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Chip Formation

Chip Formation. Machinability. relative difficulty of a machine operation with regard to tool life, surface finish, and power consumption generally softer materials - easier to machine. Metal does NOT split off ahead of cutter as in wood. Metal is sheared off at SHEAR PLANE.

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Chip Formation

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  1. Chip Formation

  2. Machinability relative difficulty of a machine operation with regard to tool life, surface finish, and power consumption generally softer materials - easier to machine

  3. Metal does NOT split off ahead of cutter as in wood

  4. Metal is sheared off at SHEAR PLANE • metal is forced ahead of tool

  5. Surface finish affected by: • speeds • feeds • depth of cut • tool shape • use of cutting fluid • rigidity of the setup

  6. Optimum chip for operator safety is figure “9”

  7. Chip breaker • curls chip to break it off • keep from tangling in machine • safer

  8. 3 basic types of chip formation

  9. 1. Continuous chip

  10. Continuous chip characteristics • better surface finish • soft or medium hardness materials that are ductile • low coefficient of friction - pass across top of well polished tool • chips curl or are straight and stringy • chip breaker used to break the chip

  11. 2. Discontinuous chip (segmented)

  12. Discontinuous chip characteristics • materials that fracture easily (cast iron) • fails or breaks after only a small amount of deformation • no chip breaker required • chips are cleaned up easily

  13. 3. Continuous chip (with built up edge on tool)

  14. Continuous chip (built of edge) characteristics • soft materials - high coef of friction • stick to top of entering edge of tool • caused by heat and pressure of cutting action • material temporarily welds to tip of cutting tool then releases • rougher surface finish • tool life shortened

  15. Solutions for built up edge • no single solution • change tool geometry • use chip breaker • cutting fluids • best combination of speeds and feeds

  16. Cutting tool geometry • positive rake • neutral rake • negative rake

  17. Positive rake tools

  18. Positive rake tool characteristics • freer cutting at low speeds • pos rake tools, cutting fluids, and higher speeds decrease tendency for built up edge - however, • large pos rake = continuous chip

  19. Negative rake tools

  20. Negative rake tool characteristics • surface disrupted more • require more power • stronger and have longer working life than positive • low cutting speeds = poor surface finish • high cutting speeds = good surface finish

  21. Most carbide tools have negative rake because: • indexable insert can be turned over • withstands more cutting pressure • higher cutting speeds used

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