1. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Chapter 5
TOOL WEAR AND TOOL LIFE
Prof. Dr. S. Engin KILIÇ
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

2. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Content
Tool Wear and Life
Machinability
Economics of Metal Cutting Operations
Optimization Criteria
Choice of Cutting Conditions
Unit Production Time
Unit Production Cost
Photos from internet sites.
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

3. Tool Life - Definitions
A tool that no longer performs the desired function is said to
have reached the end of its useful life.
Criterion to mark the end point for the tool’s life is not necessarily to correspond to a state that the tool is unable to cut the workpiece, but that it is merely unsatisfactory for the purpose.
Such tools which have consumed their lives may be
Resharpened (if applicable) and used again
Used on less restrictive operations
Disposed off
Add picture here!
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

4. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Wear
Failure of the tool to perform a desired function may be due to
Catastrophic failure
Fracture
Temperature
Gradual (progressive) failure
Forms of wear
Crater wear
Flank wear
Workpiece
Tool
Flank
Rake
Chip
Crater
wear
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

5. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Wear Mechanisms
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

6. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Wear
(f)
(g)
Taylor tool life equation:
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

7. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Wear (2)
250
200
150
100 50
0.8
0.7
0.6
0.5
0.4
0.2
0.1
0.3 C D B
Rapid
breakdown
Uniform
wear rate
Initial
Width of flank wear land VB, mm VB
Cutting time, s
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

8. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Wear (3) KT KB KM A + re
Crater
Rake
Section A-A
Zone C B N VN VC b
b/4 VB
VBmax
Wear
notch
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

9. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Life Criteria
A tool-life criterion is defined as a predetermined threshold value of a tool-wear measure or the occurrence of a phenomenon.
For HSS or Ceramic Tools
Catastrophic failure, or
VB = 0.3 mm (uniformly worn flank in zone B) or
VBmax = 0.6 mm (irregularly worn flank)
VB = 0.75 mm (HSS – finish)
VBmax = 1.5 mm (HSS – rough)
ISO
Double check!
Schey’s recommendation
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

10. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Life Criteria (2)
For Sintered Carbide Tools:
VB = 0.3 mm (uniformly worn flank in zone B), or
VBmax = 0.6 mm (irregularly worn flank), or
KT = f mm (f : feed)
VB = 0.4 mm (uniformly worn flank in zone B), or
VBmax = 0.6 mm (irregularly worn flank)
ISO
Schey’s
recommendation
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

11. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Tool Life
Tool life is defined as the cutting time required to reach a tool-life criterion.
Most important factor affecting tool life (for a given work material-tool combination) is the cutting speed.
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

12. Taylor’s Tool Life Model
Frederick W. Taylor
( )
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

13. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Taylor’s Equation
vTn = C
v : cutting speed [m/s]
T: tool life [min]
C: Constant [m/s] (cutting speed for 1 min. tool life)
Typical values of n are
0.1 HSS
0.25 Cemented Carbides
0.3 Coated Carbides
0.4 Ceramics
For an approximate value of C: take recommended value and multiply it by 1.75 (HSS) or 3.5 (Carbides).
Kennametal:
Revise the definitions
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

14. Extended Taylor’s Equation
For HSS: 0.1 < 0.17 < 0.25
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

15. MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II
Machinability
Machinability is defined as the relative ease and economy with which a material (usually a metal) can be machined using appropriate tooling and cutting conditions.
There are various criteria to evaluate machinability:
Tool life
Forces and power
Surface finish
Ease of chip disposal
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II

16. Material Properties Affecting Machinability
Ductility
Strain hardening ability
Strength
Bonding tendency between tool and workpiece
Thermal conductivity
Melting temperature
Abrassive particle content of workpiece
Existence of second-phase particles (lead, sulphur, phosphorus, etc.) which are soft or softened at high temperatures (favors machinability!)
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MFGE 307 THEORY OF MANUFACTURING TECHNOLOGY II