Effect of Machining Parameters in Ultrasonic Vibration Cutting

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Author’s Accepted Manuscript

Effect of machining parameters in ultrasonicvibration cutting

Chandra Nath, M. Rahman

PII: S0890-6955(08)00025-4DOI: doi:10.1016/j.ijmachtools.2008.01.013Reference: MTM 2243

To appear in: International Journal ofMachine Tools & Manufacture

Received date: 7 November 2007Revised date: 21 January 2008Accepted date: 25 January 2008

Cite this article as: Chandra Nath and M. Rahman, Effect of machining parameters inultrasonic vibration cutting, International Journal of Machine Tools & Manufacture (2008),doi:10.1016/j.ijmachtools.2008.01.013

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Effect of machining parameters in ultrasonic vibration cutting

Chandra Nath, M. Rahman*

Department of Mechanical Engineering, National University of Singapore,

9 Engineering Drive 1, Singapore – 117576

First author: Chandra Nath,

Institute: National University of Singapore, Singapore

Postal address: Department of Mechanical Engineering, National University of Singapore,


Tel: +65-6516 4644

Fax: +65-6779 1459

E-mail: [email protected] *Corresponding author: Prof. M. Rahman

Institute: National University of Singapore, Singapore

Postal address: Department of Mechanical Engineering, National University of Singapore,


Tel: +65-6516 2168

Fax: +65-6779 1459

E-mail: [email protected]

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Abstract

Ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-

machine materials. It is found that the UVC mechanism is influenced by three important

parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed

that determine the cutting force. However, the relation between the cutting force and these

three parameters in the UVC is not clearly established. This paper presents firstly the

mechanism how these parameters effect the UVC. With theoretical studies, it is established

that tool-workpiece contact ratio (TWCR) plays a key role in the UVC process where the

increase in both the tool vibration parameters and the decrease in the cutting speed reduce

the TWCR that in turn reduces both cutting force and tool wear, improves surface quality

and prolongs tool life. This paper also experimentally investigates the effect of cutting

parameters on cutting performances in the cutting of Inconel 718 by applying both the

UVC and the conventional turning (CT) methods. It is observed that the UVC method

promises better surface finish and improves tool life in hard cutting at low cutting speed as

compared to the CT method. The experiments also show that the TWCR, when

investigating the effect of cutting speed, has a significant effect on both the cutting force

and the tool wear in the UVC method which substantiates the theoretical findings.

Keywords: Ultrasonic vibration cutting; Tool vibration parameters, Cutting speed; Tool-

workpiece contact ratio; Cutting tool life.

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1. Introduction

Ultrasonic vibration cutting (UVC) method is a more effective cutting process over

conventional turning (CT) in terms of cutting force, cutting instability, tool blunting, tool

wear, chip generation, surface finish and so on, to machine difficult-to-cut materials such as

Ni- and Ti-based super alloys, hardened steels, optical glasses, ceramics, tungsten carbides,

etc. [1-17].This method improves productivity by saving the manufacturing time by about

5–10 % as well as the machining cost by about 30% of the cost of parts as required in the

deburring process of precision parts [18].

Along with the usual parameters for the CT method, two additional parameters: tool

vibration frequency and vibration amplitude, are considered in ultrasonic vibration cutting

(UVC) system that assist to improve cutting quality and to increase remarkable tool life by

lowering, mainly, the cutting force and improving the dynamic cutting stability.

Extensive theoretical research [12-16], simulation [17] and experimental results [8-12,

19, 20] for the UVC method mention that the lower cutting force is due to a considerable

reduction of friction between the tool and workpiece [17, 19] and the separating or pulse

cutting characteristic of the tool [12-14, 18, 21]. Previous experimental reports also

indicated that the UVC method performs better at low cutting speeds [6-8, 18-22] and at

both high tool vibration frequency and amplitude [23]. Moreover, the UVC mechanism

during the tool-workpiece interaction is basically related to these above three parameters

[3, 8, 13, 15, 20]. Therefore, the cutting force is directly related to these three parameters.

However, the relationship between the cutting force and these three parameters has not yet

been established.

Furthermore, V. I. Babitsky et al [2, 6] justified and compared the axial surface profile

and roundness profile for the cutting of Inconel 718 by applying both the CT and the UVC

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methods. However, the ability of the cubic boron nitride (CBN) tool for this excellent tough

and creep-rupture resistance alloy and the effect of cutting parameters on the cutting

performance by applying the UVC method have not yet been studied. As a hard and tough

cutting inexpensive tool material, CBN is the best choice, next only to the diamond tools.

The authors in this paper investigate firstly the mechanism of the effect of these three

parameters in the UVC process. It is theoretically understood that the amount of the cutting

force is directly related with these three parameters that establish two key factors: tool-

workpiece contact ratio and tool-workpiece relative speed (hereafter, called “TWCR” and

“TWRS”, respectively), for this intermittent cutting technique. This paper focuses mainly

on controlling the first key factor, TWCR. It is found that the increase in both the tool

vibration frequency and the vibration amplitude, and the decrease in the workpiece cutting

speed reduce the TWCR. As the TWCR decreases, the non-cutting time of the tool

increases that decreases the cutting force and enhances both increased tool life and

improved cutting quality.

This paper also investigates the effect of cutting parameters such as cutting speed and

feed rate in cutting Inconel 718. The cutting quality is evaluated in terms of three cutting

force components, tool wear, chip formation and surface roughness for both the UVC and

the CT methods. Additionally, it observes and discusses the behavior of tool failure and the

formation of the chips, at different cutting conditions, by means of scanning electron

microscopy (SEM). Finally, a comparative study has been configured to show the

advantages of the UVC method over the CT method. It is concluded that the UVC method

performs better than the CT method up to a certain cutting speed range. However, beyond

this range, the CBN tools catastrophically failed for machining of Inconel 718 in the UVC

method. The authors consider that this type of failure during ultrasonic cutting is due to a

number of consecutive high impacts between the tool and the workpiece for long durations

at a comparatively high cutting speed. The higher the cutting speed, the larger the TWCR

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is. Therefore, the cutting speed has a significant effect on cutting force and tool wear in the

UVC method that substantiates the theoretical findings. Finally, it is remarked that the

UVC method offers better cutting performance in hard and tough cutting materials at low

cutting speed and at high tool vibration frequency and amplitude.

2. Theory

2.1 Study of ultrasonic vibration cutting mechanism

Fig. 1 shows an illustration of a UVC system where a piezoelectric transducer (PZT) is

configured into the tool shank to excite the tool in any desired direction corresponding to

three conventional axes. In this study, a tangential or cutting directional type UVC system

is considered as implemented by most of the previous researchers [3, 8-16, 20]. The rest of

the cutting system in this technique is same as conventional turning set up.

Fig. 1. Schematic of ultrasonic vibration cutting

The cutting principle of the UVC method was explained by the previous researchers [8,

12, 13, 15, 20]. The tool oscillates at an ultrasonic frequency f (i.e. vibration period, fT /1= )

with a very small vibration amplitude a where the workpiece rotates with a constant cutting

speed cv . Accordingly in Fig. 2, the cutting edge starts to vibrate from the origin O and

then cuts the workpiece material during the interaction periods .., baba tt ′−′− .

Fig. 2. Pulse cutting state in the UVC method [15].

The displacement of vibrating tool is described by:

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ftatax πω 2sinsin == (1)

where x and ω are the displacement and the angular velocity of the tool, respectively.

Thus the tool vibration speed is taxvt ωω cos== & that varies from a minimum of 0)( min =tv at

any peak or valley to a maximum of afavt πω 2)( max == at midpoint of its either upward or

downward motion, except the initial tool speed at the origin O. It was realized [3, 8, 12, 13,

15, 20] that the ultrasonic cutting is satisfied if cva >ω , otherwise it becomes a conventional

cutting process. Therefore, the critical cutting speed in the UVC method is defined as

max)(2)( tcrc vafav === πω

Fig. 2 also illustrates three following basic equations that govern the UVC system:

0cos =+ bc tav ωω (at btt = ) (2)

)(sin)(sin bacba ttTvtatTa −+=−+ ωω (3)

Ttr c /= (4)

where r is the tool-workpiece contact ratio (TWCR).

Eqs.(2)-(4) formulate a final equation as obtained by [13]:

]))2/((cos[cossin2)1( 1 rafvrafrv cc πππ −−=− −

(for cvaf >π2 ) (5)

Therefore, it is clear from the final Eq. [5] that the term TWCR during ultrasonic cutting

is dependent on three vital parameters; f, a and vc. Since this technique cuts the workpiece

for a certain period in each vibration cycle, the cutting force in this method also should be

TWCR ( Ttc /= ) times of that for the continuous cutting [11, 14]. That means a lower value

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of TWCR can decrease the cutting force in the UVC system. The above Eq. [5] directly

indicates that the TWCR can be lowered by controlling those three important parameters.

In the following sections 2.2-2.4, the effect of these factors are studied theoretically first.

Then the effect of the third factor, workpiece cutting speed, is justified in the experiment in

section 4.1.

2.2 The effect of tool vibration frequency

Suppose two UVC systems vibrate at two different frequencies f1 = 20 kHz and f2 = 35

kHz with the same amplitude a = 15 µm. Hence the tool vibration period T1 is higher than

T2. Fig. 3(a) combines both the UVC systems including the tool displacement curves and

their corresponding pulse cutting states as a function of time.

Fig. 3. UVC process: (a) Tool displacement and resultant cutting force for two different

tool vibration frequencies (Subscripts: 1, 2 are for 20 kHz, 35 kHz, respectively), (b)

Relation between TWCR and tool vibration frequency, f.

Now let a workpiece, rotating with a constant cutting speed vc , engages at a1 and

disengages at b1 during the upward and downward motion, respectively, of the tool for the

low frequency UVC system. Thus the system for this case follows the same contact period

tc1 as ,...,,111111 ababab ttt ′′−′′′−′− in the consecutive vibration cycles. Similarly, the high frequency

tool for the same workpiece cutting speed follows the contact period tc2 as

,...,,222222 ababab ttt ′′−′′′−′− . It is clear from the figure that tc1 > tc2. But since T1 > T2, it can not

directly be determined whether 21 rr > or vice versa.

Fig. 3(b) plots the TWCR against the tool vibration frequency using the Eq. [5] where a =

15 µm and vc = 15 m/min. Two different values of TWCR, 1r = 0.2162 and 2r = 0.1600 can

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be found for f1 = 20 kHz and f2 = 35 kHz, respectively. Thus, it is clear that the TWCR for

a low frequency tool is higher than for a high frequency tool in the UVC system. Therefore,

the tool cutting area experiences for a short duration of pulsating cutting force when using a

high frequency tool.

Though the number of contact between the tool and the workpiece always will be higher

for a relatively high frequency cutting tool, it was experimentally reported [23] that the

increase of tool vibration frequency in the UVC system improves cutting quality and

prolongs tool life that agrees the theoretical studies.

2.3 The effect of tool vibration amplitude

Again suppose another two tangential UVC systems operate two different tool vibration

amplitudes a1 = 10 µm and a2 = 25 µm where the frequency f = 20 kHz is fixed. Thus the

tool vibration period T is same for both the systems. Fig. 4(a) illustrates a combined

diagram of two different displacement curves and corresponding pulse cutting states

against the time cycle for these two systems.

If a workpiece rotates with a constant cutting speed vc for both the conditions, then the

tool of small vibration amplitude interacts with the workpiece earlier at c1 and separates

from the workpiece later at d1 as compared to the tool of large vibration amplitude. In this

manner, let the tool for the former case follows the tool-workpiece contact time 1ct as

,...,1111 cdcd tt ′−′− in the successive passes where the tool for the later case follows 2ct as

,...,2222 cdcd tt ′−′− . It is clearly seen from Fig. 4(a) that 21 cc tt > . Thus 21 rr > because T1 = T2 .


tool vibration amplitudes (Subscripts: 1, 2 are for 10 µm, 25 µm, respectively), (b) Relation

between TWCR and tool vibration amplitude, a.

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Fig. 4(b) shows the TWCR against the tool vibration amplitude by using the final Eq.[5]

where f = 20 kHz and vc = 15 m/min. Two different values of TWCR, r1 = 0.2710 and r2 =

0.1644 can be picked out at a1 = 10 µm and a2 = 25 µm respectively where 21 rr > .

Therefore, it is obvious that the TWCR for a tool of a high vibration amplitude is lower

than for a tool of a small vibration amplitude. As the number of contacts between the tool

and the workpiece is same for both the tool conditions [see Fig. 4(a)], the tool for the

second condition favors better cutting performance in the UVC system.

Y.-L Zhang [23] experimentally investigated that the increase of tool vibration amplitude

in the UVC system improves cutting quality and saves tool life which substantiates the

theoretical findings.

2.4 The effect of workpiece cutting speed

Fig. 5(a) shows a tool displacement diagram and corresponding pulse cutting state against

time for a single tool following f = 20 kHz and a = 15 µm. Let two cutting speeds 1cv and

2cv for the workpiece be considered where, 21 cc vv < . Since 1cv is the smallest, the workpiece

for this case holds with the tool later at p1 and then separates earlier at q1 during the upward

and downward motion of the tool respectively. Accordingly, the tool-workpiece in this

condition follows the contact period 1ct as ,...,1111 pqpq tt ′−′− in the consecutive vibration cycles.

On the other hand, the workpiece of cutting speed 2cv engages with the tool earlier at p2 and

disengages later at q2 with following the tool-workpiece contact period 2ct as ,...,2222 pqpq tt ′−′− .

From the following Fig. 5(a), it is clear that 21 cc tt < and hence 21 rr < , because same

frequency was applied to the cutting tool.

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Fig. 5. UVC process: (a) Tool displacement and pulsating cutting force against time at f =

20 kHz and a = 15 µm. (Subscripts: 1, 2 are for low and high cutting speed, respectively),

(b) Relation between TWCR and workpiece cutting speed, cv .

The curve for TWCR vs the workpiece cutting speed is plotted in Fig. 5(b) by using again

the final Eq. [5]. If two different cutting speeds, 20 m/min and 40 m/min, are considered

then the TWCR is found to about 0.2536 for 20 m/min as compared to about 0.3803 for 40

m/min. Therefore, the TWCR for a low workpiece cutting speed in the UVC system is

lower than that for a high workpiece cutting speed. That means the tool experiences a short

duration of the pulsating cutting force when applying low cutting speed.

Moreover, the TWRS in the UVC method increases with the increase in cutting speed

that definitely effects cutting quality in machining. Previous experimental works [6-8, 18-

22] indicated that the UVC method improves cutting quality and saves tool life at low

cutting speed values. Therefore, low values of cutting speed are suggested to be used for

the UVC technique.

3. Experimental set up and procedure

All the cutting tests were conducted with a modern CNC lathe machine Okuma LH35-N.

One end of the workpiece was held tightly in the three-jaw chuck and the other end was

supported by the lathe centre. A Sonic impulse SB-150 device containing a PZT [see Fig. 6]

was used to vibrate the tool tip in the tangential direction. The available power source

supplied for the device was AC 100V with 50 ~ 60 Hz frequency that consumes 260 VA of

electric power. Finally, a fresh CBN tool insert (600 type) was mounted on the cutter head

in each test.

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Fig. 6. Photograph of a tool holder containing a PZT and tool insert in the UVC method.

Table 1 presents the experimental conditions used for both the CT and the UVC methods

where Table 2 and Table 3 show physical and mechanical properties of both the workpiece

Inconel 718 and the CBN tool materials, respectively. When switching off the generator of

the vibration device, the cutting becomes CT. Upon switching on, the device provides the

frequency of about 19 kHz and the amplitude of about 15 µm. Therefore, the maximum

vibrating speed of the tool tip can be calculated as afvt π2)( max = = 107.4 m/min.

In order to maintain separating type vibration cutting, the cutting speeds in all the

operations were chosen to be less than this critical speed.

Table 1: Experimental conditions

Table 2: Properties (at RT) of workpiece Inconel 718

Table 3: Properties of CBN tool inserts used

In regular intervals (about 2 minutes) of one-pass, machining was stopped in order to

observe and measure output parameters such as tool flank wear width, chip formation, and

surface roughness. A KISTLER 3-Component Tool Dynamometer was used to measure the

cutting force components for tangential, radial and axial directions. For analysis, the force

signals were measured via a Graphtec chart recorder. Also, the width of the tool wear

along the flank, VB was measured with a Toolmaker’s Microscope whilst the topography of

the tool wear and the formation of chips were examined with a Scanning Electron

Microscope (SEM). Moreover, a surface analyzer, Surtronic 10, was used to measure the

average surface roughness, Ra , throughout the experiments.

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4. Results and discussions

4.1.The effect of cutting speed on cutting force and on tool wear

Fig. 7(a) shows the effect of cutting speeds on the cutting force components for both the

cutting techniques at a feed rate of 0.1 mm/rev. It is observed that all the force components

for the UVC method are reduced up to 15-25% that is required for the CT method at all the

cutting speeds. Another finding is that, for both the cutting methods, the thrust force

component is the highest among all the components followed by the tangential component

and then the axial component.

Fig. 7. Effect of cutting speed in both the cutting methods: (a) Cutting force components,

(b) Tool flank wear width, VB after 10 minutes of cutting.

Fig. 7(b) plots the tool flank wear width, VB against the cutting speeds after 10 minutes of

cutting and Fig. 8 illustrates the CBN tool wear characteristics with the following SEM

photographs for various cutting conditions by applying both the cutting techniques. Though

highest tool wear rate was seen, the cutting operation was continued throughout all the

cutting speeds in the CT method. In contrast, the wear rate in the UVC method was

negligible at cutting speed up to 10 m/min. However, beyond this speed such as 15 m/min

and 20 m/min, the tool nose as well as the cutting edge experienced high wear rate and

eventually failed after 4 minutes of machining. Since the tools were worn out within short

time at 15 m/min and 20 m/min by applying the UVC method, the wear values for those

two cutting speeds are not shown in Fig. 7(b). Figs. 8 (a)-(f) were captured after 10 minutes

of machining while Figs. 8 (g)-(h) were taken after 4 minutes of operation.

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Fig. 8. The SEM photographs of tool wear characteristics at different cutting conditions.

(a)-(d): CT method; (e)-(h): UVC method.

Fig. 8 also shows that the CT method continuously generated BUE (Built-Up-Edge) that

left the pits and debris on the tool rake and flank faces. These pits and debris sticking on

the tool cutting area always increase the cutting force and hence increase the tool wear. In

contrast, a very small amount of BUE and pits was produced in the UVC method.

Therefore, Figs. 7-8 reveal that the removal of BUE, the separating cutting characteristic,

the consequent reduction of the surface tearing during UVC [19], aerodynamic lubrication

[1, 19] and the generation of comparatively thinner and even chips [Fig. 11] could be the

main reasons of producing both the lowest cutting force and the tool wear at less than 15

m/min in the UVC method.

However, in the UVC method, a sudden increase of force components was observed

when the cutting speed shifts from 10 m/min to 15 m/min. This is because both the TWCR

and the TWRS increase with the increase of the cutting speeds as discussed with Figs. 5

(a)-(b). Ignoring the TWRS factor in this study, the TWCRs for 10 m/min and 15 m/min

are found to be about 0.1739 and 0.2163, respectively. Hence the tool-workpiece contact

time is reduced by more than 4% in each vibration cycle if the cutting speed reduces from

15 m/min to 10 m/min. That means the tool engaged with the workpiece for a relatively

long duration at high cutting speed and also got attacked from a number of consecutive

high mutual radial and tangential impacts during the upward motion of the tool. As Inconel

718 has excellent toughness, ultimate transverse strength, yield strength and creep-rupture

resistance (see Table 2), and a relatively high tool relief angle (110) was used in the tests, it

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is assumed that the CBN tool material, which is next to diamond in hardness, could not

sustain these high impacts for a long duration in this method. It is seen in Fig. 10(b) that the

CBN tool started to wear off at the beginning of cutting at a comparatively high cutting

speed of 12.5 m/min or beyond. Though the failure is insignificant at a cutting speed of 10

m/min (see Figs. 8(e)-(f)) even after 10 minutes of cutting, it is seen in Figs. 8(g)-(h) that

the failure firstly started with fracture (or abrasion) at the tool nose-flank area and it

increased with the increase in cutting speed. Because of worsening the tool condition, the

measured cutting force components were found to be higher immediately when the cutting

speeds shift toward 12.5 m/min. Due to the long duration of tool-workpiece interaction at

these speeds (i.e. high TWCR) as compared to 10 m/min, the high number of impacts in

vibration cutting led to fatigue failure of the tool just after 4 minutes of cutting at either 15

m/min or at 20 m/min. The tool failed along with the cutting edge, starting from the tool

nose area as seen in the Fig. 8. Since the failure was very severe, it was considered to be a

catastrophic failure. Therefore, the UVC method results in long tool life at low cutting

speed.

4.2 The effect of feed rate on cutting force and on tool wear

Fig. 9(a) reveals that the cutting force increases with the feed rate in both the processes,

which means that the UVC method accords with the same rule in the CT method. However,

all the force components, at almost all the feed rates, of the UVC process are reduced

approximately to about 12-20% of that of the CT process. Moreover, the cutting force

increase rate with the feed rate is insignificant in the UVC process unlike in the CT

process.

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Fig. 9. Effect of feed rate in both the cutting methods at a cutting speed of 10 m/min: (a)

Cutting force components, (b) Tool flank wear width VB after 10 minutes of cutting.

Fig. 9(b) shows that the tool flank wear width in the CT method increases suddenly when

the feed rate is increased from 0.025 mm/rev to 0.05 mm/rev and then it maintains a steady

increase rate. In contrast, in the UVC method, the wear increases linearly with a very small

slope throughout the whole range of the feed rates. Thus it is clear that the tool wear rate in

the CT method is significantly higher than in the UVC method.

Figs. 9(a)-(b) also demonstrate that the lower cutting force components in the UVC

method reduced the tool wear rate that lengthens the tool life. At all the feed rates, it is

observed that the tool wear in the UVC method is reduced to about 12-14 % of that in the

CT method. According to these results, it is predicted that the tool life for the UVC method

is almost 7-8 times higher than that for the CT method.

4.3 Tool wear vs cutting time

Figs. 10 (a)-(b) illustrate that the tool wear rate in the UVC method is significantly lower

than in the CT method up to the cutting speed of 10 m/min. According to the following

experimental results, it is observed that the tool life in UVC of Inconel 718 is almost 4-8

times higher than that in CT up to that cutting speed limit. This is because both the TWCR

and the TWRS are low at low cutting speeds in the UVC method. Thus a small value of

both the TWCR and the TWRS results in low tool wear rate.

Fig. 10. Tool flank wear width, VB against cutting time at a feed rate of 0.1 mm/rev for (a)

CT method and (b) the UVC method.

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However, as discussed earlier, due to the high value of both the TWCR and the TWRS

beyond the cutting speed of 10 m/min, the tools eventually failed just after 4 minutes of

cutting in the UVC method. On the other hand, though 100% TWCR causes a rise in

temperature and different wear mechanisms at the tool-workpiece contact areas and elastic

and plastic deformations occur to cause fast tool wear; cutting still could be continued in

the CT method at high speed because no impact is faced by the tool edge in this method.

The above studies thus reveal that the CT method limits the repeatability of the tool

which in turn increases the production costs. On the other hand, the UVC method limits the

use of high cutting speeds with hard and tough cutting like Inconel 718.

4.4 Analysis of chip formation

Fig. 11 shows the SEM photographs of chips at different feed rates for both the cutting

methods. It can be easily observed that the CT method generated thick, uneven, short and

cracked chips whereas the UVC method produced comparatively thin, smooth and long

chips.

Fig. 11. SEM photographs of the chips produced at different cutting conditions by both the

cutting methods: (a)-(b) CT method, (c)-(d) UVC method.

The generation of thicker, uneven and cracked chips is always unfavorable to achieve a

high quality machining because these types of chips negatively affect the tool cutting area

to have non-uniform friction and generation of high temperatures, high cutting forces, high

regenerative chatter, and rapid tool wear which shorten the tool life. In contrast, non-

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continuous interaction between the tool and the workpiece in the UVC method generated

thin, smooth and long chips that did not affect the tool life significantly.

4.5 The effect of cutting speed and feed rate on surface roughness

Fig. 12(a) shows the roughness values Ra against the cutting speeds that were taken after

10 minutes of machining with both the cutting methods. Since the tools were worn out in

the UVC method after 4 minutes of cutting at 15 m/min and 20 m/min, the Ra values for

those conditions were not considered. It is observed that the Ra values increase with the

increase in cutting speeds where the increase rate for the UVC method is very insignificant,

unlike that for the CT method.

Fig. 12. Average surface roughness values, Ra in both the cutting methods after 10 minutes

of cutting: (a) against cutting speeds at a feed rate of 0.1 mm/rev, (b) against feed rates at a

cutting speed of 10 m/min.

It is also seen from Fig. 12(b) that a minimum surface roughness Ra value in the CT

method was 2.4 µm for the cutting of Inconel 718, whereas it was 0.6 µm in the UVC

method. Furthermore, the Ra values with the UVC technique did not cross 0.8 µm at the

maximum feed rate of 0.1 mm/rev. Thus the Ra values in the UVC process do not increase

markedly with the feed rates, as it does in the CT process.

Figs. 12(a)-(b) also reveal that the surface finish with the UVC method is improved by

about 75-85% over the CT method. Therefore, a high quality surface finish for tough

cutting could be achieved with the UVC method.

The above studies demonstrate that, since the TWCR is 100% in the CT method, the

generation of thick, uneven and severe cracked chips, BUE, high cutting force components,

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frictional heat, and high cutting instability, etc. deteriorated the machined surface and

finally produced a rough and coarse surface. On the contrary, only a fraction of TWCR and

consequent reduction of the surface tearing in the UVC method reduced the cutting force,

frictional force and frictional heat and produced comparatively sharper fine chips that have

less influence on the machined surface. Thus the surface finish obtained in the UVC

method is regular and smooth, which is much better than that in the CT method.

It is also observed that both the TWCR and the TWRS in the UVC method influence the

cutting quality for tough cutting superalloy Inconel 718. For example, since the TWCR and

the TWRS are the lowest for 5 m/min as compared to other cutting speeds (see section 2 for

the TWCR values), the surface finish is better for this cutting speed. Thus, as low as the

values of these key parameters, the cutting quality distinctly improves.

4.6 Comparative analysis between CT and UVC method

Lastly, Fig. 13 presents a brief comparison between the CT and the UVC methods based

on the above experimental findings. Four different output parameters; the tangential and

radial cutting force components, the flank wear width and the Ra values at a feed rate of 0.1

mm/rev were taken into account for this comparison. Since the UVC method performs

remarkably better up to a cutting speed of 10 m/min in cutting of Inconel 718, this speed

was selected as best suited for this analysis.

Fig. 13. Comparative analysis of cutting performances between the CT and the UVC

methods at selected cutting speed of 10 m/min.

The above chart shows that the UVC method, in all the cases, promises better cutting

performance than the CT process. Therefore, it is concluded that the UVC method does not

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only attain high quality cutting of difficult-to-machine materials, but it also raises the tool

life distinctly and saves machining cost.

5. Conclusions

The effect of tool vibration frequency, tool vibration amplitude and workpiece cutting

speed in the UVC method were studied theoretically. Also the effect of cutting parameters

on a superalloy Inconel 718 with CBN tools was investigated thoroughly by applying the

UVC methods. In order to compose a comparative analysis, the cutting conditions applied

in the UVC method were also considered for the CT method. The cutting force

components, the tool flank wear width, the chip formation and the surface roughness were

justified as the output parameters. Based on the theoretical studies and experimental results

achieved, the following conclusions can be compiled:

1. In the UVC technique, the cutting quality depends mainly on two important factors:

TWCR and TWRS. The cutting mechanism shows that the TWCR relies on three

independent key parameters; the tool vibration frequency, the tool vibration amplitude

and the workpiece cutting speed.

2. To achieve high quality cutting, the TWCR should be kept as low as possible. The

value of TWCR can be lowered by increasing both the tool vibration frequency and

amplitude, as well as by decreasing the workpiece cutting speed.

3. The test results show that the cutting force for the UVC method was required to about

12-25 % of that for the CT method in cutting of Inconel 718.

4. The tool flank wear in the UVC method was found to be about 12-25 % of that in CT

method when cutting up to 10 m/min. Accordingly, the tool life with the UVC method

is increased by at least 4-8 times over the CT method.

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5. A minimum Ra value of 0.6 µm was achieved with the UVC method whereas 2.4 µm

was achieved with the CT method for the same cutting condition. Hence, the cutting

quality with the UVC method was improved by about 75-85% over the CT method.

6. However, beyond the cutting speed 10 m/min, the CBN tools catastrophically failed

after 4 minutes of machining applying the UVC method. This type of failure may be

due to high TWCR when a high cutting speed was used. A number of consecutive high

impacts between the tool and the workpiece with high TWCR induced to cause fast tool

wear that agrees with the theoretical study on the effect of the third factor; the effect of

workpiece cutting speed.

7. To conclude, the UVC method has been found to be a suitable technique to achieve

high quality finish surfaces for Inconel 718; though low cutting speed range should be

maintained in this method.

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References

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diamond cutting of glasses with the aid of ultrasonic vibration, J. Mater. Process. Technol.

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aviation materials: simulations and experimental study, Ultrasonics 42 (2004) 81-86.

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vibration cutting of hard metal, Int. J. Mach. Tools Manuf. 43 (2003) 1375-1382.

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assisted turning of aviation materials, J. Mater. Process. Technol. 132 (2003) 157-167.

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alloy steel, J. Mater. Process. Technol. 192-193 (2007) 159-165.

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10. L. Balamuth, Ultrasonic assistance to conventional metal removal, Ultrasonics, July

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Process. Technol. 129 (2002) 196-199.

12. J. Kumabe et al, Ultrasonic superposition vibration cutting of ceramics, Precision

Engineering, 0141-6359/89/020071-07.

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cutting, Int. J. Mach. Tools Manuf. 42 (2002) 1677-1685.

14. J. Kumabe, M. Hachisuka, Super-precision cylindrical machining, Precision

Engineering, 0141-6359/84/020067-06.

15. M. Xiao, Q. M. Wang, K. Sato, S. Karube, T. Soutome, H. Xu, The effect of tool

geometry on regenerative stability in ultrasonic vibration cutting, Int. J. Mach. Tools

Manuf. xx (2005) 1-8.

16. A.V. Mitrofanov, V.I. Babitsky, V.V. Silberschmidt, Finite element analysis of

ultrasonically assisted turning of Inconel 718, J. Mater. Process. Technol. 153-154 (2004)

233-239.

17. A.V. Mitrofanov, N. Ahmed, V.I. Babitsky, V.V. Silberschmidt, Effect of lubrication

and cutting parameters on ultrasonically assisted turning of Inconel 718, J. Mater. Process.

Technol. 162-163 (2005) 649-654.

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20. J.-D. Kim, E.-S. Lee, A study of the ultrasonic-vibration cutting of carbon-fiber

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Special 3, pp. 279-282. Nov. 2005.

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Caption of tables: Table 1: Experimental conditions



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Table 1: Experimental conditions

Workpiece Material Inconel 718

Diameter 175 mm

Length 600 mm

Tool Material CBN (BN250)

Rake angle +100

Relief angle 110

Approach angle 300

Nose radius 0.4 mm

Cutting conditions Depth of cut 0.10 mm

Feed rate 0.025 - 0.1 mm/rev

Cutting speed 5 - 20 m/min

Vibration conditions Frequency 19 ± 1.5 kHz

Amplitude 15 µm

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Density 8.19 g/cm3

Melting temp range 1260-1336 0C

Avg. thermal exp. coeff. 13.0 μm/m.K

Specific heat 435 J/kg.K

Thermal conductivity 11.4 W/m.K

Ultimate tensile strength 1240 MPa

Yield strength (0.2% off.) 1036 MPa

Elongation in 50 mm 12%

Elastic modulus (tension) 211 GPa

Hardness 36 HRC

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CBN contents 85–90 (vol.%)

CBN grain size 3–5 (µm)

Binder Co etc.

Poission’s ratio 0.22

Thermal conductivity 100–130 (W/m K)

Thermal stability 1270 (K in air)

Hardness (GPa) 35–40 (at room temp.)

12 (at 1273 K)

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Captions of figures:

Fig. 1. Schematic of ultrasonic vibration cutting.

Fig. 2. Pulse cutting state in the UVC method.















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Cutting force components, (b) Tool flank wear width VB after 10 minutes of cutting.










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Figures:

Fig. 1. Schematic of ultrasonic vibration cutting

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Fig. 2. Pulse cutting state in the UVC method [15].

tax ωsin=

a’b’

ta tb

ta tctc

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0 5 10 15 20 25 30 35 40400

0.2

0.4

0.6

0.8

11

Tool frequency, f (kHz)

TWCR

35, 0.160020, 0.2162

(a) (b)




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(a) (b)




0 5 10 15 20 25 30 35 40400

0.2

0.4

0.6

0.8

1

Vibration amplitude, a (micron)

TWCR

10, 0.271025, 0.1644

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(a) (b)




0 20 40 60 80 100 1200

0.2

0.4

0.6

0.8

1

Cutting speed, v (m/min)

TWCR

20, 0.2536

40, 0.3803

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PZT

Tool insert

PZT holder


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01020304050607080

2.5 5 7.5 10 12.5 15 17.5 20

Cutting speed, m/min

Cut

ting

forc

es, N

Fr in CT

Ft in CT

Fa in CT

Fr in UVC

Ft in UVC

Fa in UVC

0

0.1

0.2

0.3

0.4

0.5

5 7.5 10 12.5 15 20Cutting speeds, m/min

Flan

k w

ear w

idth

, mm CT

UVC

(a)

(b)



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(d) 15 m/min, 0.1 mm/rev, CT

(a) 10 m/min, 0.05 mm/rev, CT

(b) 10 m/min, 0.1 mm/rev, CT

CT Method UVC Method

(c) 15 m/min, 0.05 mm/rev, CT (g) 15 m/min, 0.05 mm/rev, UVC

Fracture area

(f) 10 m/min, 0.1 mm/rev, UVC

No failure at nose-flank

(e) 10 m/min, 0.05 mm/rev, UVC

Failure starts at tool nose

(h) 15 m/min, 0.1 mm/rev, UVC

Fracture Catastrophic

failure

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00.05

0.10.15

0.20.25

0.30.35

0.4

0.025 0.05 0.075 0.1Feed rate, mm/rev

Flan

k w

ear w

idth

, mm CT

UVC

010203040506070

0 0.025 0.05 0.075 0.1Feed rates, mm/rev

Cut

ting

forc

es, N

Fr in CT

Fr in UVC

Ft in CT

Ft in UVC

Fa in CT

Fa in UVC

(a)

(b)


Cutting force components, (b) Tool flank wear width, VB after 10 minutes of cutting.

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0

0.1

0.2

0.3

0.4

0.5

0 2 4 6 8 10Cutting time, min

Tool

wea

r, m

m5 m/min

7.5 m/min

10 m/min

12.5 m/min

15 m/min

20 m/min

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10Cutting time, min

Tool

wea

r, m

m

5 m/min

7.5 m/min

10 m/min

12.5 m/min

15 m/min

20 m/min

(a)

(b)



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(d) 10 m/min, 0.1 mm/rev, UVC

(c) 10 m/min, 0.05 mm/rev, UVC

(b) 10 m/min, 0.1 mm/rev, CT

(a) 10m/min, 0.05 mm/rev, CT

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0.01.02.03.04.05.06.0

5 7.5 10 12.5 15 20Cutting speeds, m/min

Surf

ace

roug

hnes

s, m

icro

n

CT

UVC

01

23

45

6

0.025 0.05 0.075 0.1Feed rate, mm/rev

Surfa

ce ro

ughn

ess,

micr

on

CT

UVC

(a)

(b)




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010203040506070

1 2 3 41) T. force, N; 2) R. force, N; 3) T. wear, mm X 100;

and 3) Roughness Ra, micron X 10

CT

UVC



Effect of Machining Parameters in Ultrasonic Vibration Cutting

Documents

consecutive

toolworkpiece

ultrasonically

finite element

pulse cutting

pulse cutting

tool vibration

tool vibration