vibration as a source of information for abrasive waterjet monitoring

Journal of Naval Science and Engineering
2011, Vol.7 , No.1, pp. 71-85
VIBRATION AS A SOURCE OF
INFORMATION FOR ABRASIVE WATERJET
MONITORING
Sergej HLOCH1, Vincent PERZEL1, Pavol HREHA1,
Hakan TOZAN2* Jan VALICEK3
Department of Manufacturing Management, Faculty of Manufacturing
Technologies,
Technical University of Košice with a seat in Prešov, 080 01 Prešov,
Slovakia1
Turkish Naval Academy Dept. of Industrial Engineering, Istanbul,Turkey2
(Cor. Author)*
Academy of Science of Czech Republic, Ostrava Poruba
[email protected], [email protected], [email protected],
[email protected]*, [email protected]
Abstract
This paper deals with basic research of vibration generated during abrasive
waterjet cutting of AISI 309 and their analysis of frequency spectrum.
Experimentally controlled factor involved in experiment was abrasive mass
flow rate with values 250 and 400 g/with constant rate of speed 100
mm/min.
AŞINDIRICI SU JETİ IZLEMESINDE BILGI
KAYBNAĞI OLARAK TİTREŞİM
Özetçe
Bu makale AISI 309’un aşındırıcı su jeti ile kesiminde oluşan titreşimin ve
bunların frekans spekturum analizlerinin temel araştırması ile ilgilidir.
Deneyde kontrol edilen ilgili faktörler 250 ve 400 g lık aşındırıcı kütle akış
oranı ve 100mm/dak. lık sabit hız oranıdır.
Keywords: Abrasive waterjet, Vibration.
Anahtar Kelimeler: Aşındırıcı su jeti, Titreşim
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Vibration As A Source of Information for Abrasive Waterjet Monitoring
1. INTRODUCTION
In abrasive waterjet cutting (AWJ) of materials, especially metal, is
one of the important tasks maintaining the required quality level of the
cutting process, whereas the emphasis is placed primarily on high quality
cut surfaces of material. This quality is determined by various input factors
in the process of cutting. Description of the topography of the surfaces of
cut materials, its different quality parameter has been dealt in many
scientific projects, technical articles [1]. Some of the authors deal with the
factors entering the technological process, some technological processes of
their own, different approaches to identifying and measuring quality
deficiencies on the topography of cut surfaces, setting the entry factors for
achieving the required or predicted quality of the surface [2]. Currently,
AWJ technology is without up-to-date on-line feedback for the process
managing in real industrial or laboratory conditions [1], [3], [4]. Using the
AWJ technology, especially in cutting metal materials requires increasingly
higher demands on the quality of the finished product, but also on control
options of AWJ process. Not only in off-line, but also in on-line mode.
Control of the AWJ process quality is conditioned also by sufficient supply
of enough sophisticated data, characterizing the process by which it will be
possible to manage and regulate the AWJ process by previously predefined
requirements for decisive parameters of the final product. This is
particularly the identification and collection of data known as vibration and
acoustic emission, emerging as accompanying physical effects of the AWJ
process, especially in cutting metal materials. Data from acoustic and
vibration emission are a good diagnostic tool, which allows indirect
identification of the effects during the AWJ process, especially when cutting
materials. Vibrations are a physical phenomenon, which arises as a
accompanying phenomenon during the cutting process of material.
Vibrations of cut material are results of continuous force action of abrasive
particles in AWJ on the surfaces, particles and molecules of cut material,
which are torn and flown away by water jet out from cutting slits into the
water absorber [5]. Separation moment of cut material particle is determined
by the principle of action and reaction as well. Divided material gets the
energy pulse from the abrasive particles at very high speed (2-3 M) and high
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Sergej HLOCH, Vincent PERZEL, Pavol HREHA, Hakan TOZAN,
Jan VALICEK
kinetic energy. This energy partially catapults particles (molecules) and
partially oscillates static mass of residual material in the axis of moving
abrasive particles. These oscillations in the cut material are reflected in the
form of periodic, continuous, but non-homogeneous vibrations with uneven
amplitude and their subsequent sound demonstration in wide frequency
spectrum [6], [7]. Vibrations and their acoustic manifestations can be
measured, analyzed, sent to subsequent analysis and created conditions of
their formation, physical addresses, dependencies on the quality of cut
materials, input cut factors and propose also the input factors for the surface
quality control in the cut technology using AWJ [8].
2. STATE OF THE ART
As mentioned above, there is currently not a functioning model of
on-line process management of AWJ cutting. This problem was dealt with
by several authors. Kovacevic was dealing with indirect monitoring of
shoot-trough depth to wooden material [9]. He used as an indirect indicator
the normal forces on the workpiece generated by AWJ. Momber [7] tried to
do the online analysis of the process of AWJ cutting by acoustic emission.
Asraf et al. later proposed a model for on-line monitoring of depth of cut in
the process of AWJ flow through acoustic emission [10]. Axinte tried to
integrate the acoustic emission directly into process of AWJ cutting for the
detection of possible faults [11]. Monno et al. used vibration analysis during
AWJ cutting using oscillation technique in order to reduce waviness in the
bottom of surface created by AWJ [12]. Authors [13], [16] used acoustic
emission for on-line monitoring the depth of cut during cutting by AWJ
technology. Analysis of vibrational spectrum of the aluminum cutting was
dealt by [6]. Further authors [8] used the acoustic sound pressure level for
prediction of surface quality generated by abrasive waterjet cutting [8].
Vibrations in the process of AWJ in shoot-through of material and their
dependence on the surface roughness was dealt by [14], [15]. From the short
preview of published studies according to prediction and on-line process
management of AWJ process it is noticeable, that most writers dealt with
giving predictions by examining the acoustic emission. Vibrations in the
AWJ cutting process has been paid relatively little work. Works dealing
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Vibration As A Source of Information for Abrasive Waterjet Monitoring
with the deeper analysis of vibrations and their use for monitoring the
process of cutting material completely absent. Unsolved questions remain
the possibility of predicting the quality of surface or on-line management by
vibration emission of cut material.
3. EXPERIMENTAL SET UP
The described experiment was conducted under conditions of small
industrial company on technological equipment for cutting material
operating in standard mode. Neither on the working machine nor on the
auxiliary equipment has not been made any additional adjustments. The
experimental setup consist of an AWJ cutting system, vibration sensors
accelerometers SN 207 94 - 4 units, multiplex box Scame P and PC with
LabView 8.5 (fig.1).
Figure 1. Schematic experimental setup machine tool, work piece and diagnostic
equipment
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Sergej HLOCH, Vincent PERZEL, Pavol HREHA, Hakan TOZAN,
Jan VALICEK
Steel plate, placed on metal supports has undergone a process of separating
the material along. Cutting tool was an abrasive water jet with the
parameters set as in normal technological standard operation of cutting
metal material. In an attempt two cuts along the length of material were
made, differed with the various abrasive mass flow rates with constant
traverse speed. During the two experimental cuts, using four piezoelectric
sensors data about the vibration emission emerging on the cut material
under the influence of AWJ were collected. Data were recorded and
evaluated in the Labview 8.5. Dimensions of experimental samples and
locations of sensors are shown in figure2.
Figure 2. Experimental sample
Recorded vibration parameters: acceleration and absolute deviation
from steady state. Parameters of measured acceleration and deviation is
defined amplitude size and their progress is shown in two curves (vibrating
diagram fig. 4, frequency analysis diagram fig. 5). In the object
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Vibration As A Source of Information for Abrasive Waterjet Monitoring
measurement knowledge from the part controlled experiment is used, where
in the process of cutting metal material (AISI 309) a number of
measurements of various physical phenomena and their values were used,
not only the measurement of vibrations and their parameters. This
experiment involves two attempts of cutting metal material AISI 309 with
the same parameters, but in different input factors in the process ma, which
influenced the running of the process of cutting material as well as the
resulting quality on the cut surfaces - topography of surfaces of cut
materials. Experimental conditions were characterized by the data given in
table 1.
Table 1. Set Up of the Experiment
Factors
Experimental range
Pressure p [MPa]
350
Traverse speed v [mm.min-1]
100
Abrasive mass flow rate ma [g.min-1]
250, 400
Water orifice diameter do [mm]
0,14
Focusing tube diameter df [mm]
0,8
Standoff distance z [mm]
3
Number of passes
1
90
Angle of attack  [°]
Type of abrasive
Barton Garnet
MESH
80
Material thickness
15 mm
Target material AISI 309
steel)
(Cr – Ni
chemical composition (C 0,20%, Mn 2%, Si 1%, Cr 22 – 24%, Ni
12 – 15%, P 0,045%, S 0,03%)
mechanical properties (HRB 95,  = 0,27-0,3, E = 200 GPa, t =
515 MPa, K = 205 MPa, A = 40%, Z = 50%)
Cut material, stainless steel AISI 309 with a high proportion of alloying
materials is due to the chemical composition (Cr, Ni, Mn) characterized by
high toughness and worse machinability. It can be assumed, that the
vibration emission and vibration frequential modulation data measured will
be also similar also in cutting other types of construction steels. Flat plate of
length 200 mm was loosely laid over the water muffler for 2 hr on steel
supports- thickness 5 mm. These supports were located in distance of about
20 mm from both ends of the cut metal plate. Location of the sample during
the experiment is shown figure 3.
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Sergej HLOCH, Vincent PERZEL, Pavol HREHA, Hakan TOZAN,
Jan VALICEK
Figure 3. Scheme of position of experimental sample during AWJ cutting
During the cutting of experimental samples were recorded vibrations of cut
material. For collecting data was used system NI PXI - 1031, NI PXI - 6106
for eight-channel simultaneous collection with the sampling frequency of 30
kHz. Vibrations were recorded by uni-axial accelerometers PCB IMI 607
A11. Recorded signals were then analyzed by a tool that was created in the
object-programming environment LabVIEW 8.5.
4.
RESULT AND DISCUSSION
In the first cut was processed with abrasive mass flow ma = 400
g.min-1. In the second experiment was used technological process AWJ
with abrasive mass flow m = 250 g.min-1. Parameters as water pressure p,
abrasive size, and traverse speed of cutting head v in the process of cutting
were unchanged. Four piezoelectric vibration sensors were placed on a
metal plate from the side, along the length as shown on fig. 1. Body of
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Vibration As A Source of Information for Abrasive Waterjet Monitoring
sensors were mounted on the metal at a distance of 50 mm from the cutting
slot, so captured and recorded data are not subject to any transfer or
distortion. In comparison of the records about the process of the vibration
emission, expressed in the figure 4 are evident following findings:
Abrasive mass flow rate ma = 400 g.min-1
S1 sensor placed 25 mm from the edge of the plate:
This sensor placed at the beginning of the cut measured the flattest
curve of the vibration spectrum. The maximum amplitude was recorded in
about 5. second of the cut above the first prop having an amplitude of 1.5 g
and in about 105. second of the cut above the second prop with an amplitude
of 3 g. In the middle of the cutting process, the size of the amplitude was
reduced to the maximum 1 g without major deviations during the whole cut.
At the end of the process behind the place of support on the second prop
vibration damping up to 0.5 g. occurred.
S2 sensor placed 75 mm from the edge of the plate:
Measured course of vibration spectrum is similar to the sensor S1,
but with larger amplitudes. In the place of the first prop it is 2.5 g and in
place of the second prop 4g. In the last third of cutting were recorded
higher amplitudes compared with data from the first sensor until the end of
the cutting with the damping of vibrations behind second prop.
S3 sensor located 125 mm from the edge of the plate:
The third sensor measured the highest amplitudes for the entire
length of cutting material, size of amplitudes were about 2x higher than data
from the first sensor. The amplitude above the second prop reached 5g.
S4 sensor located 175 mm from the edge of the plate:
This sensor measured the data similar to the sensor S2.
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Sergej HLOCH, Vincent PERZEL, Pavol HREHA, Hakan TOZAN,
Jan VALICEK
Level of abrasive mass flow rate ma = 250 g.min-1
S1 sensor placed 25 mm from the edge of the plate:
This sensor measured a higher value in the first third of the cutting
process, in the second third measured a flatter curve and the last third of the
measured the amplitude increased up to 3 g, while in place of the second
prop there was recorded peak amplitude of 5g.
S2 sensor placed 75 mm from the edge of the plate:
Sensor measured wide scattering of the size of amplitude. In the first
third about 2 g, in the second third recorded decrease to 0.5 g, and in the 3rd
third increase up to 5 g in place of the second prop. This sensor measured
the largest scattering of amplitude values during the experiment.
S3 sensor placed 125 mm from the edge of the plate:
Sensor measured a similar curve during vibration as S2
S4 sensor placed 175 mm from the edge of the plate:
Sensor measured a similar curve during vibration as S1
From the analysis of vibration emission curves recorded by the 4
sensors in both experiments can be deduced the following findings:
a. In the first experimental run with higher abrasive mass flow rate
400 g/min AWJ acts as a source of vibration of cut material, the system has
the highest vibration amplitude oscillations in places where metal prop
supports its positions. At these places the entire system resonates and has a
high vibration. The measured amplitude is approximately 2 times higher
than elsewhere in the cut material.
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Vibration As A Source of Information for Abrasive Waterjet Monitoring
b. Higher mass flow of abrasive acts to the cut material probably as
damper of oscillations, therefore the height of amplitude is lower than
during second attempt with ma = 250 g.min-1
c. In the last third of the length of cut, where the material is already
largely cut, it also acts as a resonator of oscillation, therefore, measured
vibration emission curve is the highest.
d. In the middle third of the length of the cut is vibrating emission
curve the lowest, has almost flat course without resonances and
irregularities.
Analysis of the frequency spectrum of vibration emission measured
in experiments of cutting metal material by AWJ technology. From the
record of frequency spectrum shown in picture Fig. 5, the following findings
can be observed:
a.
In both experiments the shapes of curves are approximately the
same, frequency spectrum of vibration and acoustic emission has
approximately the same course.
b.
Peak values for frequency amplitude is consistently reflected in
the following bands:
1. band: 500-600 Hz, where amplitude height is about 0.003
mm to 0.005 mm
2. band: 12,500 Hz, where amplitude height is about 0.002 mm
to 0.003 mm
c.
Other frequency bands have approximately the same amplitude
of about 0.001 mm and deviations are not very striking or statistically
interesting.
Frequency band 500-600 Hz:
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Sergej HLOCH, Vincent PERZEL, Pavol HREHA, Hakan TOZAN,
Jan VALICEK
Vibration and acoustic emission in this frequency band is generated
by the resonance of cut material itself. Frequency band was changed in this
range, in response to change of shape in the process of cutting, where
dimensions, shape, weight cutting of metal material and, consequently, its
own resonance frequency were continually changed.
12.500 Hz frequency band:
Vibration and acoustic emission of around 12.5 kHz is formed by
impacts of abrasive particles on the surface of the cut material. Therefore,
frequency spectrum matches the information curve from all four sensors and
only small differences are in amplitude height. Given the fact, that in both
experiments were measured approximately the same waveforms of the
frequency ranges and their amplitudes, abrasive mass flow does not play a
major role in developing the vibration and acoustic emission in the abrasive
particles impact on the metal material in its destruction. But we can predict
change in frequency band when changing MESH numbers or when
changing other factors (type of abrasive, its specific weight, diameter of
focus tube).
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Vibration As A Source of Information for Abrasive Waterjet Monitoring
Figure 4. Diagram of vibration, Position of sensors is indicated by cursor in graphic
representation, v = 100 mm.min-1, ma = 400, 250 g.min-1, p = 350 MPa, df = 0,8 mm
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Sergej HLOCH, Vincent PERZEL, Pavol HREHA, Hakan TOZAN,
Jan VALICEK
Figure 5. Frequency analysis diagram v = 100 mm.min-1, ma = 400, 250g. min-1, p = 350
MPa, df = 0,8 mm
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Vibration As A Source of Information for Abrasive Waterjet Monitoring
5. CONCLUSION
This study deals with the examination of the course of vibration
signal and its spectrum scanned during cutting the experimental sample by
four piezoelectric accelerometers. The experimental sample was a metal
plate made of AISI 309 material. Process of experiments, measured values
give a sufficient amount of information by which you can competently
assess the AWJ process through by studying the secondary physical
processes accompanying the process of its own. Results and values of
measured amplitudes and frequency spectrum shows the link between the
input factors, their values and parameters of accompanying processes vibration and acoustic emissions. In another direction of experiments with
measurement of vibration and acoustic emission spectrum it will needed to
focus on finding a description of the relationship between the nature of the
emission spectrum and topography of surfaces, which are created by AWJ
technology, subjected to object measurement. By careful analysis of the
quality, surface roughness, their identification, assigning to the individual
courses of vibration and acoustic emission it will be possible to determine
the correlation, the relationship between the quality of cut surfaces, the
quality of AWJ process and its physical manifestations. This correlation will
be step to create and fulfillment of logical scheme of AWJ process
management using feedback from its secondary manifestations.
Analysis and data processing of vibration and acoustic emission may
be a useful additional source for the expansion and fulfillment of software
applications necessary for managing the process in the off-line or on-line
mode with the aim of quality control in various technological operations of
material cutting, possibly also in the machining process.
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