UDK 669.24:621.941:519.233.4	ISSN 1580-2949
Original scientific article/Izvirni znanstveni članek	MTAEC9, 48(2)249(2014)
OPTIMIZATION OF THE TURNING PARAMETERS FOR THE CUTTING FORCES IN THE HASTELLOY X SUPERALLOY BASED ON THE TAGUCHI METHOD
OPTIMIRANJE SIL ODREZAVANJA S TAGUCHIJEVO METODO PRI STRUŽENJU SUPERZLITINE HASTELLOY X
Abdullah Altin
Van Vocational School of Higher Education, Yuzuncu Yil University, 65080 Van, Turkey
aaltin@yyu.edu.tr
Prejem rokopisa - received: 2013-04-23; sprejem za objavo - accepted for publication: 2013-06-11
In this study the effects of the cutting-tool coating material and cutting speed on the cutting forces and surface roughness were determined using the Taguchi experimental design. For this purpose, the nickel-based superalloy Hastelloy X was machined under dry cutting conditions with three different cemented-carbide tools. The main cutting force, Fz, is considered to be the cutting force as a criterion. The mechanical loading and the abrasiveness of the carbide particles have an increasing effect on the cutting forces. According to the results of the analysis of variance (ANOVA), the effect of the cutting speeds was not important. Depending on the tool-coating material, the lowest main cutting force was found to be 538 N and the lowest average surface roughness, 0.755 ^m, both at 100 m/min with a multicoated cemented-carbide insert KC9240, whose top layer is coated by TiN. Moreover, the experimental results indicated that the CVD cutting tools performed better than the PVD and the uncoated cutting tools when turning the Hastelloy X in terms of the surface quality and the cutting forces with the current parameters. Keywords: machinability, Hastelloy X, superalloy, cutting force, surface quality
V tej študiji so s Taguchijevim eksperimentalnim sestavom določeni vplivi materiala oplaščenega rezilnega orodja, hitrosti rezanja na silo odrezavanja in hrapavost površine. V ta namen je bila superzlitina na osnovi niklja Hastelloy X obdelana pri suhih razmerah s tremi različnimi orodji iz karbidne trdine. Kot merilo je bila vzeta glavna sila rezanja Fz. Mehansko obremenjevanje in abrazivnost karbidnih delcev vplivata na povečevanje sile pri odrezavanju. Skladno z rezultati analize variance (ANOVA) vpliv hitrosti odrezavanja ni bil pomemben. Odvisno od prevleke na rezalnem orodju je bila ugotovljena najmanjša strižna sila 538 N in najmanjša povprečna hrapavost (0,755 ^m), oboje pri 100 m/min z večplastnim nanosom na vložku iz karbidne trdine KC9240 z vrhnjim prekritjem iz TiN. Rezultati poskusov so pokazali, daje pri struženju Hastelloy X s stališča kvalitete površine, sil pri rezanju pri danih parametrih CVD rezilno orodje boljše od PVD in od orodja brez prevlek. Ključne besede: obdelovalnost, Hastelloy X, superzlitina, sile rezanja, kvaliteta površine
1 INTRODUCTION	in the clamshell of a rocket, engine tailpipes, afterburner
components, cabin heaters, and other aircraft parts.4 It Nickel-based alloys constitute an important class of has also been found to be resistant in petrochemical materials that are used under demanding conditions of applications. Hastelloy X is widely used in a number of
high corrosion resistance and high-temperature strength.	industries.5 Wang,6 Richards and Aspinwall,7 Ezugwu
These characteristics together with their good ductility	and Wang,8 with Khamsehzadeh9 studied the effect of
and ease of cold working make them generally very	applied stress and temperatures generated at the cutting
attractive for a wide variety of applications; nearly all of	^^ge and they were found to influence the wear rate and,
which exploit their corrosion resistance in atmo1spheric,	hence, the tool life. Notching at the tool nose and the
salt water and various acidic and alkaline media.1Hastel-	^epth of cutting region was a prominent failure mode
loy X is a nickel-chromium-iron-molybdenum alloy that	when machining nickel-based alloys. This is due to a has been developed for high-temperature applications
combination of high temperature, high workpiece
and is derived from the strengthening particles, Ni2(Mo,
Cr), which are formed after a two-step age-hardening	strength,1^^ork hardening and abrasive chips. Kramer and
heat-treatment process. With their face-centred cubic	Hartung,10,11 observed that cemented-carbide tools used
(FCC) structure, the Ni-Cr-Mo-W alloys, known as	for machining nickel-based alloys at a cutting speed of
Hastelloys, are used for marine engineering, chemical	30 m/min failed due to the thermal softening of the
and hydrocarbon processing equipment, valves, pumps,	cobalt binder phase and the subsequent plastic defor-
sensors and heat exchangers.2 Hastelloy X is chosen by	mation of the cutting edge. Focke et al.12 examined worn
many for use in furnace applications because it has an	tools, which revealed a layer of "disturbed material"
unusual resistance to oxidizing, reducing, and neutral	beneath the crater and the cutting edge. Hastelloy is a
atmospheres. The resistance to localized corrosion ma-	registered trademark name of Haynes International Inc.
kes the alloy an attractive material as a general-purpose	The Hastelloy trademark is applied as a prefix for a
filler metal, or weld overlay.3 Hastelloy X is widely used	range of corrosion-resistant nickel-based alloys
promoted under the name "superalloys" or "highperformance alloys". Within corrosion applications, Hastelloy alloys may be chosen as a trade-off between performance, cost and other technical issues, e.g., suitability for welding. Hastelloy alloys are generally less attractive for use in acids compared to Tantaline (Tantaline is recognized as the leading performance/price option).
Nomenclature
v	cutting speed (m/min)
f	feed (mm/r)
da	axial depth (mm)
y	tool life (min)
Fm	feed (mm/min)
TL	total length
2 MATERIALS AND METHOD
2.1 Experiment Specimens
Specimens of Hastelloy X, which has an industrial usage, were prepared with dimensions of diameter 02 x 40 inches and then used for the experiments. The chemical composition and mechanical properties of the specimens are given in Tables 1 and 2, respectively. As the contents of the workpiece, chromium (21 %) and molybdenum (17 %), are high, the material is hard to machine. The material consists of approximately 50 % nickel, making the alloy suitable for high-temperature applications. The specimen was annealed and has a hardness of Rockwell B 90.
ting forces (Fx, Fy, Fz). This allows direct and continuous recording and a simultaneous graphical visualization of the three cutting forces. The technical properties of the dynamometer and a schematic figure of the experimental setup are given in Table 3 and Figure 1, respectively.
Table 1: Chemical composition of the workpiece material (Hastelloy X), w/%
Tabela 1: Kemijska sestava obdelovanca (Hastelloy X), w/%
Ni	Cr	Mo	Fe	Co	W	Mn	Al	Si	C	B
50	21	17	2	1	1	0.80	0.50	0.08	0.01	0.01
Table 2: Mechanical properties of Hastelloy X Tabela 2: Mehanske lastnosti Hastelloy X
Hardness conductivit y(HB)	Tensile strength (MPa)	Yield strength (MPa)	Breaking extension % (5 do)	Thermal (W/m K)
388	1370	1170	23.3	11.4
Table 3: Technical properties of dynamometer Tabela 3: Tehnične lastnosti dinamometra
Force interval (Fx, Fy, Fz)	-5^10 kN
Reaction	< 0.01 N
Accuracy Fx, Fy	« 7.5 pC/N
Accuracy Fz	« 3.5 pC/N
Natural frequency /o(x, y, z)	3.5 kHz
Working temperature	0^70 °C
Capacitance	220 pF
Insulation resistance at 20 °C	> 1013 Q
Grounding insulation	> 108 Q
Mass	7.3 kg
2.2 Machine Tool and Measuring Instrument of Cutting Forces
The machining tests were carried out on a JOHNFORD T35 industrial-type CNC lathe with a maximum power of 10 kW and a rotating speed between 50 r/min and 3500 r/min. During the dry cutting process, a Kistler brand 9257 B-type three-component piezoelectric dynamometer under a tool holder with an appropriate load amplifier was used for measuring three orthogonal cut-
Figure 1: Measurement of the cutting forces and a schematic figure of the dynamometer unit
Slika 1: Merjenje sil pri rezanju in shematski prikaz dinamometrske enote
2.3 Cutting Parameters, Cutting Tool and Tool Holder
The cutting speeds (50, 65, 80, and 100) m/min were chosen by taking into consideration the ISO 3685 standard, as recommended by the manufacturers. The depth of the cut (1.5 mm) and the constant feed rate (0.10-0.15 mm/r) were chosen to be constant. During the cutting process, the machining tests were conducted with three different cemented-carbide tools, i.e., Physical Vapour Deposition (PVD) coated with TiN/TiCN/TiN; Chemical Vapour Deposition (CVD) coated with TiN+AL2O3-TiCN+TiN; and WC/CO. The dimensions of the test specimens were 2 x 40 inches in terms of diameter and length. The properties of the cutting tools and the level of the independent variables are given in Tables 4 and 5. Surtrasonic 3-P measuring equipment was used for the measurement of the surface roughness. The measurement processes were carried out with three replications. For measuring the surface roughness on the workpiece during machining, the cut-off and sampling length were considered as 0.8 mm and 2.5 mm, respectively. The ambient temperature was (20 ± 1) °C. The resultant cutting force was calculated to evaluate the machining performance. The following are the details of the tool geometry CNMG inserts when mounted on the tool holder: (a) CnMG shape; (b) axial rake angle, 6°;
Table 4: Properties of the cutting tools Tabela 4: Lastnosti rezilnih orodij
Coating material (top layer)
Coating method and layers
ISO grade of material _(grade)_
Geometric form
Manufacturer and code
Variables	Level of variables			
	Lower	Low	Medium	High
Cutting speed, v/(m/min)	50	65	80	100
Feed, f/(mm/r)	0.1-0.15	0.1-0.15	0.1-0.15	0.1-0.15
Axial depth, da/mm	1.5	1.5	1.5	1.5
CVD (TiN, Al2O3, TiCN, TiN, WC)
P25-40, M20-30
CNMG120404RP
Kennametal KC9240
PVD (TiN, TiCN, TiN, WC)
P25-40, M20-30
CNMG120404FN
Kennametal KT315
P25-40, M20-30
CNMG120404MS
Kennametal K313
(c) end relief angle, 5°; and (d) sharp cutting edge. The cutting tool was mounted in the tool holder (PCLNR 2525M12) and used for such cutting tools (CNMG 120404) with an approach angle of 75°. Analysis of variance (ANOVA) was applied to the experimental study.
Table 5: Level of independent variables Tabela 5: Nivoji neodvisnih spremenljivk
Variables
Cutting speed, v/(m/min)
Feed, //(mm/r)
Axial depth, da/mm
Level of variables
Lower
50
0.1-0.15
1 5
Low
65
0.1-0.15
1.5
Medium
80
0.1-0.15
1.5
High
100
0.1-0.15
1.5
3 RESULTS AND DISCUSSION 3.1 Cutting forces ai^^ s^^^ace ro^gh^ness
After the test specimens were prepared for experimental purposes, they were measured with a three-component piezoelectric dynamometer to obtain the main cutting force. According to Figure 2, increasing the cutting speed decreases the main cutting force, excluding the area between 80 m/min and 100 m/min for K313. The lowest obtained values for the main cutting force at the cutting speeds of 50 m/min, 662 N, 65 m/min, 622 N, 80 m/min, 601 N, and 100 m/min, 538 N at a 0.1 mm/r constant feed rate, respectively. The lowest main cutting force was observed at 100 m/min cutting speed as 538 N. In Figure 2 the main cutting force depending on the cutting speed and the uncoating material of the cutting tool were changed in all the experiments. The cutting forces and surface roughness according to the experimental cutting parameters are given in Table 6. According to W. Konig, the cutting speed must be increased in order to reduce the main cutting forces.13 However, in this study, a decrease was observed in the main cutting force between 50 m/min and 100 m/min. It is thought that this case is caused by the good performance of the cutting tool. The effect of the TiN-coated carbide inserts was found to be important for the main cutting force, but the effect of the cutting speeds was not important in the analysis of variance. The main cutting force decreases in spite of increasing the cutting speed from 50 m/min to 100 m/min. As a result of the experimental data, an increase of 100 % in the cutting speed (from 50 m/min to 100 m/min), a decrease in the main cutting force with
K313 (6.5 %), KT315 (10 %) and KC9240 (19 %) was found with the 0.1 mm/r constant feed rate, and the decreasing contact surface area caused the main cutting force to decrease in comparison to the increased cutting speed. The decrement of the cutting force depends on the material type, the working conditions and the cutting speed range.14 The high temperature for the flow region and the decreasing contact area and chip thickness cause the cutting force to decrease, depending on the cutting speed.15
As is widely known, the cutting speed must be decreased to improve the average surface roughness.16 The scatter plot between the surface roughness and the cutting speed as shown in Figure 3 indicated that there was a linear relationship between the surface roughness and the cutting speed. The results of Figure 3 show that the average surface roughness decreases by 66 % with an increasing cutting speed from 50 m/min to 100 m/min
Figure 2: Change of main cutting force in Hastelloy X, according to the cutting speed: a) at f = 0.1 mm/r, b) at f = 0.15 mm/r Slika 2: Spreminjanje glavne sile rezanja materiala Hastelloy X pri hitrostih rezanja: a) f = 0,1 mm/r in b) f = 0,15 mm/r
nt e mr ie	ol to g in ut C	ed e p s	te rat)	ut o pthm) e	Fx/N	Fy /N	Fz /N	^a/um
1	K313	65	0.1		366	75	6Q1	1.7
2	K313	80	0.1		323	67	655	1.5QQ
3	K313	100	0.1		316	72	658	1.717
4	KT315	65	0.1		2Q5	132	622	1.605
5	KT315	80	0.1		281	130	601	1.41
6	KT315	100	0.1		277	130	5Q8	1.667
7	KCQ240	65	0.1		446	203	715	1.455
8	KCQ240	80	0.1		441	184	6Q4	1.368
Q	KCQ240	100	0.1		3Q3	158	538	0.755
10	K313	65	0.15		3Q8	Q6	Q1Q	3.64Q
11	K313	80	0.15		371	Q0	Q01	3.462
12	K313	100	0.15		325	78	854	3.137
13	KT315	65	0.15		358	177	863	2.66Q
14	KT315	80	0.15		356	17Q	855	1.88
15	KT315	100	0.15		335	177	830	3.132
16	KCQ240	65	0.15		527	272	Q66	1.4Q2
17	KCQ240	80	0.15		446	187	6Q6	1.405
18	KCQ240	100	0.15		436	1Q5	6Q7	1.085
Figure 3: According to cutting speed the change of the average surface roughness in Hastelloy X: a) at f = 0.1 mm/r, b) at f = 0.15 mm/r
Slika 3: Spreminjanje povpre~ne hrapavosti Hastelloya X od hitrosti rezanja: a) pri f = 0,1 mm/r in b) pri f = 0,15 mm/r
Table 6: Cutting forces and surface roughness according to the experimental cutting parameters when turning Hastelloy X Tabela 6: Sile rezanja in hrapavost povr{ine pri ustreznih parametrih poskusa rezanja pri struženju Hastelloy X
C
o
a ^
.3 ro g
1
10
11
12
13
14
15
16
17
18
13
n
:3
C )
K313
K313
K313
KT315
KT315
KT315
KCQ240
KCQ240
KCQ240
K313
K313
K313
KT315
KT315
KT315
KCQ240
KCQ240
KCQ240
13
o a
65
80
100
65
80
100
65
80
100
65
80
100
65
80
100
65
80
100

0 1
0.1
0.1
0 1
0 1
0.1
0.1
0 1
0 1
0 15
0 15
0 15
0 15
0 15
0 15
0 15
0 15
0 15
ßi S
^ /N
366
323
316
2Q5
281
277
446
441
3Q3
3Q8
371
325
358
356
335
527
446
436
Fy /N
75
67
72
132
130
130
203
184
158
Q6
Q0
78
177
17Q
177
272
187
1Q5
Fz /N
^a/um
6Q1
655
658
622
601
5Q8
715
6Q4
538
Q1Q
Q01
854
863
855
830
Q66
6Q6
6Q7
1 7
1. 5QQ
1. 717
1 605
1 41
1 667
1 455
1 368
0 755
3 64Q
3 462
3 137
2 66Q
1 8
3 132
1 4Q2
1 405
1 085
with the KCQ240 cutting tool (0 .1 mm/r constant feed rate) .
3.2 Optimization with the Taguchi Method
In this part the optimization of the turning parameters was carried out in terms of the cutting forces with the Taguchi analysis The importance order of the effects of each control factor on the turning forces was identified For this purpose, the factors selected in the Taguchi experimental design and the levels of these factors are shown in Table 7 . Taguchi's L18 2*1 3*2 mixed design was used. In the Taguchi method there are three categories, i.e., "the smallest is better", "the biggest is better" and "the nominal is better" for the calculation of the signal/noise (S/N) ratio. In this research "smallest is better" was used since the minimum of the cutting force and surface roughness was intended. In the ;th experiment, the S/N ratio can be calculated using the following equation.17-1'
1 ^ 2
rj i =-10log1„ -1 Fi^
(1)
n is the number of replications and Yi is the measured characteristic.
Table 7: Cutting parameters and levels Tabela 7: Parametri rezanja in nivoji
Control parameters
Feed rate
(A)
Cutting speed (B)
Cutting tool
(C)
Units
m/min
(mm/r)
Levels
65
0.1
KC313
o
80
0.L5
KT3L5
100
KCQ240
3.3 Confirmation Experiments
The final step of the Taguchi experimental design process includes confirmation experiments.18,1® To achieve this, the results of the experiments were compared with the predicted values using the Taguchi method and the error rates were obtained. The S/N ratios were predicted using the following model:18-20
k
r pred = r „ (r - r „)
(2)
Moreover, the optimum turning parameters were obtained for the performance characteristics using the Taguchi analysis, where m is the total mean of the S/N ratios, i is the mean S/N ratio at the optimum level and k is the number of the main design parameters that significantly affect the performance characteristics. After predicting the S/N ratios other than 18 experiments (with Eq.2), the main cutting force or Fz was calculated using the following equation:20
Ypred =10 20
(3)
2
3
4
6

1
a
Q

where Fpred is the main cutting force or Fz with regard to the S/N ratio.
3.4 Taguchi Analysis for FZ
Figure 4 shows the main effect plot for the S/N ratios, giving the effect of cutting parameters on the cutting force Fz. The smallest main cutting force is obtained with the cutting insert KT315. In this way, to achieve the minimum cutting forces it is understood that the KC9240 cutting tool should be used at a 0.10 mm/r feed rate and 100 m/min cutting speed.
After analysing the effect of the cutting parameters on the cutting force, in order to find out which Fz cutting force it effected, a variance analysis was made. According to the results of the ANOVA in Table 8, it is understood that the most effective cutting parameters that effected the cutting force was 65.99 % and the cutting speed was 11.14 %.
Table 8: ANOVA results for Fz Tabela 8: ANOVA-rezultati za Fz
Main Effects Plot for SN ratios
Source	DF	Sum of squares	Mean square	F	Prob > F	Distribution %
A	1	181805	181805	57.75	0.002	65.99
B	2	30700	15350	4.88	0.085	11.14
C	2	13213	6607	2.1	0.238	4.80
A*B	2	4024	2012	0.64	0.574	1.46
B*C	2	9391	4696	1.49	0.328	3.41
A*C	4	23792	5948	1.89	0.276	8.64
Error	4	12592	3148			4.57
Total	17	275517				100.00
3.5 Taguchi Analysis for Ra
Figure 5 shows the effect of feed rate, cutting speed and cutting-tool material on the average surface roughness. According to this figure, in order to obtain the smallest surface roughness, it is necessary to use the KC9240 cutting tool at a low feed rate (0.10 mm/r) and a
Main Effects Plot for SN ratios
Data Hsans
	56
	-57
3	
!	■58
I	
□	
rflttf. [mm/reu.)	_Cutting SoeeJ [m/min.l
	
\	
0,10 0,15	fiS 80 iOO
riiHingTnnl	
	
	
K313	KC92« KTSIS Signal-to-noiss; Smaller Is better
Figure 4: Mean response graphs of the cutting forces according to the feed rate, cutting speed and cutting tool
Slika 4: Prikaz odziva sil rezanja glede na hitrost podajanja, hitrost rezanja in rezilnega orodja
I
i:
1
i'
-6
	_riiTTirto _
	
\	
0,10 0,15	W so JOO
Cjninc tool	
	
/ S	
ion KC9240 Signsl-to-noise: Smaller is better
»rnis
Figure 5: Mean response graphs of the surface roughness according to feed rate, cutting speed and cutting tool
Slika 5: Prikaz odziva hrapavosti povr{ine glede na hitrost podajanja, hitrost rezanja in rezilnega orodja
high cutting speed (100 m/min). Besides this, in order to find out which important parameter affects the surface the roughness, the variance analysis was made with this aim. According to the results of the ANOVA in Table 9, the cutting parameters which effect the surface roughness, the cutting tool (40.38 %), feed rate, (33.15%) and 15.57 % feed speed and cutting tool's interaction were found.
Table 9: ANOVA results for Ra Tabela 9: ANOVA rezultati za Ra
Source	DF	Sum of squares	Mean square	F	Prob > F	Distribution %
A	1	4.1424	4.1424	56.56	0.002	33.15
B	2	0.18817	0.09408	1.28	0.371	1.51
C	2	5.04646	2.52323	34.45	0.003	40.38
A*	2	0.06687	0.03343	0.46	0.663	0.54
B*C	2	0.81483	0.20371	2.78	0.173	6.52
A*C	4	1.94611	0.97305	13.29	0.017	15.57
Error	4	0.29294	0.07323			2.34
Total	17	12.49777				100.00
4 CONCLUSIONS
The goal of this study was to identify the effect of turning parameters such as feed rate, cutting speed and cutting tools on the main cutting force and surface roughness using an analysis of Taguchi. The experimental design described here was used to develop the main cutting force and the surface-roughness prediction model for the Hastelloy X turning operation. The results of this experimental study can be summarized as follows:
•	The main cutting force decreased with increasing cutting speed and the cutting force increased at higher feed rates.
•	According to the analysis of Taguchi, in order to obtain the smallest cutting force and surface roughness, it was necessary to use the KC9240 cutting tool
at a low feed rate (0.10 mm/r) and a high cutting speed (100 m/min).
•	The minimum main cutting force is obtained with CNMG 120404-type multicoated TiN+AL2O3-TiCN+ TiN carbide tools, while the maximum main cutting force is obtained as 965 N with the CNMG 120404-type uncoated carbide tools. However, cemented carbide tools have no significant effect on the main cutting force when machining Hastelloy X.
•	An increasing relation between the cutting speed and the arithmetic average surface roughness as well as between the coating number and the average surface roughness is observed.
•	In the case of coated tools, the effect of cutting speed on the surface roughness is no more pronounced than the effect of uncoated cemented-carbide inserts.
•	The minimum average surface roughness is determined with CNMG 120404-type multicoated TiN+ AL2O3-TiCN+TiN carbide tools, while the maximum average surface roughness is observed with CNMG 120404-type uncoated tools. Moreover, uncoated and multiple-layer coated tools have a significantly different effect on the average surface roughness.
•	It was found that there is a positive correlation between the main cutting force and the average surface roughness.
Acknowledgments
The authors would like to express their gratitude to the University of Yuzuncu Yil for the financial support Under Project No. BAP 2012-BYO-013.
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