Device and method for inspecting a surface-treated die-cast part

Abstract

A method and a device (1) for inspecting a surface-treated die-cast part are proposed. The device comprises: a camera arrangement (3) with a first camera (3a) having a principal optical axis, an opaque screen arrangement (4) for optically shielding surface areas of the die-cast part not within the detection range of the camera arrangement (3), and a workpiece holder (5), wherein the workpiece holder (5) is configured to rotate the die-cast part around the camera arrangement (3) located inside it and around the screen arrangement (4).

Description

[0001] The invention relates to a method and a device for inspecting a surface-treated die-cast part. In particular, the present invention relates to an improved method for detecting unevenness, air inclusions, foreign body inclusions, etc.

[0002] For the housings of electric traction machines and other electric motors (PPE stator housings), 100% inspection of all machined surfaces for surface porosity must be performed during production / series manufacturing. The greatest challenge here is the interior of the stator housing, as it is a very small installation space and consists of a machined, reflective aluminum surface. Surface pores can generally be detected using laser triangulation sensors and / or cameras. Common manufacturers of such systems include Micro-Epsilon, Keyence, and Cognex. State-of-the-art test setups cannot be used within the PPE component because the installation space is too small for the known sensors / devices. Furthermore, no devices have yet been provided that can maintain the required cycle time in an automated process.

[0003] Furthermore, existing systems cannot detect very thin cracks and inclusions that do not create a depression in the material with 100% accuracy (false positives). Due to the extremely reflective surface of the interior, laser sensors also encountered problems and inaccurate measurements during testing. Additionally, the costs of providing and integrating suitable sensors are economically unviable for typical applications. Since the established approaches could not meet the requirements, manual visual inspection is still employed, significantly increasing production costs. For example, handheld mirrors are used to locate pores on the surface of the housing. Problems with this method include not only the potential for missed defects but also the number of workers required at full capacity.

[0004] Another problem is to quantitatively assess the air inclusions, impurities, unevenness, etc., and then to differentiate between "OK" and "not OK".

[0005] EP 2 957 859 A1, CN 2 06 638 605 U and WO 2023 / 222 561 A1 disclose surface inspection devices based on camera technology which may be helpful for understanding the present invention.

[0006] Based on the aforementioned prior art, it is an object of the present invention to make surface detection less subject to tolerances on the one hand, and on the other hand to be able to measure any air inclusions, impurities, unevenness, etc. that may be present, in order to classify the test specimen as "OK" or "not OK".

[0007] The aforementioned problem is solved according to the invention by a device with the features of claim 1 and a method for using such a device with the features of claim 10. The dependent claims describe preferred embodiments of the invention.

[0008] According to one aspect of the present invention, the device essentially comprises two components, which can be clustered as hardware and software. On the one hand, the testing station and, on the other hand, the evaluation system, optionally with artificial intelligence, are part of the invention. The testing station, for example, has a stepper motor which, by means of a gear and a ball-bearing rotary ring, drives a rotary table onto which the die-cast component can be placed by a robot on a production line. Thus, the PPE component can be rotated 360 degrees, enabling 100% inspection of the interior. The cameras that photograph the interior are embedded in a specially designed camera screen (light / shadow generator).This camera screen is moved by a pneumatic cylinder or other mechanism after the component is placed into position so that the cameras can capture the interior of the die-cast part. Furthermore, during the inspection process, a light source is used to generate grazing light on the inner surface of the die-cast component. This, in conjunction with the camera screen, creates diffuse light inside the part, allowing high-quality optical image data to be transferred to an evaluation unit (e.g., artificial intelligence, AI, etc.). During the evaluation of the files, all detected irregularities, inclusions, etc., are optically marked, located, or cataloged by the evaluation unit. Using a conversion based on the number of pixels used to represent each irregularity, impurity, defect, etc., the longitudinal and transverse dimensions are then determined.Thus, not only the critical pores are detected, but also the non-critical pores. After evaluation, the collected data is saved in log files, and the robot is informed of the component's status, which then decides whether the component is defective ("not OK") or not ("OK"). The use of a camera screen (hereinafter also referred to as "screen arrangement") enables the inspection of the PPE interior with a high degree of optical quality, since the extremely reflective, machined (e.g., milled) surface of the interior can be optically reproduced well by a camera. This avoids overlooking defects or unsatisfactory / erroneous measurement of them, as has occurred, for example, with laser triangulation. The light source used according to the invention is specifically designed to provide diffuse illumination of the interior of the PPE component.to achieve this of the die-cast component, enabling the creation of high-quality image files using relatively simple (and compact) cameras. Within these files, pores, air inclusions, irregularities, etc., can be analyzed using optical pattern recognition, optical object recognition, or similar techniques. Another problem solved by diffuse illumination is the fluctuating ambient light in production lines that are illuminated by daylight during the day but exclusively by artificial light at night. By using the camera screen or screen arrangement proposed according to the invention, the interference from ambient light during the illumination process can be largely eliminated, thus enabling highly reproducible test results.The camera screen / screen assembly can be manufactured as a 3D-printed screen element, which is specifically designed to fit the cavity geometry of the die-cast component. For example, a screen fitted into the cavity of the die-cast component to within a few centimeters or millimeters can be used, so that only the surface of the die-cast component illuminated by the artificial light of the device according to the invention (grazing light) is within the camera's detection range, and the entry of ambient light is largely prevented. To avoid optical artifacts, the screen can have a homogeneous color, for example, white or light gray. In other words, the screen assembly according to the invention closes any openings in the cavity of the die-cast component, at least with respect to direct light transmission, thereby enabling the generation of highly reproducible and qualitatively and quantitatively meaningful image data.

[0009] A second problem where the invention can be advantageously used is the quantitative detection of defects in the machined surface of the die-cast component. Therefore, according to the invention, high-resolution cameras with a resolution of, for example, 4608 x 2592 pixels are used. By using several such high-resolution cameras in parallel, the number of evaluable pixels per unit of time can be multiplied.

[0010] The method according to the invention can optionally be integrated into further manufacturing steps. For example, after the production and surface finishing (e.g., milling) of the die-cast component, a leak test can be performed. In this test, a cavity of the die-cast component can be pressurized, and the pressure drop on the one hand or escaping fluid on the other can be detected. After the leak test, the die-cast component can be positioned in the device according to the invention using a robot. In particular, the die-cast component can be mounted on the workpiece holder or a rotary table as a workpiece holder. A subsequent examination of the die-cast component according to the invention can also detect potential damage caused by the leak test (e.g., scratches, dents, etc.).Before the inspection process in the device according to the invention, a camera screen can be moved into the intended position within the die-cast component, and the device's light source can be switched on (if not already permanently switched on) to obtain optimal image data and optimize the contrast within the image data. Depending on the viewing angle of the camera(s) used, the die-cast components to be inspected can then be rotated (automatically), for which an electric motor may be provided. The result of the evaluation according to the invention can be saved in log files and transmitted as a message to an end-of-line test bench. If the result is satisfactory, the component can be forwarded via the logistics process to final assembly.However, should an unacceptable defect be detected in the component during evaluation (e.g., using AI), the robot places the part on a reject conveyor belt or in a suitable box. Both the inspection station according to the invention and the evaluation using artificial intelligence can optionally be universally adapted to other applications and products / die-cast components. Accordingly, the camera and lighting technology is not only suitable for indoor use but can also be used in areas and workstations flooded with daylight. The optionally usable artificial intelligence can exhibit different quality characteristics and levels of complexity. In particular, further defects in the photographed components can be detected. In commercial applications, a trade-off between the inspection time and the problems of an undetected defect will always be necessary.The quality assurance expert knows how to carry out this optimization and will set up the evaluation software / Kl accordingly.

[0011] The device according to the invention serves for the inspection of a surface-treated die-cast part, which may be designed, for example, as an electric motor housing, stator housing, brake caliper, or similar component. The surface treatment of the die-cast part may, in particular, include machining (e.g., milling). The device comprises a camera arrangement with a first camera having a principal optical axis. The principal optical axis can be considered the axis on which the pixel located horizontally and vertically centered in the camera image is arranged. Furthermore, an opaque screen arrangement is provided for the optical shielding of surface areas of the die-cast part that are not within the detection range of the camera arrangement.Furthermore, the shielding is arranged around the camera in such a way that any ambient light entering from the rear does not cause reflections on the bare inner wall of the die-cast part that could be detected by the camera. A workpiece holder, which can also be considered a sample stage (for example, with a rotary table, which can optionally be electrically driven), is set up to rotate the die-cast part around the camera assembly located inside it and around the shielding assembly. In other words, both the camera assembly and the opaque shielding assembly are located within an open cavity of the die-cast part.In particular, the shielding arrangement can be adapted to the internal surface shape / volume structure of the die-cast part to prevent contact with the part's wall and to prevent unnecessary ambient light from reaching the surface of the die-cast part within the camera's field of view. Compared to prior art arrangements, shielding is provided around the camera assembly to keep ambient light out of the field of view and to optimize the evaluation of the camera data. This increases the detection reliability both qualitatively and quantitatively, enabling the best possible detection of material or production defects and the implementation of appropriate countermeasures.

[0012] Preferably, the device further comprises a lifting device by means of which the camera arrangement and the screen arrangement can be inserted into the die-cast part (for example, lifted, pushed, lowered, or transferred). This does not preclude the possibility of rotating and / or tilting / pivoting the combination of camera arrangement and screen arrangement in order to insert the screen arrangement into the cavity of the die-cast part and to enable the detection of the unshielded surface areas according to the invention.

[0013] In particular, the camera assembly, including the screen assembly, can be inserted into the cavity of the die-cast part through an opening / bore in the workpiece holder. For this purpose, the workpiece holder can be designed as a turntable or rotating ring, so that the sample head, consisting of the camera assembly and the opaque screen assembly, remains stationary after insertion, and the workpiece holder is rotated while the die-cast part is imaged.

[0014] The camera can be positioned / mounted / aligned within the screen assembly in such a way that its optical principal axis intersects the rotational axis of the die-cast component or the workpiece holder. This typically allows for the greatest possible distance between the camera assembly and the surface of the die-cast part being imaged. In this way, the camera, which operates without complex optical components, can capture the largest possible surface area during a single imaging process.

[0015] To enable a complete image / capture of the die-cast part's surface, a motorized rotation can be provided, the angle of which can be selected depending on the camera's capture angle. For example, four angular ranges can be predefined, so that after an initial image capture, three further angular ranges (each 90 degrees) are approached and finally captured by the camera. This process, like the other steps described in this disclosure, can be fully automated. In particular, the process described above can be automatically triggered upon the placement of the die-cast component on the workpiece holder. After the result (not OK or OK) is displayed, the process automatically continues with the next die-cast part.

[0016] The basic shape of the screen arrangement can have cylindrical sections or cylindrical surface sections with different outer and / or inner diameters. In particular, a section of the surface adapted to the camera's viewing angle can be omitted or removed to enable imaging of the unshielded surface of the die-cast part according to the invention. Ambient light entering through any openings in the die-cast part shielded by the screen arrangement can be largely prevented from causing reflections on the bare inner surface of the die-cast part. In particular, the screen arrangement located inside the die-cast part eliminates the need for external darkening / shielding, thus resulting in improved and simplified handling of the die-cast part.

[0017] A left and a right wing of the screen assembly, which border the free area of ​​the casing within the camera's field of view, can be brought together behind the camera to form a light-tight shield in this area. This ensures the best possible image quality.

[0018] Preferably, the device according to the invention comprises an artificial light source for generating grazing light on the surface of the die-cast part. The light source is specifically designed to illuminate the surface area of ​​the die-cast part located within the camera's detection range. The grazing light makes irregularities, cavities, and inclusions optimally visible to the camera. This also makes it comparatively easy for the evaluation software to process the camera images. The light source can, in particular, comprise an LED light strip or an LED light source arrangement. To achieve the most homogeneous illumination possible, a diffuser in front of the light source can optically homogenize the light intensity across the solid angle.

[0019] The shielding arrangement can, for example, have a predominantly sheet-metal and / or thin-walled design. In particular, a plastic shielding can be provided to prevent deformations of the die-cast component caused by any collisions from becoming critical to the surface quality.

[0020] The shielding assembly can have a thickness of 1 mm to 10 mm, particularly 3 mm to 7 mm. These thicknesses are suitable for both optical opacity and sufficient mechanical strength. In particular, this design requires minimal space for the shielding within the die-cast part's cavity. Furthermore, the shielding assembly can be manufactured as a 3D-printed component. Specifically, automated or machine-assisted design can be achieved using a model of the die-cast part.For example, the diameter of an inner surface of the die-cast part's cavity can be further reduced (e.g., by 10 mm to 80 mm, preferably 15 mm to 30 mm) so that a sufficiently tight tolerance avoids unnecessary collisions, while diffraction effects and reflection paths between the inner wall of the die-cast part on the one hand and the outer wall of the screen arrangement on the other hand result in the lowest possible light intensities of any ambient light present in the die-cast part or the camera's detection area. For example, sections of the screen arrangement with different diameters can be connected to each other by conical sections.If two axially offset surfaces of the screen arrangement, with different outer and / or inner diameters, are transformed into one another by a truncated cone-shaped area, a milk can-shaped form can result, which opens towards the inside of the die-cast part in a cylindrical angular range for the detection areas of axially offset cameras.

[0021] According to a second aspect of the present invention, a method for using a device according to the first aspect of the invention is proposed. The method begins with inserting the camera arrangement and the screen arrangement into the die-cast part. A hydraulic and / or electric motor-driven positioning arrangement can be used for this purpose. Subsequently, a first image is captured by the camera arrangement, and then the die-cast part is rotated by means of the workpiece holder about an axis through which the main optical axis of the camera(s) passes. A second image of the rotated die-cast part is then captured by the camera arrangement in such a way that a seamless image is created by the two images. The images are then evaluated for surface irregularities using artificial intelligence.Software other than artificial intelligence can also be used (for example, deterministic algorithms for counting the pixel height / width required to capture an irregularity). Based on an (automatic) analysis of the irregularities and their quantity, a notification about the surface irregularities is then sent to a user or a control unit for managing a die-casting process. In other words, based on automatically determined information about the defect pattern, a parameter for the die-casting process can be automatically suggested or even automatically adjusted to reduce or prevent air inclusions, impurities, and irregularities in subsequently manufactured die-cast components.

[0022] Preferably, a signal can also be output to a user or a servo / motor, representing an OK or non-OK state of the die-cast part. This allows rejects to be automatically routed to a separate bin or conveyor belt, while the OK parts are fed to the subsequent process stations. Brief description of the characters

[0023] Further details, advantages and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. The drawings show: Fig. 1 a perspective view of an embodiment of a device according to the invention for inspecting a surface-treated die-cast part; Fig. 2 a perspective view of a screen arrangement with a camera arrangement of a second embodiment of a device according to the invention; Fig. 3 a perspective representation of a camera image, which is taken using the in Fig. The camera 3c shown in the image was used; Fig. 4 the result of an artificial intelligence-supported analysis of the in Fig. 3 photos shown; and Fig. 5 A flowchart illustrating the steps of an embodiment of a method according to the invention for using a device according to the invention.

[0024] Fig. Figure 1 shows a perspective view of an embodiment of a device 1 according to the invention, which has a workpiece holder 5. The workpiece holder 5 is currently awaiting the placement of a test piece (die-cast part, not shown). A sensor 12 serves to detect the component or to automatically determine the occupancy status of the workpiece holder 5. A fork-type optical sensor 10 serves to verify and track the positioning of the workpiece holder 5. The fork-type optical sensor can be used to rotate the workpiece holder 5 or the (not shown) die-cast part. A control unit 11 is also provided, by means of which the device shown is controlled. The fork-type optical sensor 10 and the sensor 12 for detecting the component can also be evaluated.Finally, it is also possible to provide information to process stations located away from the power supply and to provide information to a user via the control unit 11.

[0025] Fig. Figure 2 shows an embodiment of a device 1 according to the invention in a configuration in which the camera arrangement 3, comprising the screen arrangement 4, has been moved upwards to photograph the interior of a die-cast part (not shown) in accordance with the invention. The screen arrangement 4 has a section 4c with a small inner and outer diameter, a section 4b with an inner and outer diameter that increases downwards, and a subsequent section 4a with a large inner and outer diameter. The screen arrangement 4 is closed off at the top by a cover 4d to be lightproof (except for the area facing the user). The latter is enclosed by the two wings 8a, 8b of the screen arrangement 4.The spacing of the wings 8a, 8b and the distance of their edges from the camera assembly 3 determine the size of the area of ​​the screen assembly 4 that will later be visible in the camera image of the three cameras 3a, 3b, 3c. In other words, the wings 8a, 8b will optically frame the image of the inner surface of the die-cast part. A lifting device 7 is provided to raise the camera assembly 3 together with the screen assembly 4 into the position shown. In doing so, the screen assembly 3 and the camera assembly 4 pass through an opening / bore in the workpiece holder 5. In a lower area (below the workpiece holder 5), an LED strip is provided as a light source 6, which has an upward-directed main emission direction. In this way, grazing light can be generated on the (not shown) surface of the die-cast part, making unevenness, defects, and cavities particularly visible.

[0026] Fig. Figure 3 shows a photograph of a die-cast part 2 using the in Fig. 2. The third camera 3c shown. Surface irregularities 9 are difficult to detect with the naked eye in this arrangement. Multiple photographs, possible rotation of the die-cast part 2, and the application of artificial intelligence to the evaluation of the optical images enable improved visualization and presentation of the result, as shown in Fig. 4 is shown.

[0027] Fig. Figure 4 shows an optical illustration of a representation 9' of surface irregularities 9 (see Fig. 3) Here, surface irregularities can be automatically marked not only qualitatively but also quantitatively, indicating whether the represented die-cast part is OK or not OK. In this way, it can be automatically classified as "OK" or "reject".

[0028] Fig.Figure 5 shows steps of an embodiment of a method according to the invention for using a device according to an embodiment of the present invention. In step 100, the camera arrangement, together with the screen arrangement, is inserted into a die-cast part. This can be done by means of an electric, hydraulic, pneumatic, or otherwise driven lifting device or traversing arrangement. In step 200, a first image is captured by means of the camera arrangement. Here, the screen arrangement prevents any light that may strike the device in areas next to or behind the camera from entering the cavity of the die-cast part to be photographed. In step 300, the die-cast part is rotated about an axis through which the main optical axis of the camera passes by means of the workpiece holder. In step 400, a second image of the rotated die-cast part is captured by means of the camera arrangement.In other words, an adjacent surface area of ​​the die-cast part is subsequently photographed using the same camera. Further rotations and photographic processes can follow until the entire die-cast part has been captured by the camera / camera array. In step 500, the images are then evaluated using artificial intelligence to identify surface irregularities. Specifically, optical image recognition algorithms are used to classify surface areas as acceptable (iO) or not acceptable (nO). The surface areas classified as not acceptable (nO) can be quantified based on the number of horizontally adjacent or vertically stacked pixels to determine the acceptable extent of the surface irregularities.In step 600, information regarding the quality / quantity of surface irregularities is sent to a user and a control unit. The control unit can then automatically adjust a parameter (e.g., pressure / temperature) to control the die-casting process. In step 700, a signal is automatically sent to a user or a servo in a production / logistics line, indicating whether the die-cast part is OK or not OK. Based on this, the die-cast part can be automatically rejected or automatically fed to a subsequent production step. Reference symbol list 1 Device 2 die-cast parts 3 Camera arrangement 3a first camera 3b second camera 3c third camera 4 Screen arrangement Section 4a Section 4b 4c Section 4D lid 5 Workpiece holder 6 light source 7 Lifting device 8a, 8b Wing 9 Surface irregularity 9' Representation of surface irregularity 9 10 Fork light barrier 11 Control unit 12 sensors for component query 100 - 700 process steps

Claims

[1] Device (1) for inspecting a surface-treated die-cast part (2) comprising - a camera arrangement (3) with a first camera (3a) with a principal optical axis, - an opaque screen arrangement (4) for optically shielding surface areas of the die-cast part (2) that are not within a detection range of the camera arrangement (3), and - a workpiece holder (5) wherein the workpiece holder (5) is configured to rotate the die-cast part (2) around the camera arrangement (3) located inside it and around the screen arrangement (4). [2] Device according to claim 1 further comprising a lifting device (7) for introducing the camera arrangement (3) and the screen arrangement (4) into the die-cast part (2). [3] Device according to claim 1 or 2, wherein the workpiece holder (5) is designed as a rotary table, which is in particular configured to rotate the die-cast part about an axis through which the main optical axis of the first camera (3a) passes. [4] Device according to claim 3, wherein the device is configured to perform a motorized rotation, preferably around predefined angular ranges of the workpiece holder (5). [5] Device according to one of the preceding claims, wherein the camera arrangement (3) is received in a concave basic shape of the screen arrangement (4) and is configured to photograph a surface of the die-cast part (2) between a left wing (8a) and a right wing (8b) of the screen arrangement (4). [6] Device according to one of the preceding claims further comprising a light source (6) for generating grazing light with respect to the surface of the die-cast part (2), which is in particular designed as an LED light strip. [7] Device according to one of the preceding claims, wherein the screen arrangement (4) has a substantially, at least partially, rotationally symmetrical basic shape, wherein an outer surface of the basic shape is adapted to an inner surface of a cavity of the die-cast part (2). [8] Device according to one of the preceding claims, wherein the camera arrangement (3) comprises a second camera (3b), in particular also a third camera (3c), which each have a principal optical axis which is parallel to the principal optical axis of the first camera (3a). [9] Device according to one of the preceding claims, wherein the screen arrangement (4) has several sections (4a, 4b, 4c, 4d) which have different outer diameters and inner diameters. [10] Method for using a device according to any of the preceding claims comprising the steps: - Inserting (100) the camera assembly (3) and the screen assembly (4) into the die-cast part (2), - Capturing (200) a first image using the camera arrangement (3), - Rotating (300) the die-cast part (2) using the workpiece holder (5), - Capturing (400) a second image of the turned die-cast part (2) using the camera arrangement (3), - Evaluating (500) the images using artificial intelligence regarding surface irregularities (9) and - Output (600) of a notification of surface irregularities (9) to a user and / or a control unit (11) for controlling a die-casting process. [11] Method according to claim 10 further comprising - automatic output (700) of a signal representing an OK state or a non-OK state of the die-cast part (2).

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