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������������� �������������������������������������������� � ��������������������� �!��������"�����#����������$�%������&� �'���������� �'��() ��

!���)���*���'���)��"������������

���������������������� �+�'�����'��"�����$�%�������) �,���������!���)��"������������

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���������Drilling experiments of CFRP/Ti6Al4V laminated stack board were carried out use of a

TiAlN-coated cemented carbide drill and a TiAlCr/TiSi-coated cemented carbide drill. In the

experimental conditions described herein, tool life is longer for lowered feed speed, and a

TiAlCr/TiSi-coated cemented carbide drill has longer life than the other. Additionally, the cooling

performance between dry process and water-mist-cooling were compared. Regarding

water-mist-cooling, although the thrust is smaller, chips are much harder. They also adhere to the drill

margin and impart damage to the CFRP wall of the hole. For a number of holes less than 50,

water-mist-cooling reduces tool abrasion. However, the abrasion increases suddenly for hole

numbers greater than 50. Accordingly, for the number of holes drilled well over 50, tool life is longer

in dry processing than in water-mist-cooling.�

���� ������

Use of carbon fiber reinforced plastics (CFRP) is expanding rapidly as a structural material used in

airplanes, for which weight reduction is critical. Its weight ratio is about 50% in the latest passenger

planes. In addition, the use of titanium alloy is increasingly replacing conventional aluminum alloy.

Therefore, the frequency of hole-drilling on laminated stack board of CFRP and titanium alloy is

increasing. Based on a previous report of drilling on CFRP [1], the flank wear decreases and the thrust

force increases with increased feed. Furthermore, other problems in drilling on CFRP plate include

the difficulty of producing a clean hole and the rapid wear of tools. However, in drilling on titanium

alloy, the loss of the tool edge by adhesion occurs very often. Therefore, high speed work is difficult

because of the low thermal conductivity of titanium alloy and its use with tools. The CFRP and

titanium alloy are both difficult-to-cut materials. It is difficult to find the proper working conditions

for them. In drilling CFRP, furthermore, dry processing is preferred, although it narrows options.

There are many problems laminated stack board of CFRP and titanium alloy[2 - 7]. In this

background, drilling experiment of laminated stack board of CFRP and titanium alloy was carried out

using of coated cemented carbide drills to examine the relation between cutting conditions, cutting

resistance, tools abrasion, and the quality of finished holes.

�����������������

A machining center has been used (PCV40; Osaka Kiko Co., Ltd.). The drills that were used were

TiAlN coated cemented carbide drills (ACZ51S; Sumitomo Electric Industries, Ltd.) and

TiAlCr/TiSi coated cemented carbide drills (ACX70; Sumitomo Electric Industries, Ltd.). A

laminated stack board of CFRP (3 mm) and titanium alloy (9.5 mm) were drilled as presented in Fig.

1. The thrust and torque to the laminated stack and flank wear were measured and the hole quality was

evaluated. Tool life and the termination of drilling was defined when flank wear width reached 0.2

mm. Cutting conditions are presented in Table 1. To examine the effect of active cooling,

water-mist-cooling was applied at the top edge of drill in some series of experiments.

Advanced Materials Research Vol. 325 (2011) pp 369-374Online available since 2011/Aug/22 at www.scientific.net© (2011) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.325.369

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 134.148.29.34, University of Newcastle, Callaghan, Australia-17/03/14,18:20:02)

������CFRP/Ti6Al4V

Laminated stacks.�

������

����

������� Drilling conditions

�������

������� ������� Drilling experiments with TiAlCr/TiSi coated drill were carried out at dry

conditions. The cutting speed���was 18.8 m/min and the feed speed �was 0.2 mm/rev. Figure 2

shows the thrust and torque of the first hole and the 140th hole (� is the number of holes worked).

The thrust of the first hole in CFRP part is large at the entrance, it decreases gradually. However, in

the titanium alloy part, it is large at both the entrance and exit and has a small dent on the way. At

the entrance to titanium alloy, it is tough for the tool to bite the work. At the exit, on the other hand,

the tool must force the cap-shaped chip, as shown in the photo inset in the figure. These might

explain the shape of the thrust curve observed above. Overall, the thrust of 140th hole is larger than

that of the first. However, the thrust at penetration of the 140th hole seems similar to that at

penetration of the first hole. Furthermore, in both layers of the laminated stack board, the trust

decreases with the tool procession. The torque of the CFRP part is considerably less than that of

titanium alloy part. The torque at the exit of the first hole in the titanium alloy is slightly larger than

that at entrance. In the 140th hole, on the other hand, it is almost identical with that of the first hole

at the entrance. However at the exit, it increases with procession of tool and becomes almost double

that of the first hole. Because of advanced abrasion of drill at 140th hole, the friction between the

drill and titanium alloy might have increased. And the drilling heat easily accumulate because Ti

alloy is low thermal conductivity. Thus the thermal expansion of titanium alloy and CFRP by

increasing drilling temperature might have affected the torque in particular.

�������

2000

�����

1500

1000

500

00 5 10

���

��

�!�"#

�!�

�!�"#

�!�

���

��

�����0 5 10

���$����

0

1

2

3

4

5

Figure 3 shows the maxima of thrust and torque in the time-wave chart, as presented in Fig. 2, for

each drilling condition. Those for CFRP part (bottom) and those for titanium alloy (top) are shown

separately. The cutting speed is 18.8 m/min. In the CFRP part, not much difference of thrust and

torque are observed for different cutting conditions. In the titanium alloy part, on the other hand, the

thrust is smallest for TiAlN coated drill in dry process and at feed speed ��of 0.1 mm/rev, Fig. 3(a).

Regarding torque in the titanium alloy part, the TiAlN coated drill requires smaller torque, as shown

in Fig. 3(b). For the water-mist-cooled TiAlCr/TiSi coated drill with feed speed of 0.2 mm/rev,

although thrust is fairly reduced, torque increases suddenly for holes after the 60th.

Workpiece CFRP (3 mm)/

Titanium alloy(9.5 mm)

Drill TiAlN coated carbide (φ6 mm)

Coating strength: about 35 [GPa]

TiAlCr/TiSi coated carbide (φ6 mm)

Coating strength: about 50 [GPa]

Cutting speed 9.4 , 18.8 [m/min]

Feed speed 0.1 , 0.2 [mm/rev]

Cutting method Dry , Water-mist-cooling(100 mL/h)

����%�Cutting forces.

(a)Thrust (b) Torque

���� ��

TiAlCr/TiSi coated, Dry,

�=18.8 m/min, �=0.2 mm/rev

370 Advances in Abrasive Technology XIV

0

500

1000

1500

2000

0 50 100 150 200 250

Thru

st

N

Number of holes

TiAlN 0.2mm/rev DryTiAlN 0.1mm/rev DryTiAlCr/TiSi 0.2mm/rev DryTiAlCr/TiSi 0.2mm/rev Mist

0

1.5

3

4.5

0 50 100 150 200 250

To

rque

N

m

Number of holes

TiAlN 0.2mm/rev Dry

TiAlN 0.1mm/rev Dry

TiAlCr/TiSi 0.2mm/rev Dry

TiAlCr/TiSi 0.2mm/rev Mist

0

0.1

0.2

0.3

0 50 100 150 200 250

Fla

nk w

ear

wid

th �

�m

m

Number of holes

TiAlN 9.4m/min 0.2mm/rev Dry

TiAlN 18.8m/min 0.2mm/rev Dry

TiAlN 18.8m/min 0.1mm/rev Dry

TiSlCr/TiSi 18.8m/min 0.2mm/rev Dry

TiAlCr/TiSi 18.8m/min 0.2mm/rev Mist

��

����&����Flank wear width is shown in Fig. 4. The longest tool life was attained by TiAlN coated

drill at �=0.1 mm/rev (slower feed speed) and �=18.8 m/min. In the same cutting conditions as those

used here, the thrust and torque are increasing gradually with the number of holes, as shown in the

previous figure, which suggests a close relation between tool wear and thrust and torque. In the TiAlN

coated drill, lowered feed velocity (reducing � from 0.2 mm/rev to 0.1 mm/rev at constant � of 18.8

m/min) is more effective for improvement of tool life than lowering the cutting speed (reducing �

from 18.8 m/min to 9.4 m/min at constant � of 0.2 mm/rev).

The life of TiAlCr/TiSi coated drill was longer than that of the TiAlN coated drill because the

coating strength of TiAlCr/TiSi is 40% higher than TiAlN coating as shown in Table 1 at the same

drilling condition. The life of TiAlCr/TiSi coated drill is 140 holes in dry process and 90 holes in

water-mist-cooling. In water-mist-cooling, the initial abrasion is small, the progress of abrasion is

similar to that in dry process, and abrasion width is smaller up to 50 holes. However, the progress of

abrasion suddenly increases at the 60th hole, and 90 holes is the life span of TiAlCr/TiSi coated drill

in water-mist-cooling. Consequently, results show that water-mist-cooling does not improve the drill

life. The flank face and margin of the mist-cooled TiAlCr/TiSi coated drill after working with 90

holes is shown in the photographs of Fig. 5. The coated layer is broken away and the substrate was

exposed.

Ti

����'�Relation between cutting forces and number of holes.

(a) Thrust (b) Torque

����"�Flank wear width.

Ti

CFRP

�=18.8m/min

CFRP

Advanced Materials Research Vol. 325 371

Top and bottom views of 120th hole on CFRP layer by TiAlCr/TiSi coated drill, dry processing,

cutting speed of 18.8 m/min and feed speed of 0.2 mm/rev are depicted in Fig. 6. The peripheral of

hole on top side of CFRP layer is observed to be lifted by delamination. Furthermore, on the bottom

side, delamination and scorching of epoxy resin are apparent. These suggest damage to the CFRP

caused by the progression of tool wear.

�

��������

� ������

(���� ����� � Observation of the hole surface was done. In Fig. 7, a cut view photo of 100th hole

by TiAlCr/TiSi coated drill, dry process, cutting speed of 18.8 m/min and feed speed of 0.2 mm/rev

is shown. At this advanced stage of tool abrasion, irregular scratching in titanium alloy part and

delamination and scratching in the CFRP part are regarded as indicated by arrows. Additionally, it is

observed that two different layers of laminated board have different hole diameters.��

�

�

�

�

�

�

�

�

�

�

�

�

�

�

��

�

�

�

5.9

6

6.1

6.2

6.3

6.4

6.5

1 20 40 60 80 100 120 140

Hole

dia

met

er m

m

Number of holes

����

���������CFRP

5.9

5.95

6

6.05

6.1

1 20 40 60 80 100 120 140

Hole

dia

met

er m

m

Number of holes

����

���������Bottom of Ti

(a) Top of CFRP (b) Bottom of CFRP

�����

����)�Cut surface photograph of drilled surface (��= 100).

(a) CFRP (b) Bottom of Ti

�����

����

(a) Flank face� (b) Margin�

�=18.8 m/min, �=0.2 mm/rev, Dry

TiAlCr/TiSi coated, Water-mist-cooling,

� = 90�

����*� Photographs of holes.

TiAlCr/TiSi coated, Dry, ��= 120.�

����+�Tool wear.

TiAlCr/TiSi coated,

Dry,

�=18.8 m/min,

�=0.2 mm/rev

����,�Relation between hole diameter and number of holes.

1mm 1mm

CFRP Ti alloy

372 Advances in Abrasive Technology XIV

TiAlCr/TiSi coated,

Water-mist-cooling,

�=60�

TiAlCr/TiSi coated,

�=18.8 m/min, �=0.2 mm/rev

����-�Relation between hole diameter and number of holes.�

�����#�Photograph of tool.

Then a comparison is made of the diameters of holes in two layers just described. The two drill

tools that were used are compared in this context. The result of measurement is presented in Fig. 8.

The diameter in titanium alloy layers is that measured at the exit of the hole. In the CFRP part, the

TiAlN coated drill has made holes of greater diameter. At the 100th hole close to drill life.

Particularly, the diameter is as large as exceeding 6.4 mm, indicating the effect of the tool abrasion

(the drill tool diameter is 6 mm, incidentally). In the titanium alloy part, on the other hand, the

difference in the hole diameter by the difference of tool coating is 15 �m at maximum, indicating a

very small influence of different coatings on tools. �

.�/��������� &����0����0��������The effect of cooling is examined for a TiAlCr/TiSi coated

drill in terms of the hole diameter. A comparison is shown in Fig. 9. For drill diameter of 6 mm

water-mist-cooling yields better precision in the hole diameter in the CFRP part. Active cooling

might have suppressed a rise of CFRP temperature and thereby softening of epoxy resin, substrate of

CFRP, which might be the reason for the better hole diameter precision. In the titanium alloy part,

however, cooling produced a slightly larger hole diameter, but the difference is rather small.

��

�

�

�

Observation of the hole surface indicates that scorching does not occur on CFRP and a fine surface

is attained on titanium alloy by water-mist-cooling. The increased torque observed for holes after the

60th must have originated from the adhesion of chips on a position beyond the twisted ditch seen in

Fig. 10, which might have caused jamming of the chips. The chip is presumed, in normal operation, to

flow in the twisted ditch, curling along it by the reaction of its wall. However, in drilling at colder

temperatures by water-mist-cooling, the chip might not curl, flow along the second flank and adhere

on a position beyond the twisted ditch. And the tool wear grew suddenly. Thus the tool life using

water mist was shorter than dry process. In addition, the delamination of CFRP increased in

comparison with dry process drilling.

5.9

6

6.1

6.2

6.3

1 20 40 60 80 90 100 120 140

Hole

dia

met

er

mm

Number of holes

Dry

MistCFRP

5.9

6

6.1

1 20 40 60 80 90 100 120 140

Hole

dia

met

er

mm

Number of holes

Dry

MistBottom of Ti

(a) CFRP (b) Bottom of Ti

1mm ������������� (b) Second flank face�

1mm

Advanced Materials Research Vol. 325 373

����

�������Chip of water-mist. �����%� Cut surface of CFRP and Ti alloy with water-mist.

Figure 11shows photographs of chips. At the initial stage of drilling, the titanium alloy, the chip

shows a spiral shape. In the middle stage, it portrays a kind of choked appearance. At the stage of

penetration, it is quite long. The maximum length of the chip was 132 mm. Chips in

water-mist-cooled drilling were harder than those in dry process, which might have been caused by a

lowered cutting temperature. The CFRP hole surface is better in dry processing, although that of

titanium alloy is better in cooled drilling. In water-mist-cooled drilling, the harder chips described

above might have damaged the CFRP hole surface when they passed there. Figure 12 demonstrates

the damage to the CFRP hole wall.

1�����/

Hole-drilling experiment on CFRP/Ti6Al4V laminated stack board using coated cemented carbide

drill was performed, which revealed the following.

(1)�Small feed speed 0.1 mm/rev for TiAlN coated cemented carbide drill made the life of tool longer.

(2)�At dry process and the same settings of cutting and feed speed, the TiAlCr/TiSi coated cemented

carbide drill worked longer than the TiAlN coated one did.

(3)�The TiAlCr/TiSi coated cemented carbide drill with water-mist-cooling improved the accuracy of

diameter of at CFRP part. However, the hard chip generated in these setting damaged the hole

wall surface of CFRP.

(4)�The TiAlCr/TiSi coated cemented carbide drill in the dry process functioned longer than the same

drill with water-mist-cooling.

��2��&�� ������

We appreciate the support offered us by Grants-in-Aid for Scientific Research(C) from the Ministry

of Education, Culture, Sports, Science and Technology, and from the Mazak Foundation.

����������

[1] Keizo Sakuma, Yoshimichi Yokoo and Masafumi Seto: ������� �����������������������

���������� ���������� �� Trans. Japan Soc. Mech. Eng., Vol. 49-446 (1983), p. 1799

[2] E. Brinksmeier and R. Janssen:� ������� ��� ����� !�� � ���"�#���� ���� ���#� $��#�#����� ���

�� %��� ��%� � ������ $�� ���#��$#� �������� ��������� ��� &�������� &���#, CIRP Annals

Manufacturing Technology, Vol. 51-1(2002), p.87

[3] Islam Shyha, Sein Leung Soo, Dvid K. Aspinwall and etc:� ������� ���

��������'����'&�����������$(#� Key Engineering Materials, Vol. 447-448,(2010),p.624

[4] Kim, D. and Ramulu, M.:� ������� " �$�##� �"����)������ �� � � �"*���'%�#�������� ���������

�����#��$(#+ Composite Structures, 63(1), (2004) p. 101-114.

[5] Ramulu, M., Branson, T. and Kim, D.: &�#�������*�� ����������$��"�#����������������#��$(#+�

Composite Structures, 54(1), (2001), p.67-77.

[6] Kim, D. and Ramulu, M.:��������*�� ������������������'� �"*����*% ��$��"�#���#+Jounal

of Engineering Materials and Technology, 129(3), (2007), p.390-396.

[7] Zitoune, R., Krishnaraj, V. and Collombet, F.:���� ��� ������� $��"�#���� ���� ���� ���

����������#��$(+ Composite Structures, 92(5), (2010), p.1246-1255.

���� ����(a) �=20 (b) �=60

374 Advances in Abrasive Technology XIV

Advances in Abrasive Technology XIV 10.4028/www.scientific.net/AMR.325 Drilling of CFRP/Ti-6Al-4V Stacks 10.4028/www.scientific.net/AMR.325.369