WO2009121903A1

WO2009121903A1 - Universal test head for non-destructive ultrasound investigation and associated method

Info

Publication number: WO2009121903A1
Application number: PCT/EP2009/053865
Authority: WO
Inventors: Paul Buschke; Wolf-Dietrich Kleinert
Original assignee: Ge Sensing & Inspection Technologies Gmbh
Priority date: 2008-04-01
Filing date: 2009-04-01
Publication date: 2009-10-08
Also published as: DE102008002394A1

Abstract

The invention relates to a test head (1) for the non-destructive ultrasound investigation of an anomaly, in particular a welding melt zone, of a workpiece, comprising an array (2S, 2D, 2R) which is integrated in the test head (1) and comprises a plurality of ultrasonic transducers (2S, 2D, 2R) which can be arranged on a surface of the workpiece and can be selectively driven, individually or in segments, as ultrasonic receivers (2S) and ultrasonic transmitters (2R). The test head is distinguished by the fact that the array (2S, 2D, 2R) is of essentially annular design and the ultrasonic transducers (2S, 2D, 2R) are arranged and/or driven in such a manner that the respective ultrasound produced propagates parallel to the surface of the workpiece. The invention also relates to two associated methods for the non-destructive ultrasound investigation of an anomaly, in particular a welding melt zone, of a workpiece.

Description

Name: Universal test head for non-destructive ultrasound examination and associated method

The invention relates to a probe to be universally used for non-destructive ultrasound examination, the possibility for rapid performance of different ultrasound examinations, for example u.a. tomographic examination, for example, to detect, measure and / or represent an anomaly or, in particular, a fusion zone resulting from a welded joint in a workpiece.

For the non-destructive testing of a workpiece by means of ultrasound, suitable testing devices and methods are known. In general reference is made to the textbook by J. and. H. Krautkrämer, materials testing with ultrasound, sixth edition.

With the so-called acoustic microscopy (also known as ultrasonic microscopy), a non-destructive examination method is known, which makes it possible to image the "inside" of a workpiece. As pores or delaminations, etc. generate strong reflection signals, so that workpiece anomalies, ie errors, inhomogeneities and also weld defects, can be determined quickly and reliably., However, the equipment required for it is expensive, often not portable and the image processing takes comparatively long, so that This method is generally not suitable for industrial production monitoring.

It is also known to pass an angle test head mechanically past a test area of the workpiece. In the process, high-frequency sound pulses (about 1-10 MHz) are emitted, which are clipped into the workpiece to be tested. These penetrate into the workpiece, where they are reflected at a rear wall of the workpiece at least once. Internal anomalies (also called inhomogeneities), such as a material defect, cause sound reflections, which are received again by the angle probe and processed in the downstream ultrasound machine. It is worked in the simplest case after the pulse echo method. The angle probe or generally a transmitter preferably emits periodic ultrasonic pulses and a receiver then receives echo signals of these emitted ultrasonic pulses. The echo signals are men from the workpiece and in particular from the rear wall of the workpiece. In that regard, the test method is suitable for workpieces whose coupling surface is substantially parallel to the rear wall, so that it comes to the formation of several outgoing and longitudinal courses of the ultrasonic pulse in the workpiece. When inspecting welds, the angle probe is moved along the weld (dhidR perpendicular and parallel to the weld) until a maximum error echo is obtained. The received echo signals are displayed directly on a monitor ("A-Scan") The position and thus the location of an error in the test specimen is calculated on the basis of the known and measured data The echo amplitude is used for an estimation of the error size However, this is often not reliably possible since the Echo amplitude is subject to considerably more influences than the sound propagation time., for example, DE 102 59 658 describes a method with which the representation of a fault, Which Was ascertained With the aid of an angle test head, is improved on a display The comparison body method directly displays a scaled-up error in cross-sectional images, which are superimposed visually, so to say, for errors such as inhomogeneities in the sample to be examined Material sufficient n. It is not sufficient to comprehensively cover a welded joint, ie as far as possible on all sides. A comprehensive all-round detection of the welded joint may be required in particular for safety-relevant components, such as vehicle components, pipelines or boilers.

A similar method is known from DE 1 980 3615 B4, in which at least two different guided waves (modes) are generated with at least one specified angle in the solid to enable a determination of the error size and error type, the measured reflection values are set in relation to a reference echo in order to obtain a relative reflection value and to set the relative reflection values of the individual modes in relation to each other. This allows them to determine their size and nature. In the aforementioned method, a complex positioning, possibly also repositioning, the angle test head is required.

In the publication entitled "Spot weld analysis with 2D ultrasonic ray" by A. A Denisov, CM Shakarji, BB Lawford, R. Gr. Maev, JM Paille in J. Med. Res. Natl. Inst. Stand. Technol. Volume 109 No.2 2004; Pages 233-244 a method for investigating a spot welding by means of ultrasound is proposed in which by means of a two-dimensional, stationary array of ultrasound transmitters and receivers of the array adjacent to the workpiece area with almost perpendicular irradiation of ultrasound and thereby perpendicular to the workpiece surface propagation direction the ultrasound is scanned. This results in the problem that in most cases by the spot welding the surface of the workpiece is deformed in the area affected by the welding, and thus a coupling between the respective ultrasonic transmitter or receiver is difficult.

To solve this problem described above, it is proposed in EP 1 801 576 A1 to arrange an array of ultrasonic transmitters and receivers in the region of the workpiece surrounding the melt zone region of the weld in order to excite therein plate waves that at least partially penetrate the melt zone. The amplitudes measured during the sound transmission are used to analyze the melt zone diameter. From US 0,625,016.3 Bl a similar arrangement is disclosed wherein the transmitter and receiver arrays are constructed in EMAT technology.

In the publication entitled "Guided-wave tomographic imaging of defects in pipes using a probabilistic reconstruction algorithm" by JK Van Velsor, H. Gao, JL Rose in Insight - Non-Destructive Testing and Condition Monitoring; Issue: 9, pages: 532-537 describes the investigation of tubes for material defects by means of guided ultrasound waves generated and received by a circular array of separate ultrasonic transducers as probes, using the so-called "RAPID" algorithm for tomographic image reconstruction , The construction shown of the plurality of ultrasonic transducers is complicated and the investigation time consuming, so it is only suitable for the industrial investigation of anomalies and in particular of Schweißschmelzzonen in a workpiece.

This is where the present invention begins. It has set itself the task of providing a test head for the non-destructive ultrasound examination of an anomaly, in particular a weld fusion zone, of a workpiece. which can be used quickly and for a variety of processes and which is particularly suitable for use in an industrial production process. This object is achieved by a test head according to claim 1. An associated and correspondingly advantageous method is the subject of claims 8 and 11. The dependent claims relate to advantageous embodiments.

The test head according to the invention is suitable for the non-destructive ultrasound examination of an anomaly, in particular a weld melting zone, of a workpiece. Consequently, the term anomaly should be interpreted broadly in the context of the present invention. In general, it is intended to detect an undesirable pattern deviation (also referred to as anomaly or defect) within the workpiece based on its effect on the acoustic transmission behavior. The test head comprises an array of a plurality of ultrasonic transducers to be arranged on a surface of the workpiece and integrated into the test head. Integration according to the invention means that when placing the probe on the surface of the workpiece to be examined at the same time all ultrasonic transducers are arranged on it and thus no subsequent arrangement and alignment of individual ultrasonic transducers, such as piezo transducers is required. By the simultaneous and joint placement and placement of the transducers, i. As a result of the array, a quick alignment of the probe on the workpiece is achieved, speeding up the investigation and making it suitable for industrial scale applications.

The transducers are singular or segmental, i. in groups of a few transducers, as an ultrasonic receiver and ultrasonic transmitter selectively controllable. Due to the selective activation or control possibility, a shift of the respective transmitter is unnecessary, but for the realization of different main emission directions of the ultrasound only the activation or control of another transducer or segment is required. The implementation of the respective method is accelerated and the measurement accuracy increased.

The array is formed according to the invention substantially annular. The term annular is to be interpreted broadly. Thus, no gap-free or adjacent adjacent arrangement between the individual transducers is necessarily preconditioned. puts. The transducers are for example distributed on a circumference or are distributed on an annular circle segment defined by an outer or inner circle diameter.

According to the invention, the transducers are arranged and / or controlled in such a way that the ultrasound generated in each case propagates substantially parallel to the workpiece surface and thus parallel to the "circle" surface defined by the ring, thereby advantageously providing an arrangement offset from the region of the workpiece to be examined This makes the probe suitable for examining anomalies in which the surface immediately adjacent to the anomaly (the perpendicular projection of the surface encompassed by the anomaly onto the surface to be examined) of the workpiece is not accessible or the coupling of the respective transducers In this area, for example, due to unevenness is difficult or even impossible.This is the case, for example, in welding, where the melting zone is on the surface of the workpiece oden a deformation of the surface are present, which impedes a coupling in this area and thus an ultrasound examination.

The propagation direction according to the invention is achieved, for example, by an oblique orientation of the sound emission surface of the respective transducer, ie its main emission direction is inclined to the workpiece surface. For example, by this irradiation in a flat workpiece surface waves and - depending on its size - in its direction perpendicular to the surface thickness direction plate waves (engl.: Lamb waves) are generated. If the wavelength of the ultrasound in one dimension is comparable or large to the dimensions of the workpiece, portions of the interface will constantly interact with the shaft, causing the shaft to guide along that interface. As a result, the workpiece acts as a waveguide. Due to their low attenuation, these waves spread comparatively far and are thus particularly suitable for ultrasound examination, in particular in the case of the sound transmission measurement of the anomaly (or the welding melt zone). Preferably, the transducers are designed and / or are so controlled that the respectively emitted ultrasound is radiated in the direction of the respective opposite edge of the annular edge. In other words, radiation takes place in a substantially radially inward direction of the ring. It is not assumed that the ultrasound necessarily reaches the opposite edge. Thus, it should not be ruled out that the ultrasound thus emitted will be reflected by the anomaly, and also the probe according to the invention will be used so that the ultrasound reflected from the anomaly will be identical in a reflection measurement from receiving transducers adjacent or adjacent to the transmitting transducer are, is detected and the reflection signals thus obtained are evaluated. Such a measurement constellation can also be easily realized by the test head according to the invention.

In a preferred embodiment, the test head has a substantially centrally arranged opening for the accessibility of the workpiece. Preferably, the aperture is arranged concentrically with the annular array. This allows the test head to be already at the measuring position during machining, such as welding, of the workpiece, and its quality can be checked immediately after or during machining. If necessary, can then be immediately reworked or rewelded. As a result, the processes in the manufacturing process and the required quality assurance measures are significantly accelerated.

According to a preferred embodiment, the ultrasonic transducers of the test head or of the array are constructed in EMAT (electromagnetic acoustic transducer) technology. By using electromagnetically operating Uitraschaiiwandierπ that are comparatively temperaturunempfindhch, the test head or the method can also be found at high temperatures of the workpiece so in the immediate vicinity of a possibly not yet cooled weld.

Preferably, the array is a phased array. By phase shifting the electrical drive signals of the transducers involved in generating the ultrasound, a selectively adjustable focus is achieved and / or alignment of the ultrasound. For example, in the case of a plurality of circumferentially grouped transducers acting as transmitters, a phase-shifted drive signal is used. Due to the phase control, the array or the test head can be quickly adjusted to different dimensions of the workpiece to be examined, without the need for a structural change to the test head, for example, its Einkoppelgeometrie needed.

Due to the fact that the test head according to the invention allows an accelerated implementation of various measuring methods, it is preferably used in an industrial manufacturing process, for example in the automotive, aerospace, industry. It is particularly suitable for those methods in which the position of the anomaly to be examined is approximately known and the aim is to ensure a rapid and comprehensive examination of this anomaly. This is particularly important in a welded joint and in particular a spot welded joint where accurate and all-around detection of the weld melt zone is desired. This considerably speeds up the processes involved in the associated production process and the required quality assurance measures.

Finally, the invention also relates to an arrangement comprising a workpiece having a weld melt zone and a probe arranged adjacent to the surface of the workpiece according to one of the embodiments described above, wherein the weld melt zone is arranged in the region of the center of the annular array. The workpiece may be made of any material which is permeable to ultrasound and thermally weldable. For example, it is welded steel sheet and in particular spot-welded steel sheet, as used for example in vehicle production.

The invention further relates to a method for non-destructive ultrasound examination of an anomaly, in particular a welding melt zone, of a workpiece, in which the qualitative evaluation and visual representation is in the foreground, hereinafter referred to as tomographic method. It is characterized in that it is carried out using the probe described above. In this case, in several sampling steps of each generated a transducer or a plurality of transducer comprehensive segment of the array and then detected by the workpiece and at least partially transmitted through the anomaly or welding melt zone and / or reflected ultrasound, each with different main propagation direction by means of several, preferably adjacent, acting as a receiver transducer. A projection obtained therefrom is processed by a tomographic imaging algorithm to reconstruct an image of the anomaly or fusion zone. The thus reconstructed image is evaluated and / or displayed.

The test head according to the invention is particularly suitable for this method, whose goal is primarily the qualitative, but possibly also the quantitative examination of the anomaly or the melt zone area in the workpiece.

The inventive method comprises a plurality of scanning steps carried out in succession, in which the main propagation direction of the ultrasound changes in the plane parallel to the workpiece surface, so that a sound irradiation of the anomaly takes place in respectively different directions. The ultrasound thus generated and partly transmitted through the welded joint or also reflected ultrasound is detected at several other, also arranged around the weld positions by means of several adjacent acting as a receiver transducer or segments of the probe to a location information measured by the transducer or the derived variables.

Due to the selective controllability of the test head according to the invention, the method can be carried out quickly and easily. Due to the advantageous embodiment of the test head according to the invention, the transmitter or receivers are arranged outside the area resulting from the vertical projection of the melting zone onto the respective surface of the workpiece. It is thereby achieved that the coupling of the transducers to the surface of the workpiece is not impaired by, for example, welding connection-related deformation of the surface. In each sampling step, the propagation speed / transit time or the amplitude of the ultrasound can be determined to obtain the respective projection. It can be be measured sound arrangement or reflection arrangement. An ultrasonic pulse, a continuous ultrasound emission or an ultrasonic sweep can be used.

The signals detected in the sampling steps, i. the different projections are processed by a tomographic imaging algorithm, i. used for image reconstruction, and the generated image displayed. Suitable tomographic imaging algorithms are known to the person skilled in the art, and it is incumbent upon him, for example, to select the appropriate number of scanning steps or projections for the respective application, for example, depending on the desired resolving power. Advantageously, the "RAPID" method is used which is described in the already mentioned publication "Guided-wave tomographic imaging of defects in a pipe using a probabilistic reconstruction algorithm" by J. K. Van Velsor et al. the entire disclosure of which is incorporated by reference into this application.

Preferably, the scanning steps, i. the different main propagation directions of the ultrasound in the respective scanning steps, chosen so that a complete circumferential detection, i. a 360 ° detection, the anomaly or welding melt zone, for example, in 31 different propagation directions is performed. The visualization possible due to the tomographic imaging process may cause anomalies and defects of the welded joints, i. Deviations from the target requirements can be detected quickly and comprehensively. For example, an insufficiently formed molten zone (too small a diameter) or trapped gas pockets (pores) can be easily detected and located.

The tomographic imaging algorithm in one embodiment includes radon transformation or backprojection. Preference is given to using a filtered rear projection or a weighted rear projection with Shepp Logan core.

In the respective scanning step, the amplitude of the transmitted and / or reflected ultrasound and / or the associated transit times are preferably detected. For example, the projection of the transmission amplitude, the projection of the ratio of the transmission amplitude at different frequencies Quantities of ultrasound, recorded the projection of the propagation velocity and the projection of the pulse echo amplitude and evaluated tomographically. Further, one or more additional calibration steps may be provided including one or more measurements on an unwelded workpiece.

The test head is also suitable for a method for non-destructive ultrasound examination, in which the qualitative examination of the anomaly or the weld melt zone is not in the foreground, but the determination of their longitudinal extent at least in the direction parallel to the workpiece surface. In particular, in the spot welding of two workpieces, the extent of the expansion of this melting zone is of particular importance in order to assess the quality and thus the strength of the weld can. In this method, in several scanning steps, the ultrasound generated by each transducer or a segment of the array and then transmitted through the workpiece and at least partially through the anomaly or weld melt zone, having a different main propagation direction in each scan, is detected by means of an ultrasound generating transducer or segment substantially diametrically opposed transducer or segment. A respective measured value obtained therefrom is evaluated to determine the relevant dimension of the anomaly or the welding melt zone. For example, the travel time change or amplitude change caused by the anomaly or weld melt zone is used to determine the dimension thereof in the direction corresponding to the main propagation direction. It is the person skilled in the art to choose the number of scanning steps and the direction of the ultrasound according to the desired resolution. The test head according to the invention is also particularly suitable for this method, since the method can be performed quickly and easily by the selective controllability of the individual transducers. In the advantageous embodiment of the test head according to the invention, the transmitter or receivers are arranged outside the area resulting from the vertical projection of the molten zone onto the respective surface of the workpiece. It is thereby achieved that the coupling of the transducers to the surface of the workpiece is not impaired by, for example, welding connection-related deformation of the surface. The method described above is described in a special ders preferred embodiment with the previously described, tomographic method performed in combination.

In a further advantageous embodiment, several sampling steps are carried out at the same time in order to accelerate the implementation of the method.

The invention further relates to a welding method, wherein after the welding, in particular the spot welding, at least two workpieces, a method for non-destructive ultrasound examination is carried out according to one of the embodiments described above.

Finally, the invention relates to an apparatus for carrying out the method according to one of its previously described embodiments. The device comprises the test head in one of its embodiments described above, in order to generate in succession in several scanning steps in the direction of the weld propagating ultrasound, each with other Hauptausbreitungsrichtung and to detect the associated reflected and / or transmitted ultrasound. Furthermore, the device comprises an evaluation unit in order to evaluate the signals detected in the several scanning steps. Optionally, the evaluation unit is set up to subject the detected signals to a tomographic imaging algorithm, wherein the calculated image is displayed on an integrated or separately formed display device.

In the following the invention will be explained with reference to some schematic representations, without limiting these to the embodiment shown.

FIG. 1a schematically shows a test head 1 and the measuring arrangement resulting therefrom. As shown in the figure, the test head 1 is annular. However, the invention is not limited to an annular configuration of the probe, but essential to the invention is the arrangement of a plurality Ultraschallpiezowandlern, which are arranged in an annular array. In the present case, these are arranged on the circumference of imaginary concentric circles. In principle, each transducer can function both as a transmitter and as a receiver. In the case of the measuring arrangement shown, adjacent transducers of an imaginary ring segment each form a subarray 2S, 2D, 2R of ultrasonic piezocurrents which can be activated together, in the case of the subarray 2S these are the transducers 2S1, SS2, 2S3, 2S4. In the event that the associated transducers of the subarray act as transmitters, they are jointly phased controlled to achieve a main propagation direction of the ultrasound wave generated by the transducers substantially toward the center of the annular array of the subarrays 2S, 2D, 2R.

The array of the probe 1 with its subarrays 2S, 2D, 2R is annular and the probe has in the transducer-free area on a breakthrough 8, via which an adjacent to the test head 1 arranged surface of an unspecified and to be examined by the measuring device workpiece remains accessible.

The generally plate-shaped workpiece is connected via a to be examined by the tomographic method according to the invention, schematically indicated weld point 4 with another, also unspecified, located below the aforementioned workpiece workpiece. Welding point 4 is essentially defined by a fusion zone, also referred to as a "weld pool" or "nugget". The welding point is located approximately at the center of the imaginary concentric circles, on the circumference of the transducers of the array 1 are arranged.

FIG. 1 shows a sampling step in which the several transducers of a subarray, in this case the transducers 2S1, SS2, 2S3, 2S4 of the subarray surrounded by a box relative to the arrow 2S, are activated and are each driven out of phase with one another, such that ultrasound as lamb -Wave in the workpiece in the direction of the weld point 4 and this is generated at least partially penetrating, without requiring a corresponding orientation of the transducer. In the same sampling step shown, the diametrically opposed subarray and its circumferentially adjacent two subarrays 2R of transducers are activated as receivers and serve to detect a location or other expressed, angle-dependent characteristic, such as the propagation velocity or the amplitude of the transmitted ultrasound. Depending on the degree of focus of the ultrasound generated, other, to the radially adjacent subarray adjacent subarrays are activated as a receiver but also fewer subarrays. In the aforementioned scanning step, the subarrays 2D of the array 1 are deactivated.

The signal received by means of the subarrays 2R and the associated transducers corresponds, for example, to the characteristic curve shown in FIG. 1b via the receiver segments.

In subsequent sampling steps, one of the other subarrays is then activated as a transmitter and again activated according to at least the diametrically opposite subarray as a receiver. The method is carried out until at least all segments have been activated at least once as transmitters and thus obtain a 360 ° scan of the welded joint. The associated projections, as shown in FIG. 2, result in the welded connection 4.

Although a measuring arrangement is shown in transmission technology, it is also conceivable to carry out the method in reflection arrangement, for example by activating adjacent subarrays as receivers to the transmitting subarray.

In a preferred development of the method according to the invention, a calibration measurement is carried out to compensate for this inhomogeneity in order to compensate for the spatially inhomogeneous sound pressure distribution in the ultrasonic beam irradiated by the transmitting transducer or subarray. For this purpose, the test head 1 is placed on a region of the surface of the test piece in which there is no spot weld ("bare metal sheet.") The ultrasound pulse, which is detected by a transducer or a subarray, is recorded by the diametrically opposed subarray, the received pulse intensity being from the angular position In a subsequent calibration step, the amplification of the amplifiers processing the signals of the individual transducers of the receiving subarray is then individually adjusted in a subsequent calibration step in such a way that an ultrasonic pulse is included in all transducers of the receiving subarray Thus, an angle-dependent gain boost is implemented, which is generally the higher the farther the receiving transducer of the subarray is removed from the main direction of the emitted ultrasonic pulse. A comparable compensation of the inhomogeneous sound pressure distribution by means of the above-described calibration measurement on the bare sheet metal is not only possible with a conventional (Gaussian) sound pressure distribution, but rather can be used for any sound pressure distributions. Such any sound pressure distributions deviating from the standard configuration may be advantageous for specific test tasks or geometries.

The evaluation unit connected downstream of the test head 1 is preferably designed to carry out the method described above for compensating the spatially inhomogeneous sound pressure distribution.

FIG. 3 shows schematically how a reconstructed image of the welded joint is calculated by means of an evaluation unit by means of radon transformation by means of interpolation and filtering from the projections and can be displayed on a display device.

FIG. 4 schematically shows a further test head 1 'with an annular array of several transducers arranged in the imaginary circular ring segments 5 of the test head in EMAT technology with which the welded connection 4 is to be examined. Here comes a coil 6 as a transducer, i. as receiver and transmitter, for use. The coil is used for the electromagnetic excitation of ultrasound, here in the form of a lamb wave, in which the workpiece 4 having the welded joint. In the present case, the coil 6 denoted by 6 is activated in one scanning step and, due to its special curved configuration, generates inter alia a wave front 9 propagating in the direction of the fusion zone 4.

The melting zone 4 remains accessible via the opening 8 'in the test head despite the resting on the surface of the workpiece probe 1'. More transducers 6 can be distributed over the circumference or can be provided on transducers arranged parallel thereto in the radial direction, which are jointly controlled in subarrays. The test head 1 'is also suitable for carrying out the method described above with respect to test head 1. FIG. 5 schematically shows the implementation of a further method using the test head 1 according to the invention. This method is used to measure the molten zone of a welded joint 4. For this purpose, in each scanning step the diametrically opposed transducers or subarrays are activated or activated in pairs as transmitter 2S and receiver 2R , The ultrasound passing through the welding melt zone 4 is respectively weakened or reflected by it. On the basis of the transmitted amplitude, the extent of the welding melt zone 4 can be determined in the direction corresponding to the main direction of propagation of the ultrasound emitted by the respective transmitter (see crossing arrows in FIG. 5). Alternatively, the respectively resulting transit time or propagation speed can serve to determine the extent. Because of a strongly focused and / or a radiation with a different frequency, a plurality of subarrays-in the present case three subarrays 2S in each case-can be activated simultaneously. The number of scanning steps required for an all-round detection of the melting zone 4 can thus be reduced. The segments 2S thus transmit simultaneously and their ultrasound is measured in each case by the diametrically opposite receiver 2R. The remaining transducers 2D remain deactivated in these sampling steps. In preceding and / or subsequent sampling steps, not shown, the result obtained is used to determine the extent of the welding melt zone 4 in the direction corresponding to the respective direction of ultrasound propagation.

Claims

claims

A test head (1, 1 ') for nondestructive ultrasonic examination of an anomaly, in particular a weld fusion zone, of a workpiece, comprising an array (2S, 2D, 2R) of a plurality, on a surface of the workpiece, integrated into the test head (1, 1') ultrasonic transducers (2S, 2D, 2R) to be arranged, which can be selectively controlled individually or in segments as ultrasonic receivers (2S) and ultrasonic transmitters (2R), characterized in that the array (2S, 2D, 2R) is substantially annular and the ultrasonic transducers ( 2S, 2D, 2R) are arranged and / or controlled such that the respectively generated ultrasound propagates parallel to the workpiece surface.

2. test head (1, 1 ') for non-destructive ultrasound examination according to the preceding claim, characterized in that the ultrasonic transducers (2S, 2D, 2R) are arranged and / or controlled so that each emitted ultrasound in the direction of the respective opposite edge of annular arrays (2S, 2D, 2R) is emitted.

3. test head (1, 1 ') for non-destructive ultrasound examination according to one of the preceding claims, characterized in that the test head (1, 1') has a substantially centrally located opening for the accessibility of the workpiece.

4. test head (1, 1 ') for non-destructive ultrasound examination according to one of the preceding claims, characterized in that the ultrasonic transducers (2S, 2D, 2R) are constructed in EMAT technology.

5. test head (1, 1 ') for non-destructive ultrasound examination according to one of the preceding claims, characterized in that the array (2S, 2D, 2R) is a phased array.

6. Use of the test head (1, 1 ') according to one of claims 1 to 5 in an industrial manufacturing process, such as the automotive, aerospace industry.

7. An assembly of a workpiece having a weld melt zone and an adjacent to the surface of the workpiece arranged test head (1, 1 '), characterized by the test head according to one of claims 1 to 5 and in that the welding melt zone in the center of the annular array (2S , 2D, 2R) is arranged.

8. A method for non-destructive ultrasonic examination of an anomaly, in particular a weld melting zone, a workpiece, characterized by the use of a test head according to one of claims 1 to 5, wherein in several scanning steps of each of a transducer or a segment of the array generated and then by the workpiece and ultrasound transmitted at least partially by the anomaly or welding melt zone and / or reflected therefrom is respectively detected by a plurality of preferably adjacent transducers or segments, the direction of propagation and a projection obtained therefrom by a tomographic imaging algorithm for reconstructing an image Anomaly or the melting zone is processed and the thus reconstructed image is evaluated and / or displayed.

9. Method according to the preceding claim, characterized in that at least one 360 ° degree detection of the anomaly or welded joint (4) is carried out in the several scanning steps.

10. The method according to any one of the preceding claims 8 or 9, characterized in that the tomographic imaging algorithm comprises a radon transformation or a back projection, preferably a filtered rear projection or a weighted rear projection with Shepp-Logan core.

11. A method for non-destructive ultrasonic examination of an anomaly, in particular a weld melting zone, a workpiece, characterized by the use of a test head according to one of claims 1 to 5, wherein in several scanning steps of each of a Transducer or a segment of the array generated ultrasound and then detected by the workpiece and at least partially transmitted through the anomaly or welding melt zone ultrasound with each other main propagation direction by means of a ultrasonic generating transducer or segment substantially diametrically opposed transducer or segment is detected and a measurement value obtained from each is evaluated to determine the respective dimension of the anomaly or weld melt zone.

12. The method according to any one of the preceding claims 8 to 11, characterized in that in the respective scanning step, the amplitude of the transmitted and / or reflected ultrasound and / or the associated transit times are detected.

13. The method according to any one of the preceding claims 8 to 12, characterized in that several of the sampling steps are carried out at the same time.

14. welding method, characterized in that after welding, in particular spot welding, at least two workpieces, a method for non-destructive ultrasound examination according to one of the preceding claims 8 to 12 is performed.