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Materials Science Forum Vol. 758 (2013) pp 157-164
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/MSF.758.157
Effect of the Cutting Velocity and Heat Treatment on Turning Cutting
Forces of an SMA Cu-Al-Be Alloys
Francisco Valdenor Pereira da Silva1a, José Paulo Vogel2b,
Rodinei Medeiros Gomes1c, Tadeu Antonio de Azevedo Melo1d,
Anna Carla Araujo3e and Silvio de Barros2f
1
Department of Mechanical Engineering, UFPB, João Pessoa/PB 58059-900, Brazil
Department of Mechanical Engineering, CEFET/RJ, Rio de janeiro/RJ 20271-110, Brazil
3
Department of Mechanical Engineering, COPPE/UFRJ, Rio de Janeiro/RJ 21941-972, Brazil
2
a
[email protected], [email protected], [email protected],
[email protected], [email protected], [email protected]
d
Keywords: Metal Cutting, Cutting Forces, Shape memory alloy, Cu-Al-Be Alloy
Abstract. This work studies the effect of heat treatment and cutting velocities on machining cutting
forces in turning of a Cu-11.8%Al-0.55%Be shape memory alloys. The heat treatment was
performed to obtain samples with austenite and martensite microstructures. Cutting force was
investigated using a 3-component dynamometer in several revolutions and data were analyzed using
statistic tools. It was found that the resultant forces were higher in quenched alloy due to the
presence of Shape Memory Effect. Chip formation occurred in a shorter time in the sample without
the Shape Memory Effect.
Introduction
Shape memory alloys (SMAs) are materials that have a singular property to return to a
predetermined shape under specific thermomechanical conditions. A SMA workpiece at a
temperature below its final martensite transformation temperature has very low yield strength and
can be deformed easily. However, when heated it undergoes a change in crystal structure to
austenite phase. Additionally at certain temperature range the austenite phase can undergoes a
stress-induced transformation to martensite phase [1,2], a phenomenon that is responsible for the
SMA pseudoelasticity. As metal cutting involves high temperatures and mechanical stress, both
effects, shape memory and pseudo-elasticity, can cause many difficulties to machining these
materials. Some studies have been conducted in machinability of NiTi SMAs. It was found that the
cutting parameters, such as cutting speed and feed rate must be higher than that recommended in the
literature. This is evidenced in turning because of the poor chip breaking and the formation of burrs
which is caused by the high ductility of these materials [3].
Among the SMAs, copper based systems, as CuAlNi and CuAlBe, have been widely explored
for certain application due to their low cost and good properties [4-5]. Studies on the mechanical
properties and energy dissipation capacity of Copper-based alloys have been conducted [6].
The aim of this study is to compare the cutting forces generated during turning of quenched and
unquenched specimens of Cu-11.8%Al-0.55%Be alloys. The cutting forces were investigated for
four different cutting speed conditions.
Material Workpiece Casting
The workpieces for experimental investigation were especially casted with dimensions for
external turning in a regular lathe. Cu-11.8%Al-0.55%Be (wt%) alloy was casted in the permanent
steel mold showed in Fig. 1a. The ingots obtained after this process are shown in Fig. 1b.
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Functional and Structural Materials II
(a)
(b)
Figure 1. Workpiece Casting: (a) Permanent Mold and (b) As-cast specimens.
It is necessary to perform a heat treatment in order to obtain the shape memory effect, as Cu-AlBe alloys have no shape memory after casting. The six specimens obtained were then separated in
two groups: one group, with three workpieces, was heat-treated and the other group was machined
as casted.
The transformation temperatures for the quenched alloy in free stress state are as follow:
austenitic start, As = -28.84°C, austenitic finish, Af = -6.87°C, martensitic start, Ms = -33.63°C, and
martensitic finish, Mf= -54.56°C.
Experimental Setup for Cutting Force Measurements
The two groups described (quenched and not quenched) were submitted to machining
experiments. Before the tests, the specimens were lightly machined in order to have a regular
surface and not to induce thermal effects. Since temperature is an important variable, in order not to
achieve high temperatures, the surface taken has one short passes with 15 mm length. Figure 2a
presents the surface as it stood before testing.
(a)
(b)
Figure 2. Experimental Set-up: (a) Specimen used in the tests and (b) Dynamometer and Force
Components
Cutting forces were taken continuously by using a piezoelectric dynamometer KISTLER model
9257 BA with amplifier 5233A and data acquisition board NI/USB 6221. Acquisition rate of 1kHz
was applied. The signal processing was developed using MATLAB. The components Fx and Fy can
be seen in the scheme presented in Fig. 2b, Fz is oriented in cutting direction, normal to the plane
shown in this Figure.
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The cutting conditions are shown in Table 1 where Vc is the cutting speed, n the spindle speed, ap
the depth of cut, D the external diameter and f the feed per revolution. The design of experiments
considered two factors: one factor with two levels (with and without heat treatment) e the other
factor, Vc is cutting speed with four levels, as shown in Table 2, so 8 different experiments were
developed. Fourteen revolutions were taken as different replicates in order to consider the
experimental variance.
Table 1. Cutting Conditions
Alloy Cu-11.8%Al-0.55%Be
Vc (m/min)
4 levels
n (rpm)
1600
ap (mm)
0.50
D (mm)
30
f (mm/rev)
0.109
Table 2. Design of Experiments
Levels
135.72
140.74
145.77
Quenched
Not quenched
-
Variable
Vc (m/min)
Heat Treatment
150.79
-
Results and Discussions
In Fig. 3 it is shown the complete signals taken (14 revolutions) with Vc=150.79 m/min in a
quenched workpiece (Fig. 3a) and no quenched workpiece (Fig. 3b). It was subtracted the effects of
noise, through programmable logic suitable for both specimens.
Experimental Forces in experiment
Alloy: Cu-11,8%Al-0,55%Be quenched
300
Fz
Fy
250
Fx
Forces (N)
200
150
100
50
0
0
0.5
1
1.5
2
Time (s)
(a)
2.5
3
3.5
4
160
Functional and Structural Materials II
Experimental Forces in experiment
Alloy: Cu-11,8%Al-0,55%Be No quenched
250
Fz
Fy
200
Fx
Forces (N)
150
100
50
0
-50
0
0.5
1
1.5
2
Time (s)
2.5
3
3.5
4
(b)
Figure 3. Forces Results from experiments using Vc=150 m/min: : (a) Quenched Workpiece and (b)
No-quenched Workpiece.
Resultant force was calculated for all tests and 10 revolutions were analyzed to calculate the
maximum resultant force for each revolution, the average resultant for on each revolution, and the
peak-to-peak value. The results are shown graphically in Fig. 4 for the samples unquenched and
quenched, for all cutting speed levels. Numerically, their values are shown in Table 3.
Table 3. Resultant force by rotating piece: maximum, average and peak to peak to Cu-11.8%Al0.55%Be alloy – quenched and no quenched.
Resultant Force [N] – Cu-11.8%Al-0.55%Be Alloy
Maximum
Average
Peak-to-Peak
Vc
(m/min)
No-Quenched
Quenched
No-Quenched
Quenched
No-Quenched
Quenched
135
140
145
150
343.06
312.68
316.49
284.93
370.81
339.21
335.45
325.49
314.33
284.70
288.99
253.27
339.34
307.60
303.02
267.48
74.41
66.66
67.30
70.65
64.14
65.24
72.74
113.15
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(b)
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Functional and Structural Materials II
(c)
(d)
Figure 4. (a), (b), (c) and (d) – Results for quenched and no quenched in 10 workpiece revolutions
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Even with the ease of induction of martensite, to the case of the quenched sample, the forces
obtained during its machining started at room temperature were higher than those of sample not
quenched. Generally the resultant forces were greater for the quenched specimen than for the not
quenched one.
ANOVA analysis with two factors was applied to all results: quenched, No quenched and the
four levels of cutting velocity in the three output results (Fmax, Fmean and Fpeak-to-peak). Fig. 5 presents
the effect of cutting velocity for quenched tests (in left side) and without heat treatment (in right
side). Vertical bars represent 95% interval of confidence, F-test(9, 170, 51)= 13,332 corresponding
to p=0,00000. It is well known that cutting velocity enhance the cutting temperature. The forces
decrease with the increase of cutting velocity. Peak-to-peak forces increase only in quenched in
higher cutting velocity that can be related to phase change.
Figure 5. Effect of Cutting Velocity in Quenched (+1) and No Quenched (-1)
Tests using 95% C.I. and F(9, 170, 51)=13,332 corresponding to p=0,00000.
Fig. 6 presents the effect of Heat Treatment (Quenched =1 and No Quenched =-1) on Maximum
and Average Resultant Forces using all cutting velocities. The interval of confidence was 95% C.I.
and F-test with (3, 70) results 264,23 corresponding to p=0,00000. It confirms that the heat
treatment increases both: maximum force and mean force.
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Functional and Structural Materials II
Figure 6. Effect of Heat Treatment (Quenched =1 and No Quenched =-1) on Maximum and
Average Resultant Forces using 95% C.I. and F(3, 70)= 264,23 corresponding to p=0,00000.
Conclusions
In this paper the cutting forces generated during turning of quenched and unquenched specimens
of Cu-11.8%Al-0.55%Be alloys were investigated. Four different cutting speed levels were used to
study these forces.
The resultant forces obtained during machining of quenched samples were higher than those of
unquenched alloy. This fact can be explained by the presence of Shape Memory Effect.
Acknowledgements
The authors acknowledge the technicians Jackson da Silva Farias Brito and Ieverton Caiandre
Andrade for his contributions to the development of this work and the “Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior-CAPES”.
References
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