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

metal is forced ahead of tool
Surface finish affected by:
speeds
 feeds
 depth of cut
 tool shape
 use of cutting fluid
 rigidity of the setup

Optimum chip for operator
safety is figure “9”
Chip breaker
curls chip to break it off
 keep from tangling in machine
 safer

3 basic types of chip
formation
1. Continuous chip
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

2. Discontinuous chip
(segmented)
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

3. Continuous chip (with
built up edge on tool)
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

Solutions for built up edge
•
•
•
•
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no single solution
change tool geometry
use chip breaker
cutting fluids
best combination of speeds and feeds
Cutting tool geometry
positive rake
 neutral rake
 negative rake

Positive rake tools
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

Negative rake tools
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

Most carbide tools have
negative rake because:
indexable insert can be turned over
 withstands more cutting pressure
 higher cutting speeds used
