A method for evaluating stress distribution of thin metal strips

Abstract

A method for evaluating the stress distribution of a thin metal strip, wherein the thin metal strip is etched and cut along the rolling direction and the transverse direction to obtain a sample strip, and the sample strip is half-etched along the thickness direction, and the deflection height of the sample strip when the strip is laid flat and the side bending amount of the sample strip when placed vertically are measured. The stress distribution in the thickness direction of the strip is evaluated by the deflection height and the side bending amount of the sample strip, and the potential plate shape of the metal in the semi-etching process is judged, thereby indicating a measurement method for quantitative stress testing. When the deflection height is ≥0.5mm, it is determined that the stress distribution is uneven, and X-rays are used to measure the stress at the upper and lower surfaces, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness of the strip; when the deflection height is <0.5mm, the stress distribution is further judged by the side bending amount. When the side bending is ≥20mm, it can be judged that the stress distribution of the strip is uneven, and X-rays are used to measure the stress at the upper and lower surfaces, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness of the strip. When the side bending is <20mm, it can be judged that the thickness stress is uniform, and only the stress of a single surface needs to be measured by X-rays.

Description

Technical Field

[0001] The invention relates to the technical field of stress evaluation, and in particular to a method for evaluating stress distribution of a thin metal plate strip. Background Art

[0002] The electronics industry uses a semi-etching process to process metal parts such as heat spreaders, lead frames, etc., and has high requirements for the apparent plate shape and potential plate shape of the raw materials. In the production of thin metal sheets and strips, they generally go through processes such as hot rolling, cold rolling, heat treatment, and shearing. Each process will produce residual stress to varying degrees, especially for different parts of the strip due to uneven deformation or uneven temperature, which will also lead to inconsistent stress distribution. Although thin metal sheets and strips will subsequently reduce the internal stress of the metal sheets and strips through continuous tension annealing, stretching and straightening, etc., there is a lack of evaluation methods for the entire process flow and the internal stress of different batches, resulting in the inability to obtain effective stress feedback in each control process.

[0003] The methods for measuring internal stress can be divided into non-destructive methods and destructive methods. Non-destructive methods include X-ray method, ultrasonic method, indentation strain resistance method, magnetic method, neutron diffraction method, and destructive methods include blind hole method, strip deformation method, and incision method. The internal stress test methods for thin plates include X-ray, strip deformation method, etc.

[0004] According to the Japanese standard JBMA-T304-201, when evaluating the stress of the edge of a copper strip, the edge is divided into strips and characterized for deflection, lateral bending, torsion, etc. Considering that the deflection deformation is related to the stress distribution in the thickness direction, the test value is affected by the reverse bending and deadweight. In theory, it is proportional to the square of the strip length, inversely proportional to the thickness, and proportional to the stress gradient. This method is suitable for evaluating the stress caused by cutting at the edge of the stamping material.

[0005] For etched metal strips, the etching patterns of downstream processing plants are generally used for semi-etching to evaluate whether the stress of the strip is qualified. There is a lack of comparison for stress judgment and the evaluation results lack universality. However, it is difficult to optimize the number of test points when all stress assessments are performed using X-ray tests, and the testing cost is high. Summary of the invention

[0006] In view of the shortcomings of the above-mentioned prior art, the present invention overcomes the problems of inconsistent stress evaluation standards and high costs, and provides a method for evaluating stress distribution of thin (thickness below 1 mm) metal plates.

[0007] The present invention is achieved through the following technical solutions.

[0008] A method for evaluating the stress distribution of a thin metal strip, characterized in that the method comprises: etching the middle part of the metal strip in the rolling direction and the transverse direction to form rectangular splines with a width of 2 to 50 mm and a length of 100 ± 0.5 mm, one end of the spline is connected to the metal strip and the other end is etched open, and at the same time, the spline is half-etched in the thickness direction, and the deflection of the spline when the metal strip is placed horizontally is counted. When the deflection height of the spline at any half etching depth is less than 0.5 mm, the metal strip is placed vertically to measure the lateral deflection of the spline, and the stress distribution in the thickness direction of the metal strip is evaluated by the lateral deflection.

[0009] Furthermore, the half-etching depth of the spline is one or more of 1 / 4, 1 / 2, and 3 / 4 of the thickness of the metal plate strip.

[0010] Furthermore, when the deflection height of the spline at any half etching depth is ≥0.5mm, it can be determined that the stress distribution of the metal sheet is uneven, and X-rays are used to measure the stresses at the upper and lower surfaces, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness of the metal sheet.

[0011] Furthermore, when the lateral bending amount is ≥20mm, it can be judged that the stress distribution of the metal sheet is uneven, and X-rays are used to measure the stresses on the upper and lower surfaces, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness of the metal sheet; when the lateral bending amount is <20mm, it can be judged that the stress distribution of the metal sheet is uniform, and X-rays are used to measure only the stress on the surface of the metal sheet.

[0012] Furthermore, corrosion-resistant tape is first affixed to both sides of the metal plate strip for protection, the slits of the required spline are engraved on one side, and the slits corresponding to the semi-etched parts on the spline are engraved on the other side, and then the corrosion-resistant tape covering the semi-etched parts is removed, and etching is performed to the required depth, and finally the corrosion-resistant tape is affixed to the semi-etched parts, and then the corrosion-resistant tape on the slit parts of the required spline is removed, and the slit parts of the required spline are etched.

[0013] Furthermore, when measuring the lateral bending amount of the spline when the metal sheet is placed vertically, the length direction of the spline is parallel to the horizontal plane, and the uncorroded substrate surface (i.e., the metal sheet) in the lateral bending direction of the spline is taken as the reference line, and an image measuring instrument or a laser three-coordinate measuring machine is used to measure the lateral bending amount of the spline.

[0014] The beneficial technical effect of the present invention is: a combination of the semi-etched strip method and the X-ray method is used to systematically evaluate the stress of the metal strip, the stress distribution is determined according to the deflection or lateral bending of the semi-etched strip spline, and then the position and number of X-ray detection points are determined to fully quantify the evaluation of the strip stress and reduce the evaluation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1Torque analysis for the rotation of metal strip.

[0016] Figure 2 This is a typical stress distribution model for thin metal plates.

[0017] Figure 3 Schematic diagram of half-etching and striping of a thin metal plate, where (a) is the front-side scratching pattern and (b) is the back-side scratching pattern, and the white part is the corroded part.

[0018] Figure 4 Schematic diagram of the measurement of the spline deflection height (a) and lateral bending (b) of a semi-etched strip of metal sheet. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 The analysis of different deformation characteristic moments of the etched spline when placed horizontally is given, in which the deformation symmetry plane of the deflection is the 1 / 2 thickness plane, the rotation axis is parallel to the transverse direction of the plate and strip, namely the TD direction, the rigid thin rod under force is parallel to the normal direction of the plate and strip, namely the ND direction, the stress parallel to the surface has a rotational effect on the deflection, and RD is the rolling direction.

[0021] Figure 2 A typical stress distribution model of a thin metal plate is given. Its flatness is guaranteed before half etching, but it is found that the moment cannot be balanced after etching at different depths, resulting in bending or curling. The method of the present invention is adopted to release the deformation constraints, especially the constraints in the thickness direction, by changing the dimensions of the plate strip in the width and thickness direction, and inferring the stress distribution by etching metal splines and half etching, and testing the deflection of the splines. The relationship between the bending moment and stress of the splines can be expressed as:

[0022]

[0023] Where σ is the stress parallel to the surface of the metal strip at each point of the spline, t 0 is the remaining thickness of the spline at the half-etched position, w 0 is the width of the spline, l 0 is the length of the spline, K is the coefficient, M is the bending moment of the spline, t is the thickness, w is the width, and l is the length.

[0024] Before stress evaluation, the flatness of the metal strip needs to be measured to determine whether it meets the flatness requirements of the standard.

[0025] Specifically, a method for evaluating the stress distribution of a thin metal strip comprises: using an etching method to separate the middle part of the metal strip into rectangular splines with a width of 2 to 50 mm and a length of 100 ± 0.5 mm in the rolling direction and the transverse direction, one end of the spline is connected to the metal strip and the other end is etched open, and at the same time, the spline is half-etched in the thickness direction. Figure 3 The half-etching depth is one or more of 1 / 4, 1 / 2, 3 / 4 of the thickness of the metal strip. The spline deflection when the metal strip is placed horizontally is counted. Figure 4 (a) When the deflection height of the spline at any half etching depth is less than 0.5 mm, the spline lateral deflection is measured when the metal strip is placed vertically, see Figure 4 (b) The stress distribution in the thickness direction of the metal strip is evaluated by the side bending amount.

[0026] The stress analysis process of metal plates and strips includes protection, scratching, corrosion, measurement and other aspects.

[0027] First, use acid-resistant transparent tape to tightly cover both sides of the sample to be tested (i.e., thin metal plate). In the middle of one side of the thin metal plate, i.e., at a position greater than 12.5mm from the edge, use a steel ruler and a sharp blade to carve a rectangular strip and the corrosion seam on the edge in the middle of the thin metal plate, wherein the width of the rectangular strip is 20±0.2mm and the length is 100±0.5mm, and the length direction is parallel to the rolling direction. The corrosion seam is not carved at the starting end of the rectangular rolling direction, and the width of the corrosion seam is 0.5mm-1mm. After carving, keep the corrosion-resistant tape at that place. Carve a frame greater than 21*101mm on the other side corresponding to the etching pattern to ensure that the corrosion seam and the strip are covered, remove the corrosion-resistant tape on this side, and this side is recorded as the half-etched side.

[0028] Secondly, mix concentrated nitric acid and deionized water in a ratio of 1:10 to form a corrosive solution, place the thin metal plate steadily in the nitric acid for corrosion, and first corrode the part where the tape has been removed, that is, the half-etched surface to the specified thickness. After cleaning and drying the half-etched surface, stick it with corrosion-resistant tape, and then corrode the corrosion seam on the other side. After most of the corrosion seam is corroded, take it out of the corrosive solution and wash it in clean water, and remove all corrosion-resistant tapes. If part of it is not corroded, use a straw to absorb the corrosive solution to corrode the uncorroded part. Finally, the thin metal plate strip is thoroughly cleaned and dried. The cleaning and drying process should prevent deformation of the etched part.

[0029] Then, place the etched metal strip on the horizontal platform of the height gauge, and use the height gauge to measure the deflection height of the spline. When the deflection height is ≥0.5mm, it can be judged that the stress distribution of the metal strip is uneven, and X-rays are used to measure the stress on the upper and lower surfaces of the strip, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness. When the deflection height is less than 0.5mm, the stress distribution is judged by measuring the side bending of the spline when the metal strip is placed vertically.

[0030] When measuring the lateral bending of the spline, the thin metal strip after half-etching and stripping is clamped with flat-nose pliers and placed vertically and fixed. Figure 4 As shown in (b), the length direction of the spline is parallel to the horizontal plane and is placed under an image measuring instrument or a laser three-coordinate measuring machine. The substrate surface that is not corroded in the bending direction is selected as the reference line, and the distance from the vertex of the bending spline to the reference line is measured to obtain the bending amount of the semi-etched spline. The bending amount is used to evaluate whether the stress state of the thin metal strip is qualified. When the bending amount is ≥20mm, it can be judged that the stress distribution is uneven, and X-rays are used to measure the stress on the upper and lower surfaces of the strip, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness. When the bending amount is less than 20mm, it can be judged that the stress is uniform, and only X-rays can be used to measure the single surface stress of the metal strip.

[0031] Embodiment 1:

[0032] Take C194 copper strip with the dimensions of 0.308mm thickness, 200mm width and 250mm length (rolling direction), according to Figure 1 The spline was etched and half-etched to half the thickness of the copper strip (i.e., the thickness was 0.154 mm), wherein the width of the spline was 20 mm and the length was 100 mm. The spline bending height was measured when the copper strip was placed horizontally. Since the bending height was less than 0.5 mm, the side bending of the spline was measured when the strip was placed vertically. The measured values ​​are shown in Table 1. Since the bending height was less than 0.5 mm and the side bending was less than 20 mm when it was placed vertically, it can be judged that the stress of the copper plate was qualified, i.e., the stress distribution was uniform. The surface stress was measured by X-ray to be 25 MPa.

[0033] Table 1 Evaluation of various parameters of copper strip after etching

[0034]

[0035] Embodiment 2:

[0036] Take C194 copper strip with the dimensions of 0.308mm thickness, 200mm width and 250mm length (rolling direction), according to Figure 1 The spline was etched and half-etched to half the thickness of the copper strip (i.e., the thickness was 0.154 mm), wherein the width of the spline was 20 mm and the length was 100 mm. The deflection height of the spline was measured when the copper strip was laid flat, and the measured values ​​are shown in Table 2. Since the deflection height of the horizontally placed spline was greater than 0.5 mm, it can be judged that the stress of the copper plate was unqualified, i.e., the stress distribution was uneven. After X-ray testing, the stress of the upper surface was -170 MPa, the stress of the lower surface was -156 MPa, the stress of the 1 / 4 thickness was -100 MPa, the stress of the center (i.e., 1 / 2 thickness) was -50 MPa, and the stress of the 3 / 4 thickness was -80 MPa, and the maximum stress difference reached 120 MPa.

[0037] Table 2 Evaluation of various parameters of copper strip after etching

[0038]

[0039] Embodiment 3:

[0040] Take C194 copper strip with the dimensions of 0.308mm thickness, 200mm width and 250mm length (rolling direction), according to Figure 1 The spline was etched and half-etched to the specified depth, where the width of the spline was 20 mm and the length was 100 mm. The deflection height of the spline was measured when the copper strip was laid flat, and the measured values ​​are shown in Table 3. Since the deflection height of the horizontally placed spline was greater than 0.5 mm, it can be judged that the stress of the copper plate was unqualified, that is, the stress distribution was uneven. After X-ray testing, the stress of the upper surface was -213 MPa, the stress of the lower surface was -180 MPa, the stress of the 1 / 4 thickness was -112 MPa, the stress of the center was -34 MPa, and the stress of the 3 / 4 thickness was -147 MPa, and the maximum stress difference reached 179 MPa.

[0041] Table 3 Evaluation of various parameters of copper strip after etching

[0042]

[0043] The present invention can overcome the problems of inconsistent stress evaluation standards and high costs, and has developed a spline half-etching method. This method utilizes the deformation caused by the uneven distribution of stress in the thickness direction, and evaluates the stress difference between the center and the surface of the plate by measuring the deflection height or the lateral bending amount. This can unify the stress evaluation method and optimize the X-ray detection scheme.

[0044] The above is only a preferred embodiment of the present invention and does not limit the invention. It should be pointed out that for ordinary technicians in this field, under the technical enlightenment provided by the present invention, other equivalent improvements can be made, all of which can achieve the purpose of the present invention and should be regarded as the protection scope of the present invention.

Claims

1. A method for evaluating stress distribution of thin metal strips, It is characterized in that The method comprises: using an etching method to separate the middle part of the metal strip into rectangular splines with a width of 2 to 50 mm and a length of 100±0.5 mm in the rolling direction and the transverse direction, one end of the spline is connected to the metal strip and the other end is etched open, and at the same time, the spline is half-etched in the thickness direction, and the depth of the half-etching of the spline is one or more of 1 / 4, 1 / 2, and 3 / 4 of the thickness of the metal strip; counting the deflection of the spline when the metal strip is placed horizontally, when the deflection height of the spline at any half etching depth is less than 0.5 mm, the metal strip is placed vertically to measure the lateral deflection of the spline, and the stress distribution in the thickness direction of the metal strip is evaluated by the lateral deflection; When the deflection height of the spline at any half etching depth is ≥0.5mm, it can be judged that the stress distribution of the metal strip is uneven. X-rays are used to measure the stress of the upper and lower surfaces, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness of the metal strip. When the lateral bending amount is ≥20 mm, it can be judged that the stress distribution of the metal sheet is uneven, and X-rays are used to measure the stresses on the upper and lower surfaces, 1 / 4 thickness, 1 / 2 thickness, and 3 / 4 thickness of the metal sheet; when the lateral bending amount is <20 mm, it can be judged that the stress distribution of the metal sheet is uniform, and X-rays are used to measure only the stress on the surface of the metal sheet.

2. A method for evaluating stress distribution of a thin metal strip according to claim 1, It is characterized in that First, corrosion-resistant tape is applied to both sides of the metal strip for protection. The slits of the required spline are engraved on one side, and the slits corresponding to the semi-etched parts on the spline are engraved on the other side. Then, the corrosion-resistant tape covering the semi-etched parts is removed, and etching is performed to the required depth. Finally, the corrosion-resistant tape is applied to the semi-etched parts, and the corrosion-resistant tape on the slit parts of the required spline is removed, and the slit parts of the required spline are etched.

3. A method for evaluating stress distribution of a thin metal strip according to claim 1, It is characterized in that When measuring the lateral bending amount of the spline when the metal strip is placed vertically, the length direction of the spline is parallel to the horizontal plane, the uncorroded substrate surface in the lateral bending direction of the spline is taken as the reference line, and the lateral bending amount of the spline is measured using an image measuring instrument or a laser three-coordinate measuring machine.

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