types of chip formation, cutting temperature,etc.,

1. Types of Chip formation, Cutting
Temperature,
Cutting fluids and Tool wear

2. Actual Chip Formation
• More realistic view of chip
formation, showing shear
zone rather than shear plane
• Also shown is the secondary
shear zone resulting from
tool-chip friction
Types of chip formation
• Discontinuous chip
• Continuous chip
• Continuous chip with Built-up
Edge (BUE)
• Serrated chip or segmented chip
Machining operation
Machining operation. Animation

3. VIDEO
VIDEO
CHIP FORMATION
Discontinuous chip Continuous chip Continuous chip
with Built-Up Edge
Serrated or
segmented chip
It depends on:
Workpiece material
Tool geometry
Cutting conditions
Chip formation types

4. Discontinuous Chip
• Brittle work materials
• Low cutting speeds
• Large feed and depth of cut
• High tool-chip friction
Discontinuous Chip
Discontinuous Chip . Animation

5. Continuous Chip
• Ductile work materials
• High cutting speeds
• Small feeds and depths
• Sharp cutting edge
• Low tool-chip friction
Continuous Chip
Continuous Chip . Animation

6. • Semicontinuous - saw-tooth
appearance
• Cyclical chip forms with alternating
high shear strain then low shear
strain
• Associated with difficult-to-machine
metals at high cutting speeds
Serrated Chip or segmented chip
Serrated Chip
Serrated Chip. Animation

7. Continuous with BUE
• Ductile materials
• Low cutting speed
• High feed
• High depth of cut
Continuous with BUE

8. Cutting Temperature
• Approximately 98% of the
energy in machining is converted
into heat
• This can cause temperatures to
be very high at the tool-chip
• The remaining energy (about
2%) is retained as elastic energy
in the chip
High cutting temperatures result in the following:
• Reduce tool life
• Produce hot chips that pose safety hazards to the machine operator
• Can cause inaccuracies in part dimensions due to thermal expansion of
work material
Cutting Temperature. Animation

9. Cutting Temperature
Cutting Temperature. Animation
Cutting Temperature

10. Distribution of Heat
Heat dissipation depends on cutting speed
Cutting Speed, v
% Heat
Tool-work ---10 %
Work-chip----- 10 %
Chip-tool----- 80 % keep cutting
zone temperature
low
Cutting FluidSolution 

11. Cutting Temperature
• Analytical method derived by Nathan Cook from dimensional analysis
using experimental data for various work materials.
ΔT – Temperature rise at tool-chip interface;
U – Specific energy;
Vc – Cutting speed;
tu – Chip thickness before cut;
C – Volumetric specific heat of work material;
K – Thermal diffusivity of work material;
0.333
0.4 c uv tU
T
C K
 
   
 

12. Cutting Temperature
• Experimental methods can be used to measure temperatures in
machining
-Most frequently used technique is the tool-chip thermocouple
• Using this method, Ken Trigger determined the speed-temperature
relationship to be of the form:
T – Measured tool-chip interface temperature
Vc – Cutting speed
K, m – Constants
m
cT Kv

13. Cutting fluid is any liquid or gas that is applied to the chip or cutting tool to improve cutting performance.
Cutting fluids serve 4 principle functions:
1.To remove heat in cutting (COOLING): The energy used in the cutting process is almost exclusively transformed
into heat that goes to the workpiece, tool and chip. The effective cooling action depends on the method of
application, type of fluid, fluid flow rate and pressure.
2.To lubricate the chip-tool interface (LUBRICATION): It reduces friction forces and temperatures.
3.To wash away chips (CHIP REMOVAL): This is only applicable to small and discontinuous chips.
4.To avoid part oxidation (ANTI-CORROSION): The environment humidity in combination with the high
temperatures (500-900ºC) obtained during machining may cause part oxidation. Thus, the cutting fluid must contain
anti-corrosion additives.
Use of cutting fluids contributes to:
• longer tool life.
• Produce workpieces of accurate sizes (reduce thermal expansion).
Achieve proper surface quality of the workpiece.
• Support chip removal.
• Reduce thermal stress on machine tool.
CUTTING FLUIDS
CUTTING FLUIDS

14. CUTTING FLUIDS
METHODSOFAPPLICATION
LUBRICATION
TYPE
CONTENT
USED
VOLUME
CHARACTERISTICS
Wet machining
(using coolant)
Manual application
10 to 100
l/min
Used for manual tapping. Cutting fluids are used as
lubricants.
Flooding supply
Lubricating system of machine tools need to be cleaned from
time to time to eliminate microorganisms.
Coolant-fed tooling
or internal cooling
Some tools (typically drills) are provided with axial holes so
that cutting fluid can be pumped directly to the
cutting edge. Coolant pressures up to 80 b ars.
Coolant-fed tool
holders
Special tool holders required for milling, turning or
drilling operations. Coolant pressures up to 30 bars.
Reduced
lubrication
Minimum quantity
llubrication (MQL)
50 ml/h up
to 1-2 l/h
Cutting fluid is deposited as drops or air-oil mix. Valid
for not very demanding machining operations.
It can be external or internal.
Without
lubrication
Dry machining without
It shows economic and environmental benefits. Under
research.
Novel cooling methods are under research: high pressure cooling (> 70bar), criogenic cooling (N2, CO2),...
VIDE
O
VIDE
O

15. CUTTING FLUIDS
Manual application Flooding supply Coolant-fed tooling Coolant-fed tool holder
Cutting oils are based on mineral or fatty oil mixtures. Commonly used for heavy cutting operations.
Soluble oils is the most common (95% of the time), cheap and effective form of cutting fluid. Oil
droplets suspended in water in a typical ratio water to oil 30:1. Emulsifying agents are also added to
promote stability of emulsion, as well as anticorrosive additives.
Chemical fluids (synthetic) consists of chemical diluted in water. They may have harmful effects to the
skin.
TYPES OF CUTTING FLUID

16. Three Modes of Tool Failure
Fracture failure (Mechanical chipping)
When the cutting force at tool point becomes excessive, it leads to failure by
brittle fracture.
Temperature failure (Thermal cracking and softening)
Cutting temperature is too high for the tool material, which makes the tool
point to soften, and leads to plastic deformation along with a loss of sharp
edge.
Gradual wear
Gradual wearing of the cutting edge causes loss of tool shape, reduction in
cutting efficiency and finally tool failure.

17. Preferred Mode of Tool Failure:
Gradual Wear
Fracture and temperature failures are
premature failures.
Gradual wear is preferred because it leads to
the longest possible use of the tool.
Gradual wear occurs at two locations on a tool:
• Crater wear – occurs on top rake face
• Flank wear – occurs on flank (side of
tool)
Tool Failures

18. Flank Wear or wear land
• It occurs on the tool flank as a result of
friction between the machined surface
of the work piece and the tool flank.
• Due to Friction and abrasion.
• Increases as speed is increased.
Crater wear
• It consists of a concave section on the
tool face formed by the action of the
chip sliding on the surface.
• Direct contact of tool and chip.
• Forms cavity
Flank wear & Crater wear

19. Mechanism of wear
• Adhesion wear: Fragments of the work-piece get welded to the
tool surface at high temperatures; eventually, they break off,
tearing small parts of the tool with them.
• Abrasion: Hard particles, microscopic variations on the bottom
surface of the chips rub against the tool surface and break
away a fraction of tool with them.
• Diffusion wear: At high temperatures, atoms from tool diffuse
across to the chip; the rate of diffusion increases exponentially
with temperature; this reduces the fracture strength of the
crystals.
• Chemical wear: Reaction of cutting fluid to material of tool.

20. Preferred Mode of Tool Failure: Gradual Wear