Residual stress estimation method

Abstract

This residual stress estimation method comprises: acquiring, with a 3D form gauge, original sheet-form data that represents the three-dimensional form of one surface of a target article; slicing the target article to obtain a plurality of strips; acquiring, with the 3D form gauge, a plurality of strip-form data items respectively representing the three-dimensional forms of the plurality of strips; setting, on the strips, a plurality of gauging points aligned in the lengthwise direction of the strips; computing, on the basis of the original sheet-form data and the strip-form data, the amount of form variation in the thickness direction of the target article at each gauging point; and estimating, from the amount of form variation, residual stress in the lengthwise direction of the strips released by the slicing.

Description

Residual stress estimation method

[0001] The present disclosure relates to a residual stress estimation method.

[0002] For example, techniques for measuring residual stress in an object such as a steel plate can be broadly divided into non-destructive methods that do not involve destruction of the object, and destructive methods that utilize the stress or strain released when the object is destroyed. As disclosed in Non-Patent Document 1, an X-ray method is known as one type of non-destructive method. As disclosed in Non-Patent Document 2, a cutting method is known as one type of destructive method.

[0003] Suzuki et al., "Technological Trends in X-ray Residual Stress Measurement and Initiatives to Address Diversifying Measurement Needs," Journal of the Japan Society for Technology of Plasticity, Japan Society for Technology of Plasticity, November 2018, Vol. 1, No. 11, pp. 31-34; Kakutani et al., "Analytical Study on Residual Stress Measurement Using the Strain Gauge Cut-Off Release Method," Proceedings of the Materials Mechanics Conference, Japan Society of Mechanical Engineers, July 20, 2004, Vol. 2004, pp. 207-208

[0004] In the X-ray method, it is necessary to irradiate both the front and back surfaces of an object with X-rays. After irradiating the front surface of an object with X-rays, if the object is turned over to irradiate the back surface with X-rays, the shape of the object will change due to its own weight. This may result in a change in the value of residual stress, making it difficult to measure both the front and back surfaces under the same conditions. This problem is particularly pronounced when the object is a thin plate.

[0005] Furthermore, the X-ray method can only obtain local measurement results in one measurement, which means it takes a long time to measure the entire object, a problem that becomes more pronounced when the surface area of ​​the object is large.

[0006] In conventional cutting methods, multiple strain gauges must be attached to the surface of the object, and the object must then be cut into small pieces with the strain gauges still attached. While a single measurement can provide measurement results for the entire object, this single measurement requires a great deal of time and effort. This problem becomes more pronounced when the surface area of ​​the object is large.

[0007] An object of the present disclosure is to reduce the time required to estimate residual stress in an object.

[0008] One aspect of the present disclosure provides a residual stress estimation method, comprising: preparing a metal plate as an object; acquiring original plate shape data indicating the three-dimensional shape of one surface of the object using a three-dimensional shape measuring device; cutting the object to obtain a plurality of strips that are long in one direction within the one surface of the object and have a width in another direction within the one surface that is perpendicular to the one direction; acquiring a plurality of strip shape data indicating the three-dimensional shapes of the one surface of the plurality of strips using the three-dimensional shape measuring device; setting a plurality of measurement points aligned in the longitudinal direction of the strip on the one surface of the strip; calculating an amount of shape change in the plate thickness direction of the object at each of the plurality of measurement points before and after cutting based on the original plate shape data and the strip shape data; and estimating, from the amount of shape change, residual stress in the longitudinal direction of the strip that has been released by cutting.

[0009] According to the above method, a plurality of strips are obtained by cutting an object. Each strip is long in one direction of the object. When residual stress is released by cutting, the shape of the strip changes in the thickness direction, mainly based on the residual stress in the longitudinal direction of the strip. Therefore, before cutting, original sheet shape data indicating the three-dimensional shape of one surface of the object is obtained, and after cutting, strip shape data indicating the three-dimensional shape of that one surface is obtained for each strip. By referring to these two shape data, the amount of shape change in the thickness direction at the same measurement point before and after cutting can be calculated. Based on this amount of shape change, the residual stress in the longitudinal direction of the strip is back-calculated.

[0010] In this way, with this method, it is possible to estimate the residual stress over the entire surface of an object simply by measuring the three-dimensional shape of only one surface of the object before and after cutting with a three-dimensional shape measuring device. This reduces the time required to estimate the residual stress compared to X-ray methods and conventional cutting methods.

[0011] Estimating the residual stress may include performing a second-order differentiation of the shape change amount with respect to the longitudinal direction, and estimating the residual stress in the longitudinal direction based on the second-order differentiation value of the shape change amount.

[0012] According to the above method, the residual stress in the longitudinal direction can be calculated back based on the amount of shape change.

[0013] Preparing the object may include preparing a first object and a second object from the same plate material, and obtaining the plurality of strips may include cutting the first object to obtain a plurality of first strips and cutting the second object to obtain a plurality of second strips, and the longitudinal direction of the plurality of first strips may be perpendicular to the longitudinal direction of the plurality of second strips.

[0014] According to the above method, residual stresses in two perpendicular directions can be estimated in a short time.

[0015] According to the present disclosure, the time required to estimate residual stress in an object can be reduced.

[0016] 1. A flowchart showing a residual stress estimation method according to the present embodiment. An explanatory diagram of an object preparation process. An explanatory diagram of an original plate shape data acquisition process for a first object. An explanatory diagram of an original plate shape data acquisition process for a second object. An explanatory diagram of a strip acquisition process for a first object. An explanatory diagram of a strip acquisition process for a second object. An explanatory diagram of a strip shape data acquisition process for a first strip. An explanatory diagram of a strip shape data acquisition process for a second strip. A diagram showing the amount of shape change in the plate thickness direction at each measurement point set on a certain first strip. A diagram showing an example display of an estimation result of residual stress of a first object. A diagram showing an example display of an estimation result of residual stress of a second object.

[0017] Hereinafter, embodiments will be described with reference to the drawings. Note that the same or corresponding elements are designated by the same reference numerals throughout the drawings, and detailed descriptions thereof will be omitted.

[0018] 1, a residual stress estimation method according to this embodiment (hereinafter also simply referred to as "this method") is used to estimate residual stress in a metal plate as an object 10. The material of the plate is not particularly limited, and may be, for example, steel, aluminum alloy, or copper alloy.

[0019] This method includes an object preparation step S1, an original sheet shape data acquisition step S2, a strip preparation step S3, a strip shape data acquisition step S4, a shape change amount calculation step S5, and a residual stress estimation step S6.

[0020] In an object preparation step S1, a metal plate is prepared as the object 10, and in a strip preparation step S3, the object 10 is cut. In a shape change calculation step S5, the amount of shape change in the plate thickness direction before and after cutting of the object 10 is quantitatively derived, and in a residual stress estimation step S6, the residual stress of the object 10 is back-calculated based on the amount of shape change. In other words, this method can be classified as a destructive method among residual stress measurement techniques.

[0021] As described below, this method allows residual stress to be estimated by measuring the three-dimensional shape of an object from only one side of the object, eliminating the need to turn the object over to measure the three-dimensional shapes of both sides of the object. Therefore, this method allows residual stress to be estimated with high accuracy even if the object is a thin plate.

[0022] When a plate material is manufactured using a manufacturing method that involves cooling, a relatively large residual stress is generated in the plate material. Examples of cooling processes that can be included in the manufacturing method of the plate material include cold rolling and water quenching. As described below, this method can estimate residual stress in a short time, and therefore is suitable for use in quality control of metal plate materials manufactured using a manufacturing method that involves cooling.

[0023] (Object Preparation Process) FIG. 2 shows a coil 1 formed by winding a steel plate into a cylindrical shape as an example of the object 10. The thickness of this steel plate is, for example, in the range of 0.8 mm to 2.3 mm, and this steel plate corresponds to a thin plate material. This steel plate is also manufactured by a manufacturing method that includes a cooling process such as cold rolling or water quenching. In other words, this steel plate is a suitable example of the object 10. Below, this method will be described using an example of estimating the residual stress of the steel plate forming the coil 1 in order to verify the suitability of the manufacturing conditions for the coil 1 related to the material in research and development of the new material. Note that application examples are not limited to this, and the method can also be applied, for example, to inspecting the quality of the coil 1 prior to shipping.

[0024] The longitudinal direction of the object 10 (original plate longitudinal direction L), the width direction of the object 10 (original plate width direction W), and the plate thickness direction T of the object 10 are perpendicular to one another and form three axes of a three-dimensional Cartesian coordinate system (hereinafter referred to as "object coordinate system") whose origin is located on the object 10. The original plate longitudinal direction L corresponds to the circumferential direction of the coil 1, and the original plate width direction W corresponds to the axial direction of the coil 1.

[0025] In this example, the leading end of the steel plate is pulled out from the coil 1 and cut along a cutting line extending in the width direction W of the original plate. As a result, two objects 10 including a first object 11 and a second object 12 are separated from the coil 1 and prepared.

[0026] The first object 11 and the second object 12 are, for example, rectangular when viewed in the plate thickness direction T. One pair of opposite sides of the first object 11 is formed by a pair of side edges of the steel plate extending in the original plate longitudinal direction L, and the other pair of opposite sides extends along the original plate width direction W. The same applies to the second object 12.

[0027] In the illustrated example, the first object 11 and the second object 12 have the same size and shape as each other when viewed in the plate thickness direction T, but they may have different sizes and shapes. As a mere example, the first object 11 and the second object 12 have a length of 500 mm in the original plate longitudinal direction L and a width of 1200 mm in the original plate width direction W.

[0028] 3A and 3B are explanatory diagrams of the original plate shape data acquisition step S2. Fig. 3A shows the first object 11, and Fig. 3B shows the second object 12. In the original plate shape data acquisition step S2, original plate shape data indicating the three-dimensional shape of one surface of the object 10 is acquired by the three-dimensional shape measuring device 82.

[0029] In this example, two objects 10 are used: a first object 11 and a second object 12. Accordingly, the original plate shape data also includes two types of data: first original plate shape data corresponding to the first object 11, and second original plate shape data corresponding to the second object 12.

[0030] Referring to FIG. 3A , the first object 11 is supported by a support member 81. The support member 81 is, for example, a stage having a horizontal support surface 81a, and the first object 11 is placed on the support surface 81a. The first object 11 has a first surface 11a and a second surface (details not shown) on both sides in the plate thickness direction T. Here, the second surface is facing downward and placed on the support surface 81a, and the first surface 11a is facing upward. In other words, the above-mentioned "one surface" is the first surface 11a of the first object 11. In this example, when the first object 11 is placed on the support surface 81a, the first surface 11a faces the three-dimensional shape measuring device 82 in the plate thickness direction T of the first object 11. The three-dimensional shape measuring device 82 measures the three-dimensional shape of the first surface 11a of the first object 11 and acquires first original plate shape data indicating the measurement results.

[0031] The three-dimensional shape measuring device 82 may be configured in any manner as long as it can measure the three-dimensional shape of the first surface 11a without having to turn over the first object 11. A pair of stereo cameras 82a is a suitable example of such a three-dimensional shape measuring device 82. Instead of the stereo cameras 82a, a laser scanner may be applied to the three-dimensional shape measuring device 82.

[0032] The three-dimensional shape measured by the three-dimensional shape measuring device 82 is defined in a three-dimensional Cartesian coordinate system (hereinafter referred to as the "measuring device coordinate system") with the origin located on the three-dimensional shape measuring device 82. The depth direction (Z direction) of the measuring device coordinate system coincides with the optical axis of the stereo camera 82a and is oriented vertically. The depth direction (Z direction) coincides with the normal direction of the horizontal support surface 81a, i.e., the plate thickness direction T of the object placed on the support surface 81a. Two directions (X and Y directions) in a plane perpendicular to the depth direction (Z direction) of the measuring device coordinate system are parallel to the imaging plane perpendicular to the optical axis of the stereo camera 82a and parallel to the horizontal support surface 81a. For example, the first object 11 is aligned around the vertical axis relative to the support member 81 and thus the three-dimensional shape measuring device 82, for example, using a jig (not shown), so that the original plate longitudinal direction L coincides with the X direction and the original plate width direction W coincides with the Y direction. However, the above is just an example. In this embodiment, the optical axis coincides with the Z direction of the measuring instrument coordinate system, but this does not have to be the case. The three-dimensional shape measuring instrument 82 does not have to be disposed so as to face the first surface 11 a in the plate thickness direction T of the first object 11.

[0033] The stereo camera 82a acquires a large amount of two-dimensional position information (XY coordinates) of the first surface 11a on an imaging plane perpendicular to the optical axis, and measures depth information (Z coordinates) at the positions indicated by each piece of two-dimensional position information using triangulation, thereby acquiring shape data (XYZ coordinate data) that indicate the three-dimensional shape of the first surface 11a.

[0034] When the object coordinate system is aligned with the measuring device coordinate system as described above, a shape defined in the measuring device coordinate system can be converted into a shape defined in the object coordinate system or is substantially equivalent to that shape. That is, in the following description, a direction, position, or shape based on one of the two coordinate systems can be appropriately interpreted as a direction, position, or shape based on the other coordinate system.

[0035] 3B , the second object 12 is processed in the same manner as the first object 11. Once the first original plate shape data has been acquired, the first object 11 is removed from the support member 81, and the second object 12 is supported by the support member 81 with the first surface 12 a facing upward. That is, in this case, the above-mentioned "one surface" is the first surface 12 a of the second object 12. With the second object 12 supported by the support member 81, the three-dimensional shape measuring device 82 acquires second original plate shape data indicating the three-dimensional shape of the first surface 12 a of the second object 12. The first original plate shape data and the second original plate shape data are acquired using the same support member 81 and three-dimensional shape measuring device 82.

[0036] 4A and 4B are explanatory views of the strip preparation step S3. In the strip preparation step S3, the target object 10 is cut to obtain a plurality of strips. Each strip is long in one direction within one surface of the target object 10, and has a width in another direction perpendicular to the one direction within the one surface. The plurality of strips are aligned in the other direction.

[0037] 4A shows a plurality of first strips 21A to 21E taken from a first object 11. Here, the "one surface" is the first surface 11a of the first object 11, the "one direction" is the width direction W of the original sheet, and the "other direction" is the longitudinal direction L of the original sheet.

[0038] The first object 11 is divided into pieces in the original sheet longitudinal direction L by a plurality of division lines extending along the original sheet width direction W. The plurality of division lines extend linearly and parallel to one another. Each of the first strips 21A to 21E has an elongated rectangular shape that is long in the original sheet width direction W when viewed in the sheet thickness direction T. The plurality of first strips 21A to 21E have the same size and shape. However, this is just an example, and the sizes or shapes of the plurality of first strips 21A to 21E may be different from one another.

[0039] Hereinafter, to distinguish between the longitudinal direction and width direction (original board longitudinal direction L and original board width direction W) of the object 10, the longitudinal direction of the first strips 21A to 21E will be referred to as the "first strip longitudinal direction SL1," and the width direction of the first strips 21A to 21E will be referred to as the "first strip width direction SW1." The first strip longitudinal direction SL1 corresponds to the original board width direction W (the Y direction of the measuring device coordinate system), and the first strip width direction SW1 corresponds to the original board longitudinal direction L (the X direction of the measuring device coordinate system).

[0040] 4B shows a plurality of second strips 22A-22L taken from the second object 12. Here, the "one surface" is the first surface 12a of the second object 12. The "one direction" and "other direction" are orthogonal to the "one direction" and "other direction" of the first object 11, respectively. That is, with respect to the second object 12, the "one direction" is the longitudinal direction L of the original sheet, and the "other direction" is the width direction W of the original sheet.

[0041] The second object 12 is cut in the original sheet width direction W by a plurality of division lines extending along the original sheet longitudinal direction L. Each of the second strips 22A to 22L has an elongated rectangular shape that is long in the original sheet longitudinal direction L when viewed in the sheet thickness direction T. The multiple second strips 22A to 22L have the same size and shape. However, this is just an example, and the multiple second strips 22A to 22L may have different sizes or shapes.

[0042] Hereinafter, the longitudinal direction of the second strips 22A to 22L will be referred to as the "second strip longitudinal direction SL2," and the width direction of the second strips 22A to 22L will be referred to as the "second strip width direction SW2." The second strip longitudinal direction SL2 corresponds to the original sheet longitudinal direction L (X direction of the measuring device coordinate system), and the second strip width direction SW2 corresponds to the original sheet width direction W (Y direction of the measuring device coordinate system).

[0043] Because the dividing line is linear, the strips can be easily obtained using a general-purpose cutting tool such as a shear. The number of first strips 21A-21E and second strips 22A-22L is not particularly limited. The width of the first strips 21A-21E is within a range of 50 mm to 150 mm, preferably within a range of 80 mm to 120 mm. The same applies to the width of the second strips 22A-22L.

[0044] As a mere example, if the first object 11 and the second object 12 have a length of 500 mm in the original sheet longitudinal direction L and a width of 1200 mm in the original sheet width direction W, as described above, the first object 11 is divided into five equal parts in the original sheet longitudinal direction L, and the second object 12 is divided into 12 equal parts in the original sheet width direction W. Each of the first strips 21A to 21E has a length of 1200 mm in the first-strip longitudinal direction SL1 and a width of 100 mm in the first-strip width direction SW1. Each of the second strips 22A to 22L has a length of 500 mm in the second-strip longitudinal direction SL2 and a width of 100 mm in the second-strip width direction SW2.

[0045] By cutting, the residual stress in the first object 11 is released, and each of the first strips 21A-21E can deform in the thickness direction T from the original shape of the first object 11. The greater the residual stress released, the greater the amount of shape change. Because the widths of the first strips 21A-21E are relatively narrow, the influence of the residual stress in the width direction SW1 of the first strip is small, and the residual stress in the longitudinal direction SL1 of the first strip contributes to this deformation. Therefore, based on the amount of shape change, the residual stress in the longitudinal direction SL1 of the first strip in the first object 11 (original width direction W) can be estimated by back-calculation.

[0046] Similarly, for the second object 12 and the second strips 22A to 22L, the residual stress in the second strip longitudinal direction SL2 contributes to the deformation due to cutting of the second object 12. Based on the amount of shape change, the residual stress in the second object 12 in the second strip longitudinal direction SL2 (original sheet longitudinal direction L) can be estimated by back-calculation.

[0047] 5A and 5B are explanatory diagrams of the strip shape data acquisition step S4. In the strip shape data acquisition step S4, a plurality of strip shape data are acquired by the three-dimensional shape measuring device 82. Each strip shape data is data that indicates the three-dimensional shape of one surface of a corresponding strip.

[0048] The "one surface" here is the same surface as the "one surface" in the original sheet shape data acquisition step S2. The "three-dimensional shape measuring instrument 82" here is the same as that used in the original sheet shape data acquisition step S2. The original sheet shape data indicates the three-dimensional shape of one surface of the object 10 before it is cut in the strip preparation step S3. On the other hand, the strip shape data indicates the three-dimensional shape of the same surface of the strip taken from the object 10 after it has been cut in the strip preparation step S3, and is acquired in the same manner as the original sheet shape data.

[0049] The phrase "acquiring a plurality of strip shape data items, each indicating the three-dimensional shape of one surface of a plurality of strips, using a three-dimensional shape measuring device" is not limited to the state in which data items for all strips taken from a single object are simultaneously acquired, as shown in Figures 5A and 5B. It is sufficient that the same number of strip shape data items as the number of strips are ultimately acquired.

[0050] In this example, two objects 10 are used: a first object 11 and a second object 12. Accordingly, the strip shape data also includes two types of data: first strip shape data relating to first strips 21A-21E sampled from the first object 11, and second strip shape data relating to second strips 22A-22L sampled from the second object 12.

[0051] 5A, a plurality of first strips 21A to 21E are placed on a support surface 81a of a support member 81. The plurality of first strips 21A to 21E are supported on the support surface 81a in the same orientation and arrangement as the first object 11 in the original sheet shape data acquisition step S2. In this example, the first surface 11a of each of the first strips 21A to 21E faces the three-dimensional shape measuring device 82 in the sheet thickness direction T. The three-dimensional shape measuring device 82 acquires a plurality of first strip shape data indicating the three-dimensional shape of the first surface 11a of each of the first strips 21A to 21E.

[0052] 5B, a plurality of second strips 22A to 22L are placed on a support surface 81a of a support member 81. The plurality of second strips 22A to 22L are supported on the support surface 81a in the same orientation and arrangement as the second object 12 in the original plate shape data acquisition step S2. In this example, the first surface 12a of each of the second strips 22A to 22L faces the three-dimensional shape measuring device 82 in the plate thickness direction T. The three-dimensional shape measuring device 82 acquires a plurality of second strip shape data indicating the three-dimensional shapes of the first surfaces 12a of each of the second strips 22A to 22L.

[0053] 5A, in the shape change amount calculation step S5, a plurality of measurement points A are set on the first surface 11a of each of the first strips 21A-21E so as to be aligned in the longitudinal direction SL1 of the first strip. In the figure, circular plots representing the measurement points A are marked on the first strips 21A-21E for ease of explanation. In practice, the shape change amount calculation step S5 and the subsequent steps are realized by information processing using a terminal device 83 such as a PC.

[0054] A plurality of measurement points A are set in each first strip shape data. The measurement points A are defined by information indicating positions in a plane (for example, the first surface 11a or the imaging surface) perpendicular to the thickness direction T of the first strips 21A to 21E. In other words, the measurement points A are defined as XY coordinate values ​​in the measuring instrument coordinate system or LW coordinate values ​​in the object coordinate system.

[0055] In each of the first strips 21A to 21E, the multiple measurement points A are arranged at intervals in the first strip longitudinal direction SL1, so that the coordinate values ​​(X coordinate value or L coordinate value) of the multiple measurement points A in the first strip width direction SW1 are equal to one another. As an example, the coordinate value in the first strip width direction SW1 is set at the center of the first strip width direction SW1. The multiple measurement points A are set at a predetermined interval in the first strip longitudinal direction SL1, and two measurement points A at both ends are set on a pair of short sides of the second strips 22A to 22L. The interval is not particularly limited. As a mere example, if each of the first strips 21A to 21E has a length of 1200 mm in the first strip longitudinal direction SL1 and a width of 100 mm in the first strip width direction SW1, the interval is set to 100 mm, and 13 measurement points A are set.

[0056] Once the multiple measurement points A are set in this manner, the first strip shape data is referenced to read out depth information from the three-dimensional shape measuring device 82 at each measurement point A, i.e., information indicating the position in the plate thickness direction T. The information indicating the position in the plate thickness direction T is defined, for example, as a Z coordinate value in the measuring device coordinate system (or a T coordinate value in the object coordinate system).

[0057] The first object 11 is divided into a plurality of first strips 21A to 21E in the original sheet longitudinal direction L, and the plurality of measurement points A are arranged in each of the first strips 21A to 21E in the original sheet width direction W. Therefore, when the shape data of the plurality of first strips is captured collectively, as virtually shown in Fig. 5A, the large number of measurement points A are distributed among the plurality of first strips 21A to 21E and arranged in a matrix in the XY plane (or LW plane) perpendicular to the sheet thickness direction T.

[0058] 3A, in a shape change amount calculation step S5, the plurality of measurement points A set as described above are also set in a matrix in the first original plate shape data. The position information of the plurality of measurement points A set in the first original plate shape data corresponds to the position information of the plurality of measurement points A set in a distributed manner in the plurality of first strip shape data. Then, as before, the first original plate shape data is referenced to read out depth information of each measurement point A as seen from the three-dimensional shape measuring device 82, i.e., information indicating its position in the plate thickness direction T.

[0059] Next, for each measurement point A, the difference between the depth information read from the first original plate shape data and the depth information read from the first strip shape data is calculated, and the amount of shape change in the plate thickness direction T of the first object is calculated from this. In other words, for each measurement point A, the shape change in the plate thickness direction T caused by cutting the first object 11 is quantitatively calculated.

[0060] 3B and 5B, the same applies to the second object 12 and the second strips 22A-22L.

[0061] A plurality of measurement points A are set in each second strip shape data so as to be aligned in the second strip longitudinal direction SL2. In each of the second strips 22A to 22L, the coordinate values ​​(Y coordinate value or W coordinate value) of the plurality of measurement points A in the second strip width direction SW2 are equal to one another, and are set, for example, at the center of the second strip width direction SW2. The plurality of measurement points A are set at a predetermined interval in the second strip longitudinal direction SL2, with the two at both ends being set on the edges of the second strips 22A to 22L. As a mere example, if each of the second strips 22A to 22L has a length of 500 mm in the second strip longitudinal direction SL2 and a width of 100 mm in the second strip width direction SW2, the intervals are set to 50 mm, and 11 measurement points A are set.

[0062] As virtually shown in Fig. 5B, a large number of measurement points A are distributed among a plurality of second strips 22A to 22L and arranged in a matrix in the XY plane (or LW plane) perpendicular to the plate thickness direction T. As shown in Fig. 3B, such measurement points A are also set in a matrix in the second original plate shape data. Position information of the plurality of measurement points A set in the second original plate shape data corresponds to the position information of the plurality of measurement points A set in a distributed manner among the plurality of second strip shape data.

[0063] For each measurement point A, the amount of shape change in the thickness direction T of the second object 12 is calculated by referring to the second original plate shape data and the second strip shape data. In other words, for each measurement point A, the shape change in the thickness direction T caused by cutting the second object 12 is quantitatively calculated.

[0064] FIG. 6 is a diagram showing the amount of shape change in the thickness direction T at each measurement point A set on a certain first strip. The horizontal axis indicates the position in the first strip's longitudinal direction SL1, and the vertical axis indicates the position in the thickness direction T or the amount of shape change ΔZ. All three diagrams are line graphs, and the horizontal axis coordinates of the vertices of the lines correspond to the coordinate values ​​in the first strip's longitudinal direction SL1 for each of the 13 measurement points A. The dashed line indicates the position in the thickness direction T of the first object 11 read from the first original plate shape data. The solid line indicates the position in the thickness direction T of the first strip read from the first strip shape data. The dashed-dotted line indicates the difference between both positions at the same horizontal axis coordinate value, i.e., the amount of shape change ΔZ.

[0065] This diagram shows only one example of a total of 17 strips: five first strips 21A-21E collected from the first object 11 and 12 second strips 22A-22L collected from the second object 12. The shape change amount ΔZ is calculated for each of the remaining 16 strips in the same manner as shown in the diagram.

[0066] (Residual Stress Estimation Step) Next, in a residual stress estimation step S6, the residual stress in the strip longitudinal direction is estimated from the calculated shape change amount ΔZ. In this example, there are two types of objects 10: a first object 11 and a second object 12. The strip longitudinal direction corresponds to the original sheet width direction W for the first strips 21A to 21E taken from the first object 11, and corresponds to the original sheet longitudinal direction L for the second strips 22A to 22L taken from the second object 12.

[0067] Therefore, the residual stress σW in the original plate width direction W of the first object 11 can be estimated from the amount of shape change ΔZ for the first strips 21A to 21E. The residual stress σW at each measurement point A of the first object 11 is expressed by the following equation using Young's modulus E and plate thickness t: σW = E × (t / 2) × c1, where c1 is the amount of curvature change due to cutting the first object 11.

[0068] The curvature change amount c1 of the first object 11 is obtained by second-order differentiation of the shape change amount ΔZ due to cutting with respect to the first strip longitudinal direction SL1 (c1=d 2 ΔZ / dSL1 2 For one first strip, the curvature change amount c1 for 12 sections is obtained by differentiating the shape change amount ΔZ calculated at the 13 measurement points A. Each section is defined between two adjacent measurement points A.

[0069] The Young's modulus E and the plate thickness t are determined depending on the object 10. The shape change amount ΔZ is calculated for each measurement point A in the shape change amount calculation step S5. The shape change amount ΔZ is second-order differentiated to calculate the curvature change amount c1 for each section. The calculated curvature change amount c1, Young's modulus E, and plate thickness t can be used to estimate the residual stress σW in the first strip longitudinal direction SL1, i.e., the original plate width direction W, for each section.

[0070] This arithmetic operation is performed for all sections set in the first object 11, and the residual stress σW in the longitudinal direction SL1 of the first strip, i.e., in the width direction W of the original sheet, is estimated over the entire surface of the first object 11. For example, a total of 60 sections (12 sections × 5 strips) are set in the first object 11, and 60 estimated results of the residual stress σW are obtained.

[0071] On the other hand, the residual stress σL in the original plate longitudinal direction L of the second object 12 can be estimated from the amount of shape change ΔZ for the second strips 22A to 22L. The residual stress σL at each measurement point A of the second object 12 can also be expressed by the following equation using Young's modulus E and plate thickness t: σL = E × (t / 2) × c2, where c2 is the amount of curvature change due to cutting the second object 12.

[0072] The curvature change amount c2 of the second object 12 is obtained by second-order differentiation of the shape change amount ΔZ due to cutting with respect to the second strip longitudinal direction SL2 (c2=d 2 ΔZ / dSL2 2 For one second strip, the curvature change amount c1 for ten sections is obtained by differentiating the shape change amount ΔZ calculated at the eleven measurement points A. Each section is defined between two adjacent measurement points A.

[0073] The method for estimating the residual stress σL in the longitudinal direction of the second strip at a certain measurement point A, i.e., in the longitudinal direction L of the original sheet, from the amount of shape change ΔZ at that measurement point A is the same as described above. By performing the above calculation process for all measurement points A on the second object 12, the residual stress σL in the longitudinal direction SL2 of the second strip, i.e., in the longitudinal direction L of the original sheet, is estimated over the entire surface of the second object 12. For example, a total of 120 sections (10 sections x 12 strips) are set on the second object 12, and 120 estimated results of the residual stress σL are obtained. (Example of output of estimation results)

[0074] 7A and 7B are diagrams visualizing the estimation results of the residual stresses σW and σL. For example, such diagrams may be displayed on the display of the terminal device 83.

[0075] In the example shown in Figure 7A, the first object 11 is divided into 10 parts in the original board longitudinal direction L (X direction) and 12 parts in the original board width direction W (Y direction), thereby being schematically divided into 120 regions.

[0076] Each region is displayed in a visually distinguishable manner according to the residual stress σW. For example, each region is painted in a different color or pattern. In the illustrated example, each region is painted in five different achromatic colors, with the higher the residual stress σW, the darker the color. Each region may also be painted in a different hue.

[0077] The same applies to the example shown in Fig. 7B. The second object 12 is divided into 10 parts in the original sheet longitudinal direction L (X direction) and 12 parts in the original sheet width direction W (Y direction), so that it is schematically divided into 120 regions. These regions correspond one-to-one to the sections set in the second object 12.

[0078] In contrast, in the example shown in Figure 7A, the first object 11 is also divided into 120 regions, whereas 60 sections are set in the first object 11 in the shape change amount calculation step S5 and the residual stress estimation step S6. In the original sheet width direction W, the resolution of the diagram shown in Figure 7A is twice the resolution of the sections set for estimating the residual stress σW of the first object 11. In this case, one section may correspond to two regions adjacent to each other in the original sheet width direction W. This allows the first object 11 and the second object 12 to generate similar diagrams even if they have different numbers of sections.

[0079] As described above, this method allows residual stress to be estimated over the entire surface of an object simply by measuring the three-dimensional shape of only one surface of the object before and after cutting with a three-dimensional shape measuring device. This reduces the time required to estimate residual stress compared to X-ray methods and conventional cutting methods.

[0080] A first object 11 and a second object 12 are prepared from the same plate material. The first object 11 is cut to obtain a plurality of first strips 21A-21E, and the second object 12 is cut to obtain a plurality of second strips 22A-22L. The longitudinal direction SL1 of the first strips is perpendicular to the longitudinal direction SL2 of the second strips. This allows the residual stresses σW and σL in the two perpendicular directions to be estimated in a short time.

[0081] Although the embodiments have been described above, the above configurations are merely examples and can be modified as appropriate within the scope of the present disclosure.

[0082] The present disclosure may include the following aspects.

[0083] (Aspect 1) A residual stress estimation method comprising: preparing a metal plate as an object; acquiring original plate shape data indicating the three-dimensional shape of one surface of the object using a three-dimensional shape measuring device; cutting the object to obtain a plurality of strips that are long in one direction within the one surface of the object and have a width in another direction within the one surface that is perpendicular to the one direction; acquiring a plurality of strip shape data indicating the three-dimensional shapes of the one surface of the plurality of strips using the three-dimensional shape measuring device; setting a plurality of measurement points aligned in the longitudinal direction of the strip on the one surface of the strip; calculating an amount of shape change in the plate thickness direction of the object at each of the plurality of measurement points before and after cutting based on the original plate shape data and the strip shape data; and estimating the residual stress in the longitudinal direction of the strip released by cutting from the amount of shape change. (Aspect 2) The residual stress estimation method according to Aspect 1, wherein estimating the residual stress includes: differentiating the amount of shape change with respect to the longitudinal direction twice; and estimating the residual stress in the longitudinal direction based on a rate of change of the amount of shape change. (Aspect 3) The residual stress estimation method according to Aspect 1 or 2, wherein preparing the object includes preparing a first object and a second object from the same plate material, obtaining the plurality of strips includes cutting the first object to obtain a plurality of first strips and cutting the second object to obtain a plurality of second strips, and the longitudinal direction of the plurality of first strips is perpendicular to the longitudinal direction of the plurality of second strips.

[0084] This application claims priority from Japanese Patent Application No. 2024-041412, filed March 15, 2024. Japanese Patent Application No. 2024-041412 is incorporated herein by reference.

[0085] 1 Coil 10 Object 11 First object 11a First surface 12 Second object 12a First surface 21A to 21E First strip 22A to 22L Second strip 81 Support member 81a Support surface 82 Three-dimensional shape measuring device 82a Stereo camera 83 Terminal device S1 Object preparation process S2 Original plate shape data acquisition process S3 Strip preparation process S4 Strip shape data acquisition process S5 Shape change amount calculation process S6 Residual stress estimation process A Measurement point L Original plate longitudinal direction W Original plate width direction T Plate thickness direction SL1 First strip longitudinal direction SL2 Second strip longitudinal direction SW1 First strip width direction SW2 Second strip width direction σL, σW Residual stress ΔZ Shape change amount c1, c2 Curvature change amount E Young's modulus t Plate thickness

Claims

1. A residual stress estimation method comprising: preparing a metal plate as an object; acquiring original plate shape data indicating the three-dimensional shape of one surface of the object using a three-dimensional shape measuring device; cutting the object to obtain a plurality of strips that are long in one direction within the one surface of the object and have a width in another direction within the one surface that is perpendicular to the one direction; acquiring a plurality of strip shape data indicating the three-dimensional shapes of the one surface of the plurality of strips using the three-dimensional shape measuring device; setting a plurality of measurement points aligned in the longitudinal direction of the strip on the one surface of the strip; calculating the amount of shape change in the plate thickness direction of the object at each of the plurality of measurement points before and after cutting based on the original plate shape data and the strip shape data; and estimating the residual stress in the longitudinal direction of the strip released by cutting from the amount of shape change.

2. The residual stress estimation method according to claim 1, wherein estimating the residual stress includes: differentiating the shape change amount twice with respect to the longitudinal direction; and estimating the residual stress in the longitudinal direction based on the rate of change of the shape change amount.

3. A residual stress estimation method as described in claim 1 or 2, wherein preparing the object includes preparing a first object and a second object from the same plate material, and obtaining the plurality of strips includes cutting the first object to obtain a plurality of first strips and cutting the second object to obtain a plurality of second strips, and the longitudinal direction of the plurality of first strips is perpendicular to the longitudinal direction of the plurality of second strips.