Machining Process of Titanium Alloy Based on Green Cooling and

Lubricating Technology

ZHANG Yue1,a, HAN Li1, LI Qidong2, SUN Taili2, ZHANG Xichuan2 1School of Mechanical Engineering, Shenyang University of Technology, China

2Schoolof Material Science and Engineering, Shenyang University of Technology, China

azhangyue80@yeah.net

Keywords: Green machining, Water steam, Coolant, Lubricant, Turning, Titanium alloy.

Abstract. The machining process of titanium alloys always need special control by using coolant and

lubricant as it is one of the difficult-to-cut materials. To achieve green cutting of titanium alloy

Ti-6Al-4V with water vapor cooling and lubricating, a minitype generator is developed. Compared to

dry and wet cutting, the using of water vapor decreases the cutting force and the cutting temperature

respectively; enhances the machined surface appearance. Water vapor application also improves

Ti-6Al-4V machinability. The excellent cooling and lubricating action of water vapor could be

summarized that water molecule has polarity, small diameter and high speed, can be easily and

rapidly to proceed adsorption in the cutting zone. The results indicate that the using of water vapor has

the potential to attain the green cutting of titanium alloy instead of cutting floods.

Introduction

Titanium alloys are widely used in the aerospace, nuclear, chemical, biomedical industries and so on,

due to their excellent combination of low density, high strength to weight ratio, excellent corrosion

resistance and biocompatibility. At same times, titanium alloys are recognized as a difficult-to-cut

material [1-6]. The cutting characteristics include that: The tool–chip contact length is short. The

cutting temperature is very high. A poor tool life results from the high cutting temperatures. Titanium

has a strong chemical reactivity with most tool materials. Titanium alloy has a small cutting

deformation coefficient. Therefore cutting fluids and additives, such as water-based emulsion, are

usually applied in cutting of titanium alloy. However, some of them, especially extreme pressure

additives, contain Cl, S or P compounds which endanger to environment and people health. In the 21st

century, it is a global tendency to developing green cutting technology[4-8], for titanium alloy cutting,

such as liquid nitrogen jet, cryogenic nitrogen gas, high pressure water jet, and so on[7-10]. Water

vapor was used as environment-friendly coolant and lubricant in metal cutting [3]. The water vapor

(WV) application can reduce the cutting forces and prolong the carbide tool life in cutting of medium

carbon and stainless steel, compared to dry and wet cutting [4]. And in the cutting of difficult-to-cut

materials, water vapor can also act as coolant and lubricant [1]. There are many methods to deal with

the machining problem of titanium alloys [4]. And the aim of this paper is to investigate the control of

machining process in turning of Ti-6Al-4V by uncoated WC/Co inserts, based on green cooling and

lubricating technology by using water vapor.

Experiments

Water Vapor Generator. A special generating system for turning is developed to produce water

vapor with a primary resistance heater powered by 0.6kw and a secondary heater by 0.2kw, as shown

in Figure1. The secondary heater is controlled by a PID controller, and the temperature of water vapor

can be kept in the range of 125°C±5°C. There are two water level sensors in the generator to detect the

water line. When the water line is low, the water pump has been infusing water from tank into the

generator, until the water line up to the high sensor. An electromagnetic valve is droved by a

pushbutton for water vapor spurting out.

Advanced Materials Research Vols. 139-141 (2010) pp 681-684Online available since 2010/Oct/19 at www.scientific.net© (2010) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.139-141.681

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Experiment Equipments and Materials. As shown in Fig.1, cutting experiments were carried

out using a center lathe CA6140, powered by a 7.5kw electric motor giving a speed range of

10~1400 rev/min and a feed range of 0.014~3.16 mm/rev. The cutting tools applied were YG6

(WC +6%Co, K10 in ISO) uncoated tools and new tool was used for each experiment. A number of

angles for tool geometry were γo=14º, αo=αo

'=6

º, κr=75

º, κr

'=15

º, λs=-6

º. The workpiece used was

φ100×500 titanium alloy Ti-6Al-4V (TC4) as given in Table 1. The cutting experiments of YT15

cutting C45 steel were employed as the

comparison of machinability.

Cutting forces were obtained by 9257A

Kistler piezocrystal force sensor and 5007 charge

amplifier. Cutting temperature was measured by

thermoelectric method with X-Y function

recorder. Chip thickness was measured by using

a tool microscope. The machined surface

roughness was taken by a TR200 roughness

tester made by TIME Company, and the error is

0.001µm.

Cutting Experiments. The cutting forces

and temperature, deformation coefficient,

machined surface finish and chip appearance

investigated. The used cutting speed was 100m/min and the feed was 0.15mm/rev with the applied

depths of cutting were 1, 1.5, 2, 2.5 and 3mm; and the depth of cutting was 2mm with the feed were

0.1, 0.15, 0.2 and 0.3 mm/rev.

Cooling and Lubricating Conditions. All the

cutting experiments were completed at the

conditions of dry cutting, water-based emulsion

and water vapor. The cooling distance was 20mm

for the cutting fluid and water vapor. For the

water-based emulsion, the concentration was 5%,

the temperature was 19°C, the flux was 1L/min,

the pressure was 0.12MPa and the diameter of pipe was 5mm,. For the water team, the diameter of

nozzle was 2mm, the temperature was 125°C, the flux was 45L/min, and the pressure was 0.25MPa.

Results and Discussion

Cutting Forces. The main cutting forces of dry and wet cutting and water vapor application were

illustrated in Fig.2. and Fig.3. The results of radial cutting forces were presented in Fig.4. and Fig.5.

Among the machining characters of titanium alloys, a special one is that the main cutting force is

lower but the radial cutting force is higher than those in cutting of C45 steel.

Table1. Workpiece materials and characters

Materials Ti-6Al-4V

Chemical

composition

Al V O Fe C N

6.1 4.1 0.15 0.06 0.01 0.01

Mechanical

characters

σb [MPa] δ5 [%] ψ [%]

980 14 40

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

200

400

600

800

1000

1200

C45 Dry

Dry

Wet

WV

Fc

(N)

vc =100m/min

f =0.15mm/r

ap (mm)

Fig. 2 The Fc-ap curve in cutting experiments

0.0 0.1 0.2 0.30

200

400

600

800

1000

1200

1400

C45 Dry

Dry

Wet

WV

f (mm/r)

Fig. 3 The Fc- f curve in cutting experiments

Fc

(N)

vc =100m/min

ap=2mm

Pipeline

Buttons

Workpiece

PID controller

Tank

Waterline

Water steam generator

Indicator lights

Pressure gauge

Kistler force sensor

Fig. 1 Water vapor generator and experimental system

682 Manufacturing Engineering and Automation I

Compared with dry and wet cutting, the main cutting force reduced about 30% and 15%, and the

radial cutting forces reduced about 35% and 20%, as water vapor cooling and lubricating. All the

emulsion and water vapor present the action of cooling and lubricating in cutting of Ti-6Al-4V. In the

experiments, water vapor produced the lowest cutting force. There are several reasons for the

favorable cooling and lubricating performance of water vapor [8]. The molecule or molecule group in

water vapor has a smaller radius than that in cutting fluids. And the velocity of water vapor jet flow is

much higher than that of cutting fluids. As a result, water vapor penetrates the tool-chip interface

easily and rapidly.

Cutting Temperature. The experiment results of cutting temperatures were shown in Fig.6. The

cutting temperature of titanium alloys is much higher

than that of C45 steel, which is another machining

character of titanium alloys. Water vapor application

decreased the cutting temperature about 15% and 10%,

compared to dry and wet cutting. Water vapor gives a

better cooling action than the emulsion. In cutting, the

adhesive of titanium alloy chip on the tool face leads to

an acutely friction and generates a great lot of heat. The

cutting heat centralizes in a small region because of the

short tool–chip contact length [9]. After water vapor

enters into the tool-chip interface, lubricating film

forms immediately under the adsorption function. The

lubricating action of water vapor reduced the tool-chip

friction and the heat generation. In addition, water vapor has the capability of decalescence and heat

transformation, though the water vapor temperature is up to 100°C. Contrarily, emulsion is not easily

to penetrate the tool-chip interface and their cooling action only occurs at the outside of cutting zone.

Consequently, the water vapor cooling action is better than the emulsion in cutting of Ti-6Al-4V.

Cutting Deformation Coefficient. The deformation coefficient Λh can be calculated by Λh=hch/hD,

where the average chip thickness hch was measured by using the tool microscope, and the uncut chip

thickness hD =f·sinκr. In cutting, the deformation coefficients of titanium alloy are usually close to 1

and less than that of C45 steel. As shown in Fig.7, similarly, Λh decreased with rising feed under all

the lubricating conditions, and it is noted that the coolant and lubricant produced a tiny impact on

deformation coefficient. Accordingly, the force and heat from chip deformation were hardly

influenced. With the water vapor using, the decreases of cutting force and temperature resulted from

the decreases of friction force and heat generation on the tool-chip interface at s large extent. And this

also helps to slower the tool wear and prolong the tool life.

Machined Surface Finish. The surface finish roughness values were presented in Fig.8. As the

feed increasing, the value Ra increased. The application of water vapor gave the lowest surface finish

roughness value among the three cooling and lubricating conditions. These shown that the coolants

and lubricants can act not only on the rake face but also on the flank one. The high cutting temperature

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

50

100

150

200

250

300

350

400

C45 Dry

Dry

Wet

WV

Fp (

N)

vc =100m/min

f =0.15mm/r

ap (mm)

Fig. 4 The Fp -ap curve in cutting experiments

0.0 0.1 0.2 0.30

100

200

300

400

500

C45 Dry

Dry

Wet

WV

vc =100m/min

ap=2mm

Fp (

N)

f (mm/r)

Fig. 5 The Fp - f curve in cutting experiments

120 130 140 150 160 170 180 1900

100

200

300

400

500

600

700

800

900

C45 Dry

Dry

Wet

WV

ap=2mm

f =0.15mm/r

θ (

°C)

vc(m/min)

Fig. 6 The θ-υc curve in cutting experiments

Advanced Materials Research Vols. 139-141 683

leads to rapid wearing of cutting tool and then impact to surface finish. The action of cooling and

lubricating reduce the cutting temperature and lower the tool wear speed. As a result, machined

surface finish can be easier controlled in the ideal range.

Conclusions

Ti-6Al-4V is one of the difficult-to-cut materials, and the cutting experiments as water vapor cooling

and lubricating were carried out. Compared to dry cutting and emulsion applied, when water vapor

used, the main cutting force is lower about 30%-35% and 15%-20%, the cutting temperature reduces

bout 15%and 10%, while the deformation coefficient does not variety obviously. Water vapor

enhances the machined surface appearance to some extent. Water vapor application improves

Ti-6Al-4V machinability compared to dry and wet cutting. The excellent lubricating action of water

vapor in cutting could be summarized that water molecule has polarity, small diameter and high speed,

can be faster and easier to proceed adsorption in the cutting zone. The machining process of titanium

alloy receives available controlling. Otherwise, Water vapor has the advantages of cheap, clean for

environment, harmless for health and unneeded disposal or recycling, which are the potential for

green machining. Taking cooling and lubricating performance into account, water vapor may be a

better choice for green machining to titanium alloy.

Acknowledgements

This research reported in the paper is financially supported by National Natural Science Foundation of

China (NSFC) (50675053), Research and Development Plan of the Education Apartment of Liaoning

Province (05L301). These supports are greatly acknowledged.

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684 Manufacturing Engineering and Automation I

Manufacturing Engineering and Automation I 10.4028/www.scientific.net/AMR.139-141

Machining Process of Titanium Alloy Based on Green Cooling and LubricatingTechnology

10.4028/www.scientific.net/AMR.139-141.681 DOI References[1] R.D. Han, Y. Zhang, Y.Wang: Key Engineering Materials, Vol.375-376 (2008), pp.172-176.doi:10.4028/www.scientific.net/KEM.375-376.172

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[9] V. A Godlevski, A.V Volkov: Lubrication Science, (1997) No.9, pp.127-140.

doi:10.1002/ls.3010090203