1. Chip Formation

2. generally softer materials - easier to machine
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

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

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

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

10. 3 basic types of chip formation

11. 1. Continuous chip

12. 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

13. 2. Discontinuous chip (segmented)

14. 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

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

16. 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

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

19. Cutting tool geometry
positive rake
neutral rake
negative rake

20. Positive rake tools

21. 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

22. Negative rake tools

23. 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

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