Cutting Tool Technology Summary

Tool Life and Materials

  • Tool Life: Time a cutting tool can be effectively used.

  • Tool Materials: Key for performance includes toughness, hot hardness, and wear resistance.

Modes of Tool Failure

  • Fracture Failure: Occurs due to excessive force.

  • Temperature Failure: High cutting temperatures exceed material limits.

  • Gradual Wear: Preferred mode leading to longer tool use.

    • Types of Wear:

    • Crater wear (top rake face)

    • Flank wear (side of tool)

Tool Wear Mechanisms

  • Abrasion: Hard particles erode the tool surface.

  • Adhesion: High pressure leads to material sticking.

  • Diffusion: Atomic exchange at contact boundaries.

  • Chemical Reactions: High temperatures cause reactions (e.g., oxidation).

  • Plastic Deformation: Force deforms cutting edges.

Taylor Tool Life Equation

  • Dynamics: vTn=CvT^n = C

    • vv: cutting speed

    • TT: tool life

    • nn, CC: material-dependent parameters.

Tool Life Criteria

  • Indicators include visual wear, surface finish degradation, workpiece count, cumulative cutting time.

High-Speed Steel (HSS)

  • Maintains hardness at high temperatures better than plain carbon steel.

  • Types: Tungsten-type (T-grades) and Molybdenum-type (M-grades).

Cemented Carbides

  • Made from tungsten carbide; high hardness and good hot hardness.

  • Non-steel Cutting Grades: Used for nonferrous metals.

  • Steel Cutting Grades: Improved crater wear resistance.

Cermets and Coated Carbides

  • Cermets: Mixtures for high speed finishing.

  • Coated Carbides: Layers of TiC, TiN, etc., enhance performance.

Ceramics and Synthetic Diamonds

  • Ceramics: Used in high speed turning; low toughness.

  • Synthetic Diamonds: Applied for machining nonmetals; not for steel.

  • Cubic Boron Nitride: Hardest material for steel and nickel-based alloys machining.