Lecture: Joining Technologies for Metals

Introduction to Manufacturing

• Purpose of Manufacturing: Achieve desired size, shape, and properties of materials.
  • Processes include mechanical and chemical treatments (e.g., carburizing, nitriding).
• Material Properties: Consider mechanical, physical, chemical, and dimensional properties when selecting manufacturing processes.
• Process Complexity:
  • Simple shapes: Forging, casting.
  • Complex shapes: Machining.

Categories of Manufacturing Processes

• Zero Process: Material shifting (e.g., casting, forming).
• Negative Process: Material removal (e.g., machining).
• Positive Process: Material addition (e.g., joining).

Joining Processes

• Joining as a Positive Process:
  • Involves bringing components together to form desired assembly.
  • Includes mechanical, adhesive, and welding methods.

Types of Joining

1. Mechanical Joining:
   • Uses nuts, bolts, rivets.
   • High reliability and load capacity.
2. Adhesive Joining:
   • Uses adhesives like epoxies.
   • Sensitive to environmental conditions.
3. Welding:
   • Fusion, solid-state, solid-liquid processes.
   • Can achieve joint strength higher than base material but reliability can be an issue.

Welding Processes and Characteristics

• Welding Types:
  • Liquid-based processes: e.g., fusion welding.
  • Solid-state processes: e.g., friction welding.
  • Solid-liquid processes: e.g., brazing, soldering.
• Unique Characteristics:
  • Localized heating and differential cooling affect material properties and introduce stresses.
  • Produces residual stresses and potential for partial melting.
  • Leads to chemical, mechanical, and metallurgical heterogeneity.

Factors Influencing Joint Selection

• Joint Permanence: Mechanical for temporary, adhesive/welding for permanent.
• Reliability: High reliability for critical applications (e.g., riveted joints for aircraft).
• Environmental Conditions: Consider corrosion resistance, temperature conditions.
• Economy: Balance between cost and performance.

Welding Considerations

• Applications:
  • Resistance welding: Automobiles.
  • Thermite welding: Rail joints.
  • GTAW: High-quality joints (nuclear, aerospace).
  • Submerged arc welding: Heavy sections (engineering, pressure vessels).
• Advantages:
  • Permanent and potentially stronger than base metal.
  • Can be performed off-site.
• Disadvantages:
  • Requires expertise.
  • Hazardous fumes and poor reliability.

Conclusion

• Next Lecture: Focus on classification of joining processes and their specific applications.