Method and apparatus for non-destructive inspection of connection points of component assemblies

Abstract

The present invention is a method for non-destructive testing of a connection point (10) of a component assembly. At a first detection time, a reference image of the connection point (10) is captured, and the heads (18a, 18b) are imaged as head surfaces (20a, 20b). At a second detection time (44), a test image similar to the reference image is captured, the second detection time (44) occurring a predetermined time after the first detection time and after the excitation time, and an analysis area (42) is defined. If the temperature change is within a predefined temperature range, a "pass" value is formed. The connection point (10) is classified by comparing the sum of the subareas with the "pass" value with a reference range having at least one specified lower range, and the connection point (10) is classified as a "pass" connection if the sum is within the reference range, otherwise the connection point (10) is classified as a "fail" connection.

Description

[Technical field]

[0001] The invention relates to a method for non-destructively inspecting a connection point in a component assembly as defined in the preamble of claim 1 and to a device as defined in the preamble of claim 23. [Background technology]

[0002] Methods for non-destructive testing of connections between materials are already known in the art. Such methods are preferably based on the principle of thermography. The component assembly is heated by an excitation source and from the different temperature behavior of the components and the connection point conclusions can be drawn about the connection point. Said temperature behavior is preferably recorded using a thermal imaging camera. An evaluation system connected to both the excitation source and the thermal imaging camera is used for evaluation and classification of the connection point.

[0003] DE 10 2006 057 802 A1 discloses a method and an inspection system for non-destructive testing of resistance pressure welds. The resistance pressure weld between the substances is subjected to pulsed excitation by means of a flash lamp. The evaluation system includes a thermal imaging camera which records the temperature behavior of the bond between the substances and analyzes the time course of the received light intensity on the basis of said temperature behavior.

[0004] To obtain a better local resolution, the imaged area where the bonded connection points of the components are located is subdivided into several camera pixels by analyzing the history of each camera pixel. The evaluation and classification is performed on the basis of a time-dependent detector unit. Bonded connection points of the components with insufficient bond strength and with camera pixels assigned a "pass" value in the detector unit above a certain threshold are detected if the total area of ​​the "pass" values ​​is too small compared to another threshold. The area is determined 200 ms after excitation.

[0005] This test method can be used to determine the size of the pressure weld or heat transfer joint connecting two laminated metal sheets by recording the total area that is fully welded at a specific time, and the absolute temperature is measured at the specific time when heat radiation reaches the surface of the cover layer through the weld spot.

[0006] Other methods for non-destructive testing of material bonds by evaluating strength curves over time are also known in the art: for the sake of completeness, reference is made to DE 10 2007 042 341 A1 and DE 10 2007 050 005 A1.

[0007] Conventional test methods are mainly used for spot welded or adhesive connections. The connection points are material-to-material bonded and essentially homogeneous. Furthermore, conventional test methods are precise, time-consuming and fragmented, with each test system designed for use only in specific operating conditions. Methods for non-destructive testing of welded joints, especially spot welded joints, of two constituent layers, especially made of steel, are known in the art.

[0008] What is currently desired is a method for reliable non-destructive evaluation of the quality of mixed-component connections. In the case of mixed-component connections, two component layers, usually made of different materials, are connected via a connecting element. Unlike conventional spot welded connections, what is important in these connections is not the quality and size of the contact point between the two components, but the transition between the two components and the connecting element.

[0009] For example, poor contact between the head of the connection element and the upper material layer (cover layer) will result in poor transmission of the contact pressure and poor adhesion of the connection. Such defects can be detected purely by visual inspection.

[0010] Furthermore, for the quality of the connections of such mixed components, it is very important that there is sufficient strength between the connection element and the lower layer of the structure, the base layer, a property that cannot be evaluated purely optically since the connection points are internal to the component assembly. Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to provide a method for non-destructive testing of connection points in component assemblies, of the type defined in the preamble of claim 1, which method can be used to assess the quality of the connections in said respect.

[0012] Another object of the present invention is to provide a respective device of the type defined in the preamble of claim 23 by enhancing the corresponding device in such a way that a quick, easy and flexible testing of connection points consisting of connection elements in a component assembly is ensured whilst avoiding the abovementioned drawbacks. [Means for solving the problem]

[0013] This object is achieved for a method for non-destructively testing a connection point in a component assembly by combining the preamble and the features of claim 1 and for an apparatus by combining the preamble and the features of claim 23.

[0014] The dependent claims relate to further advantageous embodiments of the invention. The temperature behavior of the component assembly varies due to different geometrical properties of the component assembly. Furthermore, non-uniformities, in particular gaps between the base layer and the cover layer and between the connection element and the cover layer, as well as defects such as cracks, lead to different degrees of heat conduction depending on time and location in the component assembly.

[0015] In the known method, the component assembly to be tested consists of a base layer, at least one cover layer and a connecting element with a head and a shaft, at a connection point where the shaft of the connecting element is connected to the base layer, the connecting element is securely connected to the cover layer and its head presses the cover layer against the base layer.

[0016] The connecting element has a lower thermal conductivity than the cover layer, and preferably the base layer as well. This is especially true for steel-aluminium joints, which are used in many areas of lightweight construction.

[0017] The present invention was realized based on the ability to evaluate the quality of a connection based on the "thermal conductivity" of the component connection, and is based on heat conduction from the base layer through the connection elements between the base layer and cover layer and the connection points between the head and cover layer.

[0018] According to the invention, inspection of component connections of the above type is performed by means of a thermal imaging camera and an inductor located on the side of the component assembly opposite the thermal imaging camera, said inductor inductively exciting the base layer via the active surface when excited by an excitation pulse.

[0019] During the first detection, a reference image of the connection point is captured by the thermal imaging camera and the head is displayed as the head surface. During the second detection, a test image is captured in the same manner as the reference image.

[0020] The second detection time is after the first detection time and after a predetermined time has elapsed after the excitation time. In particular, said second detection time represents the time when the heat input to the head surface of a "passed" connection through the cover layer can be measured at the head surface of the connection element. In particular, at this time, the heat input through the cover layer can exceed the heat input through the shaft of the connection element.

[0021] An evaluation area is defined in the test image and / or in the reference image. The evaluation area at least partially comprises the head surface. The evaluation area is divided into sub-areas with a certain pixel unit. A temperature value is assigned to each of the sub-areas. Based on the temperature values ​​of the sub-areas corresponding to the reference image and the test image, a temperature change value is formed according to a rule basis. Based on the temperature change value basis, a "pass" value is formed if the temperature change is within a predefined temperature range.

[0022] If there is sufficient heat conduction through the cover layer in the component assembly, the connection is "passed" if, during said second detection, a sufficient number of sub-areas are found within a defined temperature range with at least one predefined lower limit due to the high thermal conductivity of the cover layer. No thermal equalization within the connection element has occurred, especially in the head area. This indicates that there are no significant defects in the entire transmission path. This makes it possible to distinguish between a "passed" connection and a faulty one.

[0023] In welded connections, for example, quality defects appear in the form of so-called cracks at the transition from the base layer to the shaft, which contain areas of trapped air around them, resulting in a reduced heat transfer to the cover layer. In particular, the heat generation in the base layer is also altered due to the induction caused by the presence of cracks extending into the base layer, which affects the heat transfer through the component assembly.

[0024] The lack of connection between the head and the cover layer also reduces the thermal conduction through the cover layer, which is reflected in the temperature change image during the second detection. Based on this, the connection point is classified by comparing the sum of the sub-areas with a "pass" value with a reference range. If said sum is within the reference range, the connection point is classified as a "pass" connection, otherwise the connection point is classified as a "fail" connection. The reference range has a lower limit, which corresponds to the size of the head.

[0025] This takes into account the fact that heating, especially in the edge region of the head, reflects heat conduction through the cover layer. Thus, the method of the present invention allows for a simple evaluation of the quality of the component connection in a single evaluation, taking into account both the connection point of the connection element to the base layer and the transition of the connection element to the cover layer of the head.

[0026] Preferably, the rule is designed to subtract the temperature values ​​of the corresponding sub-areas of the test image from those of the reference image, in particular the temperature values ​​of the sub-areas of the reference image are subtracted from those of the test image. The subtraction facilitates obtaining a temperature variation value for each pixel. The use of the temperature variation values ​​takes into account the fact that the head, due to its shape, exhibits a non-uniform radiation behavior, the effects of which are mitigated by detecting the temperature variations.

[0027] Preferably, the second detection time is selected such that there is still a temperature difference on the head surface at the second detection time at which the connection is deemed "failed". This point is determined in particular by evaluating the temperature curves of known "passing" connections using calibration measurements. This allows a reliable and reproducible classification of the connection points.

[0028] In another advantageous embodiment of the invention, in order to determine the time of the second detection, a temperature change curve of a calibration measurement of a "pass" connection is generated from the excitation time of a sub-area or an average value of at least two sub-areas of the evaluation area is generated at least until the slope of the temperature change curve becomes negative.

[0029] This means that the second detection time can be selected as a time when the temperature equalization and saturation effects occurring after the maximum temperature change are alleviated.To determine the second detection time, only the time to the maximum temperature change is taken into account, in particular only the time when the maximum temperature is reached or just before the maximum temperature is reached.

[0030] This results in a large difference in temperature change values ​​between "pass" pixels and the remaining pixels during the test procedure, allowing for meaningful classification. In another preferred embodiment of the present invention, the rules for evaluating the temperature change may include the generation of a temperature change image showing the temperature change at each pixel.

[0031] The generation of a temperature change image has the advantage that further graphic processing, in particular image processing using filter algorithms, is possible. Preferably, the second detection time corresponds to the time of the maximum temperature change of the temperature change curve, in particular a maximum temperature change of at least 2 Kelvin (K), preferably 5 K or more. Setting the second detection time at the time of the maximum temperature change makes it possible to meaningfully evaluate the individual pixels.

[0032] The temperature range is preferably determined based on the temperature change curve of a calibration measurement, so that the connection point is tested to the characteristics of the component assembly. For example, if the temperature change of a pixel is more than 5-10 Kelvin, the corresponding pixel can be assigned a "pass" value, which allows clear differentiation from surrounding areas and defects.

[0033] Preferably, said temperature curve is generated by a calibration measurement under ambient conditions when the test image is taken, thereby minimizing the influence of ambient conditions during the test procedure. Preferably, the active surface of the inductor is located in the center of the head surface in the base layer, thereby allowing a uniform and targeted excitation under the base layer of the connection element.

[0034] Preferably, the active surface and the thermal imaging camera are aligned in a straight line, which ensures that the connection point is entirely within the capture range of the thermal imaging camera.

[0035] To allow easy and automatic positioning of the active surface, the inductor is positioned based on contour detection of the head surface by a thermal imaging camera. The component assemblies, and in particular the connection elements, are heated differently due to the ambient temperature, different materials and geometric shapes. This different temperature distribution in the component assemblies allows passive detection of the head by the thermal imaging camera, since the temperature of the head of the connection elements is significantly different from the temperature of the surrounding component assemblies.

[0036] In another embodiment of the invention, the reference range has an upper limit. Setting a second limit value allows a better evaluation of the individual pixels of the test image. This allows different types of errors to be distinguished, or whether the sum of the "pass" values ​​is below a lower limit or above an upper limit. If the head of the fastener penetrates the cover layer too much, a bead may form around the head of the cover layer. This bead changes the structure of the cover layer to such an extent that an increase in radiation can be detected. This may indicate a quality defect.

[0037] Preferably, at least one boundary value is formed by a 10% tolerance on the sum of the "pass" values ​​in the reference measurements, which allows to eliminate minor and irrelevant deviations between the test image and the reference measurements.

[0038] Preferably, the evaluation range corresponds to ±20% of the head surface, which means in particular that the edge and transition areas of the connecting elements are also taken into account in the test.

[0039] In a further advantageous embodiment of the invention, the evaluation range is determined using a calculation based on a reference measurement, which allows the evaluation area to be defined quickly and automatically.

[0040] Preferably, the evaluation region is centrally located with respect to the head surface. Defining an evaluation region central to the head surface ensures at least partial evaluation of the head surface and a cylindrical region below the head surface, thereby allowing non-uniformities within the region to be detected.

[0041] Preferably, the distance between the inductor and the lower layer of the component assembly is set so that a large temperature input is generated within the component assembly. If the distance between the inductor and the component assembly is too large, the difference in the temperature change value will be too small to allow clear classification.

[0042] To remove external errors in the image of the temperature variation, a filter, such as a Gaussian filter, is applied to the image of the temperature variation, which allows the information content of neighboring pixels to be included in the evaluation.

[0043] Preferably, the component assembly is designed as a mixed construction connection, in which the base layer and the joining elements made of steel form a friction welded connection and the cover layer is made of aluminum.

[0044] In yet another advantageous embodiment of the invention, the base layer has a thickness of 0.8 to 2 mm and the cover layer has a thickness of 1.0 to 4 mm.

[0045] Preferably, the connecting element is designed as a friction element, at whose head the drive structure is provided.

[0046] Another aspect of the present invention relates to an apparatus, which includes a thermal imaging camera, a positioning means, an inductor, and an evaluation and control unit. Preferably, the excitation frequency of the inductor is between 15 kHz and 50 kHz. This prevents the excitation from penetrating too deeply into the component assembly, especially into the connection elements within the "depth range" of the cover layer. This allows the effect of heat flow through the cover layer to be fully taken into account.

[0047] Preferably, the evaluation and control unit executes the method according to the invention. Preferably, the evaluation and control unit controls the positioning means. In yet another advantageous embodiment of the invention, the positioning means comprises as connection means a C-bracket designed to fix the thermal imaging camera and the inductor to each other, said connection means being positioned relative to the connection point. This connection means allows them to be positioned accurately and automatically relative to each other.

[0048] Preferably, the positioning means comprises two independently movable sub-means, one connected to the thermal imaging camera and the other connected to the inductor, for positioning the thermal imaging camera and the inductor relative to the connection point. The sub-means are preferably designed as independently movable robotic arms. This design allows the test device to reach joints that are difficult to access, depending on the design of the robotic arm.

[0049] Preferably a thermal imaging camera is used to detect the exact location of the connection point, the detected location being used to control the positioning means.

[0050] In a further embodiment of the invention, the evaluation and control unit comprises a data storage unit, in particular for storing reference measurements and temperature profiles.

[0051] Further advantages, features and possible applications of the present invention will become apparent from the following description with reference to embodiments illustrated in the drawings. [Brief description of the drawings]

[0052] [Figure 1a-2b]Figure 1a is a cross-sectional view of a component assembly with a connection element that creates a "pass" connection. Figure 1b is a cross-sectional view of a component assembly with a different connection element that creates a "pass" connection. Figure 2a is a cross-sectional view of a component assembly with a connection element of Figure 1a that has a crack at the connection point that creates a "fail" connection. Figure 2b is a cross-sectional view of a component assembly with a connection element of Figure 1b that has a fold at the connection point that creates a "fail" connection. [Figure 2c] FIG. 2c is a cross-sectional view of a component assembly in which the connection element of FIG. 1b has insufficient penetration depth of the connection element, producing a "failed" connection. [Diagram 3] FIG. 3 is a schematic diagram showing the successive steps of the method of the present invention. [Figure 4a-4b] Figure 4a is a temperature variation image based on figure 2a, where the "pass" values ​​are visualized, and Figure 4b is a temperature variation image based on figure 2c, where the "pass" values ​​are visualized. [Diagram 5] FIG. 5 is a cross-sectional view of the device of the present invention. [Figure 6a-6b] Fig. 6a shows a perspective view of a second embodiment of a connecting element 12b Fig. 6b shows a test image of a reference measurement of the second embodiment of the connecting element 12b of Fig. 6a with an evaluation area. [Figure 7] FIG. 7 is a graph showing the temperature change in the evaluation area of ​​the test image during the second detection. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] 1a-2c respectively show schematic cross-sectional views of a connection point 10 including connection elements 12a, 12b for connecting the base layer 14 to the cover layer 16, a heat-affected zone 24 of the connection elements 12a, 12b and a heat-affected zone 26 of the base layer 14. The base layer 14 and the connection elements 12a, 12b are formed similarly and in particular have similar electrical conductivity. The cover layer 16 is arranged on the base layer 14. The connection elements 12a, 12b comprise heads 18a, 18b with head surfaces 20a, 20b and shafts 22a, 22b.

[0054] The heat-affected zones 24 of the connecting elements 12a, 12b are located in the lower regions of the connecting elements 12a, 12b. Below the heat-affected zones 24 of the connecting elements 12a, 12b is the heat-affected zone 26 of the base layer 14. The connecting elements 12a, 12b are inserted through the cover layer 16 into the component assembly consisting of the cover layer 16 and the base layer 14, and form a friction welded connection with the base layer 14.

[0055] The cover layer 16 is made of aluminum, the base layer 14 and the connecting elements 12a, 12b are made of steel. As a result, the component assembly is of mixed construction type. In one embodiment of the invention, the cover layer has a thickness of 1.0 mm to 2 mm and the base layer has a thickness of 0.8 mm to 4 mm. The connecting elements are preferably friction elements.

[0056] The arrows in figures 1a to 2c respectively indicate the heat conduction paths at the connection point 10 after the excitation time. Figure 1a shows a diagram of a "pass" connection according to a first embodiment of a connection element 12a, which in this first embodiment is provided with a drive structure 28 for the internal drive in the head 18a of the first embodiment of the connection element 12a, which is designed like a countersunk head screw.

[0057] The shaft 22a of the first embodiment of the connecting element 12a is cylindrical. The heat-affected zone 24 of the first embodiment of the connecting element 12a and the heat-affected zone 26 of the base layer 14 are homogeneous. The head 18a of the first embodiment of the connecting element 12a rests on the cover layer 16 in some areas.

[0058] FIG. 1b is a diagram of a "pass" connection according to a second embodiment of a connecting element 12b, which differs from the connecting element 12a of the first embodiment in the geometric design of the head 18b and shaft 22b of the second embodiment.

[0059] The second embodiment of the connecting element 12b has a different structure for the head 18b of the second embodiment of the connecting element 12b, which is provided for external actuation: the head surface 20b of the second embodiment of the connecting element 12b is larger in diameter than the head surface 20a of the first embodiment of the connecting element 12a.

[0060] Additionally, the head 18b of the second embodiment of the connecting element 12b has a circumferential head projection 32 that is angled towards the member assembly. The shaft 22b of the second embodiment of the connecting element 12b is cylindrical.

[0061] The heat transfer at the connection point 10 after the excitation time essentially takes place via two paths: firstly, via the shaft 22a of the first embodiment of the connection element 12a, heat is pre-transferred via the base layer 14 and the heat-affected zones 24, 26;

[0062] On the other hand, heat is conducted from the heat-affected zone 26 of the base layer 14 through the cover layer 16 to the head 18a of the first embodiment of the connection element 12a. As can be seen in Figures 1a and 1b, the heat conduction through the cover layer 16 is faster than the heat conduction through the shafts 22a, 22b of the connection elements 12a, 12b. This is because the thermal conductivity of the cover layer 18, in particular made of aluminum, is higher than that of the connection elements 12a, 12b. The second detection is selected so that the majority of the heat conduction of both paths, in particular for the induced heat through the cover layer, reaches the head surface.

[0063] 2a is a diagram of a "failed" connection according to a first embodiment of the connection element 12a. In the region of the heat-affected zone 24 of the connection element 12a and the heat-affected zone 26 of the base layer 14, the connection point 10 has a crack 30 in the side area, which is formed in the circumferential direction as a flat crack, i.e. in the shape of a cone.

[0064] Cracks 30 in the lateral regions of the heat-affected zone 26 of the base layer 14 create flat air pockets in some areas. During excitation, these air pockets create non-uniform ring-shaped induction in the base layer outside the cracks. This heat is primarily conducted laterally through the base layer 14, away from the connection point 10.

[0065] The crack 30 further inhibits heat transfer from the heat-affected zone 26 of the base layer 14 through the cover layer 16 to the head 18a of the first embodiment of the connecting element 12a. Since the specific heat capacity of the cover layer 16 is significantly higher than that of the base layer 14, it is assumed that the thermal energy of the base layer is not sufficient to significantly heat the cover layer 16 by the time of the second detection.

[0066] This heat build-up prevents effective heat transfer to the cover layer 16. The heat is mainly transferred through the welded connection between the base layer 14 and the shaft 22a of the first connecting element 12a, which heats up the head 18a of the first embodiment of the connecting element 12a. As a result, the head 18a of the connecting element 12a heats up less during the second detection than the "pass" connection, but the heated area in the center of the head, which has undergone the necessary temperature change to be evaluated as a "pass" pixel, is smaller because the edge areas of the head are not heated sufficiently by the cover layer and shaft material.

[0067] This makes it clear that the evaluation performed at the second detection is essential for the validity of the test. This type of heat transfer applies to the second embodiment of the connecting element 12b as well as to the other embodiments of the connecting element.

[0068] Fig. 2b shows a "failed" connection of the second embodiment of the connection element 12b. The "failed" connection is characterized by the fact that the second embodiment of the connection element 12b is inserted deeper into the component assembly compared to the "passed" connection of Fig. 2a (h1>h2), where h1 is the penetration depth of the second embodiment of the connection element 12b into the component assembly of Fig. 1b and h2 is the penetration depth of the second embodiment of the connection element 12b into the component assembly of Fig. 2b.

[0069] As a result, the lower part of the shaft 22b of the second embodiment of the connection element 12b forms so-called folds. A gap 27 is formed between the second embodiment of the connection element 12b and the heat-affected part 24 of the second embodiment of the connection element 12b. Therefore, heat conduction occurs around the gap.

[0070] The heat conduction at the connection point 10 in FIG. 2b mainly passes through the cover layer 16 via the heat-affected parts 24 and 26 and is transmitted to the head 18b of the second embodiment of the connection element 12b. The heat conduction through the shaft 22b of the second embodiment of the connection element 12b is suppressed by the gap 27 formed by the deeper penetration of the connection element 12b.

[0071] The deeper penetration of the second embodiment of the connection element 12b further results in the formation of beads from the cover layer 16 at the radially outer end of the head 18b of the second embodiment of the connection element 12b. The formed beads expand the heating area during the second detection. The form of heat conduction of the corresponding "non-conforming" connection also applies equally to the connection point 10 with the first embodiment of the connection element 12a and to other embodiments of the connection element.

[0072] FIG. 2c shows a "non-conforming" connection made with the second connection element 12b, which is not inserted as deeply into the member assembly as the "conforming" connection in FIG. 2a (h1 < h3). Here, h3 is the penetration depth of the second connection element 12b into the member assembly in FIG. 2c. Here, compared with FIGS. 1b and 2b, the head protrusion 32 is not connected flush with the cover layer 16.

[0073] The heat conduction at the connection point 10 in FIG. 2c basically travels from the heat-affected part 26 of the base layer 14, through the heat-affected part 24 of the first embodiment of the connection element 12a, to the shaft 22a of the first embodiment of the connection element 12a.

[0074] Heat is conducted from the shaft 22a of the first embodiment of the connecting element 12a to the head 18a of the first embodiment of the connecting element 12a. First, because the penetration depth of the connecting element 12a of the first embodiment is short, the distance (h3) over which the heat is conducted is longer than the distance (h1) of a "pass" connection of the connecting element 12a of the first embodiment, and second, the head does not engage the cover layer 16 in a way that transfers heat.

[0075] This means that, although the welded connection is intact over the entire surface of the shaft, the head 22a of the first embodiment of the connecting element 12a is heated fully and sufficiently only at a later point in time during the second detection due to insufficient contact between the head and the cover layer.

[0076] In this way, one measurement is sufficient to detect and exclude the presence of both superficial and internal quality defects. A "failed" connection with the connection element 12a of the first embodiment of Fig. 2a is also classified as a "failed" connection with the connection element 12b of the second embodiment according to the test method of the present invention.

[0077] Defects at the connection points 10 of figures 2a-2c, also in other embodiments of the connection element, are detected by the test method of the invention and classified into "passed" and "failed" connections.

[0078] 3 is a schematic diagram showing the procedure of the non-destructive testing method. This method for testing the connection points 10 is based on the principle of passive thermography, whereby the component assembly is thermally excited even on the side of the base layer 14 remote from the cover layer 16 by an excitation pulse when excited from an inductor 36 which includes the area of ​​the shafts 22a, 22b of the connection elements 12a, 12b.

[0079] The second detection time 44 is determined by a calibration measurement K, which is performed using a sample of known "good" connections. The thicknesses and materials of the connection elements 12a, 12b, base layer 14 and cover layer 16 are identical to those of the component assembly tested with the corresponding test method P during the calibration measurement K.

[0080] A calibration evaluation area 46 is defined for the calibration measurement K, which includes at least a portion of the head surface 20a, 20b. The calibration measurement K can be performed at any time prior to the test procedure. Furthermore, the calibration measurement K can also be performed multiple times, for example after a set period of time or a set number of test cycles.

[0081] The temperature change in the calibration evaluation area 46 is recorded over time. The generated temperature change curve (see FIG. 4b) includes a maximum temperature change time. This maximum temperature change time is used as the second detection time 44 of the non-destructive testing procedure. At the first detection time (preferably before the excitation time), a reference image of the connection point 10 including pixels with assigned temperature values ​​is captured by the thermal imaging camera 34.

[0082] In particular, the first detection occurs immediately before the excitation. The thermal imaging camera 34 is placed on the side of the cover layer 16, away from the base layer 14, above the heads of the connecting elements. The excitation causes heat conduction through the base layer 14 and then along different transfer / thermal conduction paths to the heads 18a, 18b of the connecting elements 12a, 12b. On the one hand, heat is conducted through the two heat-affected zones 24, 26 to the shafts 22a, 22b of the connecting elements 12a, 12b. Then, heat flows to the heads 18a, 18b of the connecting elements 12a, 12b. On the other hand, heat is conducted from the heat-affected zone 26 of the base layer 14 through the cover layer 16 to the heads 18a, 18b of the connecting elements 12a, 12b.

[0083] Due to the different materials of the cover layer and the connection elements 12a, 12b, the two heat conduction paths have different heat conduction times, which also depend on the arrangement and imperfections of the materials, among others, as seen in Figures 2a-c. The heat conduction rate of aluminum is higher (approximately 160 W / mK) than that of steel (approximately 40 W / mK), so heat is conducted faster in aluminum.

[0084] Furthermore, different insertion depths of the connecting elements 12a, 12b within the component assembly result in different heat transfer times. At a predetermined second detection time 44, a test image similar to the reference image of the joint 10 is captured by the thermal imaging camera 34. After capturing the test image, the temperature values ​​of the reference image are subtracted from the corresponding temperature values ​​of the test image.

[0085] This can also be done automatically by the detection device when the test image is captured. Corresponding temperature change values ​​are assigned to the pixels of the test image to create a temperature change image that is evaluated in evaluation area 31. Due to the different heat transfer times and heat power losses of the thermal conductors in the component assembly for the "passed" connection shown in Figures 1a and 1b and for the "failed" connection shown in Figures 2a-2c, the test images show significantly different temperature change distributions for each case.

[0086] To reduce external errors such as chips resting on the head, a filter is applied to the evaluation area 31. The evaluation area 31 includes at least a portion of the head surface 20a, 20b of the connecting elements 12a, 12b and is centrally located with respect to the head surface 20a, 20b of the connecting elements 12a, 12b. The filtered pixels in the evaluation area 31 are evaluated by temperature range.

[0087] The temperature range and reference range are based on evaluation of reference measurements of a test arrangement known to be a "pass" connection. Pixels whose temperature change value falls within the temperature range are assigned a "pass" value. In this case, pixels whose temperature change value is 5.4°C or more and 10.0°C or less are assigned a "pass" value. In this range, meaningful statements can be made about the heating behavior.

[0088] The sum of the "pass" values ​​in the evaluation area 31 is then compared to a reference range. If the sum of the "pass" values ​​is within the reference range, the connection is "pass". If the sum of the "pass" values ​​is outside the reference range, the connection point 10 is classified as a "failed" connection. The reference range within which a connection is evaluated to be a "pass" connection is selected such that the number of pixels corresponds to 90%-110% of the number of pixels on the head surface. In this case, the evaluation area 31 is designed as +20% of the head surface.

[0089] Fig. 4a is a temperature change image of a "pass" connection according to Fig. 2a, in which a "pass" value is visualized. The "pass" value is located in the head surface 20b of the second connection element 12b. The rasterized evaluation area 31 with the visualized "pass" value is also displayed in enlarged detail. The evaluation area 31 includes the head surface 20b of the second connection element 12b.

[0090] Fig. 4b is a temperature change image of a non-"pass" connection according to Fig. 2c, in which the "pass" values ​​are visualized. The "pass" values ​​are located in the head surface 20b of the second connection element 12b. Compared to Fig. 4a, the sum or area of ​​the "pass" values ​​is smaller and no longer falls within the reference range. This results in the connection point being classified as a "fail" connection. The evaluation area 31 is rasterized in the same way as the enlarged detail of Fig. 4a, and the "pass" values ​​are visualized accordingly.

[0091] 5 is a schematic cross-sectional view of an apparatus 33 according to the invention, comprising a component assembly including a connection point 10, exemplified as a connection element 12b. The apparatus 33 comprises an inductor 36, a thermal imaging camera 34, an evaluation and control unit 38 and positioning means (not shown). The evaluation and control unit comprises a data storage unit, which is able to store the results of reference and calibration measurements on the respective component assembly. Preferably, these measurements are performed for a number of different configurations of the connection point 10 and stored in the data storage unit. For example, said configurations differ in the thickness of the connection means 12a, 12b and / or the base layer 14 and / or the cover layer 16.

[0092] The thermal imaging camera 34 and the inductor 36 are each electrically connected to an evaluation and control unit 38. A positioning means (not shown), e.g. comprising a robotic arm, is also electrically connected to the evaluation and control unit 38. The inductor 36 is positioned on the side of the base layer 14 opposite the cover layer 16. The distance of the inductor 36 from the base layer 14, the diameter and the power of the inductor 36 are set to generate a sufficient temperature input at the active surface at the shaft diameter.

[0093] The thermal imaging camera 34 is positioned on the side of the cover layer 16 opposite the base layer 14. The position and distance of the thermal imaging camera 34 relative to the component assembly is selected so that the connection points, in particular the head surfaces 20a, 20b of the connection elements 12a, 12b, are located within the recording area of ​​the thermal imaging camera 34.

[0094] The thermal imaging camera 34 can also be used to detect the position of the connection point 10, in particular the head surfaces 20a, 20b of the connection elements 12a, 12b. The active surface of the inductor 36 is aligned with the thermal imaging camera 34 along an axis 42. Positioning means are used to position the inductor 36 relative to the thermal imaging camera 34 and relative to the connection point 10. The thermal imaging camera 34 and the inductor 36 are connected in a fixed position by the action of the positioning means.

[0095] In yet another embodiment, the positions of the inductor 36 and the thermal imaging camera 34 can be managed independently of each other by secondary means in the positioning means.

[0096] FIG. 6a is a diagram of a second embodiment of the connecting element 12b, particularly showing the refraction and indentation in the head region. FIG. 6b is a schematic view of the head surface 20b of the second connecting element 12b recorded during test measurement. The calibration evaluation region 46 is shown in the image. The calibration evaluation region 46 includes the head surface 20b of the second embodiment of the connecting element 12b. FIG. 6b shows different temperatures on the head surface 20b of the second embodiment of the connecting element 12b at the time of the second detection. Here, the relationship of "T1 < T2 < T3 < T4 < T5" holds.

[0097] T5 and T4 represent temperature peaks, which are the indentations on the surface of the member as shown in FIG. 6a. The temperature difference is caused by the basic head shape and other geometric structures such as refraction and indentation.

[0098] FIG. 7 is a diagram showing a temperature change curve of the change in the average temperature within the calibration evaluation region 46. The X-axis represents time (seconds), and the Y-axis represents the temperature change (°C). The temperature change curve is displayed for 3 seconds, and the maximum temperature change is about 18°C. The reference image was captured at time 0 seconds. The cross-sectional line shown in the figure represents the second detection 44 of the test procedure. This is set between the inflection point of the temperature change curve and the maximum temperature change.

[0099] The excitation is composed of an excitation period with an induction frequency of 15 kHz to 60 kHz. The excitation duration is desirably 0.1 to 0.95 seconds. The excitation amplitude varies depending on the thickness of the material and the required temperature change.

[0100] The non-destructive inspection method and the corresponding device 33 ensure a fast, easy, and flexible inspection of the connection point 10 within the member assembly including the connecting elements 12a and 12b, and make it possible to remove both internal and external quality defects.

Claims

1. A method for non-destructively inspecting a connection point (10) of an assembly of components, comprising the steps of: a base layer (14) and at least one cover layer (16), and a connecting element (12a, 12b) having a head (18a, 18b) and a shaft (22a, 22b); A connection point (10) is formed between the shaft (22a, 22b) of the connection element (12a, 12b) and the base layer (14); the cover layer (16) has a thermal conductivity greater than that of the base layer (14) and the connecting elements (12a, 12b); The non-destructive inspection is performed by a thermal imaging camera (34) and an inductor (36) disposed on a side of the component assembly opposite the thermal imaging camera (34); The inductor (36) inductively excites the base layer (14) when excited by pulse means via an active surface, and further Upon initial detection, A reference image of the connection point (10) is captured by the thermal imaging camera (34), and the heads (18a, 18b) are imaged in the reference image as head surfaces (20a, 20b); At the second detection time (44), A test image similar to the reference image is captured; the second detection time (44) occurs a predetermined time after the first detection time and after the excitation time; an evaluation area (42) is defined in the test image and / or the reference image, the evaluation area (42) including at least partially the head surface (20a, 20b); The evaluation area (42) is divided into subareas, At a particular pixel, a temperature value is assigned to the sub-region; a temperature change value is formed according to a rule based on the temperature values ​​of the corresponding sub-regions of the reference image and the test image; Based on the temperature change value, If the temperature change is within a predefined temperature range having at least one lower limit, a "pass" value is formed; The connection points (10) are classified by comparing the sum of the sub-areas having a "pass" value with a reference range having at least one specified lower limit value, The connection point (10) is classified as a "pass" connection if the sum is within a reference range; If not, the connection point (10) is classified as a "failed" connection. Non-destructive testing methods.

2. 2. The non-destructive inspection method according to claim 1, The rule is defined by subtracting a temperature value of a corresponding portion of the test image from a temperature value of the reference image; In particular, a non-destructive inspection method characterized in that temperature values ​​of a portion of the reference image are subtracted from temperature values ​​of a portion of the test image.

3. The non-destructive inspection method according to claim 1 or 2, A non-destructive testing method, characterized in that at the second detection time (44), a predetermined period is selected such that a temperature difference still exists within the head surfaces (20a, 20b) in the "failed" connections, in particular by evaluating the temperature curves of the "passed" connections.

4. The non-destructive inspection method according to any one of claims 1 to 3, A non-destructive testing method, characterized in that to determine the second detection time (44), a temperature change curve of a "pass" connection from the excitation time of the sub-area or an average value of at least two of the sub-areas of the evaluation area is generated at least until the slope of the temperature change curve becomes negative.

5. The non-destructive inspection method according to claim 4, The second detection time (44) corresponds to a maximum temperature change time in the temperature change curve; A non-destructive testing method characterized in that the maximum temperature change is particularly 2K or more.

6. The non-destructive inspection method according to claim 4 or 5, A non-destructive inspection method comprising determining a temperature range based on the temperature change curve.

7. The non-destructive inspection method according to any one of claims 1 to 6, A non-destructive inspection method, characterized in that the "pass" value is assigned at a temperature change of 5 to 10 Kelvin for a single pixel.

8. The non-destructive inspection method according to any one of claims 1 to 7, A method of non-destructive testing, characterized in that a temperature curve is generated under ambient conditions at the time the test image was captured.

9. 9. The non-destructive inspection method according to claim 8, 2. A non-destructive inspection method, characterized in that the active surface is centrally positioned with respect to the head surfaces (20a, 20b).

10. The non-destructive inspection method according to any one of claims 1 to 9, The method of claim 1, wherein the active surface is aligned with the thermal imaging camera (34).

11. The non-destructive inspection method according to claim 10, The method of non-destructive testing, characterized in that the active surface is positioned based on contour detection of the head surface (20a, 20b) by the thermal imaging camera (34).

12. The non-destructive inspection method according to any one of claims 1 to 11, A non-destructive inspection method, wherein the reference range has an upper limit value.

13. The non-destructive inspection method according to claim 12, A non-destructive testing method, characterized in that at least one boundary value is formed by a tolerance range of 10% of the sum of said "pass" values ​​of the reference measurements.

14. A non-destructive inspection method according to any one of claims 1 to 13, A non-destructive inspection method, characterized in that the evaluation area is equal to ±20% of the head surface (20a, 20b).

15. 15. The non-destructive inspection method according to claim 14, A method of non-destructive testing, characterized in that the evaluation area (42) is determined by calculation means based on reference measurements.

16. A non-destructive inspection method according to any one of claims 1 to 15, A non-destructive inspection method, characterized in that the evaluation area (42) is centrally located with respect to the head surface (20a, 20b).

17. A non-destructive inspection method according to any one of claims 1 to 16, comprising: A method of non-destructive inspection, comprising the steps of: (a) providing a first inductor to the first member; (b) providing a second inductor to the first member; (c) providing a second inductor to the first member;

18. A non-destructive inspection method according to any one of claims 1 to 17, A method for non-destructive testing, comprising generating a temperature change image and applying a filter to the temperature change image to remove external errors.

19. A non-destructive inspection method according to any one of claims 1 to 18, comprising:

4. A non-destructive inspection method, comprising: a component assembly in the form of a mixed structural joint connection.

20. 20. The non-destructive inspection method according to claim 19, The non-destructive inspection method according to claim 1, wherein the base layer (14) is made of steel and the cover layer (16) is made of aluminum.

21. 21. The non-destructive inspection method according to any one of claims 1 to 20, The base layer (14) has a thickness of 0.8 to 2 mm; A non-destructive inspection method, characterized in that the cover layer (16) has a thickness of 1.0 to 4 mm.

22. 22. The non-destructive inspection method according to any one of claims 1 to 21, 4. A non-destructive testing method, characterized in that the connecting elements (12a, 12b) are designed as friction elements.

23. An apparatus comprising: a thermal imaging camera (34), a positioning means, an inductor (36), and an evaluation and control unit (38); Apparatus, characterized in that the evaluation and control unit (38) implements the non-destructive testing method according to any one of claims 1 to 22.

24. 24. The apparatus of claim 23, 4. An apparatus according to claim 3, wherein said evaluation and control unit (38) controls said positioning means.

25. 25. The apparatus of claim 24, said positioning means comprising connection means, in particular by a C-bracket, between said thermal imaging camera (34) and said inductor (36), which are designed to be fixed to each other; The device is characterized in that said connection means is arranged relative to said connection point (10).

26. An apparatus according to any one of claims 23 to 25, comprising: The positioning means comprises two independently adjustable sub-means, One of the sub-means is connected to the thermal imaging camera (34) and the other of the sub-means is connected to the inductor (36) for positioning the thermal imaging camera (34) and the inductor (36) relative to the connection point (10).

27. An apparatus according to any one of claims 23 to 26, comprising: The thermal imaging camera (34) is designed to detect the position of the connection point (10); The detected position is used to control the positioning means.

28. An apparatus according to any one of claims 23 to 27, comprising:

4. The device according to claim 3, wherein the evaluation and control unit (38) comprises a data storage unit for storing in particular reference measurements and temperature curves.

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