Residual stress estimation method

Abstract

To shorten an estimated time of residual stress of an object.SOLUTION: A residual stress estimation method includes: acquiring original plate shape data that shows a three-dimensional shape of one surface of an object by using a three-dimensional shape measuring device; collecting a plurality of strips by cutting the object; acquiring multiple pieces of strip shape data that respectively shows a three-dimensional shape of the plurality of strips by using the three-dimensional shape measuring device; setting a plurality of measuring points aligned in a strip longer direction, on the strip; calculating a shape change amount in a plate thickness direction of the object at each measuring point based on the original plate shape data and the strip shape data; and estimating residual stress in the strip longer direction released by being cut, from the shape change amount.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a residual stress estimation method. [Background technology]

[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, the X-ray method is known as one type of non-destructive method. As disclosed in Non-Patent Document 2, the cutting method is known as one type of destructive method. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Suzuki et al., "Technological Trends in X-ray Residual Stress Measurement and Initiatives to Meet 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 [Non-patent document 2] Kakutani et al., "Analytical Study on Residual Stress Measurement Using Strain Gauge Cut-Off Method," Proceedings of the Materials Mechanics Conference, Japan Society of Mechanical Engineers, July 20, 2004, Vol. 2004, pp. 207-208 Summary of the Invention [Problem to be solved by the invention]

[0004] In the X-ray method, it is necessary to irradiate both the front and back sides of the object with X-rays. After irradiating the front side of the object with X-rays, if the object is turned over to irradiate the back side with X-rays, the shape of the object will change due to its own weight. This may change the value of residual stress, making it difficult to measure both the front and back sides under the same conditions. This problem becomes more 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 time to measure the entire object, a problem that becomes more pronounced when the object has a large surface area.

[0006] In conventional cutting methods, it is necessary to attach a large number of strain gauges to the surface of the object and then cut the object into small pieces with the strain gauges still attached. While it is possible to obtain measurement results for the entire object in a single measurement, this single measurement takes 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 invention is to reduce the time required to estimate residual stress in an object. [Means for solving the problem]

[0008] One aspect of the present invention 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 the residual stress in the longitudinal direction of the strip that has been released by cutting from the amount of shape change.

[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, 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.

[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. [Effects of the Invention]

[0015] According to the present invention, the time required to estimate the residual stress of an object can be reduced. [Brief explanation of the drawings]

[0016] [Figure 1] 3 is a flowchart showing a residual stress estimation method according to the present embodiment. [Figure 2] FIG. [Figure 3A] FIG. 10 is an explanatory diagram of an original plate shape data acquisition process for a first object. [Figure 3B] FIG. 10 is an explanatory diagram of an original plate shape data acquisition process for a second object. [Figure 4A] FIG. 10 is an explanatory diagram of a strip acquisition process for a first object. [Figure 4B] FIG. 10 is an explanatory diagram of a strip acquisition process for a second object. [Figure 5A] FIG. 10 is an explanatory diagram of a strip shape data acquisition step for a first strip. [Figure 5B] FIG. 10 is an explanatory diagram of a strip shape data acquisition step for a second strip. [Figure 6] 4 is a diagram showing the amount of change in shape in the thickness direction at each measurement point set on a certain first strip. [Figure 7A] FIG. 10 is a diagram showing an example of a display of an estimated result of residual stress of a first object. [Figure 7B] FIG. 10 is a diagram showing an example of a display of an estimated result of residual stress of a second object. DETAILED DESCRIPTION OF THE INVENTION

[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 material as an object 10. The material of the plate material 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 will be 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 including 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. However, 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 the coil 1.

[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 the 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 is true for 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 just one 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] (Original plate shape data acquisition process) 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] 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") whose origin is 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 directed 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 with respect to the support member 81 and 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 it does not have to coincide with the Z direction. The three-dimensional shape measuring instrument 82 does not have to be disposed so as to face the first surface 11a 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) indicating 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 similar to 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 12a facing upward. That is, in this case, the above-mentioned "one surface" is the first surface 12a 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 12a 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] (Strip preparation process) 4A and 4B are explanatory diagrams of the strip preparation step S3. In the strip preparation step S3, the object 10 is cut to collect multiple strips. Each strip is long in one direction within one surface of the object 10 and has a width in another direction perpendicular to the one direction within the one surface. The multiple strips are lined up 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 board longitudinal direction L by a plurality of division lines extending along the original board 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 board width direction W when viewed in the board 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-21E will be referred to as the "first strip longitudinal direction SL1," and the width direction of the first strips 21A-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 instrument coordinate system), and the first strip width direction SW1 corresponds to the original board longitudinal direction L (the X direction of the measuring instrument 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 board width direction W along a plurality of division lines extending along the original board longitudinal direction L. Each of the second strips 22A to 22L has an elongated rectangular shape that is long in the original board longitudinal direction L when viewed in the board 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 instrument coordinate system), and the second strip width direction SW2 corresponds to the original sheet width direction W (Y direction of the measuring instrument 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 just one example, if the first object 11 and the second object 12 each 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 5 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-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-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 (the width direction W of the original sheet) can be estimated by back-calculation.

[0046] Similarly, for the second object 12 and the second strips 22A to 22L, residual stress in the second strip longitudinal direction SL2 contributes to 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] (Strip shape data acquisition process) 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 process S2. The "three-dimensional shape measuring instrument 82" here is the same as that used in the original sheet shape data acquisition process 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 process 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 is cut in the strip preparation process S3, and is acquired in the same manner as the original sheet shape data.

[0049] "Acquiring a plurality of strip shape data items, each showing the three-dimensional shape of one surface of a plurality of strips, using a three-dimensional shape measuring instrument" is not limited to the state in which data items for all strips taken from a single object are acquired simultaneously, 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, the plurality of second strips 22A to 22L are placed on the support surface 81a of the 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 sheet 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 sheet thickness direction T. The three-dimensional shape measuring device 82 acquires a plurality of second strip shape data indicating the three-dimensional shape of the first surface 12a of each of the second strips 22A to 22L.

[0053] (Shape change amount calculation process) 5A, in a 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 first strip longitudinal direction SL1. 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. That is, 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 multiple measurement points A are set in this way, the first strip shape data is referenced to read out depth information from the three-dimensional shape measuring instrument 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 instrument 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 longitudinal direction L of the original sheet, and the plurality of measurement points A are arranged in each of the first strips 21A to 21E in the width direction W of the original sheet. Therefore, when the shape data of the plurality of first strips is viewed 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 thickness direction T of the first object is calculated thereby. In other words, for each measurement point A, the shape change in the 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 to 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 they are set, for example, at the center of the second strip width direction SW2. The plurality of measurement points A are set at predetermined intervals 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 the 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 given 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 longitudinal direction SL1 of the first strip for each of the 13 measurement points A. The dashed lines indicate the position in the thickness direction T of the first object 11 read from the first original sheet shape data. The solid lines indicate the position in the thickness direction T of the first strip read from the first strip shape data. The dashed and dotted lines indicate 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 taken from the first object 11 and 12 second strips 22A-22L taken 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 process) 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 first strips 21A-21E taken from the first object 11, and corresponds to the original sheet longitudinal direction L for second strips 22A-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 shape change amount 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 Here, c1 is the amount of change in curvature due to cutting of 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 amount of curvature change c1 for 12 sections is obtained by differentiating the amount of shape change ΔZ calculated at 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 according to 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 is also expressed by the following equation using Young's modulus E and plate thickness t. σL=E×(t / 2)×c2 Here, c2 is the amount of change in curvature due to cutting of 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 amount of curvature change c1 for ten sections is obtained by differentiating the amount of shape change ΔZ calculated at 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 second strip longitudinal direction SL2 at a certain measurement point A, i.e., in the original sheet longitudinal direction L, from the 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 second strip longitudinal direction SL2, i.e., in the original sheet longitudinal direction L, is estimated over the entire surface of the second object 12. For example, a total of 120 sections (10 sections × 12 strips) are set on the second object 12, and 120 estimated results of the residual stress σL are obtained. (Example of estimated result output)

[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 board longitudinal direction L (X direction) and 12 parts in the original board width direction W (Y direction), so that it is schematically divided into 120 areas. These areas correspond one-to-one to the sections set in the second object 12.

[0078] In contrast, in the example shown in FIG. 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 FIG. 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 embodiment has been described above, the above configuration is merely an example and can be modified as appropriate within the scope of the present invention.

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

[0083] (Aspect 1) A metal plate is prepared as a target object. Acquire 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 each having a length in one direction within the one surface of the object and a width in another direction perpendicular to the one direction within the one surface; acquiring a plurality of strip shape data representing the three-dimensional shapes of the one surface of the plurality of strips by the three-dimensional shape measuring device; a plurality of measurement points aligned in a longitudinal direction of the strip are set on the one surface of the strip, and a shape change amount of the object in the plate thickness direction before and after cutting at each of the plurality of measurement points is calculated 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 change in shape. A residual stress estimation method comprising: (Aspect 2) estimating the residual stress includes: The shape change amount is second-order differentiated with respect to the longitudinal direction; estimating the residual stress in the longitudinal direction based on the rate of change of the shape change amount; 2. The residual stress estimation method of claim 1, comprising: (Aspect 3) preparing the objects 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; The longitudinal direction of the plurality of first strips is perpendicular to the longitudinal direction of the plurality of second strips. 3. The residual stress estimation method according to claim 1 or 2. [Explanation of symbols]

[0084] 1 coil 10 Object 11 First Object 11a 1st surface 12 Second Object 12a 1st surface 21A~21E 1st Strip 22A~22L 2nd Strip 81 Support member 81a Support surface 82 Three-dimensional shape measuring instrument 82a Stereo Camera 83 Terminal Equipment S1 Object preparation process S2 Original plate shape data acquisition process S3 Strip preparation process S4 Strip shape data acquisition process S5 Shape change calculation process S6 Residual stress estimation process A measurement point L: Longitudinal direction of original plate W Original plate width direction T Thickness direction SL1 First strip longitudinal direction SL2 Second strip longitudinal direction SW1 1st strip width direction SW2 Second strip width direction σL,σW Residual stress ΔZ Amount of change in shape c1,c2 Curvature change amount E Young's modulus t Plate thickness

Claims

1. A metal plate is prepared as a target object. Acquire 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 each having a length in one direction within the one surface of the object and a width in another direction perpendicular to the one direction within the one surface; acquiring a plurality of strip shape data representing the three-dimensional shapes of the one surface of the plurality of strips by the three-dimensional shape measuring device; a plurality of measurement points aligned in a longitudinal direction of the strip are set on the one surface of the strip, and a shape change amount of the object in the plate thickness direction before and after cutting at each of the plurality of measurement points is calculated 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 change in shape. A residual stress estimation method comprising:

2. estimating the residual stress includes: The shape change amount is second-order differentiated with respect to the longitudinal direction; estimating the residual stress in the longitudinal direction based on the rate of change of the shape change amount; The residual stress estimation method according to claim 1 , comprising:

3. preparing the objects 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; a longitudinal direction of the plurality of first strips perpendicular to a longitudinal direction of the plurality of second strips; The residual stress estimation method according to claim 1 or 2.

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