Method and device for non-contact, non-destructive testing of a workpiece

Abstract

Method for the non-contact, non-destructive examination of a workpiece (1) comprising an electrically conductive and ferromagnetic material within the framework of an electromagnetic ultrasonic wave examination, in which the workpiece (1) is exposed at least partially to at least a static or quasi-static magnetic field and to an electromagnetic RF field that can be generated by means of an RF coil arrangement (2) and superimposed on the magnetic field, such that ultrasonic waves are formed within the workpiece (1), which, after passing through at least a region of the workpiece (1) in the region of the magnetic field and / or another static or quasi-static magnetic field, generate an RF field detectable by means of the RF coil arrangement (2) and / or another RF coil arrangement (2), which forms the basis of the examination, characterized in thatthat the workpiece (1) is inductively heated and examined by means of induction thermography using the RF field that can be generated with the RF coil arrangement (2) in temporal synchronization with the electromagnetic ultrasound wave examination.

Description

Technical FieldThe invention relates to a method and to a device for contactless, non-destructive examination of a workpiece having electrically conductive and ferromagnetic material in the context of an electromagnetic ultrasonic wave examination, in which the workpiece is exposed at least in regions to at least one static or quasi-static magnetic field and an electromagnetic RF field that can be generated with the aid of an RF coil arrangement and is superimposed with the magnetic field in such a way that ultrasonic waves form within the workpiece, which, after transmission of sound to at least one region of the workpiece in the region of the magnetic field and / or another static or quasi-static magnetic field, generate an RF field that can be detected with the aid of the RF coil arrangement and / or another RF coil arrangement and is used as the basis for the examination.Prior ArtIn many industrial fields, for example in the automobile industry or in railway engineering, safety-relevant components, such as components of brakes and of the steering system or entire railway wheels, have to be subjected to a hundred percent test during production in order to exclude surface cracks. In this context, methods are advantageous in the future which manage without a special surface treatment, which operate reliably and objectively and enable fully automatic testing of components.In addition to the investigation of possible surface defects, preferably in the form of surface cracks, knowledge about the material quality of workpieces in the entire workpiece volume is of great importance in many cases in the same way in order to be able to make an overall statement about the production quality or the current state of a workpiece.The means of the prior art non-destructive fault detection on workpieces frequently distinguish between the detection of surface defects which extend to a depth of about 1 mm from the workpiece surface and volume defects, i.e. material defects in the form of cracks, voids or similar material inhomogeneities which are situated at a depth of less than 1 mm from the workpiece surface.The standard test methods which are common, in particular used in industry, are either based on ultrasonic methods or thermographic methods. In the case of metallic workpieces, for reasons of contactless operation, recourse is made to so-called induction thermography and electromagnetically based ultrasonic methods, depending on whether the detection of surface defects or volume defects is the focus of the examination.As already mentioned, the methods of active thermography are suitable for close-surface defect inspection, see X. Madague, Theory and Practice of Infrared Technology for Non-destructive, New-York: John Wiley, 2001.For workpieces made of electrically conductive and ferromagnetic materials, inductively excited thermography, or induction thermography for short, is used to detect surface defects, in which eddy currents are generated within the workpiece material with the aid of an induction coil arranged on the workpiece surface, which eddy currents run on closed current paths. The eddy currents are deflected in or at faulty workpiece regions and must take detours around the corresponding faults, in the form of cracks or surface cracks. The local current density changed by the damage leads to a change in the temperature distribution directly at the defect which can be visualized with the aid of a thermographic camera. See also U. Netselmann, G. Walle and H. Strauss, "Use of inductive thermography for rapid and reliable misdetection of components of solid forming", in solid forming-Produkte-Perspectives, Leonberg, 2007, B. Valeske, G. Walle and U. Netselmann, "Surface tear test with active dynamic thermography-Alternative to conventional test methods", QZ-Messens und Pruf, Vol. 53, No. 3, pp. 66-69, 2008, V. Carl and G. Zenziger, "Automatic tear test with inductively excited thermography", in DGZfP-Annual Stagnung, Rosock, 2005.For deeper located defects, so-called volume defects, detection by means of ultrasound is a common test method in which electromagnetically generated and detectable ultrasonic waves are used with the aid of so-called EMUS probes, which make possible contactless generation of ultrasonic waves within the workpiece.Similarly to inductively excited thermography, an eddy current is also excited in the workpiece near the workpiece surface in the case of the so-called EMUS test technique, which eddy current forms forces directed onto the workpiece grid in interaction with a static or quasi-static, i.e. low-frequency, magnetic field within the workpiece, which forces lead to grid distortion, by means of which spatially and temporally elastic waves with frequencies in the ultrasonic range form and propagate within the workpiece. The ultrasonic waves interact with defects or material defects and generate acoustic echoes which in turn can be received and evaluated.DE 10 2009 021 233 A1 discloses a device and a method for acoustic thermography, in which the object is mechanically excited with a periodic excitation signal and the acquisition of the thermal images of the object and the periodic excitation signal are coordinated in such a way that information regarding the thermal signals represented in each case by pixels of the thermal image can be determined during one period from thermal images acquired in a plurality of periods of the periodic excitation signal.DE 103 31 070 A1 and DE 600 16 939 T2 likewise describe the detection of defects in a component by means of thermography, the component being heated in each case by ultrasonic waves generated by an EMUS transducer.From PALMER, S.B. [et al.]: Detection of surface breaking cracks using thermographic and non-contact ultrasonic methods. In: Proc. of SPIE, Vol. 7983, 2011, 79831V-1-10, a method for detecting surface defects is known, in which ultrasonic waves and heat are generated in the workpiece by means of a scanning Q-switched pulsed laser. For detecting the defects, the ultrasonic waves generated by the laser are received by means of EMAT transducers and, in addition, the shape of the region heated by the scanning laser beam is recorded by means of a thermal imaging camera.SUMMARY OF THE INVENTIONThe object of the invention is to design a method and a device for contactless, non-destructive examination of a workpiece having electrically conductive and ferromagnetic material in such a way that the detection of surface defects and volume defects within a workpiece is to be possible at the same time. Furthermore, both process variants must be carried out with the aid of a structural unit which can be handled uniformly.The solution of the object on which the invention is based is specified in claim 1. The subject of claim 9 is a device according to the solution for carrying out the method according to the solution specified in claim 1. Features which develop the concept of the invention in an advantageous manner can be taken from the subject matter of the dependent claims and from the further description, in particular with reference to the exemplary embodiments.The method according to the invention for contactless and non-destructive examination of a workpiece having electrically conductive and ferromagnetic material is based on the electromagnetic ultrasonic wave examination known per se, in which the workpiece is exposed at least in regions to at least one static or quasi-static magnetic field and an electromagnetic RF field that can be generated with the aid of an RF coil arrangement and is superimposed with the magnetic field in such a way that I form ultrasonic waves within the workpiece, which ultrasonic waves generate an RF field that can be detected with the aid of the RF coil arrangement and / or another RF coil arrangement after sonicating at least one region of the workpiece in the region of the magnetic field that serves for ultrasonic wave generation and / or another static or quasi-static magnetic field that predominates at another workpiece region, which RF field is used as the basis for the examination. According to the solution, the workpiece is inductively heated with the aid of the RF field which can be generated with the RF coil arrangement and with which the ultrasonic waves are generated within the workpiece, in synchronization with time with the electromagnetic ultrasonic wave examination, and examined by means of induction thermography. That is, the eddy currents generated by the RF field within the workpiece serve both for generating ultrasonic waves and for heating the workpiece.The method according to the invention provides for fusion of both known examination methods of inductively excited thermography and electromagnetically based ultrasonic wave examination in such a way that both methods can be applied synchronously in time to one and the same workpiece without interfering with one another. The static or quasi-static, i.e. low-frequency magnetic field is capable, on the one hand, of generating and detecting electromagnetically based ultrasonic waves with the aid of the additional RF field and, on the other hand, of contributing to the contrast increase in the inductively excited thermography.In a preferred embodiment variant, the RF coil arrangement is operated at a working frequency at which an RF field is formed which induces eddy currents within the workpiece, which eddy currents serve both for the formation of ultrasonic waves which are used as a basis for the electromagnetic ultrasonic wave examination and for the heating of the workpiece which is used in the context of induction thermography.As an alternative to operating the RF coil arrangement at a single operating frequency, it is equally appropriate to subject the RF coil arrangement to a first operating frequency at which an RF field is formed which induces eddy currents within the workpiece, which eddy currents serve for the formation of ultrasonic waves which are used as a basis for the electromagnetic ultrasonic wave examination. In addition, the RF coil arrangement is subjected to a second operating frequency at which an RF field is formed which induces eddy currents within the workpiece, which eddy currents serve for heating the workpiece and for carrying out the induction thermography, wherein the RF coil arrangement is preferably operated at both frequencies in the manner of a multiplex method, for example by means of a time-division, frequency-division or code multiplex method. In this way, it is possible to examine the workpiece synchronously in time by means of electromagnetic ultrasonic wave examination and also inductively excited thermography and in this way to record both surface and volume defects within the workpiece synchronously in time.Depending on the type of ultrasonic wave excitation used, i.e. by means of Lorenz force or magnetostriction, the static or quasi-static magnetic field is oriented horizontally or orthogonally to a workpiece surface which can be associated with the workpiece and on which the RF coil arrangement for generating the electromagnetic RF field superimposed with the magnetic field is arranged.Optionally, in the case of an orientation horizontal to the workpiece surface, the static or quasi-static magnetic field is additionally rotated about a spatial direction orthogonal to the workpiece surface, in order to be able to reliably detect crack orientations of different spatial positions. In the same way, the static or quasi-static magnetic field can be rotated about a spatial direction oriented along the workpiece surface in the case of an orientation orthogonal to the workpiece surface.It is likewise possible to provide, in addition to the static or quasi-static magnetic field oriented horizontally or orthogonally to the workpiece surface, at least one further, i.e. additional, static or quasi-static magnetic field with an orientation horizontal to the workpiece surface, which can be rotated to a spatial direction oriented to the workpiece surface. In addition to the secure, position-independent crack detection already mentioned, the signal-to-noise ratio can be improved in this way; this relates in particular to the image signals which can be detected within the scope of inductive thermography and which can experience a signal increase of up to 300%. In addition, this measure contributes to a more rapid test, since less energy has to be introduced into the workpiece with constant contrast.For the purpose of carrying out the induction thermography as unaffected as possible, at least one surface region of the workpiece, through which the RF field passes for inductively heating the workpiece, is detected by a thermographic camera in an optically freely accessible manner. Suitable measures must be taken for this purpose, so that the workpiece surface is at least not completely covered by the RF coil arrangement required for electromagnetic ultrasonic wave examination.The RF coil arrangement is preferably operated resonantly, i.e. all components of the RF coil arrangement are resonantly coordinated with one another with respect to their electrical resistance, their capacitive and inductive properties.Furthermore, a device for contactless, non-destructive examination of a workpiece having electrically conductive and ferromagnetic material for carrying out an electromagnetic ultrasonic wave examination, having the features of the preamble of claim 9, is designed such that the at least one RF coil arrangement is connected to a control unit and can be controlled such that an RF field, which can be generated by the RF coil arrangement, induces eddy currents within the workpiece, by means of which ultrasonic waves can be generated within the workpiece and which heat the workpiece such that the workpiece can be detected by means of induction thermography. In addition, the at least one RF coil arrangement is designed and attached to the workpiece such that a surface region of the workpiece through which the RF field passes for inductively heating the workpiece can be detected by a thermographic camera in an optically freely accessible manner.The control unit, which serves the at least one RF coil arrangement, is of central importance for operation both for the purpose of ultrasonic wave examination, i.e. ultrasonic wave generation and detection, and for the purpose of inductive workpiece heating. The drive unit, which is preferably designed as common power electronics, thus enables an efficient, synchronouslyable compact solution for completely examining a workpiece in the context of an ultrasonic wave as well as a thermographic examination. This opens up many possibilities, in particular in the field of application fields that can be automated.In an alternative according to the invention, the coil arrangement has at least one induction coil which provides a plurality of windings of at least one electrical conductor which are arranged according to a winding pattern which encloses at least one intermediate space between the windings which provides a viewing channel on the workpiece which is optically free for the thermographic camera.In combination or as an alternative thereto, according to the invention the at least one induction coil of the coil arrangement is made of an electrically conductive material which is transparent in a wavelength range detectable for the thermographic camera. For this purpose, the following transparent electrically conductive materials are suitable, for example: ITO (indium tin oxide), SnO 2: F, ZnO:Al, SnO 2: Sb, graphene.BRIEF DESCRIPTION OF THE INVENTIONThe invention is described below by way of example without limiting the general concept of the invention on the basis of exemplary embodiments with reference to the drawings. The following are shown: FIG. 1 is a highly schematic representation of a device for carrying out an electromagnetic ultrasonic wave examination and inductive thermography,WAYS OF CARRYING OUT THE INVENTION, INDUSTRIAL APPLICABILITYFIG. 1 schematically shows the top view of a workpiece 1, on the workpiece surface of which a coil arrangement 2 is attached. In addition, a permanent magnet arrangement 3 is provided which rests on the workpiece surface of the workpiece 1 and generates a horizontally oriented static B field B 0 within the workpiece 1. The coil arrangement 2 is connected to a drive unit 4, preferably in the form of power electronics, which can excite the coil arrangement 2 resonantly, as a result of which eddy currents 5 are induced within the workpiece 1. The eddy currents 5 are superimposed with the horizontally oriented magnetic field B 0 and generate force-induced lattice distortions within the workpiece 1, as a result of which ultrasonic waves propagating within the workpiece 1 are produced. After appropriate transmission of the ultrasonic waves of the workpiece 1 by sound and reflection, and in particular also and in particular at flaws contained within the workpiece, the ultrasonic waves generate detectable currents in combination with the horizontally oriented magnetic field B 0 in the region of the RF coil arrangement 2, which currents are used as the basis for the ultrasonic wave examination.The eddy currents 5 induced within the workpiece by the RF coil arrangement 2 likewise lead to the local heating of the workpiece 1. with the aid of a thermographic camera 6, which is directed onto the workpiece surface of the workpiece 1, in particular in the region of the RF coil arrangement 2, and is capable of detecting the free workpiece surface by a correspondingly transparent configuration of the RF coil arrangement 2 and / or by view gaps within the RF coil arrangement 2, it is possible to detect the smallest temperature differences which indicate defects close to the workpiece surface.The measurement signals obtained both with the aid of the ultrasonic wave examination and with the aid of inductive thermography are jointly detected and evaluated in a time-synchronous combination in an evaluation unit 7, so that a reliable statement about possible errors within the entire workpiece 1 can be made. The measurement signals originating from both methods are in a fixed temporal and spatial relationship to one another and are thus able to indicate an actual image about the state of a workpiece to be examined. The apparatus schematically shown in FIG. 1 is particularly suitable for detecting dynamic load conditions within a workpiece, especially since the apparatus is capable for the first time of analysing a workpiece both by means of ultrasonic wave examination and induced thermographic examination.List of reference characters1 Workpiece 2 RF coil arrangement 3 permanent magnet arrangement or electromagnet arrangement 4 drive unit 5 eddy currents 6 thermographic camera 7 evaluation unit

Claims

Method for contactless, non-destructive examination of a workpiece (1) comprising electrically conductive and ferromagnetic material in the context of an electromagnetic ultrasonic wave examination, in which the workpiece (1) is exposed at least in regions to at least one static or quasi-static magnetic field and to an electromagnetic RF field which can be generated with the aid of an RF coil arrangement (2) and is superimposed with the magnetic field in such a way that ultrasonic waves form within the workpiece (1), which, after transmission of sound through at least one region of the workpiece (1) in the region of the magnetic field and / or another static or quasi-static magnetic field, generate an RF field which can be detected with the aid of the RF coil arrangement (2) and / or another RF coil arrangement (2) and is used as the basis for the examination, characterized in that, that the workpiece (1) is inductively heated with the aid of the RF field that can be generated with the RF coil arrangement (2) in synchronization with time with the electromagnetic ultrasonic wave examination and is examined by means of induction thermography.Method according to Claim 1, characterized in that the RF coil arrangement (2) is operated at a working frequency at which an RF field is formed which induces eddy currents (5) within the workpiece (1), which eddy currents serve both for the formation of ultrasonic waves which are used as a basis for the electromagnetic ultrasonic wave examination and for the heating of the workpiece (1) which is used as part of the induction thermography.Method according to Claim 1, characterized in that the RF coil arrangement (2) is operated at a first operating frequency at which an RF field is formed which induces eddy currents (5) within the workpiece (1), which eddy currents serve for the formation of ultrasonic waves which are used as the basis for the electromagnetic ultrasonic wave examination, in that the RF coil arrangement (2) is operated at a second operating frequency at which an RF field is formed which induces eddy currents (5) within the workpiece (1), which eddy currents serve for heating the workpiece (1) and for carrying out the induction thermography, and in that the RF coil arrangement (2) is operated at both operating frequencies in the manner of a multiplex method.Method according to Claim 3, characterized in that the RF coil arrangement (2) is operated with both operating frequencies within the scope of a time-division, frequency-division or code-division multiplex method.Method according to one of Claims 1 to 4, characterized in that the static or quasi-static magnetic field is oriented horizontally and / or orthogonally with respect to a workpiece surface which can be associated with the workpiece (1), on which the RF coil arrangement (2) is arranged in order to generate the electromagnetic RF field which is superimposed with the magnetic field.Method according to Claim 5, characterized in that the static or quasi-static magnetic field is rotated about a spatial direction which is orthogonal to the workpiece surface in the case of an orientation which is horizontal to the workpiece surface, or in that the static or quasi-static magnetic field is rotated about a spatial direction which is oriented along the workpiece surface in the case of an orientation which is orthogonal to the workpiece surface.Method according to claim 5 or 6, characterised in that at least one additional static or quasi-static magnetic field is provided with an orientation horizontal to the workpiece surface, which is rotated to a spatial direction orthogonal to the workpiece surface.Method according to one of Claims 1 to 7, characterized in that, in the context of induction thermography, at least one surface region of the workpiece (1), through which the RF field passes for inductively heating the workpiece (1), is detected by a thermographic camera in an optically freely accessible manner.Device for non-contacting non-destructive examination of a workpiece (1) having electrically conductive and ferromagnetic material for carrying out an electromagnetic ultrasonic wave examination, having at least one magnet unit for generating a static or quasi-static magnetic field and at least one RF coil arrangement (2), in which the at least one RF coil arrangement (2) is connected to a drive unit (4) and can be controlled in such a way that an RF field which can be generated by the RF coil arrangement (2) induces eddy currents (5) within the workpiece (1), by means of which ultrasonic waves can be generated within the workpiece (1) and heat the workpiece (1) in such a way that the workpiece (1) can be detected by means of induction thermography, characterized in that the at least one RF coil arrangement (2) is designed in such a way and can be attached to the workpiece (1) in such a way that a surface region of the workpiece (1), is produced by the ultrasonic waves, which can be transmitted by the RF field for inductively heating the workpiece (1), can be detected by a thermographic camera (6) in an optically freely accessible manner, that the RF coil arrangement (2) has at least one electrical induction coil, and that the at least one induction coil of the RF coil arrangement (2) provides a plurality of windings of at least one electrical conductor which have a winding pattern which encloses at least one intermediate space between the windings, which represents a vision channel on the workpiece (1) optically free for the thermographic camera (6), and / or that the at least one induction coil consists of an electrically conductive material transparent for the thermographic camera (6).Device according to claim 9, characterised in that the at least one magnet unit is designed in the form of a permanent magnet or an electromagnet.Device according to claim 9 or 10, characterised in that the at least one RF coil arrangement (2) is resonantly tuned.Device according to one of Claims 9 to 11, characterized in that at least two RF coil arrangements are provided, of which a first RF coil arrangement generates the eddy currents (5) within the workpiece (1) for generating ultrasonic waves and heating the workpiece (1), and a second RF coil arrangement which serves for detecting ultrasonic waves propagating within the workpiece (1).Device according to one of Claims 9 to 12, characterized in that the at least one magnet unit is arranged rotatably or pivotably relative to the workpiece (1).Device according to one of Claims 9 to 13, characterized in that the transparent electrically conductive material consists of one of the following materials: ITO (indium tin oxide), SnO 2: F, ZnO:Al, SnO 2: Sb, graphene.

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