WORKPIECE TESTING METHOD AND WORKPIECE TESTING SYSTEM

Abstract

The invention relates to a workpiece testing method, in particular for testing workpieces (5) for internal defects (6), for example workpieces (5) made of fiber-reinforced plastic, comprising the following steps: applying ultrasonic waves (9, 19) to a workpiece (5), detecting ultrasonic signals (10, 20) generated by applying the ultrasonic waves (9, 19) to the workpiece (5), and generating ultrasonic tomogram data of the workpiece (5) from the ultrasonic signals (10, 20). The invention is characterized in that the workpiece (5) is machined, in particular milled, and the ultrasonic waves (9, 19) thus generated are applied to the workpiece (5). The invention furthermore relates to a workpiece testing system suitable therefor.

Claims

1. A workpiece testing method having the following steps: applying ultrasonic waves (9, 19) to a workpiece (5), capturing ultrasonic signals (10, 20) produced by applying the ultrasonic waves (9, 19) to the workpiece (5), producing ultrasonic tomograph data of the workpiece (5) from the ultrasonic signals (10,

20, characterized in that the workpiece (5) is machined and the ultrasonic waves (9, 19) thus produced are applied to the workpiece (5).

2. The workpiece testing method according to claim 1, characterized in that the workpiece (5) is manufactured by means of machining, by means of which the ultrasonic waves (9, 19) are produced and applied to the workpiece (5).

3. The workpiece testing method according to claim 1, characterized in that the ultrasonic signals (10, 20) of the workpiece are captured by means of a number of sensors (8).

4. The workpiece testing method according to claim 3, characterized in that the sensor (8) is mounted on the workpiece (5) prior to capturing the ultrasonic signals (10, 20) of the workpiece (5).

5. The workpiece testing method according to claim 1, characterized in that the machining of the workpiece (5) takes place by means of a tool (7) along a specified machining path.

6. The workpiece testing method according to claim 1, characterized in that the workpiece (5) is scanned by means of the ultrasonic waves (9, 19) and the ultrasonic signals (10, 20) of the workpiece (5) arising from propagation of the ultrasonic waves (9, 19) along paths (11) through the workpiece are captured, wherein the path (11) changes continuously as the machining progresses.

7. The workpiece testing method according to claim 1, characterized in that the ultrasonic tomograph data is completely or at least partially produced during the machining.

8. The workpiece testing method according to claim 3, characterized in that during the machining of the workpiece (5), position values corresponding to a momentary machining position (P1, P2) and/or a momentary path (11) between the momentary machining position (P1, P2) and a sensor position, and/or time values corresponding to a time at which the ultrasonic waves (9, 19) are produced at the associated momentary machining position (P1, P2) are continuously captured, determined, and/or provided, and/or running time values corresponding to a running time of the ultrasonic waves (9, 19) from the associated momentary machining position (P1, P2) to the sensor position are captured, determined, and/or provided.

9. The workpiece testing method according to claim 8, characterized in that a number of position values corresponding to the associated momentary machining position (P1, P2) and/or the associated momentary path (11) between the momentary machining position (P1, P2) and the sensor position, and/or a number of time values corresponding to a time at which the ultrasonic waves (9, 19) are produced at the associated momentary machining position (P1, P2), and/or a number of running time values corresponding to a running time of the ultrasonic waves (9, 19) from the associated momentary machining position (P1, P2) are associated with a plurality of captured ultrasonic signals (10, 20).

10. The workpiece testing method according to claim 9, characterized in that a back-projection algorithm is performed for producing the ultrasonic tomograph data using ultrasonic signals (10, 20) associated with the corresponding number of position values and/or the corresponding number of running time values.

11. The workpiece testing method according to claim 10, characterized in that the ultrasonic waves (9, 19) and/or the ultrasonic signals (10, 20) are filtered to a number of particular frequencies or frequency bands (17) prior to performing the back-projection algorithm, and only those ultrasonic signals corresponding to the number of particular frequencies or within the number of particular frequency bands and/or only the portion of the ultrasonic signals (10, 20) corresponding to the number of particular frequencies or within the number of particular frequency bands are captured and/or used for producing the ultrasonic tomograph data.

12. The workpiece testing method according to claim 11, characterized in that the number of frequencies or frequency bands (17) suitable for validity of the ultrasonic signals is determined.

13. The workpiece testing method according to claim 1, characterized in that the ultrasonic tomograph data produced are visualized in a subsequent imaging step as an ultrasonic tomograph (13).

14. The workpiece testing method according to claim 13, characterized in that the ultrasonic tomograph data and/or the ultrasonic tomograph (13) of the workpiece (5) is subsequently evaluated for internal defects (6) in the workpiece (5).

15. A workpiece testing system having: a distributed or local processing unit having an interface for receiving as input variables the output variables captured and output by a number of ultrasonic sensors (8), characterized in that the processing unit is set up for receiving ultrasonic signals (10, 20) as the input variables produced by applying ultrasonic waves (9, 19) to the workpiece (5) by means of machining and captured and output by the number of sensors as output variables, and for producing ultrasonic tomograph data of the workpiece (5) from the input variables.

16. The workpiece testing method according to claim 2, characterized in that the ultrasonic signals (10, 20) of the workpiece are captured by means of a number of sensors (8).

17. The workpiece testing method according to claim 16, characterized in that the sensor (8) is mounted on the workpiece (5) prior to capturing the ultrasonic signals (10, 20) of the workpiece (5).

18. The workpiece testing method according to claim 5, characterized in that during the machining of the workpiece (5), position values corresponding to a momentary machining position (P1, P2) and/or a momentary path (11) between the momentary machining position (P1, P2) and a sensor position, and/or time values corresponding to a time at which the ultrasonic waves (9, 19) are produced at the associated momentary machining position (P1, P2) are continuously captured, determined, and/or provided, and/or running time values corresponding to a running time of the ultrasonic waves (9, 19) from the associated momentary machining position (P1, P2) to the sensor position are captured, determined, and/or provided.

19. The workpiece testing method according to claim 6, characterized in that during the machining of the workpiece (5), position values corresponding to a momentary machining position (P1, P2) and/or a momentary path (11) between the momentary machining position (P1, P2) and a sensor position, and/or time values corresponding to a time at which the ultrasonic waves (9, 19) are produced at the associated momentary machining position (P1, P2) are continuously captured, determined, and/or provided, and/or running time values corresponding to a running time of the ultrasonic waves (9, 19) from the associated momentary machining position (P1, P2) to the sensor position are captured, determined, and/or provided.

20. The workpiece testing method according to claim 7, characterized in that during the machining of the workpiece (5), position values corresponding to a momentary machining position (P1, P2) and/or a momentary path (11) between the momentary machining position (P1, P2) and a sensor position, and/or time values corresponding to a time at which the ultrasonic waves (9, 19) are produced at the associated momentary machining position (P1, P2) are continuously captured, determined, and/or provided, and/or running time values corresponding to a running time of the ultrasonic waves (9, 19) from the associated momentary machining position (P1, P2) to the sensor position are captured, determined, and/or provided.

Description

[0052] A workpiece testing method according to an embodiment of the invention and the differences between the same and a known ultrasonic tomography workpiece testing method are explained in greater detail using the attached figures. They show:

[0053] FIGS. 1A and 2A principle sketches showing the producing of different ultrasonic signals under identical ultrasonic excitation as a function of the absence or presence of an internal defect in a scanned workpiece;

[0054] FIGS. 1B and 2B the ultrasonic signals produced in the absence or presence of the internal defect under identical ultrasonic excitation;

[0055] FIGS. 3 and 4 principle schematics for explaining data acquisition and back projection for tomography;

[0056] FIGS. 5-7 explain the procedure for a known ultrasonic tomography workpiece testing method;

[0057] FIGS. 8A and 9A show, in contrast, a principle sketch of a sequence of milling during a workpiece testing method according to an embodiment of the invention, wherein ultrasonic signals are captured at different momentary machining positions;

[0058] FIGS. 8B and 9B show the ultrasonic signals captured for the momentary machining positions according to FIG. 8A and FIG. 9A;

[0059] FIG. 10A shows a representation of the back projection, that is, the producing of ultrasonic tomography data in the workpiece testing method according to the embodiment of the invention shown in FIG. 8A through 9B;

[0060] FIG. 10B shows a representation of the back projection for an alternative embodiment of the invention using two ultrasonic sensors;

[0061] FIG. 11 shows a CAD model of a workpiece tested by means of the workpiece testing method principally explained in FIGS. 8A through 10A, with acoustic connection lines shown; and

[0062] FIG. 12 shows an example of an ultrasonic signal captured when executing the workpiece testing method according to FIG. 8A through 10A as a time-frequency representation.

[0063] As FIGS. 1-7 relating to a known ultrasonic tomography workpiece testing method have already been explained above, reference is now made to FIGS. 8 through 12, relating to workpiece testing methods according to embodiments of the invention.

[0064] FIGS. 8A and 9A show a workpiece 5 during milling by means of a cutter 7 at two different points in time t1 (FIG. 8A) and t2 (FIG. 9A). It is evident that the cutter 7 has been displaced from a momentary machining position P1 at the time t1 shown in FIG. 8A to a momentary machining position P2 at the time t2 shown in FIG. 9A somewhat to the right along the bottom edge of the workpiece during ongoing milling.

[0065] At the point in time t1, the milling thereby produces ultrasonic waves 9 shown as a wavefront, and at the point in time t2 ultrasonic waves 19 also shown as a wavefront, said wavefronts being not necessarily identical, but not substantially changing due to the unchanged feed speed, rotary speed, and penetration depth of the cutter 7. What can change in the course of milling, however, is an ultrasonic signal captured by an ultrasonic sensor 8 mounted on a workpiece 5. The ultrasonic signal captured at time t1 is thereby indicated by reference numeral 10, and the ultrasonic signal captured at time t2 by reference numeral 20. Furthermore, an internal defect 6 present in the workpiece is evident and said defect enters the signal path as the mill 7 passes by along the bottom edge of the workpiece and thus influences the ultrasonic signals continuously captured at the ultrasonic sensor 8.

[0066] FIGS. 8B and 9B show the different amplitude curve over time for signals 10—induced at the momentary machining position shown in FIG. 8A—and 20—induced at the momentary machining position shown in FIG. 8A. Deviations are evident after approximately two-thirds of the recorded time, that is, at a position corresponding to the position of the defect 6.

[0067] FIG. 10A illustrates how a reconstruction of inhomogeneities is performed by means of a back-projection algorithm. Along the signal paths taken between t1 and t2 at various points in time, the back projection of the associated ultrasonic responses are superimposed by means of a suitable back-projection algorithm, leading to producing an ultrasonic tomograph 13 of the workpiece 5 including an image 12 of the internal defect 6. For the back-projection algorithm, the different angular orientation of the signal paths or scanning directions must be taken into consideration, as in the conversion of a scan from only four sides, as shown in FIG. 3, said orientation leads to a sensor-centered mesh under a substantially tighter angular increment rather than to a mesh of voxels of equal size as in static tomography methods. The signal paths further do not, in reality, typically follow a straight line 11 as shown in FIG. 10A only as an example and for explanation purposes.

[0068] FIG. 10B illustrates the back-projection algorithm for an alternative embodiment of the invention, wherein two sensors are disposed on the workpiece for capturing ultrasonic signals at different positions. The signals here are overlapping signal paths between the momentary machining position and the first ultrasonic sensor on the oner hand, and between the momentary machining position and the second ultrasonic sensor on the other hand. Therefore, double the number of signals are available on overlapping paths for performing the back-projection algorithm. An even more precise image of the internal defect can thereby be created than for the embodiment of the invention wherein only one sensor is present for capturing the ultrasonic signals.

[0069] Reference is made to FIG. 11, showing a CAD model of a reference workpiece for which the workpiece testing method according to the explained embodiment of the invention can be performed. Acoustic connection lines 11 between a sensor position and three momentary machining positions at three points in time are drawn in the CAD model 14, thus corresponding to the signal paths at the three points in time during machining along an edge at the bottom of the image on a reference workpiece. It is evident that the course of the acoustic connection lines can also have a decisive influence for the back projection and therefore should be included in the back-projection algorithm. The ultrasonic tomograph shown merely as a principle in FIG. 10 can be placed on the CAD model 14, so that the location of the defect 6 and an image thereof 12 are readily evident.

[0070] FIG. 12 finally shows a time-frequency chart 16 of the ultrasonic signals captured while performing the workpiece testing method. A preferred frequency band 17 in the range just below 500 kHz is significantly evident, in which a strong signal is captured during the entire course of machining over time, so that the capturing of the ultrasonic responses and the processing thereof can be limited to said range.

[0071] Modifications of and derivations from the workpiece testing method shown and explained are possible without departing from the scope of the invention.

[0072] The workpiece testing method according to the invention is particularly well suited for testing workpieces for internal defects. The workpiece testing method according to the invention is suitable, for example, for testing workpieces made of fiber-reinforced plastic. It is thereby advantageous if the workpiece is milled and the workpiece is subjected to ultrasonic waves produced thereby.

[0073] It is further advantageous if the ultrasonic signals of the workpiece are captured by means of a single one or two preferably piezoelectric sensors. The sensor is preferably a contact sensor and is mounted on the workpiece prior to capturing the ultrasonic signals of the workpiece.

[0074] It is further advantageous thereby that the machining of the workpiece takes place by means of a tool along a specified machining path, namely along an outer contour running all around the workpiece, and particularly at a specified tool feed rate.

[0075] Each captured ultrasonic signal is further advantageously associated with: a number of associated momentary machining positions and/or a number of position values corresponding to the associated momentary path between the momentary machining position and the sensor position, and/or a number of time values corresponding to the associated time the ultrasonic waves arise at the associated momentary machining position, and/or a number of running time values corresponding to the associated running time of the ultrasonic waves from the associated momentary machining position to the sensor position.

[0076] A back-projection algorithm having an inverse radon transformation is further advantageously performed for producing ultrasonic tomograph data using the ultrasonic signals associated with the particular number of position values and/or the particular number of running time values.

[0077] The ultrasonic waves and/or the ultrasonic signals are further advantageously filtered to a number of particular frequencies or frequency bands prior to performing the back-projection algorithm and prior to associating the position values and/or running time values with the ultrasonic signals, and only those ultrasonic signals corresponding to the number of particular frequencies or within the number of particular frequency bands and/or only the portion of ultrasonic signals corresponding to the number of particular frequencies or within the number of particular frequency bands are captured and/or used for producing the ultrasonic tomograph data.

[0078] The number of frequencies or frequency bands suitable for validity of the ultrasonic signals is thereby further advantageously determined by capturing a signal strength of the ultrasonic signals at various frequencies and/or frequency bands distributed over an ultrasound spectrum during machining and by selecting one or more frequencies and/or frequency bands having increased signal strength relative to an average signal strength.

[0079] The ultrasonic tomograph data produced is thereby further advantageously visualized in a subsequent imaging step as an ultrasonic tomograph on a model of the workpiece or a workpiece segment existing or created as CAD/CAM data.

[0080] The workpiece testing system according to the invention is particularly well suited for testing workpieces for internal defects. The workpiece testing system according to the invention is suitable, for example, for testing workpieces made of fiber-reinforced plastic. The processing unit is thereby particularly integrated in a machine tool, preferably a milling machine tool. One single or two ultrasonic sensors are suitable as a number of ultrasonic sensors used for capturing and outputting output variables. The ultrasonic sensor or sensors are particularly piezoelectric sensors and preferably contact sensors suitable for mounting on the workpiece. The processing unit is particularly set up for receiving ultrasonic signals as the input variable produced by applying ultrasonic waves to the workpiece by means of milling the workpiece. The processing unit is thereby particularly set up for performing the method steps according to any one of the claims 7 through 14 and/or particularly for controlling the machine for machining, particularly for milling the workpiece for producing the ultrasonic waves and/or for controlling the machine for performing the method steps according to any one of the claim 2, 5, or 6.