U.S. patent application number 12/591955 was filed with the patent office on 2010-10-21 for arrangement of devices and a method for empirically for determining efficiency index in abrasive waterjet cutting and application thereof in a device for simultaneous control of abrasive waterjet cutting.
Invention is credited to Mladen Cvjeticanin, Mihael Junkar, Andrej Lebar, Henri Orbanic, Alojz Poredos.
Application Number | 20100267314 12/591955 |
Document ID | / |
Family ID | 42338243 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100267314 |
Kind Code |
A1 |
Cvjeticanin; Mladen ; et
al. |
October 21, 2010 |
Arrangement of devices and a method for empirically for determining
efficiency index in abrasive waterjet cutting and application
thereof in a device for simultaneous control of abrasive waterjet
cutting
Abstract
An arrangement of devices for determining an efficiency index in
abrasive waterjet cutting, i.e. the index unambiguously defining
for a certain material the shape of a cut, roughness of surfaces
created by cutting, their conical nature depending on the incidence
angle of the abrasive waterjet. The arrangement of the invention
consists of a known abrasive waterjet cutting machine (1), a
thermographic camera (2) and a computer (3), wherein a workpiece
(4) is arranged on said machine (1), said workpiece being intended
to undergo a cutting procedure; and fixed and variable process
parameters (A) of cutting are known: hydraulic, cutting, mixing,
abrasive and input parameters of said workpiece. Said thermographic
camera (2) is positioned in a way to record in front view the
entire front surface (5) of a cut in the workpiece (4) in a known
time interval, in that an adequate programme within said computer
(3) allocates to each thermographic image (6) cutting parameters
(A) that were valid for each point (B) of cutting and finally shows
them in the form of a table or chart of a relationship between the
efficiency index and one of the parameters (A).
Inventors: |
Cvjeticanin; Mladen;
(Ljubljana, SI) ; Lebar; Andrej; (Trzic, SI)
; Junkar; Mihael; (Piran, SI) ; Poredos;
Alojz; (Dol pri Ljubljani, SI) ; Orbanic; Henri;
(Ljubljana, SI) |
Correspondence
Address: |
JACOBSON HOLMAN PLLC
400 SEVENTH STREET N.W., SUITE 600
WASHINGTON
DC
20004
US
|
Family ID: |
42338243 |
Appl. No.: |
12/591955 |
Filed: |
December 4, 2009 |
Current U.S.
Class: |
451/2 |
Current CPC
Class: |
G01J 2005/0077 20130101;
G01F 1/8468 20130101; G01N 3/567 20130101; B24C 1/045 20130101 |
Class at
Publication: |
451/2 |
International
Class: |
B24C 3/00 20060101
B24C003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2009 |
SI |
P 2009 0 0110 |
Sep 17, 2009 |
SI |
P 2009 0 0250 |
Claims
1. An arrangement of devices for determining an efficiency index in
abrasive waterjet cutting, i.e. the index unambiguously defining
for a certain material the shape of a cut, roughness of surfaces
created by cutting, their conical nature depending on the incidence
angle of the abrasive waterjet, wherein said arrangement consists
of a known abrasive waterjet cutting machine (1), a thermographic
camera (2) and a computer (3), wherein a workpiece (4) is arranged
on said machine (1), said workpiece being intended to undergo a
cutting procedure; and fixed and variable process parameters (A) of
cutting are known: hydraulic, cutting, mixing, abrasive and input
parameters of said workpiece, characterised in that said
thermographic camera (2) is positioned in a way to record in front
view the entire front surface (5) of a cut in the workpiece (4) in
a known time interval, in that an adequate programme within said
computer (3) allocates to each thermographic image (6) cutting
parameters (A) that were valid for each point (B) of cutting and
finally shows them in the form of a table or chart of a
relationship between the efficiency index and one of the parameters
(A).
2. Arrangement as claimed in claim 1, characterised in that the
most adequate parameter (A) for a link to the efficiency index is
the speed of cutting.
3. Method for empirical determination of an efficiency index in
abrasive waterjet cutting by use of the arrangement as claimed in
claim 1, characterised in that prior to industrial application of
any material on its sample, cutting is performed on the arrangement
of devices described above, charts or tables are then prepared and
offered to users of the treated material, who use the data from
said tables or charts to set their abrasive waterjet cutting
device.
4. A device for the control of the abrasive waterjet cutting device
(1), characterised in that it consists of a thermal camera (2),
oriented towards the cut in a way to detect it in front view, of a
microprocessor (3) receiving the images from said camera (1),
wherein said camera evaluates each image separately based on the
data from a library (5) of data, which are needed for the creation
of control signals for a continuous changing of parameters (A) of
cutting: speed of advancement of a workpiece, waterjet pressure,
content of abrasive material in the waterjet, distance of a cutting
head (6) from a surface (7) of a workpiece (8) etc., further of a
library (9) of data (B) on the shapes of a cut with belonging
properties, especially precision and roughness of cutting and then
generates control signals for the control of said device (1).
5. Device as claimed in claim 1, characterised in that it may be
joined to a device (1) and separated from said device (10) for
cutting in industry, wherein the data (A) obtained by the device of
the invention are transferred to the device (10) in a digital or
written form, so that an operator of said device (10) can use the
data (A) as the process advances based on the current need.
Description
SUBJECT OF INVENTION
[0001] The subject of the present invention is an arrangement of
devices and a method for determining an efficiency index in
abrasive waterjet cutting, i.e. the index unambiguously defining
for a certain material the shape of a cut, roughness of surfaces
created by cutting, their conical nature depending on the incidence
angle of the abrasive waterjet and application thereof in a device
for simultaneous control of abrasive waterjet cutting.
TECHNICAL PROBLEM
[0002] The technical problem solved by the present invention is how
to design such arrangement of devices that would provide a cutting
efficiency index for a known material based on a cutting experiment
in order to use this index to define cutting parameters of the same
material in industrial application of cutting of this type, wherein
a method for determining said index should be adapted to said
arrangement and that said arrangement would render it possible to
be applied into a device for simultaneous control of waterjet
cutting that would enable immediate correct cutting without
preliminary tests on a workpiece with respect to a selected type of
cutting: [0003] a) as quick cutting as possible, yet less precise;
or [0004] b) precise, yet slower.
PRIOR ART
[0005] When a method of abrasive waterjet cutting is used in
industry, test cutting of identical or equal material should be
performed first, in order to attain the desired type of cutting
with respect to the anticipated quality of the cut-off part (shape
of the cutting surface and its inclination, precise dimensions of a
workpiece) as a function of cutting speed. All this contributes to
an economic optimum of a selected method. Preliminary tests in
industry are time consuming and cause scrap, which represents an
additional cost.
[0006] Therefore there is a need for the industry to obtain an
unambiguously defined efficiency index for a specific type of
material for the field of application of this type of cutting by
means of a special device or an arrangement or a procedure. This
index would be a basis to determine parameters for industrial
cutting devices that would yield an anticipated result with respect
to the selected parameters (shape of cutting surfaces and dimension
tolerance of a workpiece under consideration of cutting speed) for
an optimum cutting procedure. It is considerably cheaper and of a
much better quality if this index is determined for each material
on one spot foreseen for tests of this type and then available to
each user of such material. The implementation of a testing spot
and distribution of each efficiency index are not the subject of
the present invention.
[0007] Various values measured at different locations in a cutting
procedure of this type have been used as a kind of efficiency
index.
[0008] It is a know fact that sound emission within a cutting head
was linked to the properties of the surface resulting from cutting.
Further, the abrasive waterjet was optically monitored in the area
between the nozzle and the workpiece. The geometry of the nozzle
changes with use and consequently the shape of the jet changes as
well, which contributes to cutting properties. A further property
that was measured and to which the quality of cutting was linked is
temperature within the nozzle. As the nozzle is worn out, its
temperature increases during operation. The quantity of suctioned
air into the nozzle was measured as well. There is a relation
between the wear of the nozzle and a negative change in the shape
of the waterjet, owing to which cutting is much worse, i.e. the
cutting surface is less smooth and dimensions are imprecise.
[0009] A further known method is a method of measuring density of
abrasive particles in a waterjet by means of added magnetic
particles having the same density as the abrasive particles. The
properties of the waterjet were measured by a focular speedometer
with two lasers.
[0010] A high speed camera and a double laser beam have been used
as well to measure and monitor the visible jet with abrasive
particles.
[0011] The use of a thermographic camera for the monitoring of
temperature of individual points on the cutting part of a workpiece
during cutting is also known.
[0012] Further, two methods of operating abrasive waterjet cutting
are also known U.S. Pat. No. 6,021,682 (Jiyue Zeng) and U.S. Pat.
No. 6,244,927 (Jiyue Zeng).
[0013] All the mentioned processes of monitoring and measuring
abrasive waterjet cutting performed during an industrial cutting
process or outside this process as tests are characterised by the
fact that individual measuring results are implemented as
comparative data and for this reason corrections are needed as the
process advances in order to reach the desired cutting property. An
initial scrap of products can be anticipated, which is not desired.
Moreover, each device including an industrially applicable cutting
device of this type must comprise all measuring and control
instruments, which extends the time of preparation of the device
for series production and increases the costs per hour. In order to
achieve a quality result in this type of cutting, a highly trained
operator of the device is needed. All the above stated conditions
are a drawback for industrial, i.e. series application, which
results in high price and/or poor quality of the cut, in short, in
the service being uncompetitive.
[0014] So there is a need for a new way of monitoring, measuring
and even evaluating the property of cutting by abrasive waterjet
cutting, so that the above indicated disadvantages are eliminated
in industrial application.
[0015] Moreover, several devices are known that are adaptable to a
waterjet cutting device and simultaneously measure various
parameters typical of cutting of this type. Preliminary tests can
show a correlation between a selected parameter and the quality of
cutting. An adequate device uses its sensor to detect changes in
the selected parameter during cutting and automatically controls
one of the cutting parameters: water pressure, advancement of a
workpiece, removal of a cutting nozzle from a workpiece and the
like. The purpose of detecting changes is to reach a constant and
desired cut in the sense of quality of the cut with anticipated
roughness and precision, which is dictated by the aspect of economy
and technology.
[0016] According to U.S. Pat. No. 6,021,682 it is measured by means
of a pressure chamber that measures the change in pressure of a
waterjet in the area between a cutting head and a workpiece. The
change is taken into account by the control unit in determining the
speed of advancement of the workpiece during cutting for a selected
quality of cutting. Such method encounters problems in an uneven or
stepped surface adjacent to the cutting nozzle, since it is very
difficult to ensure unchanged conditions of tightness that also
have influence on the waterjet pressure.
[0017] According to U.S. Pat. No. 6,244,927 the above problem is
done away with by measuring pressure of the waterjet in the cutting
head. The pressure in the cutting head depends on its distance to
the surface of the workpiece and its thickness in the area of
current cutting. Pressure significantly changes in the initial
situation of cutting, when piercing of the waterjet through
material is effected. Control of such device is effected on the
basis of comparison with reference pressure that the cutting device
should provide for during the entire period of cutting. Such device
is adequate for large series cutting of workpieces having constant
thickness that determines the constant reference pressure. In other
cases too considerable deviations are encountered and manual
correction is needed. A question of cost efficiency of such
procedure arises in small series cutting or even in the cutting of
individual workpieces.
[0018] According to U.S. Pat. No. 5,854,744 underpressure within a
tube for the supply of abrasive granules to the waterjet is
monitored. This pressure is influenced by individual situations of
cutting. The shape of the workpiece does not have any influence in
this process, yet the reference pressure is not constant in a
workpiece that changes in dimensions and material. This method is
therefore not generally applicable.
[0019] There is a need for such abrasive waterjet cutting device
and process that could simultaneously be applicable in cutting
series workpieces but also individual ones, in cutting materially
homogeneous workpieces and even workpieces composed of several
materials. Cutting of unique workpieces is especially problematic,
since they need to be cut precisely, and what's more, such
workpiece has been machined earlier by other methods and is
composed of such material that its price prior to processing by
this process is that high that scrap would be unjustified.
Moreover, there are instances, in which no errors in cutting
whatsoever can be tolerated at all.
[0020] Apart from the above reasons the price of cutting is very
important, especially in series workpieces. The price of cutting is
influenced by the exploitation of the cutting machine, with which
the actual depreciation cost of the machine can be calculated and
this is a constituent part of the price of the machine per hour. If
actual use of a machine of this type is to be planned, the times of
preparation and the times of actual cutting for an individual
product need to be known in advance. An unexpected time for the
preparation of cutting or for corrections and even replacement of
scrap brings too many unknowns for such planning. A need for such
device and a method for the control of an abrasive waterjet cutting
device that would provide for the above-mentioned matters is
obvious.
Solution to the Technical Problem
[0021] The described technical problem is solved by a new
arrangement of devices for determining an efficiency index in
abrasive waterjet cutting, which is characterised by the use of a
thermographic camera directly recording temperature on the entire
front surface of a cut on a workpiece continuously during cutting
procedure. Based on a proved fact, namely that each highest
temperature point is measured in the current point of cutting,
cutting parameters for a selected shape of cut and the speed of
cutting can be defined by taking the cutting speed into
consideration and represented in the form of a chart. This approach
based on the device of the invention makes it possible for a
certain organisation to set the efficiency index in cutting only
once and to forward it to all users of such cutting devices, who
can use this chart and a previously selected shape of cut to set
the parameters on the cutting machine. This results in no scrap
upon a start-up of each series cutting, in a considerable shorter
time of preparation of series cutting and in higher cutting
quality. And what's more such procedure can be performed even by a
less skilled operator.
[0022] An essential characteristic of the integration of said
arrangement of devices into a device for continuous abrasive
waterjet cutting lies in that it is construed with a video camera
that monitors the shape of the cut during cutting and based on its
shape and on a previously selected criterion for quality or cutting
speed a microprocessor regulates the selected parameters on the
cutting machine: speed of movement of the workpiece, pressure of
the waterjet, content of abrasive material, distance of a cutting
nozzle from the workpiece, etc. As a result, the cut corresponds to
the selected quality. Since the shape of the cut is directly
monitored in the procedure of the invention, all problems and
drawbacks of the devices described in prior art are done away with.
The device of the invention can be used for cutting a material of
an optional shape. Its surface at the cutting head no longer has
any influence on the cutting procedure, the material may even be
inhomogeneous and the workpiece may consist of various materials.
Since self-regulation starts immediately in this procedure, even
unique workpieces can be cut without any risk of scrap. When series
cutting of workpieces fluctuating in dimensions and homogeneity of
the material are in question, automatic cutting can be performed in
optimum conditions in order to achieve selected speed and cut
quality without undesired deviations that could cause scrap. A
condition for economic optimisation of the device for abrasive
waterjet cutting on a large scale is herewith met.
[0023] The characteristics of the invention will now be explained
in more detail by way of a description of an embodiment and the
enclosed drawings, representing in
[0024] FIG. 1 a schematic view of the arrangement of devices of the
invention,
[0025] FIG. 2 a schematic view of the procedure of the
invention,
[0026] FIG. 3 a schematic view of a flat surface of a
workpiece,
[0027] FIG. 4 a chart of efficiency index for two variables, [0028]
e.g.: advancement speed and cut roughness,
[0029] FIG. 5 a schematic view of the application in the device for
simultaneous cutting control with an abrasive waterjet according to
the first embodiment; and
[0030] FIG. 6 a schematic view of the application in the device for
simultaneous cutting control with an abrasive waterjet according to
the second embodiment.
[0031] An arrangement of devices for determining an efficiency
index in abrasive waterjet cutting, i.e. the index unambiguously
defining for a certain material the shape of a cut, roughness of
surfaces created by cutting, their conical nature depending on the
incidence angle of the abrasive waterjet consists of a known
abrasive waterjet cutting machine 1, further of a thermographic
camera 2 and a computer 3. A workpiece 4 is arranged on said
machine 1, said workpiece being intended to undergo a cutting
procedure. Control of the machine 1 for cutting a certain shape is
performed in a known way and is normally a constituent part of said
machine 1. It is important for the present invention that fixed and
variable process parameters A of cutting are known: hydraulic,
cutting, mixing, abrasive and input parameters of a workpiece. The
arrangement is characterised in that said thermographic camera 2 is
positioned in a way to record in front view a front surface 5 of a
cut in the workpiece 4 in a known time interval (number of images
per time unit).
[0032] An adequate programme within said computer 3 allocates to
each thermographic image 6 cutting parameters A that were valid for
each point B of cutting. Monitoring of cutting can help define an
unambiguous link between the current highest temperature detected
by said thermographic camera 2 and each cutting point B that is
shaped like a step. Monitoring further shows that the shape of the
front surface 5 of the cut in said workpiece 4 is curved in side
view. A square function is the most appropriate as the best
approximation in a mathematical notation of this curvature, or in a
slower cutting even a linear approximation is appropriate.
Inventor's observations and findings of cutting on which the above
allegations are based, are not subject of the present invention,
but originating points therefor. The regularity of said originating
points is confirmed by tests performed by the arrangement of
devices of the invention and the procedure of the invention
performed by the inventor.
[0033] By monitoring the shape of a cut and by evaluating the
profile of its surface that can be described by roughness and
corrugation and dimensional precision typical values can be
determined for such monitored type of cutting and for each
individual material and for known process parameters A therefor as
measured and recorded in said computer 3. The final result is a
table or chart of a relationship between the efficiency index and
one of the parameters A, preferably the one, which is the most
adequate piece of data for each setting of the abrasive waterjet
cutting machine, preferably the speed of cutting. The technical
problem set hereinbefore is herewith solved, which was the goal of
the invention.
[0034] The table or chart so prepared is then available to each
user of any material in an optional known way. The user uses the
table or chart to set the cutting machine, with which the
anticipated quality and economical nature of cutting are achieved,
if proper setting is applied. FIG. 3 shows a schematic view of a
cutting flat surface of a workpiece, wherein the abscissa (x)
represents the distance of each cutting point from the starting
point of cutting, the ordinate (y) represents the thickness of the
workpiece. FIG. 4 represents the final result in the form of a
chart, where the abscissa (x) represents the efficiency index in
cutting and the ordinate (y) represents the roughness of the
cutting surface, whereas the curve (z) shows the speed of
advancement of the workpiece with other parameters A being
constant.
[0035] The procedure of determining the efficiency index has the
following characteristics: prior to industrial application of any
material on a sample workpiece 4, cutting 10 is performed on the
arrangement of devices described above. Charts 11 or tables are
then prepared and offered to users of the treated material, who use
the data from said tables or charts to set their abrasive waterjet
cutting device 12.
[0036] Said tests can therefore be carried out in optional adequate
institutions in one place only once for one type of material. Data
are distributed in an optional way, either in paper form or
electronically via the Internet bearing in mind the principle
whether these information are payable or already included in the
price of the material.
[0037] The present invention can also be applied directly on an
abrasive waterjet treating machine. Two embodiments are hereinafter
represented and shown in FIG. 5 and FIG. 6, wherein the following
reference numbers refer to said figures.
[0038] A device for the control of the abrasive waterjet cutting
device 1 consists of a thermal camera 2, oriented towards the cut
in a way to detect it in front view. A microprocessor 3 receives
the images from said camera 1 and each image is evaluated
separately, which will be explained in more detail later. A
computer 4 that comprises said microprocessor 3 contains a library
5 of data needed for the creation of control signals for a
continuous changing of parameters A of cutting: speed of
advancement of a workpiece, waterjet pressure, content of abrasive
material in the waterjet, distance of a cutting head 6 from a
surface 7 of a workpiece 8 etc. The computer 4 further includes a
library 9 of data B on the shapes of a cut with belonging
properties, especially precision and roughness of cutting.
[0039] Since the number of images per time unit in said thermal
camera 2 is harmonised with the stroke of operation of said
microprocessor and with the speed of changing of said cutting
parameters A, it is achieved that in real time said microprocessor
3 changes the parameters A in a way that the cut always remains
within the limit of a selected shape of the cut B.
[0040] The second embodiment intended for abrasive waterjet cutting
devices for large-series workpieces foresees that test cutting for
each known material at various parameters A is performed only at
one location on sample workpieces 8 with said device 1 of the
invention in order to decrease the costs of purchase and to check
the existing devices, which are not yet adapted to such control. A
curve is obtained for each selected parameter, which defines the
cutting quality at various values of a selected parameter.
[0041] Such measurements may be performed by selected institutions
or by the manufacturer of a material, who can then offer these
charts C or adequate tables to the buyers of the material intended
to be cut by the method of abrasive waterjet cutting. The operator
of the device 10 for cutting--without the device of the
invention--sets parameters B on his device 10 based on these charts
C or table and immediately obtains the desired cut. Tables or
charts C may be provided digitally and the user may enter them into
a computer of the cutting device, if the latter is so advanced.
These data can be obtained on the basis of tests or even the
manufacturer of these devices may provide them to the owners. The
purchase costs of an abrasive waterjet cutting device intended for
large-series cutting are therewith decreased.
[0042] It is understandable that a man skilled in the art may
construct other embodiments based on the above disclosure, without
circumventing the essence of the invention defined in the appended
claims.
* * * * *