Elsevier Editorial System(tm) for Materials and Design Manuscript Draft Manuscript Number: Title: CUTTING FORCES IN TURNING OF GRAY CAST IRON USING SILICON NITRIDE BASE CUTTING TOOL Article Type: Original Paper Keywords: Silicon nitride, Cutting force, Gray cast iron. Corresponding Author: José Vitor Candido Souza, Ph. Corresponding Author's Institution: Instituto Nacional de Pesquisas Espaciais (INPE) First Author: José Vitor Candido Souza, Ph. Order of Authors: José Vitor Candido Souza, Ph.; Maria do Carmo Nono, PhD; Claudio Augusto Kelly, PhD; Marcos Valério Ribeiro, PhD; Olivério Moreira de Macedo Silva, PhD Abstract: This paper present the results of an experimental investigation on the effect of cutting forces on turning gray cast iron with silicon nitride (Si3N4) based ceramic tool. Turning experiments were carried out at five different cutting speeds and feed rates with depth of cut was kept constant. Tool performance was evaluated with respect to tool wear, temperature, surface finish produced and cutting forces generated during turning. The Si3N4 based ceramic cutting tool showed highter performance to increase cutting speed. These results can be associeted at good high temperature strength and contains graphite flakes in grey cast iron.
INPE - INSTITUTO NACIONAL DE PESQUISAS ESPACIAIS
S.J.Campos-SP, January, 16, 2007. Av. dos Astronautas,1.758 Jd. Granja CEP 12245-970 São José dos Campos - SP - Brasil Tel: 55-12-3945-6679 3945-6989 Fax: 55-12-3945-6717 To: Editor-in-Chief:
Professor K.L. Edwards
School of Engineering
University of Derby
Kedleston Road
Derby
DE22 1GB
UK Ref.: Submission of Manuscript to Materials & Design
Dear Professor Edwards,
We are pleased to submit our paper entitled “CUTTING FORCES IN TURNING OF
GRAY CAST IRON USING SILICON NITRIDE BASE CUTTING TOOL” for your
considerations. This is an original contribution for publication at Materials & Design.
My address for further correspondence is the following:
Prof. Dr. José Vitor C. de Souza
Av. dos Astronautas.1758,Jd. Granja – CEP: 12227-010 São José dos Campos –
SP.Brasil. Tel: 55 (12) 3945-6000 or 55-12-3945-6679
e-mail: [email protected]
Thank you once more for your attention.
sincerely yours,
José Vítor Cândido de Souza
Cover Letter
CUTTING FORCES IN TURNING OF GRAY CAST IRON USING SILICON NITRIDE BASE CUTTING TOOL
J.V.C. Souza1, M. C.A. Nono1, C. A. Kelly2 M. V.Ribeiro3, O.M.M. Silva4
1INPE - Av. dos Astronautas,1.758, S. J. Campo s - SP, CEP. 12245-970, Brazil
2FAENQUIL-DEMAR – Polo Urbo Industrial, Gleba AI-6, s/n, Lorena - SP, CEP. 12600-000, Brazil
3FEG-UNESP – Av.Ariberto Ferreira da Cunha, 333, Guaratinguetá – SP, CEP. 12516-410, Brazi
4CTA-IAE/AMR - Pça. Marechal do Ar Eduardo Gomes, 50, S. J. Campo s - SP, CEP. 12228-904, Brazil
[email protected] / [email protected]
Abstract
This paper present the results of an experimental investigation on the effect of
cutting forces on turning gray cast iron with silicon nitride (Si3N4) based ceramic tool.
Turning experiments were carried out at five different cutting speeds and feed rates with
depth of cut was kept constant. Tool performance was evaluated with respect to tool
wear, temperature, surface finish produced and cutting forces generated during turning.
The Si3N4 based ceramic cutting tool showed highter performance to increase cutting
speed. These results can be associeted at good high temperature strength and contains
graphite flakes in grey cast iron.
Keywords: Silicon nitride, Cutting force, Gray cast iron.
* Corresponding author. Tel.: +55 (12) 3945-6679, 39456989, FAX: +55 (12) 3945-6717
E-mail address: [email protected] / [email protected] (J.V.C. Souza).
Manuscript
1. Introduction
The term ceramics is applied to a range of inorganic materials of widely varying
uses. Generally these materials are non-metallic and in most cases have been treated at a
high temperature at some stage during manufacture. Ceramics are far less ductile than
metals and tend to fracture immediately when any attempt is made to deform them by
mechanical work [1]. They are often of complex chemical composition and their
structures may also be relatively complex.
Ceramics in recent years have been sought in many applications due to their
improved properties like good thermal shock resistance, good high temperature
strength, creep resistance, low density, high hardness and wear resistance, electrical
resistively, and better chemical resistance [2]. On the negative side, they feature low
ductility and fracture toughness at room temperature and standard pressure so that
fracture will occur once the atomic linkage forces are exceeded [2]. Therefore in
machining test using ceramic materials is a big challenge and quite expensive affair
because of their inherent brittleness. Recent work on the machining of compacted
graphite iron, Souza, 2004 has confirmed that brittleness of cutting tools ceramics can
be a big problem in the quality surface finish [3]. Cutting forces are widely recognized
as an optimum performance estimator of machining operations. Many authors, compiled
in the trend reports by Van Luttervelt et al. [2] and Ehman et al. [4], have addressed
their research work to the prediction and measurement of these forces. Both force
modulus and direction are directly related to different aspects of the removal process,
with a clear influence on the efficiency of the operation and the quality of the machined
part [5].
Thus, cutting force is result of the extreme conditions at the tool-workpiece
interface. This interaction can be directly related to the tool wear and, in the worst of the
cases, to the failure of the tool [6] and [7]. Consequently, tool wear and cutting forces
are related to each other, although that relationship is different for each different wear
mechanism (flank, crater, tool breakage). Cutting forces are also related with chatter and
process instability [7] and [8]. Chatter results in a loss accuracy of machined parts or in
damages of the machines structure.
In order to analyze the different situations that may arise during a machining
operation, in this paper the analysis utility, based on the simultaneous measurement of
the three orthogonal components of the cutting force (Fx, Fy, and Fz, measured with a
dynamometer and the current position of the tool in machining centre, is presented. The
performance of turning tests are a main step for turning optimization of gray cast iron.
In this paper was focus, three case studies will be shown. Process of manufacture
cutting tools, characterization and finally apply in turning tests. However it must be
remarked that the system has been developed only for running machining tests and
diagnostics, since in an industrial environment dynamometric devices such as the one
here used are not applied because of their high cost.
1.2. Machinability of gray cast iron
The presence of graphite particles in gray cast iron, renders this material to have
good machinability by nearly all criteria, especially when compared to steels. Low rates
of tool wear, high rates of metal removal, relatively low cutting forces and power
consumption are the characteristics of cast iron. The surface of the machined cast iron,
however, is rather matt in character. When machining gray cast iron the graphite
particles determine cutting forces and surface roughness while the matrix determines the
tool life [9] and [10].
When a steel part is replaced with ductile iron, better machinability is considered
to be the most important gain. Although there is no definite information in the published
literature that gray cast iron has better machinability than steels, data obtained from
manufacturers like General Motors shows that parts manufactured from gray cast iron
leads to improvement in tool life by 20–900% when compared to the heat treated forged
steels. Very fine surface finishes can be obtained on gray cast iron. For machining gray
cast iron, it is possible to find some practical cutting parameters value from the
machining handbook [11], [12] and [13].
1.3. Surface finish
One of the important parameters in evaluating the performance of a cutting tool is
the surface quality it produces on the machined work piece. It is well known in turning,
the surface quality largely depends upon the accuracy of replication of cutting nose on
the work surface. An ideal tool material is the one which can ensure high fidelity of its
nose replication, thereby ensuring good control over the surface quality [14]. The
advantage of machining using ceramic cutting tools is generally seen in higher levels of
surface finish obtained compared to that of other conventional tools such as cemented
carbides. While dimensional accuracy is controlled by flank wear of the turning tools,
the surface quality largely depends upon the stability of the cutting nose. Therefore the
variation of surface roughness with cutting speed it will be presented in this paper.
1.4. Influence of cutting force in the work material
The ceramic cutting tools have an advantage in the machining of hard work piece
materials. The variation of main cutting force with cutting speed on machining steel
(45HRC) using Ti[C,N] mixed alumina ceramic cutting tool is presented in paper [15].
In this paper it can be noted that the cutting forces of the ceramic cutting tool decrease
with cutting speed. The decrease of cutting force with respect to cutting speed when
using Ti[C,N] mixed alumina ceramic cutting tool shows that this type of ceramic
cutting tool can machine the work piece material with high speed and at low cutting
forces. The lower cutting forces result in a lower distortion of work piece [15], which
improves the surface finish while machining with the ceramic cutting tools.
In general the ceramic cutting tool materials produce good surface finish for
harder work piece materials. The surface finish of the work material improves with
cutting speed. Wuyi Chen et al. reported that surface finish was improved with
increasing cutting speed during machining medium hardened steel using CBN tools
[16]. It was reported that the ceramic tools exhibited superior performance as compared
to the carbide tools, especially at higher machining speeds, both in terms of tool life and
surface finish of the work-piece [17].
2. Materials and experimental procedure
The composition of Si3N4 ceramics were prepared 77.90Si3N4– 4.8Y2O3–
4.80CeO2–10.0AlN– 2.50Al2O3 (in wt.%) was produced and characterization. In this
work, they were produced using powders of α-Si3N4 (H.C. Starck, Germany,
d=3.2 g/cm3), α-Al2O3 (Alcoa Chemicals, Brazil, d=3.98 g/cm3), Y2O3 (H.C. Starck,
d=5.03 g/cm3), CeO2 (H.C. Starck, d=2.70 g/cm3) and AlN (H.C. Starck, d=3.26 g/cm3).
Suspensions comprising 100 g of appropriate powder mixture were prepared. The
suspensions were planetary-milled in an Al2O3 cube (i.e., milling container) for 3 h,
using 250 g of Si3N4 balls of different sizes. The weight loss of the Si3N4 balls and the
cube was always measured. The results indicated that the contamination level
introduced in this stage was <0.2 %. After drying (100 °C, 24 h), the powders were
sieved (100 mesh). Samples (16.36mm x 16.36mmx 7.5mm) were prepared by uniaxial
pressing (50 MPa) following by isostatic pressing (300 MPa, 2 min). The green samples
were embedded in a mixture of powders of Si3N4 and BN (70: 30 weight ratio) inside a
graphite crucible and sintered at 1850 °C for 2 h, in nitrogen atmosphere (0.1 MPa) with
a heating rate of 25 oC/min.
2.2. Characterizations
To remove any possible superficial layer formed at the surface of the samples
during sintering, the sintered samples were rectified and then polished until mirror
finishing at both sides. After cleaning in ultrasonic bath with acetone and then with
distilled water, the samples were stored in an oven of 100 °C to avoid water uptake from
atmospheric humidity.
Relative density of the samples after sintering was determined by Archimedes
method, correlating with the theoretical density of the mixtures. The weight loss was
determined by measurement of weight, before and after sintering. The phase
composition of the sintered samples was determined by X-ray diffraction analysis
(Phillips PW1380/80), using CuKα radiation, slow scanning and 0.02 °/s step. The
microstructures were observed by SEM investigations of polished surface after having
them chemically etched by molten NaOH/KOH mixtures at 500 °C for 5 min.
Hardness was determined by Vickers indentations under a load of 20 N, for 30 s.
Fracture toughness was calculated by the crack length emerging from the indentation
marks, using the equation proposed by Evans and Charles for Palmqvist shaped cracks
[18].
2.3. Cutting performance
All experiments were carried out on a computer numerical control (CNC) lathe
(Romi, Mod. Centur 30D) under dry cutting condition. The ceramic insert were cut and
ground to make SNGN120408 (12.7 mm×12.7 mm, 4.76 mm thickness, 0.08 mm nose
radius and 0.2 mm×20° chamfer) Fig.1.
Figire 1
A tool holder of CSRNR 2525 M 12CEA type (offset shank with 15° [75°] side
cutting edge angle, 0° insert normal clearance and 25 mm×25 mm×150 mm) was used
for the cutting experiments. The cutting performance of the silicon nitride base tools
was tested by machining gray cast iron. The Chemical composition and mechanical
properties of the gray cast iron were given in Table 1.
Table 1
The cutting tests for machining of gray cast iron were performed at a cutting
speed of 180, 240, 300, 360, 420 m/min with a feed rate of 0.12, 0.23, 0.33, 0.40, and
0.50 mm/rev and a constant depth of cut of 1.0 mm. The dimension of work material
was 105 mm in diameter and 300 mm in length. The wear of the tools was determined
by measuring the wear depth on the flank face by using a were measured using a
toolmakers microscope. To complete analysis of tool life was considered at finish
surface (Ra and Ry) using a surface roughness tester (Mitutoyo Surftest 402 series 178)
was adopted and to measure at temperature work-piece/cutting tools was used an
infrared pyrometer. Flank wear of 0.3 mm (ISO 3685) and variation abrupt of Ry has
been used as end tool life criterion. A three-force component analogue dynamometer
capable of measuring cutting forces during turning was utilized in test. A computer
connection for data acquisition was also made and calibrated. The analogue data can be
evaluated numerically on a computer and when required can be converted back to
analogue. A schematic illustration of measured forces is given in Fig. 2 [19].
Figire 2
The machining tests on grey cast iron work piece were chosen because the
ceramics are generally used to machine cast iron [20]. Grey cast iron contains graphite
flakes and it is widely used in the manufacturing industry [21].
3. Results
3.1. Properties of cutting tools
The relative density of the specimens after gas-pressure sintering process
presented values higher than 98.12 ± 0.14 % for this composition, demonstrating that
dense ceramics were obtained. Phase analysis by X-ray diffraction revealed only the
presence of β-Si3N4 indicating that the α-β-Si3N4 transformation has been completed
and, furthermore, that the additives formed an amorphous intergranular phase Fig.3.
Figire 3
The specimen investigated yielded ceramic materials of high hardness, more than
18.65 ± 0.15 GPa and the fracture toughness values are near to 5.96 ± 0.12 MPa m1/2.
These results can be attributed to several factors such as the high relative density, the
complete α-β-Si3N4 transformation, but mainly due to microstructural aspects Fig.4 [22
and 23].
Figire 4
The mass loss during the sintering was about 2.50 % sample. This behavior
demonstrates the viability of using Y2O3–CeO2–AlN–Al2O3 as sintering additive,
promoting important sintering activity for the composition. Thus, the sintering
parameters applied are adequate to produce ceramics cutting tools at high density.
3.2. Variation of machining forces with cutting speed
The variations of machining forces with cutting speed in shown in Fig. 5. It is
seen that after an initial rise, the cutting force component decrease in magnitude as the
cutting speed increases. With low cutting speed, the cutting wedge tends to plow on the
work surface, resulting in higher order cutting force, but as the cutting speed increases,
the cutting becomes more or less steadier, with a consequent reduction in cutting force
component.
Figire 5
From the Fig. 5, it can be seen that the cutting force component was greater than
the thrust force component by a considerable margin. These results were in agreement
Lanna, 2004 and indicate that the material removal has occurred in ductile manner
without fracture thus preventing the occurrence of a brittle material removal [24]. The
effect of variations in operating parameters may be seen in cutting forces and surface
temperatures, but knowledge of what takes place internal to the workpiece is extremely
desirable.
During machining, a considerable amount of temperature rise occurs in the cutting
zone Fig. 6 and 7.
Figire 6
Figire 7
This heat has to be normally dissipated by the work-piece, tool, chip and the
surroundings. But in gray cast iron machining, since the work-piece is a good conductor
of heat, a major portion of the heat developed at the cutting zone has to be dissipated by
the tool and chip. Therefore, the dependence of temperature on cutting speed will exert
a greater influence on the tool performance especially at higher speeds. With lower
order cutting velocity, the cutting wedge of the tool tends to plow on to the work surface
resulting in a marginally higher order force. As the cutting speed increases, the cutting
becomes steadier with a consequent reduction in cutting force components. The
decrease in cutting forces above a cutting velocity of 300 m/min can be attributed to the
possible thermal degradation of the gray cast iron. The other two components of the
machining force, namely, the thrust and feed forces also exhibited a similar trend.
3.3. Variation of machining forces with feed of cut
The effects of the variations of the feed of cut on the machining forces were
studied using the cutting velocity of 300 m/min, and with a tool having a negative rake
angle of 20◦. The variations of machining forces with the variation in feed of cut are
shown in Fig. 8.
Figire 8
All the three components of the machining force are seen to increase with the feed
of cut. The cutting force dominates over the thrust and feed force components clearly
indicating the material removal by plastic deformation.
3.4. Surface roughness
Surface finish was shown to be improved by increasing cutting speed (Fig. 9),
though the improvement was very limited.
Figire 9
Producing a better surface finish at higher cutting speed is not something unusual
in metal cutting [25]. It is observed that the surface finish is not affected by the
increased tool flank wear. In all cutting conditions, the variation of surface finish with
the flank wear is insignificant. The surface roughness values remained almost constant
although the flank wear increased with the increase of time to feed and depth of cut
constant. However, the magnitude of surface roughness is higher for lower cutting
speed. When increase cutting speed and feed rate constant (0.33 mm/rev), surface finish
even improved with the increase of flank wear (Fig. 10).
Figire 10
However in this paper observe that increasing wear of cutting tool improved the
roughness of the workpiece. These results have been common when using ceramic
cutting tools on machining gray cast iron [26].
3.5. Flank wear
Fig. 11 shows the flank wear progression with increasing cutting length for
Vc=300 m/min, feed rate of 0.33 mm/rev and depth of cut was kept constant at 1.0 mm.
Figire 11
Flank wear measurements were taken at an interval of every 1500 m length cut.
With the workpiece diameter of 105 mm and employed depth of cut of 1 mm, when the
tests were stopped when the maximum flank wear value (VBmax) exceeded 0.3 mm. In
this was represent one micrographs of cutting tools that use in machining longer time
because in others conditions flank wear exhibited low and similar wear behaviors at all
cutting speeds Fig. 12. In this Figure can be seen more clearly the average flank wear
(VBmax), in which shows the in Fig. 11 by the corresponding maximum cutting length
(in m).
Figire 12
It is clearly seen that flank wear rate curves is linear with cutting length indicating
that cutting tools have had long life was agreement [19].
4. Conclusions
The results of turning of gray cast iron using silicon nitride base tools were
presented. The effect of cutting speed and feed of cut on machining forces were
analyzed. Studies have indicated that:
1. The Si3N4 based ceramic cutting present important performance in high-speed
turning of gray cast iron. The low wear of the insert suggests that this tool is suitable for
machining gray cast iron.
2. The cutting process becomes more and more stable as the speed increases. The
accommodation during cutting at the highest speed can be better. This might suggest
that high-speed machining is more and more stable for the tool–work–machine system
under consideration, with decrease in the force components up to speed of 300 m/min.
3. As the feed of cut is increases the machining forces also increase.
4. Several it is possible observe that all the two components of the roughness are
seen to decrease with the length of cut.
5. Surface finish of the work part is not influenced by the tool wear. However,
increasing speed, feed or depth of cut does influence the surface finish.
6. The cutting force decreases with increasing cutting speed owing to the high
temperatures generated at the cutting zone. The decrease in the cutting force obtained
with Si3N4 based ceramic cutting tool is more to machining gray cast iron. This, together
with the results obtained for flank wear and surface roughness, indicates that, among
many tools Si3N4 will have the most suitable tool, for turning of gray cast irons at high
cutting speeds.
Acknowledgement
The authors would like to thank for financial support by CAPES and FAPESP.
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Kelly, Torneamento do ferro fundido vermicular utilizando pastilhas cerâmicas à base
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[16] W. Chen, Cutting forces and surface finish when machining medium hardness steel
using CBN tools. Int. J. Mach. Tools Manufact. 40 (2000), pp. 455–466.
[17] A. Chakraborty, K.K. Ray and S.B. Bhaduri, Comparative wear behavior of
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Process. 15 (2000), pp. 269–300.
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List of captions for illustrations
Fig. 1. Photograph of silicon nitride based insert.
Fig. 2. Force components measured in turning tests [26].
Fig. 3. XRD pattern of sintered ceramic cutting tool, using Cu Kα radiation.
Fig. 4. Microstructure of cutting tools.
Fig. 5. Typical variation of machining forces with cutting speed.
Fig. 6. Temperature vs feed to vc = 300m/min.
Fig. 7. Temperature vs cutting speed to f = 0.33mm/rev.
Fig. 8. Forces vs feed to vc = 300m/min.
Fig. 9. Surface roughness vs cutting speed to. f=0.33 mm/rev, ap=1.0 mm.
Fig. 10. Surface roughness vs cutting speed to f=0.33 mm/rev, ap=1.0 mm.
Fig. 11. Flank wear vs cutting length vc = 300m/min, f=0.33 mm/rev, ap=1.0 mm.
Fig. 12. Micrograph of cutting tool after machining to cutting length of 7500m.
List of captions for table
Table 1. Chemical composition and mechanical properties of gray cast iron used for
cutting test (Hick, 2000)
Fig1
Fig2
10 20 30 40 50 60 70 800
100200
300400500
600700
αααααααα αααααααααααα ααααααααααααaaa a aaa
ααααa ββββββββββββ
ββββββββββββ
ββββ
ββββ
ββββ
ββββ
ββββ
ββββ ββββββββββββ
ββββββββ
ββββ
ββββ
ββββ
Inte
nsity
(a.u
)
2θθθθ (0)
ββββ- Si3N4
a- Y3Al5012
αααα-Si3N4
Fig3
2µm
Fig4
-60 0 60 120 180 240 300 360 420 480
0
100
200
300
400
500 Cutting force Thrust force Feed force
Forc
e (N
)
Cutting speed
Fig5
0,0 0,1 0,2 0,3 0,4 0,5-100
0
100
200
300
400
500
600
700
800
Tem
pera
ture
( o C
)
Feed f (mm/rev)
Temperature x Feed to Vc= 300m/min
Fig6
-60 0 60 120 180 240 300 360 420 480-100
0
100
200
300
400
500
600
700
800
Tem
pera
ture
( o C
)
Cutting speed (m/min)
Temperature x Cutting tools to f=0,33mm/rev
Fig7
0,0 0,1 0,2 0,3 0,4 0,5 0,6
0
100
200
300
400
500
600
700
800
Forc
e (N
)
Feed f (mm/rev)
Cutting force Thrust force Feed force
Fig8
-60 0 60 120 180 240 300 360 420 480-0,50,00,51,01,52,02,53,03,54,04,55,0
Rou
ghne
ss R
a ( µµ µµ
m)
Cutting speed Vc (m/min)
Roughness Ra x cutting tools to f=0,33mm/rev
Fig9
-60 0 60 120 180 240 300 360 420 480
0
5
10
15
20
25
30
Rou
ghne
ss R
y ( µµ µµ
m)
Cutting tools Vc (m/min)
Roughness Ry x Cutting tools to f=0,33mm/rev
Fig10
0 1500 3000 4500 6000 7500 90000,000,050,100,150,200,250,300,35
Vc = 300m/min, f=0.33 mm/rev, ap=1.0 mm
Flan
k w
ear
(mm
)
Cutting length (m)
Fig11
1mm
Fig12
Chemical composition of gray cast iron C S P Si Mn Cu Cr Ni Mo 3.04 0.11 0.068 2.58 0.42 0.05 0.07 0.02 0.005
Mechanical Properties Hardness HB 205 Tensile strength MPa 245 Fatigue strength MPa 100
Table1