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INFLUENCE OF CUTTING TOOL´S WEAR ON INNER
MICROSTRUCTURE OF CHIPS
Jiří Šimeček
Petr Beneš
Antonín Kříž
FACULTY OF MECHANICAL ENGINEERING DEPARTMENT OF MATERIAL SCIENCE AND TECHNOLOGY
WBU
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Problems of temperature field measurement within cutting zone
• important for determination of testing condition (e.g. PVD coatings)
• still unsolved problem – amount temperature within cutting zone?
• numerical solution, analytical models – still inaccurately, lack of verification
=> experimental metods – direct metods, indirect metods
contact m.
contactless m.(IR sensor-based, thermovision systems)
(termocouples)
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Indirect methods of temperature measuring• thermal influence to cutting materials = metallographic changes
+ accuracy of determination of thermal influences
+ without spurious phenomena
- absolute temperature can´t determine without etalons
- souitable for some specific materials
- time-consuming methods
DEFORMATION TEMPERATURE AFFECTED AREA
(DTAA)
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• chips represent the valuable object of research - lots of metallographic information in internal structures:
• DTAA
• zone of chip material remelting,
• changes of microhardness, etc.
• zone of dynamic recrystallization
• smelting zone
• structural changes • chemical composition change
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chips study can allow to measure :
• stressed state in cutting zone
• distribution of stress
• temperature distribution
• heat balance
Especially suitable for „segment chip“ - titanium alloys, stainless steels,
hardened steels, etc.
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Original structure - Martenzite
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Tool steel ČSN 41 94 52.6 (EN 62SiMnCr4)
DTAA
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Some severe problems of DTAA measuring:
a) Breaking off the chip edge (during metallographic preparation)
b) Failure of method in case of very high temperature (whole cross-section is affected by heating)
?Evidence of high
temperature treatment due to excessive tool`s wear
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Some characterictic zones were found from the microscopic chips observation that support the significant influence of temperature effects on chips microstructure:
1) Zone of material smelting
Cross section of chips which were made by milling of steel
ČSN 41 94 37.4
(EN X210CrW12)
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2) Zone of carbide dissolving
t = 33 min. t = 27 min.Cross section of chips
which were made by milling of steel ČSN 41 94 37.4
(EN X210CrW12)
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3) Zone of material embrittlement
Cross section of chips which were made by
milling of steel ČSN 41 94 37.4 (EN X210CrW12)
• The embrittlement material zone = area where steel burning occured
•non-reversible changes in steel structure • steel burning happens usually by temperature around 150°C under the solidus
• steel ČSN 419437 - temperature higher than 1200°C
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It is evident that temperatures in DTAA of cutting material are higher than it is written in some literature sources
Verification by FEM (AdvantEdge)
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Effect of width DTAA on radius of chip ⇒ important information about temperature conditions in cutting zone
D2<D1<D3
Shape of chips according to ISO
Color of chip ≈ tempering temperature…
laboratory findings: higher tempering temperature = continuous chip
11/33
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11,27
15,27
20,41
9,49
14,27
24,75
12,06
18,79
21,3320,6
11,1912,27
0
14,8113,24
0
5
10
15
20
25
30
1 2 3
Časov ý úsek náběru třísek (fáze obrábění)
Šířk
a D
TOO
[m.1
0-6]
TiN TiAlSiN TiAlN TiAlN-400°C TiAlN-800°C
TiN
TiA
lSiN
TiA
lN
TiA
lN -
400°
C
TiA
lN -
800°
C
TiN
TiA
lSiN
TiA
lN -
400°
C
TiA
lN -
800°
C
TiA
lN
TiN
TiA
lSiN
TiA
lN
TiA
lN -
400°
C
TiA
iN -
800°
C
•3 type of PVD coatings – TiN, TiAlN, TiAlSiN
• for reason of practical cutting test – deposited on cutting tools (cutting tip) (sintered carbide – ISO K20)
•workpiece - tool steel ČSN 19 452.6 (EN 210CrW12) (55 HRC)
• cutting tips with TiAlN were heated in air - 400, 800°C for a period of 15 min.
Measuring of DTAA by chips originated from turning
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• TiAlN influence oxide film Al2O3 – low thermal conductivity = high level of DTAA in 1.period
• loss of coating in 2.period – TiAlN 800°C – heat removal by substrate (thermal conductivity of sintered carbide K20 – 120 W/m.K)
• 3.period – TiAlSiN – complex oxide films based on TiO2, Al2O3, SiO2
• 3.period – TiAlN – contact place dislocation between chip and tool – contact via tool face with retain system TiAlN + Al2O3
11,27
15,27
20,41
9,49
14,27
24,75
12,06
18,79
21,3320,6
11,1912,27
0
14,8113,24
0
5
10
15
20
25
30
1 2 3
Časov ý úsek náběru tř ísek (fáz e obrábění)
Šířk
a D
TOO
[m.1
0-6]
TiN TiAlSiN TiAlN TiAlN-400°C TiAlN-800°C
TiN
TiA
lSiN
TiA
lN
TiA
lN -
400°
C
TiA
lN -
800°
C
TiN
TiA
lSiN
TiA
lN -
400°
C
TiA
lN -
800°
C
TiA
lN
TiN
TiA
lSiN
TiA
lN
TiA
lN -
400°
C
TiA
iN -
800°
C
Preheated coatings before machining
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Verification:
Oxidic films can act as effective thermal barrier
Most effective oxide film (from TiN, TiAlN, TiAlSiN) is complex oxide film developed on TiAlSiN
• within the frame of practical mechining test was took place the measurement of both chip temperature and tool by using a termovision + measuring of cutting force (moment of tool`s failure, influence of build-up on tool etc.)
218245
352
218236
267
233
340
433
314 309 318
212229
519
0
100
200
300
400
500
0,5 1,5 3
t [min.]
T [°
C]
TiAlSiN TiN TiAlN TiAlN 400°C TiAlN 800°C
Chip temperatures in all period of cutting for different systems of PVD coatings detected by termovision
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7,4911,03
37,7
20,317,2
32,9
70,5
40,4
25,7
36,4
97,5
50 49,144,5
6,9
15,4
53,1 53,4
5,8
23,9
68,2
61,6
0
10
20
30
40
50
60
70
80
90
100
0 12 24 27
čas náběru [min.]
šířk
a TO
O [m
-6]
1s 3s 5s 1n 3n 5n
7,493,5
26,720,3
-3,1
15,7
37,640,4
-14,7
10,7
97,5
-47,5
-0,9-4,6
6,9 8,5
37,7
0,35,8
18,1
44,3
-6,6
-60
-40
-20
0
20
40
60
80
100
0 12 24 27
čas náběru [min.]
přírů
stek
/úby
tek
TOO
[m
.10-
6]
1s 3s 5s 1n 3n 5n
…and DTAA for milling
Differential expression of DTAA
• confirmation of running-in phase
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……………..Conclusions ?
Thank you for your attention