Method for monitoring residual compressive stresses of components in a shot peening process

Abstract

The invention relates to a method for monitoring the residual compressive stresses generated in a component (18) during shot peening. The method comprises the following steps: introducing (A) a test body (22) into the shot peening process, the test body being processed in addition to the component (18). Measuring (B) a magnetic characteristic variable of the test body (22) after the shot peening process, and determining (C) the absolute measurement value of the residual compressive stresses preserved for the magnetic characteristic variable from calibration data.

Description

Technical Field

[0001] This invention relates to a method for monitoring residual compressive stress generated in a component during shot peening, comprising the step of introducing an inspection body into the shot peening process, and machining the inspection body in addition to the component. Additionally, this invention relates to an apparatus for performing the method. Background Technology

[0002] Shot peening is a common practice when treating metal parts to improve or restore fatigue resistance, or component strength. Spherical abrasive is used to impact the surface of the part, creating very small spherical plasticized areas and introducing residual compressive stress into the part through the shot-peened surface. It is desirable to control the intensity of shot peening, as intensity above or below a critical strength range can result in suboptimal fatigue resistance or generally lower component strength.

[0003] One method for controlling shot peening intensity is the Almentest test, which uses an Almen-Streifen strip, whose curvature (often called arc height) allows for the measurement of intensity. The Almen-Streifen strip is a thin, precision strip made of 1070 steel (with controllable hardness and thickness), tightened onto a retaining device that prevents the strip from bending until the bolts are loosened. The strip is then exposed to the shot stream under the same conditions as the part being peened. After the strip has been peened for a predetermined duration, it is removed from the retaining device and the arc height (bending point) is measured.

[0004] GB 2475214 B discloses a method for determining the shot peening intensity on the shot-peened surface of a workpiece. For this purpose, an Almen test strip is fixed to the shot-peened surface. After machining, the Almen test strip is removed to determine the arc height and thus the shot peening intensity on the shot-peened surface.

[0005] The drawback of the Alman test is that it requires determining the blasting energy. However, it lacks certainty regarding the direct impact on the target material, namely the residual compressive stress that plays a decisive role in the strength of the component. Furthermore, the clamping conditions of the strips used in the Alman test must be maintained very precisely, making the measurement method tedious. Moreover, at higher blasting intensities and with concentrated shot peening, small pieces only undergo localized plasticization, significantly distorting the results of bending measurements and rendering them unreliable. Additionally, only standardized materials can be used, which in most cases are incompatible with the materials to be processed, thus preventing reusability. Summary of the Invention

[0006] The objective of this invention is to provide a method by which residual compressive stress in shot-peened components can be fed back to an absolute measurement method more simply and accurately.

[0007] This task is solved by the method according to the invention. The invention is characterized by measuring the magnetic characteristic parameters of the test specimen after the shot peening process, and obtaining the absolute measurement value of the residual compressive stress preserved for the magnetic characteristic parameters based on calibration data.

[0008] Here, the magnetic characteristic parameters according to the invention are values ​​obtained by means of a magnetic measurement method, representing the residual compressive stress in the test specimen and the selected material. The magnetic measurement method here enables non-destructive measurement of the relative residual compressive stress of the test specimen. In a preferred embodiment, the magnetic characteristic parameters are obtained using Barkhausenrauschen (Barkhausenrauschen) noise. Alternatively, these characteristic parameters are determined using superimposed permeability.

[0009] Here, the absolute measurement of residual compressive stress is the value of the absolute residual compressive stress of a given test specimen. These values ​​are preferably determined by means of X-ray diffraction, which is typically a destructive measurement method.

[0010] Here, calibration data establishes the correlation between given magnetic characteristic parameters and absolute residual compressive stress for a given component and material type. Therefore, by simply performing the calculation of magnetic characteristic parameters during operation, the absolute measurement of residual compressive stress can be determined more accurately. This eliminates the need to wait for time-consuming measurements of absolute characteristic parameters, making this method more economical.

[0011] In a preferred embodiment of the invention, calibration data is created based on multiple test pieces having selected materials and conditions, for which magnetic characteristic parameters are correlated with absolute measurements of residual compressive stress. This assigns various absolute measurements to magnetic characteristic parameters for component types having selected materials and conditions, allowing these absolute measurements to be obtained from the magnetic characteristic parameters during operation. This is preferably performed on the components prior to shot peening to minimize the number of defects.

[0012] In another preferred embodiment of the invention, the process parameters of the shot peening process are adjusted when the obtained magnetic characteristic parameters deviate. By continuously monitoring the magnetic characteristic parameters, deviations exceeding tolerances can be identified during operation. Based on these deviations, process parameters, such as the abrasive used, the spray pressure, or the beam diffusion, can be changed to achieve the desired values. This avoids the production of defective products or minimizes the number of such parts. The method can thus be performed more economically, and the quality of the produced components can be improved.

[0013] Preferably, in the case of an inspection piece, in addition to magnetic characteristic parameters, the absolute value of residual compressive stress is also measured, as needed. This has the advantage of identifying deviations early in the production process or in the material. When such deviations occur, calibration data cannot provide reliable information about the absolute value of the compressive stress. Therefore, these deviations can be identified early to minimize the number of defective products and improve quality.

[0014] In a favorable extension scheme, the calibration data is updated when there is a deviation between the calibration data and the absolute measured value. This replaces the previous data with the new data. This corrects for the standard deviation caused by the process, thereby improving the accuracy of the measurement.

[0015] Advantageously, the test piece is positioned at the measurement location of a dummy component (Dummy-Bauteil) constructed in the form of a component before being introduced into the shot peening process. Here, the dummy component has the same geometric dimensions as the component. Additionally, a receiving portion for introducing the test piece is formed in the dummy component. The measurement location is on the dummy component where the residual compressive stress obtained for the component should be determined. Because the geometry of the component affects the obtained residual compressive stress, the residual compressive stress obtained for the component can be determined more accurately. This improves the quality of the component.

[0016] In another advantageous embodiment, the test specimen is positioned at the measurement location of the dummy component, a location inaccessible for the absolute measurement of residual compressive stress and / or the measurement of magnetic characteristic parameters, and is removed from this location for measurement after the shot peening process. An inaccessible measurement location is understood as a location where measurement can only be achieved by disrupting the surrounding area, such as the bottom of a borehole. However, by disrupting the surrounding area, the measurement results are distorted by the transfer of residual compressive stress, making it impossible to accurately represent the residual compressive stress. Thus, it is also possible to accurately measure residual compressive stress in inaccessible areas.

[0017] According to a suitable embodiment, the surface of the test specimen subjected to the shot peening process is planar. A planar surface has the following advantages: especially for absolute measurement methods, such as X-ray diffraction, no surface preparation is required, and residual compressive stress can be determined more accurately.

[0018] According to a suitable implementation, the test specimen uses the same material and / or the same size ratio and / or the same pretreatment as the component. By using the same material, the obtained residual compressive stress can be determined more accurately for that material. Size ratio is understood to mean that the test specimen has, for example, the same material thickness as the component. This minimizes the deviation of residual compressive stress between the component and the test specimen caused by material thickness, thereby improving measurement results.

[0019] The pretreatment according to the present invention should be understood as treatments such as heat treatment, edge layer hardening, coating, etc. By performing the same pretreatment on the test body, the deviation of residual compressive stress caused thereby can be eliminated, thereby improving the accuracy of the measurement results.

[0020] This task is additionally addressed by means of an apparatus for performing the method. This apparatus includes shot peening equipment for shot peening components; a measuring device for measuring the magnetic characteristic parameters of the test specimen; a measurement value processing device that outputs an absolute measurement value of the residual compressive stress based on the magnetic characteristic parameters; and a process control device that controls the process parameters of the shot peening equipment based on the absolute measurement value of the residual compressive stress.

[0021] Here, calibration data is stored in the measurement processing device, and the residual compressive stress is calculated based on the calibration data. In a preferred embodiment, the measuring device and the measurement processing device can also be arranged together in a common device. With such a device, the advantages mentioned regarding the method can be obtained. Attached Figure Description

[0022] Embodiments of the invention are shown in the accompanying drawings and described in more detail below. The drawings show: Figure 1 Embodiments of an apparatus for performing the method according to the invention. Figure 2 According to embodiments of the method of the present invention, and Figure 3 Examples of components and dummy components with inspection bodies. Detailed Implementation

[0023] exist Figure 1 An embodiment of an apparatus for performing the method according to the invention is shown. In this embodiment, the apparatus has a processing line 14 on which components 18 are arranged. In addition to components 18, inspection bodies 22 are occasionally arranged on the processing line 14 in place of the components. The apparatus also has a shot peening apparatus 26 in which components 18 and inspection bodies 22 are shot peened sequentially.

[0024] After shot peening, the inspection piece 22 is removed from the processing line 14 and supplied to the measuring device 30. In the measuring device 30, magnetic characteristic parameters are obtained, for example, using Bavarian noise. The values ​​obtained by this method are transmitted to the measurement value processing device 34, which assigns the absolute measurement value of the residual compressive stress to the magnetic characteristic parameters based on stored calibration data.

[0025] The absolute measurement of residual compressive stress is transmitted to the process control device 38, which adjusts the process parameters of the shot peening equipment 26 as necessary based on these values, so that the absolute measurement obtained after shot peening equipment 26 is again within the pre-given tolerance range.

[0026] Figure 2 An embodiment of the method according to the invention is shown. In a first step A, an inspection body 22 is provided during shot peening, except for component 18, such that the inspection body 22 undergoes the same shot peening process as component 18. In a next step B, the magnetic characteristic parameters of the inspection body 22 are determined after the shot peening process. Based on these magnetic characteristic parameters, in a subsequent step C, absolute measurements are determined based on calibration data.

[0027] Based on the absolute measurement value, the spraying process is adjusted in step A. After step C, however, in step D, which is performed only as needed, the test body 22 is provided to the absolute measurement method for determining the residual compressive stress. The obtained value is then provided to the calibration data in step C for correction if necessary.

[0028] exist Figure 3 The figure shows an embodiment of component 18 and a dummy component 42 with a test body 22. A possible embodiment of component 18 is shown in sub-figure a. Component 18 has a deep material notch 46. The bottom 50 of the material notch 46 is inaccessible for magnetic measurement methods and, for example, X-ray diffraction. Before the bottom 50 can be measured, the material defining the two sides 54 of the notch 46 must be removed.

[0029] Sub-figure b shows a dummy member 42 having a lateral channel 58 in the region of the bottom 50 through which the test piece 22 can be inserted into and removed from the dummy member 42. This allows the test piece 22 to be measured after shot peening without damaging the test piece 22 and thus distorting the measurement results. Sub-figure c shows an embodiment of the test piece 22. The test piece is here constructed as a planar plate.

Claims

1. A method for monitoring residual compressive stress generated in a component (18) during shot peening, comprising the following steps: - The inspection body (22) is introduced into (A) during the shot peening process, and the inspection body is also processed in addition to the component (18). The feature is that, after the shot peening process, the magnetic characteristic parameters of the test body (22) are measured (B), and The absolute measured value of the residual compressive stress preserved for the magnetic characteristic parameter (C) is obtained based on the calibration data. In the case of a test body (22), in addition to the magnetic characteristic parameters, the absolute value of the residual compressive stress is also measured.

2. The method according to claim 1, characterized in that, Calibration data is created based on multiple test bodies (22), and the magnetic characteristic parameters are correlated with the absolute measured values ​​of the measured residual compressive stress for the calibration data.

3. The method according to claim 1 or 2, characterized in that, If the magnetic characteristic parameters are found to be deviated, the process parameters of the shot peening process are adjusted.

4. The method according to claim 1 or 2, characterized in that, The calibration data is updated when there is a deviation between the calibration data and the absolute measured value.

5. The method according to claim 1 or 2, characterized in that, The test object (22) is placed at the measurement position of the dummy component (42) constructed in the form of component (18) before being introduced into the shot peening process.

6. The method according to claim 5, characterized in that, The test piece (22) is arranged at the measurement position of the dummy component (42), which is inaccessible for the absolute measurement of residual compressive stress and / or the measurement of the magnetic characteristic parameters, and the test piece is removed from the measurement position for measurement after the shot peening process.

7. The method according to claim 1 or 2, characterized in that, The surface planar structure of the test body (22) subjected to the shot peening process.

8. The method according to claim 1 or 2, characterized in that, Compared to the component (18), the test body (22) uses the same material and / or the same size ratio and / or the same pretreatment.

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