Flexible Assembly System’s Fastening Theory - Part 2

Overview

• Topic: Fastening Theory Part 2 - Friction Factors and Tightening

Key Points

Clamp Load and Torque

• Clamp Load: The force keeping parts from separating.
  • Goal of fastening
• Friction: Major factor preventing torque translation into clamp force.
  • About 90% of torque is spent overcoming friction (threads and bearing surfaces).
  • Only ~10% of applied torque creates clamp load.

Friction Factors

1. Tolerances
   • Tighter tolerances lead to smoother fit and consistent results.
2. Alignment
   • Proper alignment prevents unnecessary rubbing/shearing.
   • Misalignment affects tightening consistency.
3. Surface Finish
   • Sanded/polished surfaces produce less friction than brushed/textured surfaces.
4. Materials Used
   • Friction varies with material rigidity (e.g., plastics vs. steel).
   • Materials with lower frictional coefficients consume less torque.
5. Lubrication
   • Type and amount of lubricant affects friction between threads during tightening.
6. Special Fastener Types
   • Examples: Thread forming fasteners, nylon-insert lock nuts.
   • Introduce unique friction factors.
7. Materials in Bolted Joint
   • Gaskets/soft objects add resistance when compressed.

Design Considerations

• Maintaining constant friction is crucial for accurate and reliable tightening results.

Conclusion

• This concludes Part 2.
• Part 3 will cover different torque tools and safety concerns.
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