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Tool failure detection method for high-speed milling using vibration signal and reconfigurable bandpass digital filtering

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This paper presents a monitoring method for on-line detection and indication of the occurrence of a cutting tool failure during high-speed face milling. The method consists of processing of the vibration signal using a reconfigurable infinite impulse response (IIR) bandpass digital filter and statistical techniques. The healthy tool threshold and the filter passband are adjusted and configured based on the cutting parameters that were set up during the machining process. For this process, sets of filter coefficients are pre-calculated for a number of defined insert passing frequencies ranges. The method is verified on-line during machining tests that are carried out at different tool failure levels and using various cutting parameters. In all experimental tests, the method allows the tool condition to be detected and indicated correctly. The proposed method is therefore shown to be simple, fast, computationally efficient, and reliable for the detection and indication of the presence of several types of tool failures for various cutting parameters, and the use of this method does not require any modification of the machine tool structure.
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1 23
The International Journal of
Advanced Manufacturing Technology
ISSN 0268-3768
Volume 81
Combined 5-8
Int J Adv Manuf Technol (2015)
81:1187-1194
DOI 10.1007/s00170-015-7302-0
Tool failure detection method for high-
speed milling using vibration signal and
reconfigurable bandpass digital filtering
P.Y.Sevilla-Camacho, J.B.Robles-
Ocampo, J.Muñiz-Soria & F.Lee-
Orantes
1 23
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ORIGINAL ARTICLE
Tool failure detection method for high-speed milling using
vibration signal and reconfigurable bandpass digital filtering
P. Y. Sevilla-Camacho
1
&J. B. Robles-Ocampo
2
&J. Muñiz-Soria
2
&F. Lee-Orantes
1
Received: 7 November 2014 /Accepted: 11 May 2015 /Published online: 19 May 2015
#Springer-Verlag London 2015
Abstract This paper presents a monitoring method for on-
line detection and indication of the occurrence of a cutting
tool failure during high-speed face milling. The method con-
sists of processing of the vibration signal using a
reconfigurable infinite impulse response (IIR) bandpass digi-
tal filter and statistical techniques. The healthy tool threshold
and the filter passband are adjusted and configured based on
the cutting parameters that were set up during the machining
process. For this process, sets of filter coefficients are pre-
calculated for a number of defined insert passing frequencies
ranges. The method is verified on-line during machining tests
that are carried out at different tool failure levels and using
various cutting parameters. In all experimental tests, the meth-
od allows the tool condition to be detected and indicated cor-
rectly. The proposed method is therefore shown to be simple,
fast, computationally efficient, and reliable for the detection
and indication of the presence of several types of tool failures
for various cutting parameters, and the use of this method does
not require any modification of the machine tool structure.
Keywords Tool failure .High-speed machining .Vibrat ion
signal .Reconfigurable bandpass digital filter .Tool condition
monitoring
1 Introduction
In manufacturing industries, process automation is one of the
main issues of interest. High-speed machining (HSM) is one
example of a highly automated process. However, despite this
high level of automation, the quality of the machining of the
workpiece cannot be always guaranteed because of the cutting
tool conditions. When a tool is worn or broken and the prob-
lem is not detected during the machining process, it affects
both the production performance and the production costs.
Therefore, cutting tool condition monitoring (TCM) is a major
issue in HSM. However, there are very few dedicated TCM
research projects for HSM. Some of the monitoring algo-
rithms that have been developed and reported are based on
measurement of physical variables related to the cutting tool
conditions, such as the feed and spindle motor currents [1,2],
the cutting force [3,4], and the tool vibration [510]. This last
signal has been widely used because it offers better character-
istics than other tool monitoring variables, including (1) a
periodic shape that resembles the cutting force, (2) an ability
to provide sufficient information about the toolscondition,
(3) robustness, (4) reliability, (5) applicability, (6) low cost,
and (7) easy measurement implementation without any need
for machine tool modifications.
However, these algorithms are intended for specific ma-
chining operations with fixed cutting conditions, and this
limits their industrial application because machining processes
are carried out using variable cutting parameters. Other limi-
tations of some of these systems include low processing
speeds and inappropriate analysis techniques. This is because
nonlinear and nonstationary high frequency signals are gener-
ated during HSM processes, and the proposed techniques re-
quire high computing power to provide a reliable indication of
the cutting tool condition. Also, the TCM analysis techniques
in some studies are based on fast Fourier transforms (FFTs);
*P. Y. Sevilla-Camacho
perlitas13@yahoo.com
1
Ingeniería Mecatrónica, Universidad Politécnica de Chiapas, Tuxtla
Gutiérrez, Chiapas 29082, México
2
Cuerpo Académico de Energía y Sustentabilidad, Universidad
Politécnica de Chiapas, Tuxtla Gutiérrez, Chiapas 29082, México
Int J Adv Manuf Technol (2015) 81:11871194
DOI 10.1007/s00170-015-7302-0
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however, the effectiveness of this signal spectral analysis
method is limited, because FFTs cannot identify transient
and nonlinear signals. Finally, one other limitation of these
systems is the type of sensors used, which are sometimes
expensive or can be difficult to place on the machine tool.
This paper presents a reliable and reconfigurable monitoring
method for on-line detection and indication of the presence of
a tool failure during HSM. The vibration signal is obtained
using an accelerometer and is processed digitally using a
reconfigurable infinite impulse response (IIR) bandpass digi-
tal filter (4th order).
The use of digital filter for TCM also has been proposed in
[11]. However, this method presents some differences in com-
parison with our proposed method. In [11], only tool breakage
is detected. This detection is based on that, for a broken cutter,
the frequency strength of the same frequency components
increases. For this reason, a bandpass filter between the tool
passing frequency (TPF) and insert passing frequency (IPF)
minus tool passing frequency is applied. The overall peak to
peak difference of the filtered samples in spindle load for each
tool rotation is used to calculate the relative energy index
(REI) and indicated the tool condition. Unlike of the afore-
mentioned method, our proposed method detects differenttool
failure levels. The detection is based on any change in the tool
condition that generates changes in the frequency components
of the vibration signal. The major changes are located between
the IPF and the first harmonic. For that, a bandpass filter is
applied for these cutoff frequencies. Then, the filtered signal is
processed using statistical techniques such as sum of absolute
values and arithmetic mean value methods. The processed
vibration signal is compared with a preset healthy tool thresh-
old to detect and indicate through an alarm signal the presence
of a tool failure. The digital filter passband and the healthy
tool threshold are configured and set up as functions of the
cutting parameters.
2 Tool failure detection algorithm
The proposed detection algorithm consists of the detection of
vibration signal that is generated during the cutting process
(Fig. 1). This signal is detected by an accelerometer and ac-
quired using a data acquisition device (DAQ). Prior to the
acquisition of the data, the vibration signal is conditioned
using an antialiasing filter, which is implemented with a
40 dB/decade low-pass Butterworth analog filter. This filter
limits the acceleration signal to a bandwidth of 2.4 kHz,
allowing a sampling frequency (f
s
) of 25 kHz. The sampled
signal is then processed using the reconfigurable IIR bandpass
digital filter (4th order). This filtering process provides an
output signal that only contains representative features of cut-
ting tool failures and thus enables failure detection. The digital
filter passband is reconfigured as a function of IPF, which
depends on the cutting parameters that are set up during the
machining process. For this process, sets of filter coefficients
are pre-calculated for a number of IPF ranges.
The healthy tool threshold is obtained by applying statisti-
cal techniques to the digitally filtered vibration signal. This
signal is acquired from a machining test that was carried out
using a healthy tool and using the same cutting parameters as
the monitored machining test.
The statistical techniques used to obtain the healthy tool
threshold value are the arithmetic mean value and sum of
absolute values techniques.
2.1 Reconfigurable IIR digital f iltering
The proposed algorithm is based on the 4th-order IIR
bandpass digital filtering of a vibration signal, which is ac-
quired using an accelerometer. The upper and lower cutoff
frequencies of the filter band are the IPF and its first harmonic,
respectively. The IPF is given by the following expression:
IPF ¼szð1Þ
where sis the spindle speed (rps) and zis the number of inserts
on the cutting tool.
Bandpass digital filtering is proposed because any change
in the tool condition generates changes in the frequency com-
ponents of the vibration signal, i.e., a milling process carried
out using a healthy cutting tool generates different frequencies
to those generated using a damaged tool. Frequencies between
the IPF and its harmonics are generated when the cutting tool
is defective, but this does not occur when the tool is healthy.
The major changes are located between the IPF and the first
harmonic [10]. Based on these vibration patterns, which de-
pend on the tool condition, bandpass filtering can be used to
extract important and representative features of cutting tool
failures and thus ease their detection. The use of digital filter-
ing as a signal processing technique is also considered because
it offers computational efficiency, high accuracy, high perfor-
mance, and simple, fast reconfiguration of the filter
parameters.
In this paper, an IIR digital filter is used because it has a
much better frequency response than a finite impulse response
(FIR) filter of the same order. Another advantage of IIR filters
over FIR filters is that IIR filters usually require fewer coeffi-
cients to execute similar filtering operations, and IIR filters are
also faster and require less memory space and computing
power. These factors enable these filters to detect the tool
conditions and indicate them on-line.
An IIR digital filter has the following equation:
ynðÞ¼
X
N
i¼0
aiyniðÞþ
X
N
j¼0
bjxnjðÞ ð2Þ
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where a
i
and b
j
are the constant coefficients and Ndenotes the
filter order.
The constant coefficients are a set of constants that are
calculated and stored using any standard digital filter design
tool. This tool also determines the minimum order filter.
The constant coefficient calculus is designed for a specific
set of bandpass filter frequency specifications, such as the
sampling frequency, passband frequencies, and stopband fre-
quencies, while the minimum order filter calculus is determine
for a specific set of bandpass filter magnitude specifications,
such as passband ripple and stopband attenuation.
Therefore, when the signal is filtered for a specific pass-
band and magnitude specifications, Eq. (2) uses the required
set of stored coefficients and the calculated minimum order
filter.
In industrial applications, the cutting process is carried out
at various spindle speeds with numerous inserts on the tool.
These changes in the cutting parameters generate different
values for the IPF and its harmonics. Therefore, the digital
filter passband must be reconfigured as a function of the cut-
ting parameters that were set up during the machining process.
The digital filter reconfiguration is performed by changing the
set of filter coefficients. In this research, FDATool of MATL
AB was used to calculate and store the sets of filter coeffi-
cients for a fixed set of several passbands and stopband fre-
quencies. The values of passband and stopband frequencies
were defined in function of a number of predefined IPF ranges
and its first harmonic (see Table 1). For example, if the IPF
frequency is a value between 300 and 325 Hz, then its first
harmonic is a value between 600 and 650, respectively. There-
fore, the passband needs to be located between 300 and
650 Hz, which are the minimum and maximum frequency
values. In this case, the proposed passband was located from
400 to 500 Hz, whereas the stopband frequencies were 350
and 550 Hz.
Fig. 1 Detection algorithm
Table 1 Digital filter passbands and stopbands for predefined IPF
ranges
IPF range (Hz) Passband frequencies (Hz) Stopband frequencies (Hz)
Fpass1 Fpass2 Fstop1 Fstop2
300IPF 325 400 500 350 550
325< IPF350 425 550 375 600
350< IPF375 450 600 400 650
375< IPF400 475 650 425 700
400< IPF425 500 700 450 750
425< IPF450 525 750 475 800
450< IPF475 550 800 500 850
475< IPF500 575 850 525 900
500< IPF525 600 900 550 950
525< IPF550 625 950 575 1000
550< IPF575 650 1000 600 1050
575< IPF600 675 1050 625 1100
600< IPF625 700 1100 650 1150
625< IPF650 725 1150 675 1200
650< IPF675 750 1200 700 1250
675< IPF700 775 1250 725 1300
700< IPF725 800 1300 750 1350
725< IPF750 825 1350 775 1400
750< IPF775 850 1400 800 1450
775< IPF800 875 1450 825 1500
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The calculated filter coefficients are returned as row vectors
band aof length N+1.
For this example, the set of calculated filter coefficients is
showninTable2. This set of filter coefficients for the
reconfigurable IIR bandpass digital filter is the same for all
IPFs in that range.
The FDATool also calculated the minimum order for filters
with passband ripple of 1 dB and stopband attenuation of
3 dB. For this case, the calculated order was 4th.
2.2 Healthy tool threshold
In this algorithm, arithmetic mean value and sum of absolute
values of the digitally filtered vibration signal is taken as a
reference value to set up a healthy tool threshold.
The arithmetic mean value is applied to obtain a mathemat-
ical representation of the typical value of the sum of absolute
and to reduce the noise in the data.
u¼1
8 SPRðÞ
X
8 SPRðÞ
i¼1
yi
jj ð3Þ
The healthy tool threshold is determined by monitoring
eight complete spindle rotations (8 [SPR]) with the tool in
healthy cutting condition. The number of samples for a single
SPR is not a constant due to the sampling frequency (f
s
)isset
to 25 kHz and the spindle speed (s) is variable. The number of
SPR is obtained according to Eq. (4).
SPR ¼fs
s

¼25 kHz
s
 ð4Þ
Finally, the healthy tool threshold is calculated by adding a
tolerance value to the arithmetic mean value obtained. This
tolerance was obtained experimentally.
T¼uþu¼2uð5Þ
2.3 Sum of absolute values of the filtered signal
The detection algorithm is based on the sum of absolute values
of the digitally filtered vibration signals [see Eq. (6)]. This
statistical technique is used to obtain a numerical parameter
to describe the tool condition.
The number of processed samples is for one complete SPR
[see Eq. (4)]. The vibration signal is acquired using the same
cutting parameters that were used for the preset of the healthy
tool threshold.
u¼X
SPR
i¼1
yi
jj ð6Þ
2.4 Decision-making
The decision-making is based on a comparison between a set
healthy tool threshold (see Eq. [5]) and the sum of absolute
values of the digitally filtered vibration signal [see Eq. (6)].
The comparison is made to indicate the tool condition. When
the sum of absolute values (u) is greater than the set healthy
tool threshold (T), an alarm signal is activated to indicate
cutting tool failure. Otherwise, the alarm signal remains inac-
tive. This indicator thus permits operator interventions during
the machining process.
3Experimentalsetup
To test the proposed method, a DM 4326 numerically con-
trolled, three-axis, high-speed vertical machining center is
used. The workpiece material used throughout the experi-
ments is aluminum alloy 6061-T6 in rectangular blocks. The
cutting tool is an indexable face mill with a diameter of 60 mm
and three triangular carbide inserts. The workpiece feed direc-
tion is along the positive X-axis.
The experimental setup is shown in Fig. 2. The vibration
signal, generated during the cutting process in the Xmachin-
ing directions, is detected using a biaxial ADXL321 acceler-
ometer with an acceleration range of ±18 g, which is fitted to
the vise jaws.
The signal is acquired using an NI USB-6215M series
multifunction DAQ device. The acquired signal is processed
and analyzed on-line using LABVIEW. Prior to the acqui-
sition of the data, the vibration signal is conditioned using an
antialiasing filter.
A series of machining tests is carried out during the down
milling process with an axial depth of cut (a
p
) of 3 mm, a
radial depth of cut (a
e
) of 30 mm, and variable cutting speeds
(V
c
), feed rates (V
f
), and cutting tool conditions (see Table 2).
All the experiments were performed with dry inserts.
Figure 3shows the various condition levels of the cutting
inserts that were used for the tests. The insert in a healthy
cutting condition is shown in the left column, and the middle
and right columns show inserts with partial and severe wear,
respectively. The widths of the wear land were 0.5 mm for a
partial wear and 1 mm for a severe wear. In addition,
Tabl e 2 Set of calculated filter coefficients for an IPF between 300 and
325 Hz
i0 1234
a13.9089 5.7545 3.7813 0.9358
b5.3229e04 0 0.0011 0 5.3229e04
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machining experiments are performed with one insert missing.
These experiments with the missing insert are intended to
simulate very severe failure or breakage of the cutting tool.
4 Analysis of experimental data and results
Figure 4a shows the waveforms of the original vibration
signals, which were obtained from experimental tests car-
ried out under various tool conditions, using a cutting tool
with three inserts, a spindle speed of 117 rps, and a feed rate
of 73 mm/s. As shown in the figure, the waveforms are
composed of several frequency components that belong to
the various parameters that are part of the cutting process.
To verify the frequency components of the signals, the sig-
nals were processed by the continuous wavelet transform
(CWT). Figure 5shows the 2D contour plot of the CWT
time-frequency maps. As can be seen, only frequencies of
351, 702, and 1053 Hz are generated when the cutting tool
is healthy. These frequencies correspond to the IPF and its
harmonics, respectively. However, when the cutting tool
presents a failure, additional nonlinear and transient fre-
quencies are generated. These dominant peak frequencies
appear between the IPF and its first harmonic, which are
351 and 702 Hz, respectively.
It is important to mention that the CWT time-frequency
maps of all the tests (see Table 2) present the same behaviors
aforementioned for both healthy and failure tool. But it is
obvious for their respective IPF.
The presence of others frequency components, which do
not belong to the tool condition, makes it difficult to use a
conventional signal processing technique for tool failure
detection. To overcome this problem, a reconfigurable IIR
bandpass digital filter (4th order) was applied to the original
vibration signals to extract only the frequency components
that are representative of the cutting tool condition.
Figure 4b shows the waveforms of the vibration signals
when processed using the reconfigurable IIR bandpass digital
filter. This figure clearly shows that the waveform level ob-
tained when using a healthy cutting tool is smaller than the
Fig. 2 Experimental setup
Fig. 3 Condition levels of the
cutting inserts used for the
experimental tests
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levels obtained when using the damaged cutting tools. This
difference in the levels occurs because the digital filter only
passes signal frequencies within a specific frequency range
and rejects all other frequencies outside this range.
Fig. 4 Waveforms of original
and filtered vibration signals
acquired from the machining tests
performed at s=117 rps, V
f
=
73 mm/s, cutting tool with three
inserts, and different tool
conditions
Fig. 5 CWT time-frequency
maps of vibration signals from the
machining tests performed at s=
117 rps, V
f
=73 mm/s, and
different tool conditions: athree
healthy inserts, b2 healthy inserts
and 1 partially worn insert, c2
healthy inserts and 1 severely
worn insert, and d2healthy
inserts and 1 missing insert
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For this experimental test, the IPF is 351 Hz. Therefore, the
digital filter passband is set to 450600Hz(seeTable1). If the
filter is applied to the vibration signal generated with healthy
cutting tool, the generated frequencies of 351, 702, and
1053 Hz are rejected. As a result, the waveform level of the
filtered signal is close to 0. However, if the filter is applied to
the vibration signal generated with a damaged cutting tool, the
frequencies between the range of 450 and 600 Hz are passed.
And as a result, a waveform level for the filtered signals is
generated.
Analysis of the digital filtered signals allows on-line detection
of the presence of tool failure in graphical form. To obtain a
numerical parameter that allows the cutting tool condition to be
indicated to the machining operators, the statistical technique of
the sum of absolute values was then applied to the digitally
filtered signals. Figure 6shows the final results obtained when
applying this technique to vibration signals acquired from the
machining tests performed at s=117 rps, V
f
=73mm/s,anddif-
ferent tool conditions. The first 14 results correspond to the vi-
bration signal from experimental tests carried out using a healthy
tool.Theresultsfromtests15to35correspondtotestscarried
out using a tool with one partially worn insert, while those from
tests36to56correspondtotestscarriedoutusingatoolwithone
severely worn insert, and finally those from tests 57 to 70 corre-
spond to tests carried out using a tool with one insert missing.
From Fig. 6, it is evident that all values obtained from the
tests using the damaged tool are higher than the set healthy
tool threshold. In contrast, all values obtained from the tests
using a healthy tool are smaller than the set healthy tool
threshold. As a result, an alarm could be activated to indicate
the occurrence of cutting tool failure.
Several experimental tests (see Tables 2and 3) using a
variety of cutting parameters were performed to validate the
algorithm. In all tests, similar results were obtained. This
clearly demonstrates that the proposed method indicates and
detects correctly the cutting tool condition. Also, this demon-
strates that the different spindle speeds and feed rates do not
interfere with the detection.
5Conclusions
This paper demonstrates that the proposed vibration signal
processing method, which is based on a reconfigurable IIR
Tabl e 3 Experimental test arrangement
Spindle speed
(rps)
Feed rate
(mm/s)
Tool condition
117 73 3 healthy inserts
117 73 2 healthy inserts and 1 partially worn
insert
117 73 2 healthy inserts and 1 severely worn
insert
117 73 2 healthy inserts and 1 missing insert
125 75 3 healthy inserts
125 75 2 healthy inserts and 1 partially worn
insert
125 75 2 healthy inserts and 1 severely worn
insert
125 75 2 healthy inserts and 1 missing insert
133 67 3 healthy inserts
133 67 2 healthy inserts and 1 partially worn
insert
133 67 2 healthy inserts and 1 severely worn
insert
133 67 2 healthy inserts and 1 missing insert
142 83 3 healthy inserts
142 83 2 healthy inserts and 1 partially worn
insert
142 83 2 healthy inserts and 1 severely worn
insert
142 83 2 healthy inserts and 1 missing insert
Fig. 6 Sum of absolute values of
the digitally filtered vibration
signals acquired from the
machining tests performed at s=
117 rps, V
f
=73 mm/s, and
different tool conditions
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bandpass digital filter (4th order) and statistical techniques,
allows the on-line detection and indication of the occurrence
of cutting tool failure. The bandpass digital filter is used to
extract an important representative feature related to cutting
tool failure. This feature is the presence of frequencies located
between the IPF and its harmonics.
The use of IIR bandpass digital filtering for failure detec-
tion offers several advantages, including easy implementation,
simple detection of the tool conditions, fast and simple recon-
figuration of the filter parameters, and rapid processing with
very little memory space and computing power required.
The sum of absolute values technique, when applied to the
digitally filtered vibration signal, generates a numerical pa-
rameter that is used to indicate the tool condition. When a
cutting tool fails, this parameter is higher than the set healthy
tool threshold.
An important element of the proposed method is that the
healthy tool threshold used for decision-making and the pass-
band of the digital filter are both adjusted and configured
based on the cutting parameters that were set up during the
machining process. Therefore, this method is suitable for in-
dustrial applications. In addition, the reconfiguration feature
of the proposed method means that it can be applied to differ-
ent machining processes where the occurrence of tool failure
generates frequencies in the range between the IPF and its
harmonics.
Another important conclusion is that the installation of the
accelerometer does not require any modification of the ma-
chine tool structure and does not interfere with the cutting
process. This sensor also reduces the cost of implementation
of the TCM method when compared with other methods.
All experimental results showed 100 % detection and indi-
cation of cutting tool failure. The results presented here dem-
onstrate that that the proposed method is a simple, efficient,
fast, reliable, and economical method for on-line detection and
indication of the presence of several types of tool failure with
various cutting parameters in high-speed face milling.
The algorithm has been tested using a personal computer as
the processor unit, but it can also be implemented with a
system-on-chip (SoC) approach to obtain an on-line, real-
time, and compact monitoring system.
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... The monitoring results are easily interfered with by cutting fluid and chips, so the direct method is not suitable for the machine tool processing site [12,13]. The indirect method collects sensor signals, such as force [14,15], vibration [16,17] and acoustic emission [13], extracts data features and establishes a feature map relationship between monitoring signals and tool wear condition. ...
... In the first set of experiments, data from C1 and C4 cutters (a total of 17,684 samples) are used as a training set to generate model M1+4, which is tested using data from C6 cutters. In the second set of experiments, data from C1 and C6 cutters (17,190 samples in total) are invoked as a training set to produce model M1+6, which is tested using data from C4 cutters. In the third experiment, the training set of C4 and C6 tool data (17,414 samples in total) are used to obtain the model M4+6 and the data of the C1 tool are utilized to test the model. ...
Article
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Tool wear is a key factor in the machining process, which affects the tool life and quality of the machined work piece. Therefore, it is crucial to monitor and diagnose the tool condition. An improved CaAt-ResNet-1d model for multi-sensor tool wear diagnosis was proposed. The ResNet18 structure based on a one-dimensional convolutional neural network is adopted to make the basic model architecture. The one-dimensional convolutional neural network is more suitable for feature extraction of time series data. Add the channel attention mechanism of CaAt1 to the residual network block and the channel attention mechanism of CaAt5 automatically learns the features of different channels. The proposed method is validated on the PHM2010 dataset. Validation results show that CaAt-ResNet-1d can reach 89.27% accuracy, improving by about 7% compared to Gated-Transformer and 3% compared to Resnet18. The experimental results demonstrate the capacity and effectiveness of the proposed method for tool wear monitor.
... Compared with the direct method of post-process inspection, the indirect method can effectively monitor tool wear without halting machining, helping to improve machining efficiency. Sevilla et al [11] used reconfigurable digital bandpass filtering to the vibration signal to extract the characteristic features of tool faults and compared them with the features of a healthy tool signal for tool fault detection. Maia et al [12] proposed a new spectral analysis method for associating acoustic emission signals with the tool wear state to detect wear mechanisms and monitor tool wear progression. ...
Article
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Machining is the primary method used for producing parts and equipment. Tool wear is inevitable during this process and directly impacts the quality of the finished parts. Accurately recognising the tool wear status helps to reduce the risk of processing failure and improve overall processing efficiency. By establishing a mapping relationship between tool wear information and its associated status characteristics, accurate recognition of tool wear can be achieved. This paper proposes a novel intelligent recognition approach for tool wear state in machining process based on vibration signals. The EMDResNeStTime module uses empirical mode decomposition (EMD) and two-dimensional convolution to extract the main trend features of vibration signals, and the sequence-global-encoding module uses the self-attention mechanism to extract the global features of vibration signals, are designed. A new multi-feature parallel-time feature extraction backbone is constructed using these two modules. The use of this backbone effectively improves the ability of the network model to extract key features of complex trends in vibration signals. Experimental results show that the proposed method achieves 71.65%, 74.89%, 71.36% and 72.78% in accuracy, precision, recall and F1 score, respectively. Compared with other network models, it achieves higher recognition accuracy and more stable performance. The ablation experiment further confirms the classification effectiveness of the method used in this network model. The model can accurately recognise the tool status during the cutting process based on monitoring data, which will facilitate the implementation of a more effective tool change strategy in intelligent manufacturing and improving processing efficiency.
... For this reason, this paper refers to the experimental methods used in previous TBM studies and artificially introduces different types of tool breakage faults to carry out a small amount of cutting experiments with broken tools, and then obtain the fault signals required for model training. [50][51][52]. It should be noted that although these fault signals are not obtained at the moment of tool breakage, they can still provide reliable input for the monitoring model and help the machine tool stop quickly within a few milliseconds after the tool breakage event to minimize economic losses. ...
Article
Tool breakage monitoring (TBM) during milling operations is crucial for ensuring workpiece quality and minimizing economic losses. Under the premise of sufficient training data with a balanced distribution, TBM methods based on statistical analysis and artificial intelligence enable accurate recognition of tool breakage conditions. However, considering the actual manufacturing safety, cutting tools usually work in normal wear conditions, and acquiring tool breakage signals is extremely difficult. The data imbalance problem seriously affects the recognition accuracy and robustness of the TBM model. This paper proposes a TBM method based on the auxiliary classier Wasserstein generative adversarial network with gradient penalty (ACWGAN-GP) from the perspective of data generation. By introducing Wasserstein distance and gradient penalty terms into the loss function of ACGAN, ACWGAN-GP can generate multi-class fault samples while improving the network's stability during adversarial training. A sample filter based on multiple statistical indicators is designed to ensure the quality and diversity of the generated data. Qualified samples after quality assessment are added to the original imbalanced dataset to improve the tool breakage classifier's performance. Artificially controlled face milling experiments for TBM are carried out on a five-axis CNC machine to verify the effectiveness of the proposed method. Experimental results reveal that the proposed method outperforms other popular imbalance fault diagnosis methods in terms of data generation quality and TBM accuracy, and can meet the real-time requirements of TBMs.
Article
Tool condition monitoring (TCM) is crucial for smart manufacturing and cutting vibration signal is proven to be highly related to tool wear state. In this paper, a wireless smart tool holder is designed for online vibration signal sensing for TCM with accelerometer embedded close to vibration source and signal processing circuits integrated, showing good performance of vibration sensing ability compared with traditional wired ways. Cutting experiments are designed with cutting parameters of great varied range to guarantee the generalization ability of TCM algorithm for different machining conditions and vibration signal of whole tool life cycle is collected by smart handle. Then feature extraction and selection are studied to provide valuable information and artificial neural network algorithm is realized. Results show the algorithm has an accuracy of 85.0% with poor performance in distinguishing some wear states. To solve this problem, an optimized method based on two ANNs in series with new feature sets is proposed. The optimized algorithm has an accuracy of 90.0% with an accuracy increase of 16.8% and the average predicted probability increase of 15.0% in initial wear samples. In spite of speed sacrifice, the optimized algorithm makes progress in recognition accuracy and data confidence level.
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Tool condition forecasting (TCF) is a key technology for continuous drilling of CFRP/Ti stacks, as the tool wear is always rapid and severe, which may further induce unexpected drilling quality issues. However, for drilling CFRP/Ti stacks, the cutting spindle power and vibration signals change are complex, influenced by many factors due to the different materials properties. The TCF for drilling CFRP/Ti stacks remains challenging, as the sensitive features are difficult to extract, which decide the accuracy and robustness. Aiming to monitor and forecast tool wear of drilling CFRP/Ti stacks, an in-process TCF method based on residual neural network (ResNet) and long short-term memory (LSTM) network has been proposed in this paper. Using the cutting spindle power and vibration signals preprocessed by the proposed method, the LSTM network with the ResNet-based model integrated can forecast tool-wear values of the next drilling holes. A case study demonstrated the effectiveness of TCF, where the results using raw measured signals and preprocessed datasets are tested for comparison. The mean absolute error (MAE) using raw signals is 45.01 μm, which is 2.20 times bigger than that using preprocess signals. With the proposed method, the data preprocessing for drilling CFRP/Ti stacks can improve the tool-wear forecasting accuracy to MAE 20.43μm level, which meets the demand for online TCF.
Article
Intelligent real-time monitoring of tool wear is significant to ensure the quality of workpieces and the efficiency of machining. However, various factors in the machining process can cause large variations in the monitoring signals, making it difficult to accurately predict tool wear values. To solve this, a tool wear prediction method based on domain adversarial adaptation and squeeze-and-excitation channel attention multiscale convolutional long short-term memory network (SE-DAAMSCLSTM) is proposed. A feature extractor combining multiscale convolution and channel attention with the introduction of domain adversarial mechanism was constructed to extract domain-independent multiscale spatiotemporal features that characterize tool wear, thus enabling accurate prediction of tool wear values. By validating the model on milling datasets and comparing it with conventional prediction methods, the results show that the model enables accurate prediction with variation in tool monitoring signals, demonstrating the superiority of the method in predicting tool wear.
Article
The tool is an important part of machining, and its condition determines the operational safety of the equipment and the quality of the workpiece. Therefore, tool condition monitoring (TCM) is of great significance. To address the imbalance of the tool monitoring signal and achieve a lightweight model, a TCM method based on WGAN-GP and ShuffleNet is proposed in this paper. The tool monitoring data are enhanced and balanced using WGAN-GP, and the 1D signal data are converted into 2D grayscale images. The existing ShuffleNet is improved by adding a channel attention mechanism to construct the entire model. The tool wear state is recognized through experimental validation of the milling dataset and compared with those through other models. Results show that the proposed model achieves an accuracy of 99.78 % in recognizing the wear state of tools under imbalanced data while ensuring a light weight, showing the superiority of the method.
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Titanium alloys are widely used in the aerospace industry for applications requiring high strength at elevated temperature and high mechanical resistance. However, titanium alloys are classified as extremely difficult-to-cut materials owing to their physical, chemical, and mechanical properties, which result in the low material removal rate and the short tool life. This paper presents an experimental research of the tool wear patterns and relevant wear mechanisms during high-speed milling of Ti-6Al-4V with cemented carbide inserts. SEM-EDX analysis showed that nose wear and edge wear were the main tool failure modes during high-speed milling process, which were different from the wear patterns under traditional cutting conditions. Adhesion, attrition and diffusion wear mechanisms, as well as the cracks were responsible for the tool wear.
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Ti-6Al-4V alloy is an attractive material in many industries due to its unique and excellent combination of strength to weight ratio and their resistance to corrosion. However, because of its low thermal conductivity and high chemical reactivity, Ti-6Al-4V alloy is generally classified as a difficult-to-cut material that can be characterized by low productivity and rapid tool wear rate even at conventional cutting speeds. It is well known that tool wear has a strong relationship with the cutting forces and a sound knowledge about correlation between cutting forces variation and tool wear propagation is vital to monitor and optimize the automatic manufacturing process. In the present study, high-speed end-milling of Ti-6Al-4V alloy with uncoated cemented tungsten carbide tools under dry cutting conditions is experimentally investigated. The main objective of this work is to analyze the tool wear and the cutting forces variation during high-speed end-milling Ti-6Al-4V alloy. The experimental results show that the major tool wear mechanisms in high-speed end-milling Ti-6Al-4V alloy with uncoated cemented tungsten carbide tools are adhesion and diffusion at the crater wear along with adhesion and abrasion at the flank wear. The cutting force component in the negative y-direction is more dominant of the three components and displays significantly higher magnitudes than that of the other two components in x- and z-directions. The variation of cutting force component F y has a positive correlation with the tool wear propagation, which can be used as a tool wear indicator during automatic manufacturing process.
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This paper describes a tool-wear monitoring procedure in a metal turning operation using vibration features. Machining of EN24 was carried out using coated grooved inserts, and online vibration signals were obtained. The measured tool-wear forms were correlated to features in the vibration signals in the time and frequency domains. Analysis of the results suggested that the vibration signals' features were effective for use in cutting tool-wear monitoring and wear qualification.
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This paper introduces the design and implementation of a simple yet efficient technique for Infinite Impulse Response (IIR) bandpass filters that can be used for simultaneous multiple frequency estimation applications. The technique, which is implemented on a dsPIC microcontroller, uses variable data sampling rates and a table of predefined filter coefficients simultaneously to dynamically adjust its pass band precisely to the range of interest. The technique developed may be deployed to provide a more reliable and efficient algorithm which can be flexibly utilised as part of a modular development of high performance, reliable sensing systems. The developed system is described in detail in the context of the e-Monitoring of a milling cutting process. In this case spindle speed and spindle load signals from a machine tool have been used as a source of information relating to the health of the cutting process being undertaken.
Article
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In this study, the relationship between vibration and tool wear was investigated during end milling. For this purpose, a series of experiment were conducted in a vertical milling machine. An indexable CBN insert and AISI D3 cold work tool steel hardened to 35 HRC were used as material twin in the experiments. The vibration was measured only in the machining direction, which has more dominant signals than in the other two directions. The measurements were taken by using an acceleration sensor assembled on a machinery analyzer. Tool wear was measured by a toolmaker's microscope. It was observed that there was an increase in vibration amplitude with increasing tool wears. This situation was evident especially by monitoring vibration of displacement type. It was also observed that the first three multiplies of tooth passing frequency (1×, 2×, 3×) gave the best information about the tool wear. Results showed that there was no considerable increase in the vibration amplitude until a flank wear value of 160 μm was reached, above which the vibration amplitude increased significantly.
Article
This research presents a method for detecting tool failures in high-speed face milling. This method detects tool failures from vibration signature maps. Tests were carried out at different tool failure levels, spindle speeds, feed rates, and workpiece mountings. Vibration signals were obtained with an accelerometer and processed using the continuous wavelet transform methodology. The vibration signature maps showed that healthy cutting tools produce a periodic insert passing frequency and its harmonics. In contrast, a damage tool generates additional nonlinear and transient frequencies at nonsynchronous frequencies. The experimental results agree with vibration signature maps obtained from a simulated cutting force model. The proposed method is effective as a tool failure detection method when transient and nonlinear behaviors are presented in face milling process. Moreover, the proposed method showed good results at different process parameters and for several types of tool failures. Finally, it is important to point out the use of accelerometers because they present several advantages against other types of sensors. Advantages such as low cost, wide bandwidth, and easy implementation are important characteristics for tool condition monitoring in high-speed machining.
Article
Unattended machining plants require intelligent monitoring systems, able to detect the different events that can happen during the machining process. In particular, the control of tool wear is an important objective of a monitoring system when dry machining is applied. This work evaluates the suitability of a tool wear monitoring system based on machine tool internal signals. It presents a sensorless monitoring procedure for the dry and high-speed milling of aerospace aluminium alloys. Dry high-speed experiments were performed using aluminium Al 7075-T6 workpieces. The sensor data from internal signals were compared and analyzed, assessing the deviation in representative variables in time and frequency domains. The signal analysis confirmed the relevance of cutting force signals for tool wear monitoring in the high-speed milling of aluminium alloys.
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Machine condition plays an important role in machining performance. A machine condition monitoring system will provide significant economic benefits when applied to machine tools and machining processes. Development of such a system requires reliable machining data that can reflect machining processes. This study demonstrates a tool condition monitoring approach in an end-milling operation based on the vibration signal collected through a low-cost, microcontroller-based data acquisition system. A data acquisition system has been built through interfacing a microcontroller with a signal transducer for collecting cutting vibration. The examination tests of this developed system have been carried out on a CNC milling machine. Experimental studies and data analysis have been performed to validate the proposed system. The onsite tests show the developed system can perform properly as proposed.
Article
Tool condition monitoring, mainly tool breakage detection for high-speed machining (HSM), is an important problem to solve; however, the techniques or types of sensors applied in other research projects present certain inconveniences. In order to improve tool breakage monitoring systems, a simple, effective, and fast method is presented herein. This method is based on the discrete wavelet transform (DWT) and statistical methodologies. The effectiveness of the method is based on the measurements of the feed-motor current signals using inexpensive sensors. It is well-known that during the cutting process, the motor current is related to the tool condition. The current consumption changes when the tool is broken as compared to when the tool is in normal cutting condition. This difference can be obtained from the waveform variances between the signals in order to ascertain the tool condition. The algorithms of this research project consist of obtaining compressed signals from the I rms feed-motor current signals applying the DWT. Then from these compressed signals, we detect the asymmetries between them. The arithmetic mean value is applied to asymmetries of consecutive machining lengths to reduce noise in the data having a mean value of a series of asymmetries; also, a normal cutting threshold is set up in order to make decisions regarding the tool conditions so as to detect tool breakage. Therefore, this research project shows a low-cost monitoring system that is simple to implement.
Conference Paper
Optimum performance of machining process relies on the availability of the information about process conditions for process monitoring and feedback to the process controller. Tool condition is the most crucial and determining factor to machine tool automation, hence online tool condition monitoring is of great industrial interest. A research work of tool condition monitoring for high speed machining is introduced in this paper. It employs multi-modal sensing which includes accelerometer, acoustic emission (AE) sensor and dynamometer, and advanced signal processing to monitor a high speed milling process. The results show that the frequency bands of wavelet decomposition which cover the frequency of cutter revolution are the most important bands among the spectrum. The energy distribution of signal shifts from low frequency to high frequency while tool wear develops. Wavelet analysis has the advantages of going deeper to the nature of physical phenomenon. The results based on time-frequency domain analysis are not so easy to be influenced by the noise and the cutting parameters which has always been a big problem for time-domain analysis.