Dry high speed milling of nickel-based superalloy/Nikelio superlydinio sausasis greitasis frezavimas.
Benghersallah, M. ; Boulanouar, L. ; Lecoz, G. 等
1. Introduction
Nickel-based superalloys are widely employed in the aerospace
industry, in particular in the hot sections of gas turbine engines, due
to their high-temperature strength and high corrosion resistance. They
are known to be among the most difficult-to-cut materials. Attention is
focussed on the Inconel 718 family in the following paragraphs [1-2]. A
major part of their strength is maintained during machining due to their
high-temperature properties. They are very strain rate sensitive and
readily works harden, causing further tool wear. The highly abrasive
carbide particles contained in the microstructure cause abrasive wear
and the poor thermal conductivity leads to high cutting temperatures up
to 1200[degrees]C at the rake face [3]. Nickel-based superalloys have
high chemical affinity for many tool materials leading to diffusion wear
also the welding and adhesion of nickel alloys onto the cutting tool
frequently occur during machining causing severe notching as well as
alteration of the tool rake face due to the consequent pull-out of the
tool materials. Due to their high strength, the cutting forces attain
high values, excite the machine tool system and may generate vibrations
which compromise the surface quality. The difficulty of machining
resolves itself into two basic problems: short tool life and severe
surface abuse of machined workpiece [4, 5]. The heat generation and the
plastic deformation induced during machining affect the machined
surface. The heat generated usually alters the microstructure of the
alloy and induces residual stresses. Residual stresses are also produced
by plastic deformation without heat. Heat and deformation generate
cracks and microstructural changes, as well as large microhardness
variations [6]. Residual stresses have consequences on the mechanical
behaviour, especially on the fatigue life of the workpieces [7, 8].
Residual stresses are also responsible for the dimensional instability
phenomenon of the parts which can lead to important difficulties during
assembly [9, 10]. Extreme care must be taken therefore to ensure the
surface integrity of the component during machining. Most of the major
parameters including the choice of tool and coating materials, tool
geometry, machining method, cutting speed, feed rate, depth of cut,
lubrication, must be controlled in order to achieve adequate tool lives
and surface integrity of the machined surface [6, 8].
In this study we are testing the performance of cutting inserts
with coatings based on (TiN, TiCN, TiA1N, A1TiN). The determination of
the milling system which consumes less power. The study of modes of wear
and morphology during dry machining of Inconel 718 [11].
2. Experimental procedure
2.1. Workpiece materials/tool and equipments
2.1.1. Worked materials
The workpiece material used was a rectangular block of Inconel 718
superalloy (220x120x120 mm) with a nominal chemical composition
referenced Table 1.
2.1.2. Cutting tool
Down milling operations were performed, the cutting tool was an end
mill of 16 mm diameter with two carbide inserts SandvikCoromant R390 and
presented on Fig. 1.
[FIGURE 1 OMITTED]
Fig. 1 a) milling cutter Coromill 390 and b) insert geometry
[Sandvik coromant]
Machining tests are conducted by down milling mode presented on
Fig. 2.
[FIGURE 2 OMITTED]
The tree commercial coatings were used on carbide compositions are
referenced on Table 2.
Machining tests were realised on a High Speed Machine Roders RP600
instrumented with power controllers Wattpilote[TM] developed by the
society DIGITAL WAY. These controllers allow to record the spindle and
the feed motors power consumptions. Power controllers are usually
employed to monitor the tool wear and tool breakage. To discuss about
the tool wear phenomenon, it is necessary to observe, to measure and to
quantify it. Two machines are used.
The optical microscope TESA and it software TESA VISIO is used to
observe the tool wear evolution along the cutting tests. It permits to
determinate the tool life. The qualification criterion is the
degradation of the tetragonal insertions. Classically, in industry, it
is considered that acuity tool is degraded after a clearance wear of 0.3
mm [12]. This criterion is used to determinate the test end.
A Veeco NT1100 (Wyko[R]) Optical Profiler, using the white light
interferometry technique presented by Devillez et al [12] is employed to
monitor cutting parameters and to generate 3D images of the wear
patterns of the cutting tools. This technique was also used with the
same objectives [12].
Surface roughness Ra was measured using a portable Mitutoyo Surf
Test 301.
2.1.3. Identification of optimum cutting conditions
Strategy of experiments.
Machining lengths of 220 mm with C1 insert to determine the cutting
conditions to evaluate during the characterization study.
The results of the first tests allow us to choose the following
conditions cutting. Thus, three will be tested-coatings, TiN, TiCN,
TiA1N and nanocristalin coating A1TiN. Three cutting speeds for having
given in phase 01 of good results, 50, 80 and 130 m/min to go beyond
what has already been achieved in other studies. Feed per tooth fz are
0.05 and 0.1 mm/t, chosen not to ramp up and cause vibrations.
2.2. Study of type of wear and surface roughness
The second phase relates to the study of flank wear of inserts and
surface roughness of machined work piece and power evolution. The
experimental design adopted for studying the effect of three cutting
speed and two feed per tooth values.
3. Results and discussion
Three areas of investigation are studies to characterize the
machinability of nickel based superalloy (Inconel 718). In dry high
speed milling with multilayer coated carbide inserts, first axis is the
monitoring of flank wear Vbmax average cutting time. Second axis is a
measure of the roughness Ra of machined surface and its evolution with
cutting time. The third axis is the reports in real time the spindle
power consumed to determine the best machining conditions with minimum
power consumption.
3.1. Evolution of flank wear Vbmax for the tree inserts testing
The first test is made according to the following conditions: Figs.
3-8 show the curves of the flank wear
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
[FIGURE 8 OMITTED]
Vbmax depending on the machining time Tm. Each curve represents a
test insert and cutting conditions.
Processing results from wear and records the values of roughness
have obtained the following Table 5.
Evolution of tool life T, min for the tree inserts testing
according the adopted cutting conditions.
[FIGURE 9 OMITTED]
Fig. 9 Dependence tool life T on cutting speed Vc and feed per
tooth fz for the three inserts tested
For all tests, the best tool life was obtained by cutting the
insert C2. Increasing the cutting speed decreases tool life. It is the
same for the feed rate per tooth of the cutter. For the regime (Vc = 50
m/min, fz = 0.1 mm/t) results are better than those obtained with the
feed per tooth (0.05 mm/t) for C1 and C2 inserts. The C3 coated insert
(A1TiN nanocrystalline) did not give good results compared to the other
two tested inserts.
[FIGURE 10 OMITTED]
The best results of roughness are obtained with insert C2. The
value of the smallest roughness is achieved with the cutting regime (Vc
= 80 m/min; fz = 0.05 mm/t) by the C2 insert. The poorer surface
roughness was obtained by the C1 insert.
3.3. Evolution of spindle power consumption
Watt pilot sensors are enabled; we can get the evolution of the
spindle power according to the machining time. For all tests milling
spindle power shave been identified. We show the values obtained for the
following conditions (Vc = 80 m/min, fz = 0.1 mm/t, ap = 0.5 mm) and (Vc
= 130 m/min, fz = 0.05 mm/t, ap = 0 5 mm) because the results are
significant for both cutting conditions; Fig. 11, show the dependence of
spindle power evolution on the machining time for three inserts testing.
For regime (Vc = 80 m/min, fz = 0.1 mm/t), we notice that the spindle
power decreases. This is mainly due to the efficient flow of chips and
very favorable cutting conditions. There was not a strong adhesion of
the chip.
[FIGURE 11 OMITTED]
[FIGURE 12 OMITTED]
For regime (Vc = 130 m/min; fz = 0.05 mm/t, ap = 0.5 mm; ae = 8 mm)
we notice an increase in spindle power at the end of machining; this is
because of the wear inserts. Cutting speed has reduced the tool life of
the inserts. The insert C2 gave the best results. The values of the
roughness of the machined surface are low. The best roughness is
obtained with the C2 insert.
The roughness value decreases during the running-phase of edge
inserts. A small groove is formed by wear, it acts as a scraper, which
improves the surface finish. Subsequently, the roughness increases to
exceed the originally recorded at the beginning.
For the cutting speed Vc = 130 m/min, for inserts C1 and C3 the
value of the roughness starts decreasing and then increasing with the
wear evolution of the sharp edge of plates. This is not the case for the
C2 insert where the roughness increases with machining. The graph of
tool life inserts shows that the C2 insert registered the largest
cutting performance. Tool life for C1 inserts has similar values, for C3
insert the tool life has decreased for speed Vc = 130 m/min. Tool life
for this insert is very low to be used in industrial applications.
4. Morphological investigation of wear inserts
Fig. 13 show the wear morphology of the C2 inserts tested. Picture
of wear have been taken by video microscope for following cuttings
conditions: (Vc = 80 m/min; fz = 0.1 mm/t; ap = 0.5 mm; ae = 8 mm).
Pictures 1, 2, 3, 4 shows the progression of wear on the rake face and
flank face after (1, 4, 7, 9 min) cutting time.
[FIGURE 13 OMITTED]
In Fig. 13 we show the different wear caused by friction and
adhesion of the chip. On the picture number 4 we see the breakdown of
the spout of the insert. For the other inserts wear occurs in the same
way but with a higher speed, especially for the insertC1.
5. Conclusion
The experimental study permits to conclude about the machinability
of ainconel 718 superalloy.
1. Machinability of this material is hard.
2. The responsible of the major wear is due to its superior
properties which conduce to a notch and a cutting face chipping.
3. Thus, the cutting inserts for milling have different kinds of
wears: a progressive wear of the flank face characterised by a notch of
the part in contact with the top part; and a severe chipping in the
cutting face.
4. During the high speed machining of hard metals characterised by
a hard machinability, it is recommended to reduce the admissible flank
wear criteria Vbmax to [Vb] = 0.2 mm.
5. The chipping, by it length and it depth can be another criteria
to considerate. The experiment allows to say that the most appropriate
cutting speed in term of cutting forces is 130 m/min but with a cutting
speed of 80 m/min, the tool life begin acceptable. Moreover, the coating
C2 is the most efficient with high speed and dry cutting conditions.
6. Practically, the study has confirmed that the implementation of
the Wattpilote system to the Roders RP600 for the machining control is
efficient. It gives the opportunity to follow the evolution of the
cutting process in term of power. Power curves of X, Y and especially Z
axes are in phase with the wear curves. The power improving during the
milling process is probably linked to the tool wear. Theoretically, it
is possible to follow and to control the inserts wear with the power
help. The methodology adopted for the tests and the criteria considered
to quantify the parameters integrated in the process give a
qualification of the tool without incertitude.
7. Thus, two inserts have been awarded with the aim of industrial
applications and the coating C2 has proved it particular effectiveness
for hard metal machining.
8. The future prospects can be resumed to resolve the problem of
the fast coating pull out of the cutting face, it is necessary to
develop, on another study, the phenomenon of the chip adhesion and the
coating properties. Thus, a local lubrication on the cutting face by an
air blow mixed with a freeze and lubricant properties liquid could
improve the results.
http://dx.doi.org/ 10.5755/j01.mech.19.2.4149
Received Mai 31, 2011 Accepted February 11, 2013
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M. Benghersallah *, L. Boulanouar *, G. Lecoz **, D. Dudzinski **
* Laboratoire de recherche entechnologie avancee etproduction
mecanique (LRTAPM); Universite Badji Mokhtar Annaba BP12 23000, Annaba;
Algeria, E-mail:Bengher_moh@yahoo.fr
** Laboratoire de Physique et Mecanique des Materiaux UMR CNRS
7554, ISGMP-Batiment C, Ile du Saulcy, 57045 METZ, Cedex 01, France
Table 1
Chemical composition (in weight percent)
Ni Fe Cr Nb Mo Ti Al Ti+Al Ti
Nb Al
52.58 20.06 20.10 3.20 1.79 1.13 1.14 0.71 0.99
Table 2
Commercial coatings inserts testing
C1 Fine grain bicarbide rich in cobalt
Multilayer TiN+TiCN, Chemical vapour deposed (CVD)
C2 Fine grain bicarbide High toughness Multilayer
TiN+TiCN+TiAlN, Physical vapour deposed (PVD)
C3 Midle grain carbide AlTiNnanocrystalline, (PVD)
Table 3
Selected conditions of the study
Vc fz ap ae Remarks
35 0.05 0.5 8 Pronounced wear and vibration
35 0.1 0.5 8 Low vibration and temperature rise
50 0.05 0.5 8 Vibration and ship adhesion
50 0.1 0.5 8 Low vibration and chip adhesion
80 0.05 0.5 8 Vibrations of low amplitude and fast heating
80 0.1 0.5 8 Low Vibration and temperature rise
100 0.05 0.5 8 Vibration and temperature rise
100 0.1 0.5 8 High Vibration and temperature rise
130 0.05 0.5 8 Low vibration and temperature rise
130 0.1 0.5 8 Temperature rise and pronounced wear
150 0.05 0.5 8 Temperature rise
150 0.1 0.5 8 Temperature rise
Table 4
Adopted conditions of the study
Vc, m/min fz,mm/t ap, mm ae, mm
50 0.05 0.5 8
50 0.1 0.5 8
80 0.05 0.5 8
80 0.1 0.5 8
130 0.05 0.5 8
130 0.1 0.5 8
Table 5
Experimental values
Insert C1 Insert C2 Insert C3
No. Vc, fz, T, Ra.av, T, Ra.av, T, Ra.av,
m/min mm/t min [micro]m min [micro]m min [micro]m
1 50 0.05 5.8 0.38 7.5 0.27 3 0.41
2 50 0.1 5.2 0.59 8.4 0.35 2.5 0.52
3 80 0.05 6 0.32 8 0.13 2.5 0.38
4 80 0.1 4 0.42 7.1 0.22 2 0.43
5 130 0.05 3.5 0.26 6.5 0.18 2 0.25
6 130 0.1 3.2 0.49 5.5 0.34 1.5 0.36
