Dye penetrant testing method for the non-destructive testing of a test object and test device

Abstract

The invention relates to a dye penetrant method for the non-destructive testing of a test object (12), comprising the steps of irradiating the test object (12) provided with a fluorescent dye (30) with excitation photons (20) so that fluorescence photons (28) are generated, and detecting fluorescence photons (28), comprising the steps of detecting a delay time (t) of the fluorescence photons (28) between the impact of the excitation photons (20) on the test object (12) and the emission of the fluorescence photon (28.1) and determining surface defects (32) of the test object (12) based on the delay times (t).

Description

[0001] The invention relates to a dye penetrant method for the non-destructive testing of a test specimen, comprising the steps of (a) irradiating the test specimen provided with a fluorescent dye with excitation photons so that fluorescence photons are generated, and (b) detecting fluorescence photons emitted by the test specimen due to the excitation photons.

[0002] According to a second aspect, the invention relates to a testing device for the non-destructive testing of test specimens, in particular for surface or edge zone defects, comprising (a) a holder for holding the test specimen, (b) a light source, in particular a laser, for irradiating the test specimen with excitation photons and (c) a detector, in particular a camera, for detecting fluorescence photons emitted by the test specimen due to the irradiation with the excitation photons.

[0003] Dye penetrant methods are used in non-destructive testing of test specimens to check for surface defects. Surface defects include cracks, especially microcracks, and imperfections such as blowholes, pores, or indentations. A fluorescent dye is applied to the test specimen and partially removed if necessary, leaving the fluorescent dye only in areas that are difficult to access for cleaning. These are usually surface defects.

[0004] The higher the demands placed on the test specimen, the smaller the surface defects that must be detected. It has been found that very fine cracks cannot be reliably detected using the conventional dye penetrant method.

[0005] The invention is based on the object of reducing disadvantages in the prior art.

[0006] The invention solves the problem by a generic dye penetration method with the steps of detecting the respective delay time of the fluorescence photons between the emission of the excitation photon triggering the fluorescence photon, in particular the excitation photons, onto the test piece on the one hand and the detection of the fluorescence photon on the other hand and determining surface defects of the test piece based on the delay times.

[0007] The invention further solves the problem by a generic testing device having an evaluation unit configured to automatically carry out a method comprising the steps of (i) detecting the respective delay time of the fluorescence photons between the emission of the excitation photons onto the test object and the detection of the fluorescence photon and (ii) displaying an image of the test object based on the delay times and / or calculating at least one defect parameter encoding an extent of surface defects of the test object from the delay times.

[0008] According to the invention, the use of a fluorescence lifetime microscope for non-destructive testing for cracks and / or surface or edge zone defects in components is also provided.

[0009] The invention also relates to a manufacturing device for manufacturing a product from at least two components, comprising (a) a system for manufacturing at least a first component and (b) a testing device according to the invention, which is arranged and designed for testing, in particular automatically, this component. Preferably, the manufacturing device comprises an assembly system for assembling the product using the tested component, wherein the manufacturing device is preferably designed such that only components found to be free of defects are used. Instead of "component," the term "part" could also be used. If the component is tested, it can also be called a test piece.

[0010] An advantage of the invention is that the detection of surface defects can generally be performed more quickly than with conventional dye penetrant methods. The reason for this is that by detecting surface defects based on the delay times, interfering signals, such as those from reflected photons or photons generated by scattering, can be suppressed, since their delay times differ from those of the fluorescence photons. This makes it possible to eliminate background signals.

[0011] Another advantage is that surface defects can be detected with comparatively high reliability. This is because photons emitted by the test specimen that are not fluorescence photons can be discriminated against. Determining surface defects therefore depends significantly less on the preparation of the test specimen.

[0012] In other words, the invention allows for sufficiently suppressing background effects and effects caused by impurities in the specimen, allowing the actual signal caused by surface defects to be captured with higher contrast. In other words, the image contrast or selectivity for different fluorophores is increased based on the determined delay times.

[0013] In the context of the present description, the test object is understood to mean in particular any object, in particular a component, a product, a vehicle, an aircraft such as an airplane, a machine, a travel time component such as a car component, a railway component or an aircraft component.

[0014] The test specimen may be a bearing component, in particular a rolling bearing component, in particular a rolling element. The test specimen may, in particular, be a bolt, a medical implant, a prosthesis, in particular an endoprosthesis, or a gas turbine component, in particular a guide vane or rotor blade.

[0015] Preferably, however, the test specimen is not a bearing component, in particular not a rolling bearing component, in particular not a rolling element.

[0016] A surface defect is understood to mean, in particular, a crack, for example, a microcrack. A microcrack is understood to mean, in particular, a crack whose extent in both spatial directions along the surface of the test specimen is less than 0.5 mm, in particular less than 0.25 mm.

[0017] A bearing component is understood to mean, in particular, any component used in a bearing. The bearing can be a plain bearing, a magnetic bearing, or a rolling bearing. Whenever reference is made to a rolling bearing or rolling bearing component in the following, this always generally also includes a bearing or bearing component and a plain bearing, or a plain bearing component and a magnetic bearing or magnetic bearing component.

[0018] The edge zone refers specifically to the area of ​​the test specimen that extends from the surface to the depth that is altered by machining, particularly by cutting. The mechanical stress on the test specimen is generally limited to the edge zone.

[0019] A fluorescent dye is understood, in particular, to be a substance that exhibits spontaneous light emission shortly after excitation with light. Preferably, the spontaneous emission of light, i.e., fluorescence, decays exponentially. The corresponding half-life, also called the fluorescence lifetime or decay constant, is preferably at least τ = 1 ns.

[0020] Capturing fluorescence photons is understood to mean detecting. In other words, the impact of a fluorescence photon on a corresponding detector generates a signal, particularly an electrical one, which is captured and / or recorded.

[0021] Detecting the delay time is understood, in particular, as a process that allows for determining the delay time between the excitation photons striking the test object and the emission of the fluorescence photon. Thus, it is possible for the delay time to include the flight time of the excitation photons and the fluorescence photons. It is also possible for the delay time to be modulated by an intensity variation time with which the excitation light from the excitation photons is modulated according to one embodiment.

[0022] Determining surface defects means any process that enables defective areas of the test specimen to be distinguished from non-defective areas, in particular in which a defective area of ​​the test specimen is distinguished from a non-defective area.

[0023] The error parameter can be, for example, a number, a vector, or an image. It is possible, but not necessary, for the error parameter to encode the location where the error occurred. It is sufficient for the error parameter to encode that a surface defect was detected at some point within a measurement area on the test piece.

[0024] A holder is understood in particular to mean a device by means of which the test object can be brought into a predetermined position relative to the light source and / or the detector.

[0025] Preferably, the dye penetrant test is carried out according to ASTM E 1417 or ISO 3452-2.

[0026] It is advantageous if the mount is designed to rotate the test piece. Particularly preferably, the mount is designed to automatically rotate the test piece along at least two axes that are not parallel to each other.

[0027] It is advantageous if the test specimen is a rolling element. For example, the rolling element is made of ceramic. Cracks, even microcracks, can lead to the rolling element breaking. Therefore, it is beneficial for the operational reliability of the rolling bearing if even microcracks can be reliably detected. The rolling element can be a sphere, a cylinder, or a truncated cone, for example.

[0028] However, the test specimen can also be made of metal, especially steel, and / or plastic.

[0029] The excitation photons can have a wavelength in the visible range, the UV range or the infrared range.

[0030] It is advantageous if the delay time of the fluorescence photons is recorded with spatial resolution. This means that for each detected fluorescence photon, in addition to the delay time, the location on the test specimen from which the fluorescence photon was emitted is determined.

[0031] Preferably, sensitivity levels according to ISO 3452-1 and 3452-2 and / or EN 571 are three or four. This enables efficient penetration into cracks.

[0032] Irradiation can be point-based, linear, or area-based. Fluorescence photons can also be captured point-based, linear, or area-based. In particular, the fluorescence photons can be captured using a line-scan camera or an area-scan camera. This can reduce measurement time with the appropriate setup. For example, the detector can be a point, line, or area detector.

[0033] Preferably, the method according to the invention is carried out automatically.

[0034] According to a preferred embodiment, the method comprises the step of applying the fluorescent dye to the test specimen. Preferably, the method comprises the step of removing a portion of the fluorescent dye after applying the fluorescent dye to the test specimen and before irradiating it with excitation photons and recording the delay time. The removal of fluorescent dye is preferably carried out in accordance with ISO 3452-1 and 3452-2 and / or EN 571. In particular, the removal of fluorescent dye is carried out such that, in areas with surface defects, at most one-fifth, in particular at most one-tenth, of the fluorescent dye is removed per area as in areas without surface defects. As is usual with dye penetrant methods, this serves to reduce background radiation.

[0035] Removal may, for example, be carried out by abrasion, wiping, blowing, or rubbing. Preferably, removal is carried out in such a way that fluorescent dye is substantially completely removed from areas of the surface without surface defects.

[0036] Preferably, determining surface defects based on the delay times comprises the step of successively detecting the delay times of the fluorescence photons for all points of a measurement area on the surface of the test object. Preferably, determining surface defects based on the delay times also comprises the step of issuing a warning message when a surface defect has been detected. The warning message is issued, for example, when a defect parameter encoding the extent of a surface defect exceeds a predetermined threshold.

[0037] The warning message can be perceptible by humans and / or machines. For example, the warning message is an optical or electrical signal. The warning message encodes the information that a surface defect has been found. It is possible, but not necessary, for the warning message to encode the location where the surface defect was found. In particular, it is possible for the warning message to merely encode the information that a surface defect has been detected at some point on the measuring area. If the method is carried out automatically, as provided according to a preferred embodiment, the warning message can, for example, lead to the test specimen being rejected.

[0038] Alternatively or additionally, determining surface defects of the test object based on the delay times comprises the step (a) spatially resolved detection of the delay times of the fluorescence photons, so that a delay-time-dependent number of fluorescence photons is obtained. According to one embodiment, determining surface defects of the test object based on the delay times comprises the step (b) displaying in an image only those fluorescence photons whose delay times lie within a predetermined acceptance interval. The image preferably encodes the number or wavelength of the detected fluorescence photons. For example, the spatially resolved detection of the delay times is carried out using single-photon measurement. The acceptance interval is selected in particular such that photons originating from reflections or scattering processes are discriminated against.In this way, a user or an image analysis system, such as artificial intelligence, can detect surface defects with high accuracy.

[0039] Alternatively or additionally, the detection of surface defects comprises the steps of (a) spatially resolved detection of the delay times of the fluorescence photons, thereby obtaining a delay-time-dependent fluorescence photon count, and / or (b) displaying an image showing a ratio of the fluorescence photon counts of two different delay times and / or different spectral ranges. In this way, a high contrast is created between areas with surface defects and areas without surface defects.

[0040] Again alternatively or additionally, the determination of surface defects is carried out by (a) adjusting the delay-time-dependent number of fluorescence photons with (i) a first decay function f1, which describes the dependence of the fluorescence photons emitted per unit of time as a function of a first decay constant τ1 and a first, in particular spatially resolved, prefactor n 0,1 and (ii) at least one second decay function which describes the dependence of the fluorescence photons emitted per unit of time on a second decay constant τ2, which differs from the first decay constant, and a second, in particular spatially resolved, prefactor n 0,2 and preferably (b) determining the surface defect, in particular only, from one of the spatially resolved prefactors and / or displaying the spatially resolved prefactors in an image.

[0041] Fitting with decay functions is more computationally intensive, but provides high contrast between areas with and without surface defects, especially with a low number of detected fluorescence photons. It is possible to use three, four, or more decay functions. Fitting could also be referred to as "fitting." The prefactor is the factor in front of the exponential function. This number could also be called the amplitude, even if the exponential function does not have a complex-valued exponent.

[0042] For the first decay function f1, in particular, f1(t) = n 0,1 *exp(-τ1t) + a1. For the second decay function f2, in particular, f2(t) = n 0,2 *exp(-τ2t) + a2.

[0043] Preferably, the number of fluorescence photons is determined spatially resolved and / or optionally displayed in the image. The feature that the number of fluorescence photons is determined spatially resolved is understood in particular to mean that the number of fluorescence photons is determined as a function of the position on the test specimen from which the corresponding fluorescence photon was emitted.

[0044] Alternatively, surface defects can be determined by calculating the spatially resolved first moment of the spatially resolved delay-time-dependent fluorescence photon count and determining the surface defect, in particular only, from the spatially resolved moment. This calculation is less computationally intensive than fitting, thus resulting in a shorter evaluation time.

[0045] To further increase the evaluation accuracy, it is advantageous to deconvolve the delay-time-dependent fluorescence photon count with a transfer function of a test device used to detect the delay-time-dependent fluorescence photon count before determining the delay times. Deconvolution is understood to mean performing the inverse function of the mathematical convolution.

[0046] The acceptance interval preferably has a lower limit in the form of a minimum delay time. The minimum delay time is greater than the flight time of photons reflected or scattered from the test object. The scattering can be Raman scattering, for example.

[0047] Preferably, the minimum delay time is greater than the decay time of fluorescent radiation from the material of the test specimen and / or dirt adhering to the specimen. This allows corresponding measurement results to be eliminated, thus increasing the contrast.

[0048] The acceptance interval can also be selected to suppress the fluorescence photons. This can be used, for example, to determine the contamination of the test specimen.

[0049] The method preferably comprises the step of discriminating and / or filtering out measurement events of photons whose wavelength lies outside a predetermined target wavelength interval. This reduces background radiation and radiation due to reflections. Fluorescence photons have lower energy and thus a longer wavelength than the excitation photons. The target wavelength interval is preferably selected such that excitation photons are not included. Discrimination is understood as ensuring that corresponding photons are not included in the error parameter or are included only to a negligibly small extent. In this way, only selected fluorescence photons are detected. Instead of selected fluorescence photons, one could also speak of frequency-selected fluorescence photons.

[0050] The selected fluorescence photons can be evaluated and / or displayed as described above.

[0051] The test specimen can be irradiated with excitation photons using a pulsed light source, in particular a pulsed laser. Alternatively or additionally, the irradiation can be performed using an intensity-modulated light source, in particular an intensity-modulated laser. The light source can also be a diode or a flash lamp. The pulsed laser is, for example, a picosecond laser. The half-width of a picosecond laser is preferably at most 1000 ps, ​​preferably at most 100 ps, ​​and particularly preferably at most 50 ps.

[0052] The error parameter can also be an area measure that indicates the size of regions in which the area-specific emission density of, in particular, selected, fluorescence photons is above a predefined fluorescence threshold. In other words, this area measure measures the size of the regions from which many non-discriminated, in particular selected, photons were emitted.

[0053] The error parameter can also be a maximum value of the emission density of, in particular, selected, fluorescence photons. In particular, the error parameter can also be a, in particular weighted, average of several individual error parameters or a vector with several error parameters.

[0054] Preferably, the test device has an application device for automatically applying a fluorescent dye to the test specimen. This eliminates the need for manual preparation.

[0055] The inspection device may include a removal device for automatically removing a portion of the fluorescent dye. This removal device removes the fluorescent dye, at least predominantly, only in areas where no surface defect is present.

[0056] According to one embodiment, the receptacle is designed to be attached to the test specimen. This is particularly advantageous when the test specimen is larger and / or heavier than the test fixture.

[0057] According to one embodiment, the inspection device preferably has a drive for moving the light source and / or the detector and / or a measuring head relative to the test piece. In this way, a large portion of the test piece's surface can be inspected for surface defects.

[0058] According to a preferred embodiment, the testing device is designed for independent movement, in particular along the test piece. For this purpose, the testing device can have one, two, or more motors and / or actuators. For example, the testing device can be part of a testing robot that is designed for reversible positive, frictional, material, or magnetic attachment to the test piece.

[0059] If the test device is operated in artificial, periodically fluctuating ambient light, it is advantageous to reduce the background radiation by conducting the measurements during a minimum brightness. According to one use of the expression, the test device has a brightness sensor for detecting the ambient brightness. Preferably, the evaluation unit is configured to automatically (i) time-dependently detect the ambient brightness, (ii) determine a periodic change in brightness, and (iii) control the light source and / or the detector such that only those fluorescence photons are detected whose excitation photons struck the test object during a low-brightness time interval in which the ambient brightness is less than an average ambient brightness. It is particularly advantageous if the irradiation and / or detection only takes place during the minimum ambient brightness.

[0060] The camera is preferably a time-slot camera and / or a time-of-flight camera. Time-slot cameras are also known as gated cameras, while time-of-flight cameras are also known as time-of-flight cameras.

[0061] Preferably, the test specimen is moved relative to the detector and / or the light source. According to one embodiment, the test specimen is scanned. In other words, the fluorescence photons are detected from a plurality of different locations on the test specimen.

[0062] The invention also includes a test specimen that has been tested using a method according to the invention and is assigned a test certificate certifying the test result. In particular, the entirety of the test specimen tested in this way and the test certificate is also according to the invention. A product containing the test specimen and to which the test certificate is assigned is also according to the invention.

[0063] Preferably, the test device has a measuring head by means of which an impact point at which the excitation photons strike the test object and from where the fluorescence photons are detected can be positioned on the test object.

[0064] According to one embodiment, the testing device and / or the fluorescence lifetime microscope and / or the fluorescence lifetime measuring device is designed as an endoscope. In this way, test specimens located inside turbines, such as aircraft turbines, such as rotor blades or guide vanes, can be tested.

[0065] Preferably, the testing device comprises a charging station for automatic pre-cleaning of the test specimen.

[0066] The removal station can also be referred to as a washing station. It serves, in particular, for automatic intermediate cleaning. The testing device, which according to a preferred embodiment is an automatic testing device, preferably has two or more modules, such as a pre-rinse station for washing the test pieces and a post-rinse station for washing the test pieces.

[0067] The application device can be designed as a penetration station, also called a penetration station, for spraying the fluorescent dye and / or for immersing the test specimen in fluorescent dye.

[0068] Preferably, the testing device comprises a dry developer station for, in particular, automatic inspection and / or checking of the test specimens for complete coverage by the fluorescent dye.

[0069] The testing device preferably comprises an emulsifier station for applying an emulsifier. A stop bath for stabilizing the emulsion is preferably arranged downstream of the emulsifier station in the direction of material flow. The testing device preferably comprises a drying station for drying the test specimen provided with fluorescent dye. For example, the drying station comprises a drying oven, preferably for drying at a minimum of 40°C, in particular 50°C, preferably at least 60°C, and preferably at a maximum of 90°C, in particular at a maximum of 80°C.

[0070] Preferably, the testing device comprises a loading system and / or an unloading system for automatically loading the testing device with test pieces and / or for passing the test pieces on to the further production process after testing.

[0071] The invention is explained in more detail below with reference to the accompanying drawings. Fig. 1 a schematic view of a test device according to the invention for carrying out a method according to the invention, Fig. 2a a histogram of a first measurement plotting the number of received fluorescence photons against the respective delay time, Fig. 2b a histogram of a second measurement plotting the number of received fluorescence photons against the respective delay time, Fig. 2c a first image of a test specimen, in which all received fluorescence photons are plotted, Fig. 2d a second image that differs from the first image in that photons that have a minimum delay time of, for example, t min =11 ns, were discriminated against, Fig. 2e a schematic representation of Fig. 2c Fig. 2f a schematic representation of Fig. 2d and Fig. 3 a manufacturing device according to the invention

[0072] Fig. Figure 1 shows a testing device 10 for non-destructive testing of a component in the form of a test piece 12 for surface or edge zone defects. The testing device 10 has a holder 16 for holding the test piece 12 and a light source 18 for irradiating the test piece 12 with excitation photons 20.i (i = 1, 2, ...), which form excitation light 22.

[0073] The test device 10 also has a detector 24, in particular in the form of a single-photon detector 26, for detecting fluorescence photons 28.j (j = 1, 2, ...) emitted by a fluorescent dye 30 contained in a surface defect 32. The surface defect 32 is, for example, as shown in Fig. 1 schematically drawn around a crack 33. The detector 24 is connected to an evaluation unit 34, which may have a screen 36, but this is not necessary.

[0074] The holder 16 can be designed to automatically rotate the test piece 12, for example about a vertical axis V and / or a horizontal axis H.

[0075] The detector 24 can be, as in Fig. 1, a detector can be used that detects the fluorescence photons 28.j only from a point of incidence A on the test object 12. However, it is also conceivable that the detector 24 comprises or is formed by a camera or a detector array.

[0076] To carry out a dye penetration method according to the invention, the test specimen 12 is first wetted with the fluorescent dye 30. For this purpose, the fluorescent dye 30 is, for example, sprayed on, or the test specimen 12 is immersed in the fluorescent dye 30. The fluorescent dye 30 is, for example, a fluorescent dye according to ISO 3452-1 and 3452-2 and / or EN 571 Level three or four, for example Magnaflux ZL-37 from Magnaflux GmbH, Essingen, Germany. The fluorescent dye 30 penetrates surface defects, for example, the crack 33. A portion of the fluorescent dye 30 is then removed, for example, by blowing off, in particular with compressed air, or rubbing with a textile. This can be done automatically or manually.

[0077] The test specimen 12 is then connected, for example, placed on the holder 16, either automatically or manually. The excitation light 22 is emitted, for example, in pulsed form, onto the point of impact A by means of the light source 18. The light pulse emitted by the light source 18 preferably has a duration of no more than 10 ps. Fluorescence photons 28.j, which emanate from the surface O of the test specimen at the point of impact A, are guided by a lens 38 into the same light path along which the excitation light 22 was directed onto the surface O.

[0078] In a beam splitter 40, the fluorescence photons 28.j, which form the excitation light 42, are guided to the single-photon detector 26. This detects a delay time t for each registered fluorescence photon 28.j jat which the fluorescence photon 28.j was registered. This results in a histogram H: t → n(t), which plots the number n of fluorescence photons of the fluorescence photons 28.j registered in a time interval t+Δt against the delay time t.

[0079] Fig. 2a shows a first histogram H1, Fig. Figure 2b shows a second histogram H2. Fig. Figure 2c shows a first image B1, which displays a spatially resolved histogram B: x,y,t → n(t) that represents the number n of fluorescence photons 28.j over the position (x,y). The larger the number n of fluorescence photons, the brighter the corresponding pixel.

[0080] From the evaluation unit 34 (see Fig. 1) those fluorescence photons 28.j can be discriminated whose delay time t j lies outside an acceptance interval I.

[0081] The test specimen 12 is continuously moved by a drive of the holder 16, so that the surface O of the test specimen 12 is scanned. As an alternative to the term "scanning," one could also speak of "scanning." The location (x, y) of the impact point A is determined from the speed of the rotational speeds around the vertical axis V on the one hand and the horizontal axis H perpendicular to it. This location (x, y) is assigned to the corresponding histogram.

[0082] Fig. 2d shows an image B2, where a minimum delay time t min of the acceptance interval I = [t min ,...t max ] was chosen to discriminate photons caused by reflections or scattering processes. It can be seen that the surface defect F is significantly more visible. The acceptance interval was I = [6 ns, 20 ns].

[0083] The Fig. 2e and Fig. 2f show schematic representations of images B1 and B2 respectively.

[0084] Images B1 and B2 are displayed on screen 36. There, they can be viewed by a person.

[0085] Alternatively, the evaluation unit 34 can determine the maximum brightness value from the spatially resolved delay times B: x,y,t → n(t), which represents an error parameter F. If the error parameter F exceeds a predetermined threshold value F S , the evaluation unit 34 can output an error message. This codes that the test object 12 is faulty. For example, the test object 12 is then automatically rejected.

[0086] Fig. Figure 3 schematically shows an automatic manufacturing device 44 with a system 46 for producing a component in the form of the test piece 12. This component is wetted, for example, in flight, with the fluorescent dye 30. Alternatively, the test pieces 12 are supported on a conveyor, for example, a chain. For example, the test pieces 12 are immersed in a fluorescent dye bath.

[0087] Subsequently, the portion of the fluorescent dye 30 not trapped in surface defects is optionally emulsified with an emulsifier. The excess fluorescent dye 30 is then rinsed off with water 48 by a removal device 49 and then placed onto the holder 16 by a robot 50. If the measurement described above reveals that the test piece 12 is defective, it is conveyed, for example, to a reject container 52. Otherwise, the test piece 12 is fed to an assembly system 54 for further assembly, resulting in a product 56.

[0088] Fig. 4 shows a further embodiment of a testing device 10 according to the invention in the form of a testing robot 58, which in Fig.4 is shown enlarged. The testing robot 10 has a receptacle 16, which is designed as a fastening device 60 and has, for example, three fasteners 62.i. The fasteners 62.i can, for example, comprise suction cups. By means of the three fasteners 62.i, the testing device 10 can be firmly attached to the test object 12, which, for example, as in the present case, is formed by an aircraft 64.

[0089] By means of a drive 66, which can be designed, for example, as an xy table, a measuring head 68 can be positioned such that the point of impact A can be positioned, i.e., fixed, on the surface O of the test piece 12. The evaluation unit 34 or a separate controller is designed to control the fastening device 60 such that the testing robot 58 moves along the surface O of the test piece 12.

[0090] An optional brightness sensor 70 detects the ambient brightness of the test object 12. If the test object 12 is illuminated by an artificial light source, the brightness typically fluctuates with the line frequency of the light source. The evaluation unit 34 detects these brightness fluctuations and controls the light source 18 and the detector 24 so that a measurement is only performed at the minimum ambient brightness. The test device 10 is a fluorescence lifetime measuring device. List of reference symbols 10 Test device 12 candidates 16 recording 18 Light source, laser 20 excitation photons 22 Excitation light (double) 24 detector 26 single-photon detectors 28 fluorescence photons 30 fluorescent dye 32 surface defects, edge zone defects 33 crack 34 Evaluation unit 36 screen 38 lens 40 beam splitters 42 Excitation light (double) 44 Manufacturing device 46 Appendix 48 Water 49 Removal device 50 robots 52 reject containers 54 assembly plant 56 Product 58 inspection robots 60 fastening device 62 fasteners 64 aircraft 66 drive 68 measuring head 70 Brightness sensor Δt time unit, time interval τ1 first decay constant τ2 second decay constant A Point of impact B Image f1 first decay function f2 second decay function F Surface defects H horizontal axis i counting index j counting index I Acceptance interval M measuring range n Number of fluorescence photons n 0,1 first prefactor n 0,2 second prefactor O Surface P error parameters Ps threshold t Delay time t min Minimum delay time V vertical axis x Position coordinates along the surface y Position coordinates along the surface

Claims

[1] Dye penetrant method for non-destructive testing of a test specimen (12), comprising the steps (a) irradiating the test specimen (12) provided with a fluorescent dye (30) with excitation photons (20) so that fluorescence photons (28) are generated, and (b) detecting fluorescence photons (28), characterized by the steps (c) detecting a delay time (t) of the fluorescence photons (28) between the impact of the excitation photons (20) on the test piece (12) and the emission of the fluorescence photon (28.1) and (d) Determining surface defects (32) of the test specimen (12) based on the delay times (t). [2] Dye penetration method according to claim 1, characterized by the steps (a) applying a fluorescent dye (30) to the test specimen (12) and (b) thereafter and before irradiating the test specimen (12) with excitation photons (20), removing part of the fluorescent dye (30). [3] Method according to one of the preceding claims, characterized by that the determination of surface defects (32) of the test specimen (12) based on the delay times (t) comprises the following steps: (a) successively recording the delay times (t) of the fluorescence photons (28) for all points of a measuring area on the surface (O) of the test piece (12) and (b) issuing a warning message when a surface defect (32) has been detected and / or comprising the following steps: (a) spatially resolved detection of a delay time (t) of the fluorescence photons (28) so that a delay-time-dependent fluorescence photon number (n) is obtained and (b) displaying only those fluorescence photons (28) whose delay times (t) lie within a predetermined acceptance interval (I) in an image (B) and / or Displaying an image (B) showing a ratio of the fluorescence photon numbers two different delay times (t) and / or different spectral ranges. [4] Method according to one of the preceding claims, characterized by that the determination of surface defects (32) of the test specimen (12) based on the delay times (t) comprises the following steps: (a) Adjusting the delay-time dependent fluorescence photon number (n(t)) with (i) a first decay function (f1) which determines the dependence (n(t)) of the fluorescence photons (28) emitted per unit of time on a first decay constant (τ1) and a first, in particular spatially resolved, prefactor (n 0,1 ) and (ii) at least one second decay function which determines the dependence of the fluorescence photons (28) emitted per unit of time on a second decay constant (τ2) which differs from the first decay constant (τ1) and on a second, in particular spatially resolved, prefactor (n0,2 ) and (b) Determining the surface error (32) from one of the spatially resolved prefactors (n 0,1 , n 0,2 ) and / or displaying the spatially resolved prefactors (n 0,1 , n 0,2 ) in one image (30). [5] Method according to one of the preceding claims, characterized by , that (a) the acceptance interval (I) has a lower limit in the form of a minimum delay time (t min ) which is greater than the flight time of reflected or scattered photons on the test object (12) and / or method according to one of the preceding claims and / or (b) the minimum delay time is greater than the decay time of fluorescent radiation from the material of which the test piece (12) is made and / or from dirt adhering to the test piece (12). [6] Testing device (10) for the non-destructive testing of test specimens (12), in particular for surface or edge zone defects (32), with (a) a holder (16) for holding the test specimen (12), (b) a light source (18), in particular a laser, for irradiating the test specimen (12) with excitation photons (20), (c) a detector (24), in particular a camera, for detecting fluorescence photons (28) emitted by the test specimen (12) as a result of the irradiation, (d) an evaluation unit (34) which is arranged to automatically (i) detecting a delay time (t) of the fluorescence photons (28) between the impact of the excitation photons (20) on the test piece (12) and the emission of the fluorescence photon (28.1) and (ii) displaying an image (B) of the test specimen (12) based on the fluorescence photons (28) whose delay times (t) lie within a predetermined acceptance interval (I) and / or (iii) calculating at least one error parameter (P) encoding an extent of surface defects (32) of the test specimen (12) from the selected fluorescence photons (28). [7] Test device (10) according to claim 6, characterized by (a) an application device for applying a fluorescent dye (30) to the test specimen (12) and (b) a removal device for removing a portion of the fluorescent dye (30). [8] Test device (10) according to one of claims 6 or 7, characterized by , that (a) the holder is designed to be attached to the test specimen, (b) the test device has a drive (66) for moving the light source (18) and / or the detector (24) and / or a measuring head (68) relative to the test object (12), and (c) is designed to move independently, in particular along the test specimen (12). [9] Test device (10) according to one of claims 6 to 8, characterized by (a) a brightness sensor (70) for detecting ambient brightness, (b) wherein the evaluation unit (34) is arranged to automatically (i) time-dependent detection of ambient brightness, (ii) Determining a periodic brightness change and (iii) controlling the light source (18) and / or the detector (24) so ​​that only fluorescence photons (28) are detected whose excitation photons (20) have struck the test object in a low-brightness time interval in which the ambient brightness is less than an average ambient brightness. [10] Manufacturing device (44) for producing a product (56) from at least two components, with (a) a plant (46) for producing the first component (), (b) a testing device (10) according to one of claims 6 to 7, which is arranged and designed for, in particular automatically, testing of this component () and (c) if necessary, an assembly system (54) for assembling the product (56) using the tested component (). [11] Manufacturing device (44) according to claim 10, characterized by that it comprises a bearing manufacturing device for manufacturing a bearing, in particular a rolling bearing (56) from at least two rolling bearing components, in particular at least one rolling body. [12] Use of a fluorescence lifetime microscope or fluorescence lifetime measuring device for non-destructive testing for surface defects (32), in particular cracks, in surfaces (O) of components .

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