ement of Machining Performance using Hybrid Rotary ... · Ultrasonic Assisted Milling (HRUAM)...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 23 (2017) pp. 13506-13513

© Research India Publications. http://www.ripublication.com

13506

Improvement of Machining Performance using Hybrid Rotary Ultrasonic

Milling (HRUAM) for Hardened D2 Tool Steel Materials

R. Azlan1,2,*, R. Izamshah1, M.S. Kasim1, M. Akmal1 and MAHM Nawi3

1)Precision Machining Group, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka,

Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia. 2)Department of Mechanical Engineering, Politeknik Muadzam Shah, Lebuhraya Tun Razak,

26700 Muadzam Shah, Pahang, Malaysia. 3)Department of Mechanical Engineering Technology, Faculty of Engineering Technology,

Universiti Malaysia Perlis, 02100 Padang Besar, Perlis, Malaysia. *Corresponding e-mail:

*Orcid: 0000-0002-4959-1054

Abstract

This paper demonstrate the effectiveness of Hybrid Rotary

Ultrasonic Assisted Milling (HRUAM) technique in

improving the machining performance for AISI D2 tool steel

material. The high strength of these materials (>50 HRC)

contribute to its poor machinability ratings. Some of the

common problems in dealing with this material are roughed

machined surface, high machining force, high cutting

temperature and rapid tool wear. Experimental investigation

to compare between HRUAM and conventional machining

for different set of parameters namely cutting speed, feed rate

and machining depth on the surface roughness value has been

done to confirm the effectiveness of the proposed technique.

Taguchi Orthogonal array design with 3 factors was used as a

design matrix for analyzing the effect of each parameter. The

experimental results indicated that the surface roughness was

improved from 1.81 m (conventional) to 0.19 m

(HRUAM) almost 89.50 % improvement in the same cutting

condition. In addition, from ANOVA result indicated that

speed, feed rate and vibration frequency are the most

dominant factor affecting the surface roughness value. The

findings from the deliberately conducted experiments can be

used for improving the production time and cost in mold

fabrication by eliminating the manual polishing process.

Keywords: Ultrasonic assisted machining; Surface

roughness; Hardened steel

INTRODUCTION

Hardened D2 tool steel are widely used in the mold and die

industry especially for injection molding tools, cold forming

tools and precision engineering parts [1-2]. Most of the

applications required an excellent surface finish as it will

reflect on the appearance of the product. Due to the high

strength of these materials (>50 HRC) conventional

machining process resulting in rough machined surface and

required special machining technique in order to maintain the

quality of the part. In general, the effectiveness of machining

performances such a surface roughness are greatly dependent

with the cutting parameters namely cutting speed, feed rate

and depth of cut [3-6]. The optimal combination of cutting

parameter will produce a good result while wrong

combination will result in vice versa. However, from the

literatures it shows that even though optimal cutting

conditions were employed, the produced surface roughness

still beyond the permissible tolerances. In current industry

practice the process will continue by manual polishing [7-

11]. In addition, others problems encountered with

conventional machining of hardened tool steel material are

rapid tool wear, high machining force and high machining

temperature [12-15].

To solve the discrepancies with the conventional machining

technique, one of the possible alternative are by combining

with the ultrasonic frequency known as Ultrasonic-assisted

machining (UAM). It is well known that UAM has been

proven to improve many conventional machining processes

such as grinding, drilling, and turning [16-20]. The

advantages of using UAM are it can maximize the material

removal rate, decreased the machining forces and improve

the surface finish by reducing the peak height produced from

the milling cutter. However most of the UAM technique was

mainly employed for hard and brittle materials such as glass,

quartz and ceramic. Therefore, this paper propose a new

technique by applying ultrasonic frequency to the rotating

milling cutter for AISI D2 tool steel material known as

Hybrid Rotary Ultrasonic Assisted Milling (HRUAM).

In addition, this paper will investigate on the effect of

HRUAM machining parameters (cutting speed, feed rate

depth of cut, vibration frequency and vibration amplitude) on

machining performance namely surface roughness.

Furthermore, this paper will compare on the effectiveness of

applying ultrasonic vibration with the conventional

machining.



13507

METHODOLOGY

The experimental test was perform to compare on the

effectiveness of applying ultrasonic vibration with the

conventional machining. In addition, all the machining

parameter involve in HRUAM process (cutting speed, feed

rate depth of cut, vibration frequency and vibration

amplitude) will be investigate to identify its contribution on

the surface roughness value.

AISI D2 steel with 512 HRC was used as the material. The

block dimension is 120 mm x 100 mm x 15 mm (l x w x h).

Prior to the experiment, the raw material was skimmed down

to 0.5 mm using vertical milling machine to remove any

surface defects from preceding manufacturing process [16].

The chemical compositions of this material were 1.55 % C,

0.3 % Si, 0.4 % Mn, 11.8 % Cr, 0.8 % Mo and 0.8 % V. The

slot milling test were performed using 3-axis CNC milling

machine, type HAAS VF-1. An ultrasonic BT40 tool holder

was employed with frequency ranging from 20,000 Hz to

27,000 Hz that generate an amplitude vibration up to 3 m.

Figure 1 shows the rotary ultrasonic assisted machining

device and experimental setup used in the experiment.

A straight integral shank tool holder type EPH Hybrid TAC

Mills and multilayer TiAlN coated carbide insert were used

as the cutter. Figure 2 and Table 1 depicted the specification

of both holder and insert respectively.

Figure 1: Experimental setup

Figure 2: Tool holder specification

Table 1: Cutter inserts specification

The surface roughness value of machined surface was

measured using portable surface roughness Mitutoyo SJ-301

model. The instrument is calibrated before the measurement

process is executed. For each machining slot that has been

machined, the average value of surface roughness, Ra from

10 reading was measured and taken for the analysis

according to ISO 3274: 1996 standard. In addition, optical

microscope was used for microscopic observation of the

machined surface.

All machining tests were carried out in dry machining

conditions. In this experiment, totals of 54 run were carried

out that consist of 5 factors with 3 levels according to

Taguchi design method. The total number of experimental

runs was generated from the combination of 27 of

conventional machining and 27 of ultrasonic assisted

machining. The independent machining parameters involved

in this study were cutting speed, feed rate, depth of cut,

frequency vibration and amplitude vibration as shown in

Table 2. The arrangement of experiments runs shows in Table

3.

Table 2: Level of machining parameters

Parameters Low Medium High

Cutting speed (rpm) 30 90 150

Feed rate (mm/min) 2 25 45

Depth of cut (m) 10 20 30

Frequency (kHz) 20 23 27

Amplitude (m) 1 2 3

Analysis of variances (ANOVA) was used to investigate the

significance of variable parameters on surface roughness

[20]. Analysis of variances (ANOVA) was used to identify

which factor has significant effect on the surface roughness

value. In this experiment, P-value of less than 0.05 was set as

a significance level. In addition, an empirical model was

developed in order to model the relationship between the

input factor and the surface roughness.



13508

RESULT AND DISCUSSSION

Table 4 tabulated the surface roughness results obtained from

both conventional machining and HRUAM respectively.

From the obtained result, it clearly shown that the present of

ultrasonic vibration and varying machining parameter

affected the surface roughness value. The surface roughness

value for both conventional machining and HRUAM varied

between 1.81 m to 6.65 m and 0.19 m to 5.50 m

respectively. From the result, it shows that the surface

roughness values for HRUAM are lower compared to

conventional machining for every run. An improvement of up

to 89.50% average surface roughness value, Ra was achieved

using the HRUAM method compared to conventional

machining with the same machining condition.

The lowest surface roughness values obtained from the

experiments was at Run 13 with 0.19 m using the

combination of 150 rpm (cutting speed), 5 mm/min (feed

rate), 30 m (depth of cut), 23,000 Hz (frequency vibration),

and 2 m (vibration amplitude). While, the highest surface

roughness values was obtained by conventional machining

with the value of 6.65 m on Run 37 for 30 rpm (cutting

speed), 45 mm/min (feed rate) and 30 m (depth of cut).

From the observation, it indicates that feed rate was the major

factor that affects on the magnitude of surface roughness.

Further analysis was performed using ANOVA to confirm the

hypothesis. Figure 4 shows the comparison graph of average

surface roughness value, Ra between conventional machining

and rotary ultrasonic assisted machining for each run.

Analysis of Variances (ANOVA) was used to further analyze

on the effect of each factor towards the surface roughness

value. Table 5 depicted the ANOVA result obtained. Total of

8 factors and interaction were selected as the model term and

7 factors were term as the residual. The selected model F-

value of 15.77 implies that the model term is significant. The

values of “Prob>F” less than 0.0500 indicates that the model

are significant. The ANOVA correlated with the probability F

value. The result of ANOVA analysis showed that the value

of probability was small, Prob>F, less 0.0001 %.

Table 3: Experimental runs for both conventional and ultrasonic machining



13509

Table 4: Arrangement of experimental runs

Figure 4: The comparison graph of surface roughness, Ra between conventional machining and rotary

ultrasonic assisted machining



13510

In response to ANOVA, it shows that A, B, D and F are

significant model terms. These results show that machining

parameters namely speed, feed rate, frequency of vibration

and machining technique affect the average surface

roughness, Ra value. On the other hand, depth of cut (C) and

amplitude (E) shows weak effect on the surface roughness

value. "R-Squared" of 0.7634 of the model shows that the

model terms are statistically significant. The final

mathematical model of the response and factors were:

Sqrt (Surface Roughness) Ultrasonic = 3.09606 – 8.64343E-004A+0.015449B+0.010055C-0.057748D-0.13427E-1.63156E-004AC-9.48273E-005AD+ 7.54763E-004AE (1)

Table 5: Analysis of variance (ANOVA) for surface

From Equation (1) the mathematical model indicated that

surface roughness is dependent on the speed (A), feed (B),

frequency of vibration (D) and amplitude (E) with the

average error between the predicted value and an

experimental less than 10 %. Figure 5 and 6 shows the 3D

response surface and contour plots graphs. It indicated that

higher cutting speed with lower feed rate produced the lowest

surface roughness value, compared with the lower cutting

speed and lower feed rate.

Figure 5: The 3D surface graph shows two (2) machining

factors (speed, feed rate) which affects to the surface

roughness (Ra) value

Figure 6: The contour graph plot shows the two (2)

machining factors (speed, feed rate) which affects to the

surface roughness (Ra) value.

Figure 7 and 8 show the interaction of surface roughness

between cutting speed and depth of cut when the constant of

feed rate. It indicates that minimum surface roughness

occurred on condition of higher cutting speed and lower

depth of cut. While, Figure 9 and 10 presents the 3D response

surface and contour plots for surface roughness (Ra)

respectively. From this figure, it can be seen that the value of

surface roughness decreased with increasing of cutting speed

and increasing of maximum frequency (27,000 kHz). The

lowest surface roughness value is on cutting speed of 90 rpm

and frequency of 27,000 kHz with 0.19 m.

Figure 11 and 12 show the macroscopic observation of the

machined surface for Run 26 between conventional

machining and HRUAM. It can be observed that machined

surface texture using HRUAM has very fine surface texture

with smaller cutter feed mark compared to conventional

machining. In addition it indicated that the peak to peak

values of curved striped cutter marks generated by HRUAM

are lower with consistent transverse marks compared to the

conventional machining. The peak to peak value of curved

striped cutter marks generated by conventional machining

was rough, uneven and non-uniform of transverse cutter

marks.


factors (speed, depth of cut) which affects to the surface

roughness (Ra) value.



13511


machining factors (speed, depth of cut) which affects to the



factors (speed, frequency) which affects to the surface

roughness (Ra) value.

A further analysis was perform on microscopic scale

observation of machined surface by using the Alicona Infinite

Focus. It shows that the machined surface textures produced

a conical shape topography features. Figure 13 and 14 shows

the machined surface topography between conventional

machining and HRUAM respectively for Run 22 with cutting

speeds of 150 rpm, feed rate of 5 mm/min, depth of cut of 30

m.

It shows that the machined surface topography spacing gap

using HRUAM are fine with constant cutter marks as well as

closely spaced compared to conventional machining. The

microscopic scale observation indicated that the present of

ultrasonic vibration in the axial direction has creates

hammering action that increase the localized stress force on

the surface. This localized stress flattened the cutter marks

left by the cutter teeth thus reducing the peak height and

improving the surface roughness value.


machining factors (speed, frequency) which affects to the


Figure 11: Machined surface for conventional machining

Figure 12: Machined surface for Hybrid rotary ultrasonic

assisted machining

Figure 13: Machined surface topography for

conventional machining

Figure 14: Machined surface topography for hybrid

rotary ultrasonic assisted machining



13512

CONCLUSION

In this paper, experimental work was carried out to compare

on the improvement of machining performance namely

surface roughness between hybrid rotary ultrasonic assisted

machining and conventional machining for AISI D2 hardened

material. In addition, the effects of machining parameter

(cutting speed, feed rate, depth of cut, frequency of vibration,

amplitude vibration) toward surface roughness value was also

been investigate.

The results from this study indicate that improvement on

machined surface roughness value up to 89.50% can be

achieved by using HRUAM compared to conventional

machining with the same cutting conditions. The minimum

machined surface roughness which can be achieved by using

HRUAM is 0.19 m with 90 rpm (cutting speed), 5 mm/min

(feed rate), 20 m (depth of cut), 27 kHz (frequency

vibration) and 3 m (amplitude vibration). The second part of

this work, confirm that only cutting speed (Vc), feed rate (f)

and ultrasonic frequency have major effects towards

machined surface roughness value.

The observed microscopic machined surface results for

conventional machining indicate large feed marks with

scratches and irregularities appear on the machined surfaces

compared to HRUAM. It was also observed that the chip

produced by HRUAM were uniform, smooth and short.

Further research could be carried out to establish the effect of

machining parameters (cutting speed, feed rate and depth of

cut) on others machining performances such as cutting force,

tool wear and tool material.

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ement of Machining Performance using Hybrid Rotary ... · Ultrasonic Assisted Milling (HRUAM)...

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