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

Abstract

The invention relates to a dye penetration method for the non-destructive testing of a test object (12), said method comprising the steps of: irradiating the test object (12), which has been provided with a fluorescent dye (30), with excitation photons (20) such that fluorescent photons (28) are produced, and detecting fluorescent photons (28), wherein by way of the steps of detecting a delay time (t) of the fluorescent photons (28) between when the excitation photons (20) hit the test object (12) and when the fluorescent photon (28.1) is emitted, and determining surface faults (32) of the test object (12) based on the delay times (t).

Description

[0001] Dye penetrant method for non-destructive testing of a test specimen and test device

[0002] 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.

[0003] According to a second aspect, the invention relates to a testing device for the non-destructive testing of test specimens.

[0004] Dye penetrant methods, such as those known from DE 102019 209 408 A1 and DE 10 2013 213 369 B3, 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, so that the fluorescent dye remains only in areas that are difficult to access for cleaning. These are usually surface defects.

[0005] 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.

[0006] The invention is based on the object of reducing disadvantages in the prior art. The invention solves this problem by means of a generic dye penetration method comprising 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 and the detection of the fluorescence photon, and of determining surface defects on the test piece based on the delay times.

[0007] The invention further solves the problem by a testing device designed 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, which has (d) 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 specimen and the detection of the fluorescence photon, and (ii) displaying an image of the test specimen based on the delay times and / or calculating at least one defect parameter that encodes an extent of surface defects of the test specimen.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] According to a preferred embodiment, the testing device is connected to a system for producing the first component, wherein the system for producing the first component is preferably part of a manufacturing device for producing a product, and wherein the manufacturing device is designed to produce a product from at least two components. The testing device is preferably arranged for automatically testing the first component.

[0010] The manufacturing device preferably comprises an assembly system for assembling the product using the two components. The manufacturing device is preferably a bearing manufacturing device for manufacturing a bearing, in particular a rolling bearing, from at least two rolling bearing components, in particular at least one rolling element.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] Preferably, however, the test specimen is not a bearing component, in particular not a rolling bearing component, in particular not a rolling element.

[0018] 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.

[0019] 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 also generally refers to a bearing or bearing component and a plain bearing, or a plain bearing component and a magnetic bearing or magnetic bearing component.

[0020] 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.

[0021] 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 T = 1 ns.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 any point within a measurement area on the test piece. A fixture is understood, in particular, to be a device by means of which the test piece can be brought to a predetermined position relative to the light source and / or the detector.

[0026] Preferably, the dye penetrant test is carried out according to ASTM E 1417 or ISO 3452-2.

[0027] 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.

[0028] 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. 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 fluorescent dye is preferably removed in accordance with ISO 3452-1 and 3452-2 and / or EN 571. In particular, the fluorescent dye is removed in such a way 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 generated between areas with surface defects and areas without surface defects.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 fi, which indicates the dependence of the fluorescence photons emitted per unit time as a function of a first decay constant TI and a first, in particular spatially resolved, prefactor no, 1, and (ii) at least one second decay function, which indicates the dependence of the fluorescence photons emitted per unit time as a function of a second decay constant T2, which differs from the first decay constant, and a second, in particular spatially resolved, prefactor no, 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.

[0040] The feature that the prefactor is spatially resolved is understood in particular to mean that the prefactor is dependent on the location. Prefactors are preferably determined for at least 100, in particular at least 500, in particular at least 1500, in particular at least 10,000, different locations.

[0041] Fitting with decay functions is more computationally intensive, but provides a 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 fi, in particular, fi (t) = no,i*exp(-xit) + ai. For the second decay function f2, in particular, f2(t) = no,2*exp(-T2t) + 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. Alternatively, surface defects are determined by calculating the spatially resolved first moment of the spatially resolved delay-time-dependent number of fluorescence photons and determining the surface defect, in particular only, from the spatially resolved moment. This calculation is less computationally intensive than fitting, thus achieving a shorter evaluation time.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 to mean ensuring that corresponding photons are not included in the error parameter or 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.

[0049] The selected fluorescence photons can be evaluated and / or displayed as described above.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Preferably, the testing device has an application device for automatically applying a fluorescent dye to the test specimen. This eliminates manual preparation. The testing device can have a removal device for automatically removing a portion of the fluorescent dye. By means of this removal device, the fluorescent dye is removed, at least predominantly, only in those areas where no surface defect is present.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Preferably, the testing device comprises a charging station for automatic pre-cleaning of the test specimen.

[0063] 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 specimens and a post-rinse station for washing the test specimens. The application device can be designed as a penetration station for spraying the fluorescent dye and / or for immersing the test specimen in the fluorescent dye.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The invention also provides for the use of a fluorescence lifetime microscope or fluorescence lifetime measuring device for non-destructive testing for surface defects, in particular cracks, in the surfaces of components.

[0069] According to the invention, there is also provided a fluorescence lifetime microscope or a fluorescence lifetime measuring device which is designed to automatically carry out a method comprising the steps of (a) irradiating a test specimen provided with a fluorescent dye with excitation photons so that fluorescence photons are generated, (b) detecting fluorescence photons, (c) detecting a delay time of the fluorescence photons between the incidence of the excitation photons on the test specimen and the emission of the fluorescence photon, and (d) determining surface defects of the test specimen based on the delay times (t), and preferably outputting a defect parameter which encodes an extent of surface defects of the test specimen from the delay times.

[0070] The invention is explained in more detail below with reference to the accompanying drawings.

[0071] Figure 1 is a schematic view of a testing device according to the invention for carrying out a method according to the invention,

[0072] Figure 2a shows a histogram of a first measurement, which plots the number of received fluorescence photons against the respective delay time,

[0073] Figure 2b is a histogram of a second measurement plotting the number of received fluorescence photons against the respective delay time,

[0074] Figure 2c shows a first image of a test specimen, in which all received fluorescence photons are plotted,

[0075] Figure 2d shows a second image which differs from the first image in that photons which fall below a minimum delay time of, for example, tmin=11 ns were discriminated,

[0076] Figure 2e is a schematic representation of Figure 2c

[0077] Figure 2f is a schematic representation of Figure 2d and

[0078] Figure 3 shows a manufacturing device containing a testing device according to the invention

[0079] 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. The testing 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, ...), which are emitted by a fluorescent dye 30 contained in a surface defect 32. The surface defect 32 is, for example, a crack 33, as schematically shown in Figure 1. The detector 24 is connected to an evaluation unit 34, which may have a screen 36, but this is not necessary.

[0080] 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.

[0081] The detector 24 can, as shown in Figure 1, be a detector 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.

[0082] 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.

[0083] 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 in which the excitation light 22 was directed onto the surface O.

[0084] In a beam splitter 40, the fluorescence photons 28.j , which form the excitation light 42, are guided to the single-photon detector 26. For each registered fluorescence photon 28.j , the single-photon detector records a delay time tj at 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 28.j measured in a time interval t+Δt against the delay time t.

[0085] Figure 2a shows a first histogram H1, and Figure 2b shows a second histogram H2. 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 location (x,y). The larger the number n of fluorescence photons, the brighter the corresponding pixel.

[0086] The evaluation unit 34 (see Figure 1 ) can discriminate those fluorescence photons 28.j whose delay time tj lies outside an acceptance interval I.

[0087] The test specimen 12 is continuously moved by a drive of the holder 16, so that the surface 0 of the test specimen 12 is scanned. Alternatively 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.

[0088] Figure 2d shows an image B2 in which a minimum delay time tmin of the acceptance interval I = [tmin,...tmax] 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]. Figures 2e and 2f show schematic representations of images B1 and B2, respectively.

[0089] The images B1, B2 are displayed on screen 36. There they can be examined by a person.

[0090] 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 Fs, the evaluation unit 34 can output an error message. This codes that the test object 12 is defective. For example, the test object 12 is then automatically rejected.

[0091] 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 rest on a conveyor, for example, a chain. For example, the test pieces 12 are immersed in a fluorescent dye bath.

[0092] 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.

[0093] Figure 4 shows a further embodiment of a testing device 10 according to the invention in the form of a testing robot 58, which is shown enlarged in Figure 4. 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 have, for example, 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. 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 impact point A on the surface 0 of the test object 12 can be positioned, i.e., fixed. 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 0 of the test object 12.

[0094] 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.

[0095] List of reference symbols

[0096] 10 Test device 68 Measuring head

[0097] 12 Test item 70 Brightness sensor

[0098] 16 recording

[0099] 18 Light source, laser At time unit, time interval

[0100] 20 Excitation photon TI first decay constant

[0101] 22 Excitation light (double) T2 second decay constant

[0102] 24 Detector A Impact Point

[0103] 26 Single photon detector B Image

[0104] 28 Fluorescence photon fi first decay function

[0105] 30 Fluorescent dye f2 second decay function

[0106] 32 Surface defects, edge zonesF Surface defects H Horizontal axis

[0107] 33 crack i counting index

[0108] 34 Evaluation unit j Counting index

[0109] 36 Screen I Acceptance interval

[0110] 38 lens M measuring range

[0111] 40 beam splitters n number of fluorescence

[0112] 42 excitation light (double) photons

[0113] 44 Manufacturing device no,i first prefactor

[0114] 46 Annex no. 2 second pre-factor

[0115] 48 Water O Surface

[0116] 49 Removal device P error parameters

[0117] 50 robot hp threshold

[0118] 52 Reject container t delay time

[0119] 54 Assembly system tmin Minimum delay time

[0120] 56 Product V Vertical Axis

[0121] 58 inspection robots x location coordinates along the

[0122] 60 Fastening device surface

[0123] 62 Fastener y location coordinates along the

[0124] 64 aircraft surface

[0125] 66 drive

Claims

Patent claims 1. Dye penetrant method for non-destructive testing of a test specimen (12), comprising the steps Irradiating the test specimen (12) provided with a fluorescent dye (30) with excitation photons (20) so that fluorescence photons (28) are generated, and Detecting fluorescence photons (28), characterized by the steps 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 piece (12) based on the delay times (t).

2. Dye penetration method according to claim 1, characterized by the steps - applying a fluorescent dye (30) to the test specimen (12) and - 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 in that the determination of surface defects (32) of the test piece (12) based on the delay times (t) comprises the following steps: - successive recording of the delay times (t) of the fluorescence photons (28) for all points of a measuring area on the surface (0) of the test piece (12) and - issuing a warning message when a surface defect (32) has been detected and / or comprises the following steps: - 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 - 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 of two different delay times (t) and / or different spectral ranges.

4. Method according to one of the preceding claims, characterized in that the determination of surface defects (32) of the test piece (12) based on the delay times (t) comprises the following steps: Adjusting the delay-time-dependent number of fluorescence photons (n(t)) with a first decay function (fi) which specifies the dependence (n(t)) of the fluorescence photons (28) emitted per unit of time as a function of a first decay constant (TI ) and a first prefactor (no,i), and at least one second decay function which specifies the dependence of the fluorescence photons (28) emitted per unit of time as a function of a second decay constant (12) which differs from the first decay constant (TI) and a second prefactor (no, 2) and Determining the surface defect (32) from one of the spatially resolved prefactors (no,i , no, 2) and / or displaying the spatially resolved prefactors (no,i , no, 2) in an image (30).

5. Method according to claim 4, characterized in that the prefactor is spatially resolved.

6. Method according to one of the preceding claims, characterized in that - the acceptance interval (I) has a lower limit in the form of a minimum delay time (tmin) which is greater than the flight time of reflected or scattered photons at the test object (12) and / or method according to one of the preceding claims and / or - 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).

7. Test device (10) for non-destructive testing of test specimens (12) with (a) a holder (16) for holding the test specimen (12), (b) a light source (18) for irradiating the test specimen (12) with excitation photons (20), (c) a detector (24) for detecting fluorescence photons (28) emitted by the test specimen (12) due to the irradiation, (d) an evaluation unit (34) which is arranged to automatically 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 displaying an image (B) of the test object (12) based on the fluorescence photons (28) whose delay times (t) lie within a predetermined acceptance interval (I) and / or 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).

8. Test device (10) according to claim 7, 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).

9. Test device (10) according to one of claims 7 or 8, characterized in 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 trained to move independently.

10. Test device (10) according to one of claims 7 to 9, characterized by a brightness sensor (70) for detecting an ambient brightness, wherein the evaluation unit (34) is set up for automatic time-dependent detection of the ambient brightness, determination of a periodic brightness change and control of the light source (18) and / or the detector (24) such 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. 11 . Test device (10) according to one of claims 7 to 10, which (a) with a system (46) for producing the first component of a manufacturing device (44) for producing a product (56) from at least two components and (b) is arranged and designed to test the first component.

12. Use of a fluorescence lifetime microscope or fluorescence lifetime measuring device for non-destructive testing for surface defects (32) in surfaces (O) of components.

Images