Welding Technology: Resistance Spot Welding

Study Notes

Welding Processes

Resistance Spot Welding (RSW)
- Definition: A process in which faying surfaces are joined in one or more spots by the heat generated by resistance to the flow of electric current through workpieces held together under force by electrodes.
- Process: Electric current is passed through the workpieces, causing resistance heating, which produces a fused nugget of weld metal.
- Advantages:
  - High speed (< 0.1 seconds)
  - Excellent for sheet metal applications
  - No filler metal required
- Limitations:
  - Higher equipment costs
  - Unfavorable power line demands
  - Nondestructive testing difficulties
  - Low tensile and fatigue strength
Resistance Seam Welding (RSEW)
- Definition: A process in which heat generated by resistance to the flow of electric current is combined with pressure to produce a welded seam.
- Classifications:
  - Roll spot welding
  - Reinforced roll spot welding
  - Leak-tight seam welding
Projection Welding (PW)
- Definition: A variation of resistance welding in which current flow is concentrated at the point of contact with a local geometric extension of one (or both) of the parts being welded.
- Advantages:
  - Can be used in difficult resistance-welding applications
  - Allows for multiple welds at once
  - Faster manufacturing process
Flash Welding (FW)
- Definition: A resistance welding process in which a butt joint weld is produced by a flashing action and the application of pressure.
- Process: Melting and forging process that produces welded joints with strengths equal to those of the parent materials.
- Components of a typical flash-welding machine:
  - Machine bed
  - Movable platen
  - Clamping assemblies
  - Equipment for controlling motion
  - Welding transformer
  - Controls and monitors
  - Vent/flash catcher
High-Frequency Induction Welding (HFIW)
- Definition: A process that uses high-frequency alternating current (ac) resistance heating to melt and join metals.
- Characteristics of high-frequency current:
  - Skin effect
  - Proximity effect
- Applications:
  - Welding of tubes and pipes
  - Welding of aluminum and copper
High Energy Density (HED) Welding Processes
- Definition: Processes that use high-energy density to produce precise welds with minimal distortion.
- Types:
  - Electron Beam Welding (EBW)
  - Laser Beam Welding (LBW)
Electron Beam Welding (EBW)
- Definition: A process that uses a focused beam of electrons to melt and join metals.
- Advantages:
  - Deepest single-pass weld penetration
  - Fast travel speeds
  - Low heat input
- Limitations:
  - High initial start-up costs
  - Not portable
  - Part fit-up is critical
  - Produces x-rays
Laser Beam Welding (LBW)
- Definition: A process that uses a focused beam of light to melt and join metals.
- Advantages:
  - Single-pass weld penetration up to 3/4" in steel
  - High travel speed
  - Low heat input
  - No filler metal required
- Limitations:
  - High initial start-up costs
  - Not portable
  - Part fit-up is critical
  - Metals with high reflectivity (e.g., copper, aluminum) are difficult to weld
Friction Welding (FRW)
- Definition: A process that uses frictional heat to join metals.
- Types:
  - Inertia friction welding
  - Direct-drive friction welding
- Advantages:
  - Fast welding process
  - Can join dissimilar metals
  - Correct part geometry
  - Easily automated
- Limitations:
  - High initial start-up costs
  - Parts must be able to rotate about an axis of symmetry
  - Free machining alloys are difficult to weld
  - Non-forgeable materials cannot be friction welded
Ultrasonic Welding (USW)
- Definition: A process that uses high-frequency vibration to produce a weld.
- Advantages:
  - Permits joining of thin materials to thick materials
  - Permits dissimilar metal joints
  - Provides joints with good thermal and electrical conductivity
  - No filler material required
- Limitations:
  - Requires special equipment
  - Not suitable for all materials
Explosion Welding (EXW)
- Definition: A process that uses explosive force to create an electron-sharing metallurgical bond between two metal components.
- Advantages:
  - Can be used to join dissimilar metals
  - No heat transfer to the component metals
  - No appreciable temperature increase in the metals
- Limitations:
  - Requires specialized equipment and expertise
  - Not suitable for all materials