1. Tool life and surface integrity in turning titanium alloy
이름: 김신희
실험실:재료강도 및 미소역학

2. 목차 1 Introduction 2 Experimental procedure 3 Results and discussions 4
Conclusions

3. Introduction High chemical reactivity Low modulus of elasticity
Titanium alloys have been classified as “difficult-to-machine” materials
Low thermal conductivity
Increase the temperature
Tool wear off very rapidly
High chemical reactivity
Low modulus of elasticity
High strength

4. Introduction P.D. Hartung and B.M. Kramer H.J. Siekmann
1955
How to machine titanium, Tool Engr. 35
H.J. Siekmann
1974
University of Birmingham
R.M. Freeman and Ph.D. Thesis
1982
Tool wear in titanium machining, Ann. CIRP 31
P.D. Hartung and B.M. Kramer
1983
Study on machining of titanium alloys, Ann. CIRP 32
N. Narutaki and A. Murakoshi
1986
Evaluation of principal wear mechanisms of cemented carbides and ceramics used for machining titanium alloy IMI 318, Master. Sci. Technol. 2
P.A. Dearnley and A.N. Grearson
1991
Turning aerospace titanium alloys, IDR 2
C.A. Brookes, R.D. James and F. Nabhani

5. Introduction Tool material Steel cutting gradesof ISO standard
Cemented carbides(硬质合金)
‘P’ grades of ISO standard
Not suitable
Thermal properties
High wear rate
Machine titanium alloys
Co(钴cobalt) content of 6wt.%
Straight cemented carbides(WC-Co)
A WC(碳化钨wolfram carbide) grain size between 0.8 and 1.4μm
Optimum performance

6. Introduction 2.Cutting speed 3.chip/tool length
Rapid chipping at the cutting edge
finally
Inserts catastrophically fail
Higher cutting speed
Rapid cratering and/or plastic deformation of the cutting edge
The temperature generated which tends to be concentrated at the cutting edge closer to the nose of the inserts
reason
3.chip/tool length
Smaller heat affected area
Shorter chip/tool contact length
Cutting speeds are limited to about 45m/min

7. G. Byrne, J. Barry and P. Young A.M. Arao, M. Wise and D. Aspinwall
Introduction
1968
Surface integrity in conventional machining-chip removal processes, Technical Paper NO. EM68, ASTME
W. Field and W. Koster
1979
The effect of machining on surface integrity, The Metal and Materials Technology, April
D.W. Watson and M.C. Murphy
1997
Surface integrity of AlSi9 machined with PCD cutting tools, Ann. CIRP 46
G. Byrne, J. Barry and P. Young
1998
Tool life and workpiece surface integrity evaluations when machining hardened AISI H13 and AISI E52100 steels with conventional ceramic and PCBN tool materials, Technical Paper NO. MR95-159, SME
A.M. Arao, M. Wise and D. Aspinwall

8. The surface of titanium alloys is easily damaged
Introduction
Surface integrity
Poor machinability
The surface of titanium alloys is easily damaged
Surface and subsurface alterations
Plastic deformation
microcracking
Phase transformation
Residual stress effects
The heat generated during cutting is a main sours of damage to the surface

9. Introduction Aims of this work
Investigate tool wear and surface integrity effects when machining titanium alloy Ti-6Al-2Sn-4Zn-6Mo with carbide tools.

10. Experimental procedure
Workpiece materials
The workpiece had a microstructure which consisted of elongated alpha phase surrounded by fine, dark etching of beta matrix.
Nominal chemical composition of the titanium alloys(in wt.%)
Work material
Chemical composition(wt.%) V Al Sn Zr Mo
N(MAX)
O(MAX)
H(MAX)
C(MAX) Fe
(MAX)
Ti-6Al-2Sn-4Zn-6Mo - 6 2 4
0.04
0.15
0.0125
경계강도
신장율
탄성계수 강도
Mechanical properties of tested material
Work material
Ultimate tensile strength(Mpa)
Elongation(%)
Modulus of elasticity(10^6Mpa)
Hardness
(HBS/10mm/3000kg)
Ti-6246
1170 10
11.3

11. Experimental procedure
Reason of using Ti-6246
Ti-6246 is widely used titanium alloy
High strength
Depth hardenability
Elevated temperature properties
Up to 450℃

12. Experimental procedure
Both of the inserts consisted of 94 wt.% tungsten carbide
2. Cutting tool materials
MR4-883
MR3-890
Properties of the cutting tools used
Insert designation(ISO)
Hardness(HNV)
Density
(g/cm³)
Surface condition
Substrate grain size(µm)
CNMG MR4-883
1760
14.95
Uncoated
1.0
CNMG MR3-890
1753
14.92
0.68

13. Experimental procedure
3. Machining tests
Test machine
Cincinnati Milacron CNC lathe, Cinturn 10CC which was controlled by Achramatic 850 controller.
Cutting conditions
Cutting conditions for the experimental work
Cutting condition
Dry cutting condition
Tool tested
883-MR4 and 890-MR3
Cutting speed, V(m/min)
100,75,60,45
Depth of cut (mm) 2
Feed rate (mm/rev)
0.25 and 0.35
Tool geometry
Approach angle:95°, side rake angle:-6°,back rake angle:-6°,end relief angle:6°,side relief angle:6°

14. Experimental procedure
4. Wear measurement
Wear were measured by using a microscope with magnification of 10×.
The International Standards Organisation (ISO) has suggested a standard for tool life testing
The criteria listed was used as a basis for rejecting a tool:
When the average flank wear reached 0.4mm or maximum flank wear reached 0.7mm.
When the notch at the depth of cut reached 1.00mm.
When the crater wear depth reached 0.14mm.
When the surface finish on the work material exceeded 6µm on centre line average.
When flaking or fracture occurred.
Cutting was stopped when any of the above occurred.
Cutting was abandoned and the tools were discarded and when catastrophic fracture of the edge was observed.

15. Results and discussions
Tool wear
Tool life
subsequently
Influence
Influence
Wear mechanisms
Diffusion
Abrasion
Attrition
Chipping
Plastic deformation

16. Results and discussions
Flank face wear
Cutting speeds
dry
Flank wear rate
Feed rates

17. Results and discussions
Initial stage: flank wear rate ≈ nose wear rate
Next stage: flank wear rate < nose wear rate
High cutting temperature and stress on the flank face close to nose, yield strength of the tools reduce, nose wear rate increase
Flank wear: 890 insert > 883 insert
Maximum flank wear is the limit factor which controll the tool life.

18. Results and discussions
High stress
Chipping process
Smooth wear pattern
High temperature
Dissolution-diffusion wear mechanism

19. Results and discussions
2. Tool life
Effect of feed rate on tool life
Feed rate of 0.25mm/rev
-Both inserts have good tool life under all cutting speeds
-A significant tool life increment generated at 60m/min
Feed rate of 0.35mm/rev
-Both inserts failed within 10s at cutting speed 100m/min
Cutting speed
Feed rate
Temperature
Cutting force
Tool life
Good tool life

20. Results and discussions
Good tool life
At cutting speed 75m/min both inserts wore rapidly and tool lives were short (40s).
Feed rate
Tool life

21. Results and discussions
2) Effect of cutting speed on tool life
0.25
890
Good tool life
0.35
890
Plastic deformation even detected at low cutting speed 45m/min.
High temperature
Tools loose strength
Plastic deformation
Cutting speed
Cutting speed
Tool life

22. Results and discussions
3. Surface finish and surface integrity
Surface finish
Surface finish tends to become
rougher toward the end of tool life
As the tool wore and approach the
end of their life, the roughness increase
Significantly.
60m/min
Highest roughness
5.28µm
Cutting speed
Roughness
Roughness
Tool life
Deformation on the flank face or workpiece material adherence at tool nose

23. Results and discussions
The surface roughness for all cutting speeds tend to increase as the tools approached their lives.
Insert 890 compared with 883:
Highest roughness:
890(7.0µm) > 883(5.28µm)
Lowest roughness:
890(3.6µm) < 883(4.5µm)
Average roughness:
890 ≈ 883
100m/min
Highest roughness
7.0µm

24. Results and discussions
Microhardness tests
Hardness beneath the machined surface 0.01mm
Average hardness of the base material
High cutting temperature
Low thermal conductivity of Ti alloy
Hardness beneath the machined surface 0.02mm
Average hardness of the base material

25. Results and discussions
0.07mm beneath the machined surface at all cutting condition hardness increased drastically
Wear on the edge affect the microstructure
The greatest surface hardening took place when machined with worn tools
Hardness had minimal increment when the feed rate was increased from 0.25 to 0.35m/rev at the initial cutting stage.
Machined with higher flank wear the hardness of the disturbed layer of the machined surface increased significantly.
Cutting speed
hardness
Same feed rate
Highest hardness
490HV
Worn insert
45m/min
0.35mm/rev
0.005mm beneath the machined surface
890 insert

26. Results and discussions
Work-hardening effect caused the increment in the hardness.
The microstructure were less disturbed, the increment in the hardness was small.
0.32mm beneath the machined surface, the hardness difference is less than 3% at the initial cutting stage.
By worn tool, hardness 0.42mm beneath the machined surface is similar to base material.
Similar behaviour was also observed for 883-MR4 insert.
Depth beneath the machined surface
Hardness
approach
Hardness of the base material
890 insert

27. Results and discussions
Metallurgical alterations
Microstructure of machined surface after 10s of cutting at 100m/min and feed rate of 0.35mm/rev with 883 insert.
Microstructure of machined surface after 9min of cutting at 45m/min and feed rate of 0.35mm/rev with 890 insert.
Smooth surface
Less disturbed layer
Severe plastic deformation
Thicker disturbed layer
Machined with nearly worn or worn tool led to the irregular surface, which consist of tearing and plastically deformed surface.
Prolonged machining with nearly worn tools also produced severe plastic deformation and thicker disturbed layer on the machined surface.

28. Conclusion
Straight grade cemented carbides are suitable for use in machining titanium alloy Ti The wear resistance and cutting edge strength of insert CNMG are superior to insert CNMG (finer grain size).
The dominant wear mechanisms for cemented WC-Co tools are dissolution/diffusion and plucking at tool edge.
Maximum flank wear at nose was more severe than flank and rake face wear. It always controlled the tool life.
Severe tearing and plastic deformation of the machined surface were observed when machining titanium alloy, especially after prolonged machining under dry cutting condition.
At the initial stages of cutting the plastic flow of microstructure was not detected. However, at the end of cutting(when the tool failed) severe plastic flow, tearing and deformation of the microstructure was detected.
This caused the formation of a white layer of hardened material on top of the machined surface, the thickness of which was less than 0.01mm.
The top layer of the machined surface experience work-hardening process, hence the hardness is higher than the average hardness of the workpiece materials. However, the material beneath the top layer is softer as a result of over-ageing of the materials.

29. Thank you