     • Metal inert gas
       • Same as TIG but consumable rod
   • Slag - Protects weld from atmosphere on cooling - must be removed