U.S. patent application number 11/916140 was filed with the patent office on 2008-12-11 for method for machining a workpiece.
This patent application is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Wolfgang Mutscheller.
Application Number | 20080306620 11/916140 |
Document ID | / |
Family ID | 35759123 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080306620 |
Kind Code |
A1 |
Mutscheller; Wolfgang |
December 11, 2008 |
Method for Machining a Workpiece
Abstract
The invention relates to a method for machining a workpiece (20)
on a numerically controlled machining device (9), whereby two or
more machining steps (11, 12, 13) are provided for machining the
workpiece (20). A machining data record (28) for controlling and/or
adjusting the numerically controlled machining device (9) can be
run in a control and/or adjustment device (26) of the numerically
controlled machining device (9) together with a program (30) for
operating the control and/or adjustment device (26). The machining
data record (28) is used together with the program (30) for
operating the control and/or adjustment device (26) to generate
simulation data (47) in a simulation step. Subsequently, simulated
material removal data (49) are generated from the simulation data
(47) by means of a material removal simulation. The invention
provides a simple method of controlling the machining steps of
workpieces that are produced in a plurality of machining steps.
Inventors: |
Mutscheller; Wolfgang;
(Stuttgart, DE) |
Correspondence
Address: |
HENRY M FEIEREISEN, LLC;HENRY M FEIEREISEN
708 THIRD AVENUE, SUITE 1501
NEW YORK
NY
10017
US
|
Assignee: |
Siemens Aktiengesellschaft
Munchen
DE
|
Family ID: |
35759123 |
Appl. No.: |
11/916140 |
Filed: |
May 26, 2006 |
PCT Filed: |
May 26, 2006 |
PCT NO: |
PCT/EP06/62637 |
371 Date: |
June 27, 2008 |
Current U.S.
Class: |
700/109 ;
700/108 |
Current CPC
Class: |
G05B 19/4097
20130101 |
Class at
Publication: |
700/109 ;
700/108 |
International
Class: |
G05B 19/401 20060101
G05B019/401; G06F 19/00 20060101 G06F019/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2005 |
DE |
10 2005 025 338.5 |
Claims
1.-10. (canceled)
11. A method for machining a workpiece on a numerically controlled
processing machine in two or more machining steps, the method
comprising the steps of: executing in a control device of the
processing machine a machining data record for machining the
workpiece together with a program for controlling the numerically
controlled processing machine, generating, in a simulation step,
simulation data from the machining data record in conjunction with
the program that controls the numerically controlled processing
machine, and generating, in a material removal simulation step,
from the simulation data simulated material removal data.
12. The method of claim 11, wherein data from the machining data
record or from the program that operates the control device, or
both, are used in the material removal simulation.
13. The method of claim 11, further comprising the step of
generating simulated geometry data of the workpiece from the
material removal data.
14. The method of claim 13, further comprising the steps of
machining a workpiece in a first machining step in accordance with
a first machining data record, and comparing the measured geometry
data of the workpiece with the simulation data.
15. The method of claim 11, further comprising the steps of
machining a workpiece in a first machining step in accordance with
a first machining data record, measuring geometry data of the
workpiece, calculating from the measured geometry data of the
workpiece material removal data, and comparing the calculated
material removal data with the simulated material removal data.
16. The method of claim 14, further comprising the steps of
calculating for a current machining step a difference between the
measured geometry data and the simulated geometry data or between
the measured material removal data and the simulated material
removal data, and modifying a machining data record of a subsequent
machining step depending on whether the difference exceeds a
threshold value.
17. The method of claim 15, further comprising the steps of
calculating for a current machining step a difference between the
measured geometry data and the simulated geometry data or between
the measured material removal data and the simulated material
removal data, and modifying a machining data record of a subsequent
machining step depending on whether the difference exceeds a
threshold value.
18. The method of claim 11, wherein the machining data record is
created using a CAD/CAM system.
19. The method of claim 11, wherein simulated data or measured data
or calculated data, or a combination thereof, are transferred to a
CAD/CAM system.
20. The method of claim 11, wherein the simulation step or the
material removal simulation step, or both, are carried out on the
control device or on a simulation computer.
21. A system for machining a workpiece on a numerically controlled
processing machine, comprising a control device configured to
execute a machining data record for machining the workpiece
together with a program for controlling the numerically controlled
processing machine, to generate simulation data from the machining
data record in conjunction with the program that controls the
numerically controlled processing machine, and to generate from the
simulation data simulating material removal data; and a measuring
probe for measuring the machined workpiece.
Description
[0001] The present invention relates to a method for machining a
workpiece on a numerically controlled machining device, two or more
machining steps being provided for machining the workpiece. Such a
method also includes a simulation method for three-dimensional
machining by a CNC-controlled machining device, in particular a
milling machine, and a descriptive data record required for this
purpose.
[0002] In the case of CNC-controlled machining devices, a workpiece
is either directly coded by a programmer or the workpiece is
modeled using a CAD system and is then converted into an equivalent
CNC part program. In this case, the CNC part program and the CAD
model correspond to idealized machining instructions for the
machining device. The CNC program is loaded into a CNC controller
and the machining device is controlled in accordance with the CNC
program. If the workpiece which has been manufactured in this
manner is within the desired manufacturing tolerances of an ideal
workpiece, no problems arise with this procedure. However, if the
manufactured workpiece does not meet the requirements imposed on
it, the question arises as to which variations can be used as a
basis for manufacturing a satisfactory workpiece.
[0003] Although it is possible to change individual machining
instructions and/or individual operating parameters of the
machining device in succession, to manufacture a new workpiece and
then to check this newly manufactured workpiece in order to correct
faults, this procedure is very laborious and is also intensive in
terms of costs, materials and time. This is also very particularly
true because it is often not known where to look for the cause of
the discrepancies between the actually manufactured workpiece and
the desired workpiece.
[0004] When manufacturing, in particular, complex parts, in
particular parts with a high volume of removed material, as occur,
for example, in aircraft construction or else in turbine
construction for power plants, a plurality of process steps with
different tools are necessary. Since there is no CAD model for the
individual subprocesses for producing a part, the part being a
workpiece, the quality of the subprocesses cannot be directly
measured at present. Only the result of the overall process can be
measured on a measuring machine or else on the manufacturing
machine. This means that even faults which occurred as early as in
the first process step can only ever be discovered after the entire
part, for example a turbine blade, has been completed. This
procedure may result in the following problems, for example: [0005]
parts/workpieces are always finished even when irreparable damage
to the part, which was not detected, occurred as early as shortly
after the beginning of manufacture. Valuable machine time is thus
wasted; [0006] the previously customary practice of measuring the
parts on a measuring machine is very cost-intensive since, on the
one hand, the measuring machines for large parts are very expensive
and, on the other hand, the chucking of the workpieces, which are
sometimes very large, onto the measuring machine is extremely
complicated; [0007] production faults are often only detected weeks
after the parts have been manufactured, with the result that a
whole series of parts has been incorrectly manufactured in this
time under certain circumstances; [0008] faults which have been
detected in the previously known manner can be uniquely associated
with a subprocess in the rarest cases, with the result that fault
correction is again very complicated because all subprocesses have
to be examined.
[0009] The object of the present invention is to provide a possible
way of detecting faults during stepwise machining of a workpiece in
a considerably faster, simpler and/or more cost-effective manner
than in the prior art.
[0010] The object is achieved by means of a method for machining a
workpiece that has the features as claimed in claim 1. Dependent
claims 2 to 9 develop further inventive methods for machining
workpieces. Claim 10 relates to a system for carrying out one of
the inventive methods.
[0011] In the inventive method for machining a workpiece on a
numerically controlled machining device, two or more machining
steps are needed to machine the workpiece and are accordingly also
provided. A machining data record, which can be executed in a
control and/or regulating device of the numerically controlled
machining device together with a program for operating the control
and/or regulating device, is provided for the purpose of
controlling and/or regulating the numerically controlled machining
device. The machining data record is, for example, at least one
part program. The machining device is, in particular, a machine
tool or else a production machine or an automatic handling machine.
A machine tool may be provided, for example, for the following
machining operations: drilling, milling, grinding, turning etc. The
machining device has a control and/or regulating device, for
example an NC controller or else a CNC controller, such controllers
either being integrated in the machining device or else being
functionally assigned to it. An operating system which is also
referred to as an NC core (NCC) is needed to operate the control
and/or regulating device. This NC core represents runtime software.
Simulation data are generated according to the inventive method.
These simulation data are generated in a simulation step from the
machining data record together with the program (NCC) for operating
the control and/or regulating device. The simulation can be carried
out in one or else more steps. The simulation data are, in
particular, the data which are produced as a result of the part
program being processed by the NCC. In order to calculate these
simulation data, it is possible to use either the real NC core on
the control and/or regulating device or else a simulated NC core.
The simulated NC core may also be referred to as a virtual NC core
(VNCC), the latter running, for example, on a computer which is not
provided for controlling and/or regulating the machining device. In
a further developed embodiment, the VNCC is integrated in the
control and/or regulating device. Furthermore, according to the
inventive method, the simulation data are passed to a material
removal simulation after they have been generated, simulated
material removal data being generated from the simulation data. The
geometry data of the workpiece can then be calculated from the
simulated material removal data following a particular and/or any
desired machining step by means of a calculation involving the
original geometry data of the workpiece and just the material
removal data. The geometry data following an x-th machining step
are then advantageously compared with actually measured geometry
data following the x-th machining step. If the measured geometry
data correspond to the calculated--simulated--geometry data, the
next machining step can be carried out. If the measured geometry
data do not correspond to the calculated--simulated--geometry data,
the discrepancy of the geometry data can be calculated. The
discrepancy can be used as a basis for determining, in an automated
manner, whether the workpiece to be machined can be used further by
means of remachining or whether the workpiece to be machined must
be withdrawn from further machining. In an advantageous manner, a
machining record is either modified for a subsequent machining
step, or else the machining record is recalculated for a machining
step that is to be newly inserted, in an automated manner with the
aid of the differing geometry data.
[0012] A simulation of an operation of machining a workpiece is
used in the inventive method. In this case, the data record which
describes the machining operation on the machining device--the
machining data record--is used. Consequently, a desired machining
operation by means of idealized machining instructions for the
machining device can be determined on the basis of a descriptive
initial data record. The initial data record is the description
data record in this case.
[0013] The inventive method can be used to overcome fundamental
disadvantages of the previously known method for machining a
workpiece in a plurality of machining steps on a numerically
controlled machining device.
[0014] NC verification software has previously been used for
simulation but said software simulated the program for operating
the machining device only to an insufficient extent. The software
of the NC core itself is now used according to the invention to
generate the simulation data. In this case, however, a virtual NC
core (VNCC), that is to say an NC core which does not run on the
machining device itself, can also be used. Since the VNCC
reproduces the control behavior exactly, even minor geometric
discrepancies which are generated by control functions, for example
a compressor, rounding of corners or tool correction, can be
detected as early as during simulation. As a result of the fact
that such control functions which are present in the NC core are
concomitantly taken into account when generating the simulation
data, the accuracy of the latter is considerably increased. These
data and the subsequent material removal simulation can be used to
calculate the geometry data of intermediate steps in the operation
of machining a workpiece in a very accurate manner. Accurate
control of the precision of machining progress is thus always
ensured since measured data can be compared with simulation
data.
[0015] It is consequently advantageous if data are taken from the
machining data record and/or from the program for operating the
control and/or regulating device, the NC core, in the material
removal simulation. For the rest, the use of the material removal
simulation is also important because the NC core (NCC) or the VNCC
has already concomitantly taken into account tool geometries, for
example, in its initial data. Since different tools with different
tool geometries can be used to manufacture the same workpieces
using only one machining data record, that is to say only one part
program for example, the NCC or the VNCC calculates different
initial data on the basis of the tool geometry known to it. These
possible variations can be corrected again using the material
removal simulation. Simulated geometry data of a workpiece which
can be used for intermediate measurements in order to verify that
an operation of machining a workpiece is taking place correctly can
consequently be generated from material removal data. Tool-specific
data, for example radii of milling tools, are advantageously
automatically transferred from the NCC or the VNCC to the material
removal simulation.
[0016] In one advantageous refinement, the material removal
simulation is used to generate a measurement program for each
substep. It was previously the case that only the CAD model was
available as a reference for measurement. That is to say only the
completely machined part could ever be measured correctly. NC
verification software with an attributed VNCC is now able to
exactly represent the material removal for each machining step. It
is thus able to generate a desired geometry after each step, said
desired geometry corresponding to a CAD model for each process
step. It is thus possible to reference the result of each substep
to a geometry model and to generate the predefined desired values
for control measurements after each step. These predefined desired
values are in the form of measurement programs, for example, which
are loaded onto the machine controller. The corresponding
measurement program then exists for each machining program or
program section.
[0017] The inventive method now makes it possible to directly check
the result of each individual machining step on the machining
device by introducing a measuring probe instead of the tool and
executing a measurement program, for example. A machine operator
can directly identify whether the result of the machining operation
is in the permitted tolerance range by comparing the desired and
actual values which can both be logged. In the event of a fault,
the process is immediately interrupted and fault analysis can be
started.
[0018] This procedure is considerably simpler than the conventional
method since the fault can be associated with a single machining
step. It also avoids valuable machine time being wasted with a part
which has already been destroyed. If the result of each substep is
positive, the measurement records provide the proof that the
overall process was successful and the part produced corresponds to
the specifications. There is thus no need for a separate
measurement on a measuring machine. If the quality of the
simulation and of the measurement is intended to be checked in the
machining device using a measuring probe, it is additionally
possible to use a measuring machine.
[0019] In order to improve the stability of the process of checking
machining steps using simulation data, the machining device is
periodically calibrated. This is ensured, for example, by means of
a method which is used to monitor the state of the machining device
and thus also its geometric quality at regular intervals of time.
This is also known under the phrase "Electronic fingerprints for
machine tools and production machines".
[0020] In another advantageous refinement, the NC core is
integrated in a material removal simulation. This considerably
improves, for example, the NC programs as early as at the
programming station. Integration also affords the advantage that a
reference geometry which makes it possible to automatically measure
the partial results on the machining device is generated for each
subprocess.
[0021] As a result of the inventive method, problems when machining
a workpiece can be detected at the earliest possible time. It is
possible to avoid the manufacturing process being continued and
thus expensive machine time being wasted if incorrect material
removal has taken place. The method highly simplifies fault
analysis since faults can be directly associated with a subprocess.
Causes of faults are detected more rapidly and can thus also be
eliminated more rapidly. The expensive infrastructure for
separately measuring the finished parts which is required according
to the prior art can be dispensed with as a result of the inventive
method without resulting in losses of quality.
[0022] In the case of an inventive method, it is possible to
machine a workpiece in a first machining step in accordance with a
first machining data record and to measure geometry data of the
workpiece, after which the measured geometry data of the workpiece
are compared with the simulated geometry data. If the geometry data
do not correspond or if the predefined tolerances have been
exceeded, a new machining data record which can be used to further
machine the workpiece in corrected form in a subsequent machining
step can be generated early on.
[0023] Geometry data can be compared, for example, as follows. A
workpiece is machined in a first machining step in accordance with
a first machining data record, after which geometry data of the
workpiece are measured. Material removal data are then calculated
from the measured geometry data of the workpiece, after which the
calculated material removal data are compared with the simulated
material removal data. In another advantageous refinement, the
simulation is carried out in real time in parallel with the actual
machining of the workpiece or else after the workpiece has been
machined in a machining step since it is thus also possible to use
data from the real NC core for the virtual NC core. Examples of
such data are, in particular, fluctuating variables such as room
temperature, fault messages etc.
[0024] In one advantageous refinement, as already commented above,
the difference between the measured geometry data and the simulated
geometry data or between the measured material removal data and the
simulated material removal data is calculated, after which a
machining data record which is provided for a subsequent machining
step is modified depending on whether a difference threshold is
exceeded.
[0025] The simulation of the NC core that is carried out in the
invention can be carried out, for example, on the control and/or
regulating device and/or on a simulation computer.
[0026] In addition to the method, the invention also relates to a
corresponding system for carrying out the method. The system is
designed in such a manner that, in addition to a means for
simulating the program for operating a control and/or regulating
device, it also has a means for simulating material removal.
Furthermore, it advantageously also has a means for measuring the
workpiece to be machined.
[0027] Examples of further advantages and details emerge from the
following description of an exemplary embodiment. In this case:
[0028] FIG. 1 shows a basic illustration of a method for machining
a workpiece in accordance with the previously known prior art,
[0029] FIG. 2 shows a basic illustration of an inventive method,
and
[0030] FIG. 3 shows a basic illustration of a machining device in
diagrammatic form.
[0031] The integrated system 1 which is illustrated in FIG. 1 and
is intended to manufacture complex parts is known according to the
prior art. The complex parts, that is to say parts/workpieces which
need to be machined in a plurality of steps 11, 12, 13, are modeled
in a CAD (Computer Aided Design) system 3. A CAM (Computer Aided
Manufacturing) system could also be used, for example, instead of
or else in addition to the CAD system 3. The CAD system 3
generates, together with a post-processor, the part programs 5
needed to machine a workpiece. The part program 5 is an NC program.
One single NC program and/or a plurality of NC programs 5 with a
plurality of tool changes may be generated for the overall process
of machining a workpiece, for example. However, it is also possible
to generate a separate NC program for each tool. Machining with a
tool corresponds to a subprocess. The NC programs 5 are then tested
using a verification system 7. The verification system 7 has NC
verifications software, for example. Vericut.RTM. is one example of
such verification software. During verification, collisions between
chucking of the workpiece, for example in a machine tool, and the
workpiece are checked, in particular. At the same time, a material
removal simulation is used to check whether the NC programs result
in the desired workpiece geometry. That is to say the result of the
material removal simulation is compared with the original CAD
model. If correspondence is within the fixed fault tolerances, the
programs are released for manufacture and are transmitted to the
machine controller of a machine, in particular a machining device
9. The workpiece is manufactured using the NC programs 5, which may
last several hours to days, particularly in the case of parts
(workpieces) having a high degree of material removal, for example
approximately 95%. High degrees of material removal exhibit
material removal of more than 80%, in particular. The machining
device 9 carries out various steps 11, 12 and 13 in the operation
of machining the workpiece or workpieces. By way of example, only
three machining steps 11, 12 and 13 are shown in the illustration
according to FIG. 1 but further steps are indicated in step 12. The
finished workpiece is then measured in a measuring step 15 on a
measuring machine and is either certified 35 or segregated 37. This
operation may again last several days to weeks. If the workpiece is
segregated 17, it may either be remachined 19 in a remachining
device (if too little material has been removed) or must be
definitively scrapped 21. In both cases of scrapping 21 and
remachining 19, however, production must be stopped and the source
of the fault must be determined with laborious manual work. The
practice of finding the source of the fault is used to reduce the
segregation rate.
[0032] Possible types of faults which advantageously have to be or
can be identified are listed below: [0033] a faulty geometry of the
parts [0034] a machine fault [0035] incorrect dimensions of a blank
[0036] dynamic problems during machining (for example: running-on
faults) [0037] faulty chucking of the part/workpiece [0038] tool
problems [0039] temperature influences during machining [0040]
deformation of the part/workpiece during the machining process
(bending, curvature)
[0041] The previously known method for machining a workpiece in a
plurality of steps may entail at least one of the disadvantages
specified below: [0042] a fault is detected only after complete
machining; if a problem occurs as early as in the first substep,
work is nevertheless continued until the fault is detected; machine
time is lost in this case; [0043] production is continued until the
fault has been detected; this may mean that a large number of
additional faulty parts are produced, which entails a corresponding
loss of time and material; [0044] the operation of measuring the
parts on the measuring machine 15 requires a complicated and costly
infrastructure; [0045] it is very difficult to associate a problem
with a subprocess or a specific source of faults; [0046] NC
verification systems 7 according to the prior art have the
disadvantage that the control behavior is emulated; this inevitably
results in situations in which the material removal simulation
corresponds only approximately to reality and geometric faults in
the part program therefore cannot always be detected.
[0047] The illustration according to FIG. 2 shows, by way of
example, an inventive method for machining a workpiece on a
machining device. The machining device may be in the form, for
example, of a milling machine or else another machine tool, for
example a drilling machine or turning machine. The machining device
could also be in the form of an industrial robot or a special
machine.
[0048] In contrast to FIG. 1, FIG. 2 illustrates NC verification
software comprising a virtual NC core VNCC. This results in a
verification system 8 which has been extended by the VNCC. In this
case, the emulation software for a CNC system has been replaced
with the VNCC. This enables an integrated system 2 which is
improved in comparison with FIG. 1. Since the VNCC reproduces the
control behavior exactly, even minor geometric discrepancies which
are generated by control functions, such as a compressor, rounding
of corners or tool corrections, can be detected as early as during
simulation. Furthermore, the extended verification system 8 has a
material removal simulation. The material removal simulation is
used to generate a measurement program for each substep 11, 12 or
13 of a machining operation. It was previously the case that only
the CAD model was available as a reference for measurement. That is
to say only the completely machined part could ever be measured
correctly. The extended NC verification software with the
attributed VNCC is now able to exactly represent the material
removal for each machining step 11, 12 and 13. It is thus possible
to generate a desired geometry after each step, said desired
geometry corresponding to a CAD model for each process step. It is
thus possible to reference the result of each substep to a geometry
model and to generate the predefined desired values for control
measurements after each step. These predefined desired values are
in the form of measurement programs 45 which can be loaded onto a
machine controller. The corresponding measurement program 45 then
exists for each machining program or program section. This makes it
possible to directly check the result of each individual machining
step 11, 12 and 13 on the machine 9 by, for example, introducing a
measuring probe and executing the measurement program 45. A machine
operator can directly identify whether the result of the machining
operation is in the permitted tolerance range by comparing the
desired and actual values which are both logged. In the event of a
fault, the process is immediately interrupted and segregation 17 is
carried out. Segregation 17 can be followed by scrapping 21 or
remachining 19 depending on the severity of the fault. For
remachining 19, which is advantageously carried out on the
machining device 9 again, a CAD/CAM system, for example, is used to
generate at least one remachining NC program. If segregation 17 is
required, fault analysis may be started. This fault analysis may
result in one or more NC programs 5 being modified. This procedure
is considerably simpler than the conventional method since the
fault can be associated with a single machining step. It also
avoids valuable machine time being wasted with a part which has
already been destroyed. If the result of each substep is positive,
the measurement records provide the proof that the overall process
was successful and the part produced corresponds to the
specifications. In order to improve the stability of the machining
process, it is possible to periodically calibrate the machining
device. This is ensured by means of a method which is used to
monitor the state of the machine and thus also its geometric
quality at regular intervals of time (Electronic fingerprints for
machine tools and production machines).
[0049] The integrated system 2 according to FIG. 2 thus shows both
a verification system 8 which has been extended by a VNCC and
additional measurement programs 45 for measuring steps 41, 42 and
43. These additional measuring steps 41, 42 and 43 make it possible
to check each machining step 11, 12 and 13. However, it is not
compulsory for each machining step to also be followed by a
measuring step. The number of measuring steps 41, 42 and 43 can be
advantageously freely selected.
[0050] The illustration according to FIG. 3 shows a machining
device 9 in diagrammatic form. The machining device 9 has a control
and/or regulating device 26. This control and/or regulating device
26 is provided for processing machining data records 28. A program
30 is provided for the processing operation. This program is an NC
core which is used as a type of operating system for the control
and/or regulating device 26. The machining data record 28 is
provided for the purpose of describing the operation of machining a
workpiece 20 with a tool 22. The illustration according to FIG. 3
also shows a simulation computer 32 which can be used, for example,
to simulate the NC core. This then corresponds to a virtual NC core
(VNCC).
* * * * *