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

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)

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)

• 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

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.

Original structure - Martenzite

Tool steel ČSN 41 94 52.6 (EN 62SiMnCr4)

DTAA

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

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)

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)

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

It is evident that temperatures in DTAA of cutting material are higher than it is written in some literature sources

Verification by FEM (AdvantEdge)

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

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

• 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

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

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

……………..Conclusions ?

Thank you for your attention