Sheet metal shearing edge quality evaluation method and punching die

Abstract

The invention discloses a sheet metal shearing edge quality evaluation method and a punching die. The sheet metal shearing edge quality evaluation method comprises the following steps: S1, designing a shearing sample containing different curve edge characteristics; s2, trimming the metal plate by adopting a punching die matched with the shearing samples, setting different shearing process parameters at different curve edge characteristics, and obtaining a plurality of shearing samples containing different curve edge characteristics; and S3, according to the distribution diagram of different area heights on the shearing section of the shearing sample, obtaining an evaluation index of the shearing section of the shearing sample, and evaluating the quality of the shearing edge of the metal plate. The shearing edge quality of the metal plate under different shearing process parameters can be comprehensively evaluated, so that the optimal shearing process parameters of the metal plate are determined.

Description

Technical Field

[0001] The invention relates to the field of sheet metal stamping manufacturing, and relates to a metal sheet shear edge quality evaluation method and a punching die. Background Art

[0002] With the increasingly stringent requirements of countries around the world for environmental protection and the popularization of new energy vehicles, the proportion of lightweight materials (including advanced high-strength steel, aluminum alloy and other materials) used in car bodies has gradually increased.

[0003] In the development process of body parts made of advanced high-strength steel, aluminum alloy and other materials, stamping is the main production process. Blanking and shearing are necessary steps from sheet metal to final parts, and the quality of shearing edges directly affects the formability of parts and the final product quality of parts. Among them, factors affecting the quality of shearing edges include shear gap, blade angle, shearing angle and edge shape. How to determine the most suitable shearing edge process parameters for this type of material through an evaluation method is very important to improve part development efficiency and ensure part quality.

[0004] In the process of automobile development, the design of body structural parts is an important part. In order to shorten the development cycle, in the synchronous engineering stage, designers must consider both the functional requirements of parts and the process design of parts to avoid continuous rework in the manufacturing stage and affect the delivery of parts. Among them, automobile structural parts have many flanging features, and the flanging process is divided into elongation, compression and straight flanging. If the design is improper or the matching of parts and materials is not considered, there will be unacceptable flanging forming defects, including tearing and severe wrinkling. An important design parameter of the flanging feature is the flanging height. Designers mainly refer to empirical formulas or previous design experience, and often problems arise in the subsequent part manufacturing process.

[0005] Chinese patent CN 201716222 U provides a die for preparing unidirectional tensile test specimens of sheet materials. By replacing three sets of concave dies of different sizes, three sets of different convex-concave gaps are formed, so that the sheet materials of the same thickness can be punched out with tensile test specimens under different gaps to obtain single-tension specimens with different shear qualities. This method can only be used for the preparation of single-tension specimens, and the influence of the cutting edge angle and the punching angle on the cutting edge quality cannot be considered.

[0006] The paper "The Influence of Blanking Quality on the Edge Forming Performance of TRIP780" by Zhou Ming et al. provides a single-item tensile specimen blanking die. In addition to achieving different gaps by replacing the die insert, the cutting edge angle of the punching punch is also designed. The shortcoming of this method is that the design of the cutting edge angle is inconsistent with the actual cutting edge definition, and it also cannot consider the influence of the punching angle and specimen shape on the cutting edge quality.

[0007] Chinese patent publication number CN114509554A discloses a method for determining the blanking quality of steel plates. The method comprises the following steps: performing a punching test on a steel plate to be blanked of a preset thickness, replacing the punching punch and the die, and performing a cross-sectional analysis on the obtained blanking discs. If there is no delamination phenomenon, it is determined that the blanking quality of the steel plate sample to be blanked is excellent. The technology mainly focuses on the evaluation of the delamination of the blanking section of the steel plate at different gaps, and cannot be implemented for the evaluation of the trimming quality under other shearing process parameters.

[0008] It can be seen that there is currently no evaluation method that can be used to evaluate the trimming quality of metal sheets corresponding to different trimming states in actual stamping applications. Especially for some new products, it cannot provide effective guidance on shearing process parameters, affecting the project development cycle. Summary of the invention

[0009] In view of the problem in the prior art that it is impossible to evaluate the trimming effects of metal sheets in different states during the actual stamping process, the purpose of the present invention is to provide a method for evaluating the quality of sheared edges of metal sheets and a punching die, and to design a shearing specimen containing different curved edge features, and to adopt different shearing process parameters at different curved edge features, so as to comprehensively evaluate the sheared edge quality of metal sheets under different shearing process parameters, thereby determining the optimal shearing process parameters for metal sheets.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] A first aspect of the present invention provides a method for evaluating the quality of sheared edges of metal sheets, comprising the following steps:

[0012] S1, design shear specimens with different curved edge features;

[0013] S2, using a punching die matching the shearing specimen to trim the metal sheet, setting different shearing process parameters at different curved edge features, and obtaining a plurality of shearing specimens containing different curved edge features;

[0014] S3, obtaining an evaluation index of the shear section of the shear specimen according to a distribution diagram of heights of different regions on the shear section of the shear specimen, and evaluating the quality of the sheared edge of the metal sheet.

[0015] Preferably, in step S1, the boundary of the shear specimen containing different curved edge features contains no less than three straight line segments and three curved line segments.

[0016] Preferably, the curved segment includes an inner concave segment and an outer convex segment.

[0017] Preferably, in step S2, a distance Δ between a boundary of the shear specimen and a boundary of the metal sheet is ≥5 mm.

[0018] Preferably, in step S2, the shearing process parameters include a shearing gap δ, a cutting edge angle α and a cutting edge angle β.

[0019] Preferably, the punching die comprises an upper die and a lower die that match and cooperate with shear specimens with different curved edge features;

[0020] The upper die comprises a pressure ring, an upper pressure insert disposed below the pressure ring, a trimming punch and a trimming insert disposed on the trimming punch; a gap is left between the trimming insert and the upper pressure insert;

[0021] The lower die comprises a concave die and a lower pressure insert disposed on the concave die; the upper surface of the lower pressure insert matches the lower surface of the upper pressure insert;

[0022] The shear gap δ is the distance between the adjacent surfaces of the lower pressing block and the trimming block, and its value is 5% to 20% of the thickness t of the metal sheet; and / or

[0023] The trimming angle α is the angle between the tangent direction of the metal sheet and the horizontal direction, and its value does not exceed 25°; and / or

[0024] The cutting edge angle β is the angle between the lower surface of the trimming insert and the horizontal direction, and its value range is 0° to 10°.

[0025] Preferably, in step S3, the evaluation index includes the bright area height h f The ratio h to the shear specimen thickness t f / t, the straightness of the boundary between the bright area and the tearing area λ and the height of the burr area h b The ratio h to the shear specimen thickness t b / t.

[0026] Preferably, in step S3, the quality of the sheared edge of the metal sheet is evaluated as follows:

[0027] First compare the ratio of the burr area height to the shear specimen thickness h b / t, when h b / t≤10%, continue to compare the straightness λ of the boundary between the bright area and the tearing area. When the absolute value of λ is ≤0.05mm, compare the ratio of the height of the bright area to the thickness of the shear specimen h. f / t, when h f When / t≤10%, it is determined that the shear edge quality of the metal sheet is excellent.

[0028] Preferably, the method further comprises step S4 of determining the shearing process parameters of the metal sheet by transversely comparing the evaluation indexes of the shear sections of the shear specimens under different shearing process parameters.

[0029] The second aspect of the present invention provides a punching die used in the metal sheet shear edge quality evaluation method as described in the first aspect of the present invention, comprising an upper die and a lower die that match and cooperate with shear specimens with different curved edge features;

[0030] The upper die comprises a pressure ring, an upper pressure insert disposed below the pressure ring, a trimming punch and a trimming insert disposed on the trimming punch; a gap is left between the trimming insert and the upper pressure insert;

[0031] The lower die comprises a concave die and a lower pressing material insert arranged on the concave die; the upper surface of the lower pressing material insert matches the lower surface of the upper pressing material insert.

[0032] Preferably, the upper surface of the lower pressing material insert and the lower surface of the upper pressing material insert are arranged as inclined surfaces which match each other.

[0033] Preferably, the lower surface of the trimming insert is an inclined surface.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The metal sheet shear edge quality evaluation method of the present invention designs shear specimens with different curved edge features and uses different shear process parameters to prepare them, so as to obtain shear specimens corresponding to multiple shear process parameters in one punching, thereby comprehensively evaluating the shear edge quality of the metal sheet under different shear process parameters, thereby determining the optimal shear process parameters for the metal sheet;

[0036] 2. The present invention comprehensively considers the edge shape of different positions of the body structure parts, as well as multiple shearing process parameters including shearing gap, shearing angle and cutting edge angle that may affect the quality of the sheared edge. By means of the method of the present invention, evaluation tests are carried out on different metal sheets to obtain the optimal shearing process parameter design to guide actual production, improve production efficiency and ensure the quality of parts;

[0037] 3. The punching die of the present invention can adapt to different shearing process parameters, can flexibly adjust the cutting angle and the shearing gap, and obtain shearing samples with different curved edge features prepared by different shearing process parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0039] Figure 1 It is a schematic flow chart of the metal sheet shear edge quality evaluation method of the present invention;

[0040] Figure 2is a schematic diagram of the structure of a shear specimen including different curved edge features of the present invention;

[0041] Figure 3 It is a structural schematic diagram of the punching die of the present invention;

[0042] Figure 4 is a schematic diagram of the punching die of the present invention in a sharp-angle cutting state;

[0043] Figure 5 is a schematic diagram of the punching die of the present invention in a blunt-angle trimming state;

[0044] Figure 6 Schematic diagram of the punching die of the present invention in the cutting state with different cutting edge angles;

[0045] Figure 7 is a schematic diagram of a shear section of a shear specimen of the present invention;

[0046] Figure 8 Schematic diagrams of shear cross sections of shear specimens corresponding to different shear gaps in the embodiments of the present invention, wherein the shear gap δ of (a) is 5%t, the shear gap δ of (b) is 10%t, the shear gap δ of (c) is 15%t, and the shear gap δ of (d) is 20%t, where t is the thickness of the metal plate;

[0047] Fig. 9 yes Figure 8 The height distribution diagram of different areas of the shear section of the shear specimen shown;

[0048] Fig.10 Schematic diagrams of shear sections of shear specimens corresponding to different trimming angles in an embodiment of the present invention, wherein the trimming angle α of (a) is 0°, the trimming angle α of (b) is 5°, and the trimming angle α of (c) is 10°;

[0049] Fig.11 yes Fig.10 The height distribution diagram of different areas of the shear section of the shear specimen shown;

[0050] Fig.12 Schematic diagrams of shear sections of shear specimens corresponding to different edge angles according to an embodiment of the present invention, wherein the edge angle β of (a) is 0°, the edge angle β of (b) is 5°, and the edge angle β of (c) is 10°;

[0051] Fig.13 yes Fig.12 The height distribution diagram of different areas of the shear section of the shear specimen shown;

[0052] In the figure, 1, metal sheet, 2, shear test specimen, 3, blank holder, 4, upper pressure insert, 5, lower pressure insert, 6, die, 7, trimming punch, 8, trimming insert. DETAILED DESCRIPTION

[0053] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0054] Blanking and shearing are necessary steps in the stamping process from blank to final part of metal sheet. The quality of shearing directly affects the formability of the part and the final product quality of the part. Among them, factors affecting the quality of shearing include shear gap, edge angle, shearing angle and edge shape. How to determine the most suitable shearing process parameters for this type of material through an evaluation method is very important to improve part development efficiency and ensure part quality.

[0055] The evaluation method of the prior art only considers certain specific process parameters and cannot evaluate the cutting effect of the plate under different states during actual punching. The present invention proposes a metal plate shear edge quality evaluation method, which has functions and effects that the prior art does not have. The present invention first proposes a sheet material form containing different curve edge features, and defines different shearing process parameters at different curve edge features to evaluate the shear edge quality of the metal plate under different shearing process parameters, so as to obtain the best shearing process parameters; at the same time, the present invention also proposes a punching die that can flexibly adjust the punching angle and shear gap, so as to define different shearing process parameters at different curve edge features.

[0056] Combination Figure 1 As shown, a method for evaluating the quality of sheared edges of metal sheets provided by the present invention comprises the following steps:

[0057] S1, design shear specimens with different curved edge features;

[0058] Considering that the shape of the edge is one of the important factors affecting the quality of the sheared edge, it is preferred to design a shear specimen with different curved edge features. The boundary of the shear specimen includes straight segments and curved segments, and each has no less than three segments. The curved segments include concave segments and convex segments. In a specific embodiment, the shear specimen after shearing can be designed as Figure 2 For the plate shape shown, three curved segments can be designed, namely, concave segments R2 and R3, and convex segment R1, which correspond to different radius values ​​respectively; five straight segments can be set, namely, L1, L2, L3, L4, and L5, and different shearing process parameters can be designed for each straight segment, and the number of straight segments can be appropriately increased or decreased according to actual conditions.

[0059] S2, using a punching die to trim the metal sheet, setting different shearing process parameters at different curve edge features, and obtaining multiple shearing specimens designed in step S1;

[0060] Combination Figure 3 to Figure 6 As shown, a punching die matching the shear specimen designed in step S1 is designed, and the punching die can adapt to different shear process parameters. The punching die includes an upper die and a lower die that cooperate with each other; the upper die includes a pressure ring 3, an upper pressure insert 4, a trimming punch 7 and a trimming insert 8, the upper surface of the upper pressure insert 4 is a plane, and the lower surface is an inclined surface; the lower die includes a die 6 and a lower pressure insert 5, the upper surface of the lower pressure insert 5 is an inclined surface matching the lower surface of the upper pressure insert 4, and the lower surface of the lower pressure insert 5 is a plane.

[0061] When preparing the shear specimen, first install the punching die on the forming test machine, install the edge holding ring 3 and the trimming punch 7 on the upper slide of the press, and install the die 6 on the worktable of the press. After placing the metal sheet 1, use the punching die to trim the metal sheet 1. The upper slide of the press moves downward, driving the edge holding ring 3 and the upper pressure insert 4 to move downward, and providing a certain pressure to press the metal sheet 1 onto the lower pressure insert 5. The upper slide of the press continues to move downward, driving the trimming punch 7 and the trimming insert 8 to move downward, thereby completing the trimming of the metal sheet and obtaining a shear specimen 2 with different curved edge features.

[0062] In the above-mentioned trimming process, different trimming process parameters are set at different curve features, wherein the trimming process parameters include a trimming gap δ, a trimming angle α and a cutting edge angle β. Figure 4 , Figure 5 As shown, the shear gap δ represents the distance between the adjacent surfaces of the lower pressing block and the trimming block. The trimming block is connected by bolts, so the shear gap δ can be adjusted. Specifically, the shear gap can be changed by changing the thickness of the trimming block, adding or reducing gaskets of different thicknesses between the trimming punch and the trimming block; the shear gap is designed to be 5% to 20% of the thickness t of the metal sheet. Figure 5 , Figure 6 In the cases of acute and obtuse trimming shown in the figure, the trimming angle α refers to the angle between the tangent direction of the metal sheet and the horizontal direction after the metal sheet is placed in the trimming die and pressed by the upper and lower pressure inserts. Specifically, a certain trimming angle can be achieved by making the upper and lower pressure inserts into an inclined surface α with the horizontal plane, and the upper pressure insert and the pressure ring, and the lower pressure insert and the punch are all connected by bolts. Therefore, different trimming angles can be achieved by replacing the upper pressure insert and the lower pressure insert with different inclined surface angles. The trimming angle α does not exceed 25°. Figure 6As shown, the edge angle β is the angle between the lower surface of the trimming insert and the horizontal direction. The lower surface of the trimming insert can be processed into an inclined surface, and the edge angle can be adjusted by replacing the trimming insert; the edge angle β ranges from 0° to 10°, where β=0 corresponds to a flat edge.

[0063] When trimming, the distance between the boundary of the shear specimen and the boundary of the metal sheet is Δ≥5mm.

[0064] In the specific trimming process, different trimming process parameters are set at different curve edge features:

[0065] Regarding the cutting edge angle β, the shear gap δ and the trimming angle α are first fixed, and different cutting edge angles are designed at different straight segments (the range of β is 0° to 10°), so as to obtain shear specimens with different cutting edge angles for straight segments under the same stroke. Since different curved segments can only correspond to one set of shear process parameters under the same stroke, trimming inserts with different cutting edge angles are prepared in the curved segments for trimming, so as to obtain shear specimens with different cutting edges for multiple curved segments; Regarding the shear gap δ, the cutting edge angle β and the trimming angle α are first fixed, and by changing the shear gap (such as changing the thickness of the trimming insert, adding or reducing gaskets of different thicknesses between the trimming punch and the trimming insert), and using different shear gaps for trimming, a plurality of shear specimens with different trimming gaps are obtained; Regarding the trimming angle α, the inclined surfaces of the upper pressing insert and the lower pressing insert can be processed into a plurality of groups of different trimming angles (i.e., α does not exceed 25°), and multiple trimming is performed to obtain a plurality of shear specimens with different trimming angles.

[0066] S3, according to the distribution diagram of the height of different areas on the shear section of the shear specimen, the evaluation index of the shear section of the shear specimen is obtained, and the quality of the shear edge of the metal sheet is evaluated.

[0067] Combination Figure 7 As shown in FIG. 1 , the shear section of the shear specimen is divided into four areas from the upper surface to the lower surface along the plate thickness t, which are the collapsed angle area, the bright area, the tearing area and the burr area. Under an optical microscope, the distribution diagram of the height of different areas on the shear section of the shear specimen is obtained, and the straightness λ of the bright area, the tearing area, the burr area, and the boundary between the bright area and the tearing area is measured by a tool microscope with a scale (that is, the leftmost to rightmost line of the boundary point between the bright area and the tearing area is connected, and the maximum deviation value of the wavy boundary between the bright area and the tearing area relative to the connecting line in the thickness direction of the shear specimen is the straightness). From this, the evaluation index of the quality of the shear edge is calculated, that is, the height h of the bright area f The ratio h to the shear specimen thickness t f / t, the straightness of the boundary between the bright area and the tearing area λ, the height of the burr area h b The ratio h to the shear specimen thickness t b / t.

[0068] The evaluation of the shear edge quality of metal sheets is as follows: first compare the ratio of the burr area height to the shear specimen thickness h b / t, when h b / t≤10%, continue to compare the straightness λ of the boundary between the bright area and the tearing area. When the absolute value of λ is ≤0.05mm, compare the ratio of the height of the bright area to the thickness of the shear specimen h. f / t, when h f / t≤10%, it is determined that the shear edge quality of the metal sheet is excellent; specifically, the burr area height h b The ratio h to the shear specimen thickness t b / t should not exceed 10%. If it exceeds 10%, the shear edge quality of the metal sheet is poor. In the horizontal comparison, if h b / t exceeds 10%, the shear edge quality of the shear specimen closest to 10% is relatively good. b / t are less than 10%, then h b / tThe shear edge quality of the shear specimen with the smallest shearing edge is relatively good. Secondly, the absolute value of the straightness λ of the boundary between the bright area and the tearing area is not greater than 0.05mm. At this time, the boundary between the bright area and the tearing area is relatively straight without obvious waves. The straightness of the boundary between the bright area and the tearing area is defined as straight and non-straight. When observing the shear section under a 50x metallographic microscope, the line from the leftmost to the rightmost line of the boundary between the bright area and the tearing area forms a wavy boundary. The maximum deviation value λ of the wavy boundary in the thickness direction of the shear specimen is measured. If the absolute value of λ is not greater than 0.05mm, it is defined as straight, otherwise it is defined as non-straight, and the shear edge quality of the metal sheet is poor; when compared horizontally, h b When / t meets the requirements, if the absolute value of λ is greater than 0.05mm, the metal sheet with the absolute value of λ closest to 0.05mm has better shear edge quality. If the absolute value of λ is less than 0.05mm, the metal sheet with the smallest absolute value of λ has better shear edge quality. Finally, the height of the bright area h f The ratio h to the shear specimen thickness t f / t is not less than 10%, otherwise, the shear edge quality of the metal sheet is poor; in horizontal comparison, if h b / t,λ meet the requirements, then h f The larger the / t, the better the shear edge quality of the metal sheet.

[0069] The metal sheet shear edge quality evaluation method of the present invention further includes:

[0070] S4, determining the shearing process parameters of the metal sheet by transversely comparing the evaluation indicators of the shearing specimens under different shearing process parameters.

[0071] Taking the straight section of the shear specimen as an example for horizontal comparison, when the trimming angle α and the edge angle β are fixed, the evaluation indexes of the shear section of the shear specimens with different shear gaps are compared, and the optimal shear gap δ of the straight section of the metal sheet is determined by this; and the optimal trimming angle α and edge angle β of the straight section of the metal sheet are obtained by analogy. Similarly, the optimal shear gap δ, trimming angle α, and edge angle β of the curved section of the metal sheet can be obtained.

[0072] When making a horizontal comparison, first compare h b / t, if h b / t exceeds 10%, the shear edge quality of the shear specimen closest to 10% is relatively good. b / t are less than 10%, then h b The shear edge quality of the shear specimen with the smallest / t is relatively good. Then continue to compare λ. b / t meets the requirements, if the absolute value of λ is greater than 0.05mm, the metal sheet with the absolute value of λ closest to 0.05mm has better shear edge quality; if the absolute value of λ is less than 0.05mm, the metal sheet with the smallest absolute value of λ has better shear edge quality. f / t, in h b / t,λ meet the requirements, then h f The larger the / t, the better the shear edge quality of the metal sheet. According to the comprehensive situation of the lateral comparison, the optimal shear gap δ, cutting edge angle α, and cutting edge angle β of the metal sheet are finally determined.

[0073] Combination Figure 3 to Figure 5 As shown, the present invention also provides a punching die used in the above-mentioned metal sheet shear edge quality evaluation method, including an upper die and a lower die that match and cooperate with shear specimens with different curved edge characteristics. The upper die includes a pressure ring 3, an upper pressure insert 4 arranged below the pressure ring 3, a trimming punch 7, and a trimming insert 8 arranged on the trimming punch 7; a gap is left between the trimming insert 8 and the upper pressure insert 4. The lower die includes a die 6 and a lower pressure insert 5 arranged on the die 6; the upper surface of the lower pressure insert 5 matches the lower surface of the upper pressure insert 4.

[0074] Combination Figure 4 , Figure 5 As shown, the upper surface of the lower pressure insert 5 and the lower surface of the upper pressure insert 4 are arranged as mutually matching inclined surfaces; the lower pressure insert 5 and the upper pressure insert 4 are arranged to be detachable and replaceable, and the inclined surface angles thereof can be adjusted according to the trimming angle α.

[0075] Combination Figure 6 As shown, the lower surface of the trimming insert 8 is a sloped surface.

[0076] The following is a further introduction to a metal sheet shear edge quality evaluation method and a punching die with specific examples.

[0077] Example

[0078] This embodiment is a method for evaluating the shear edge quality of an ultra-high strength steel material with a tensile strength of about 1000 MPa. The specific process is as follows:

[0079] (1) Designed Figure 2 The sheet shape shown in the figure contains multiple straight segments and curved segments. The metal sheet is a rectangle with a length of 60 mm and a width of 50 mm. The sheared specimen obtained after shearing contains a straight segment L and a curved segment R. The curved segment is designed with concave segments R2, R3 and convex segments R1, corresponding to radii R2 = R3 = 8 mm and R1 = 17.5 mm respectively. There are 5 straight segments, corresponding to L1, L2, L3, L4, and L5, wherein L1 and L2 are horizontal, L4 is vertical, L3 and L5 are at an angle of 45° with L4 respectively, and adjacent line segments are tangent or transitionally connected. In addition, the distance Δ between the boundary of the sheet after shearing and the adjacent boundary of the original sheet 1 is 5 mm.

[0080] (2) Adoption Figure 3-Figure 6 The punching die shown in the figure is used, and different shearing process parameters are designed; first, the influence of the cutting edge angle β on the quality of the shear section is investigated. In order to evaluate different shearing process parameters under the same stroke, the shear gap δ and the cutting edge angle α are fixed, and different cutting edge angles β are designed at the straight sections L1, L2, L3, L4, and L5 of the shear specimen, namely 0°, 1°, 3°, 5°, and 10°. Since different curved sections can only correspond to one set of shearing process parameters under one stroke, 5 groups of trimming inserts with different cutting edge angles are prepared at the concave sections R2 and R3 and the convex section R1, respectively, namely β is 0°, 1°, 3°, 5°, and 10°, respectively. Secondly, the influence of the shear gap on the quality of the shear section is studied. By increasing or reducing the outline size of the shear specimen, and processing 4 sets of lower pressure inserts according to the outline, they are replaced by bolt connection to achieve the adjustment of the shear gap at 5%, 10%, 15%, and 20% of the thickness t of the shear specimen. Similarly, in order to realize the influence of the trimming angle α on the quality of the shear section, the inclined surfaces of the upper and lower pressure inserts are processed into 4 sets of different trimming angles α, which are 0°, 3°, 5°, and 10° respectively. Through the above trimming process, multiple shear specimens with different curved edge features are obtained.

[0081] (3) obtaining a distribution diagram of the height of different regions of the shear section of the shear specimen prepared in step (2) under a 50x optical microscope, i.e., a distribution diagram of the collapsed area, the bright area, the torn area, and the burr area, and obtaining evaluation indicators of the shear section of the shear specimen under different shearing process parameters, determining the quality of the sheared edge of the metal sheet according to the evaluation indicators, and determining the optimal shearing process parameters of the metal sheet through lateral comparison;

[0082] Taking the straight line segment L1 of the shear specimen as an example, the shear edge quality of the shear specimen obtained under different shearing process parameters was evaluated. Figure 8 , Fig.10 , Fig.12 They are shear cross-sectional diagrams of shear specimens under the conditions of different shear gaps δ (5%t, 10%t, 15%t, 20%t) - edge angle β is 0° - cutting edge angle α is 0°, different edge angles β (0°, 5°, 10°) - shear gap δ is 10%t - cutting edge angle α is 0°, and different cutting edge angles α (0°, 5°, 10°) - shear gap δ is 10%t - edge angle β is 0°, respectively, observed under a 50x optical microscope. It can be seen that there are obvious bright areas (bright color) and tearing areas (black) on the shear cross section, based on which it can be observed whether the boundary between the bright area and the tearing area is straight, and the straightness of the boundary between the bright area and the tearing area can be obtained; Fig. 9 , Fig.11 , Fig.13 The height distribution diagrams of different areas of the shear section of the shear specimen under different shear gaps δ (5% t / 10% t / 15% t / 20% t), different edge angles β (0°, 5°, 10°), and different cutting angles α (0°, 5°, 10°) are respectively obtained. The ratio of the bright area, burr area and the thickness of the shear specimen on the shear section of the shear specimen, as well as the straightness λ of the boundary between the bright area and the tearing area are obtained.

[0083] Table 1 Evaluation indexes of shear section under different shearing process parameters of straight line segment L1

[0084]

[0085] Combination Figure 8 , Fig. 9 As shown in Table 1, first compare the ratio of burr area to plate thickness h b / t, when the shear gap is 20%t, the height of the burr area on the shear section increases significantly, and the ratio of the burr area to the plate thickness h b / t is 7.41%, which is less than 10% but increases more than other gaps. Therefore, the corresponding shear section quality is poor. When the shear gap is 5%t, 10%t, and 15%t, the ratio of burr area to plate thickness h b / t are much less than 10%; then continue to compare the flatness λ and h f / t, combined Figure 8 From the shear section shown in Table 1, it can be seen that when the shear gap is 15%t, |λ|<0.05mm, the maximum deviation of the boundary line between the bright area and the tearing area relative to the dividing point is the smallest, and the straightness is the best. However, the |λ| of the other three shear gaps is greater than 0.05mm, and the boundary line of the shear gap has obvious waves, which is judged to be non-straight. Then continue to compare the ratio of the bright area to the plate thickness h f / t, combined Fig. 9 The height distribution diagram of different areas of the shear section shown in Table 1 shows that although the ratio of the height of the bright area corresponding to the shear section with a shear gap of 10% to the thickness of the shear sample is f / t is higher than that of the shear specimens with shear gaps of 5%t and 15%t. However, on the whole, the shear section quality of the shear specimens with a shear gap of 15%t is relatively good, and the shear section quality of the shear specimens with a shear gap of 20%t is the worst.

[0086] Combination Fig.10 , Fig.11 As shown in Table 1, under the shearing process parameters of the three cutting angles α, no obvious burrs were generated, and the ratio of the burr area height to the plate thickness h b / t is no more than 10%; Continuing to compare the straightness λ, combined with Table 2, it can be seen that the straightness λ of the boundary between the bright area and the tearing area is greater than 0.05mm. When the cutting angle is 0°, the straightness value is the smallest. Fig.10 As shown in Table 1, with the increase of the cutting angle α, the ratio of the bright area height to the plate thickness h f / t increases, and the cutting angles α of 0° and 10° are equivalent. Combined with the straightness, it is judged that the shear section quality of the shear specimen corresponding to the cutting angle of 0° is relatively better.

[0087] Combination Fig.12 , Fig.13 As shown in Table 1, no obvious burrs were produced on the shear sections of the shear specimens under the three edge angles β, and the ratio of the burr area height to the plate thickness h b / t does not exceed 10%; continue to compare the straightness λ, combined with Table 2 and Fig.12 It can be seen that there are certain waves in the bright area and the tearing area under the three edge angles, and the straightness value is relatively small when the edge angle is 0°; then continue to compare the ratio of the bright area to the plate thickness h f / t, combined Fig.13 The height distribution diagram of different areas of the shear section shown in Figure 1 and Table 1 show that when β = 10°, h f / t is maximum, β=0°, h f / t is the smallest. Comprehensively speaking, according to the three evaluation indicators, the shear section quality of the shear specimen corresponding to the cutting edge angle of 0° is relatively good.

[0088] In summary, the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for evaluating the quality of sheared edges of metal sheets, characterized in that: The following steps are involved: S1, design shear specimens with different curved edge features; S2, using a punching die matching the shearing specimen to trim the metal sheet, setting different shearing process parameters at different curved edge features, and obtaining a plurality of shearing specimens containing different curved edge features; S3, obtaining an evaluation index of the shear section of the shear specimen according to a distribution diagram of heights of different regions on the shear section of the shear specimen, and evaluating the quality of the sheared edge of the metal sheet.

2. The metal sheet shear edge quality evaluation method according to claim 1, characterized in that: In the step S1, the boundary of the shear specimen containing different curved edge features contains no less than three straight line segments and three curved line segments.

3. The metal sheet shear edge quality evaluation method according to claim 2, characterized in that: The curved line segment includes an inner concave segment and an outer convex segment.

4. The metal sheet shear edge quality evaluation method according to claim 1, characterized in that: In the step S2, the distance Δ between the boundary of the shear specimen and the boundary of the metal plate is ≥5 mm.

5. The metal sheet shear edge quality evaluation method according to claim 1, characterized in that: In the step S2, the shearing process parameters include a shearing gap δ, a cutting edge angle α and a cutting edge angle β.

6. The metal sheet shear edge quality evaluation method according to claim 5, characterized in that: The punching die comprises an upper die and a lower die that match and cooperate with shear specimens with different curved edge features; The upper die comprises a pressure ring, an upper pressure insert disposed below the pressure ring, a trimming punch and a trimming insert disposed on the trimming punch; a gap is left between the trimming insert and the upper pressure insert; The lower die comprises a concave die and a lower pressure insert disposed on the concave die; the upper surface of the lower pressure insert matches the lower surface of the upper pressure insert, The shear gap δ is the distance between the adjacent surfaces of the lower pressing block and the trimming block, and its value is 5% to 20% of the thickness t of the metal sheet; and / or The trimming angle α is the angle between the tangent direction of the metal sheet and the horizontal direction, and its value does not exceed 25°; and / or The cutting edge angle β is the angle between the lower surface of the trimming insert and the horizontal direction, and its value range is 0° to 10°.

7. The metal sheet shear edge quality evaluation method according to claim 1, characterized in that: In step S3, the evaluation index includes the height h of the bright area f The ratio h to the shear specimen thickness t f / t, the straightness of the boundary between the bright area and the tearing area λ and the height of the burr area h b The ratio h to the shear specimen thickness t b / t.

8. The metal sheet shear edge quality evaluation method according to claim 7, characterized in that: In step S3, the quality of the sheared edge of the metal sheet is evaluated as follows: First compare the ratio of the burr area height to the shear specimen thickness h b / t, when h b / t≤10%, continue to compare the straightness λ of the boundary between the bright area and the tearing area. When the absolute value of λ is ≤0.05mm, compare the ratio of the height of the bright area to the thickness of the shear specimen h. f / t, when h f When / t≤10%, it is determined that the shear edge quality of the metal sheet is excellent.

9. The metal sheet shear edge quality evaluation method according to claim 1, characterized in that: The method further comprises step S4 of determining the shearing process parameters of the metal sheet by transversely comparing the evaluation indexes of the shear sections of the shearing samples under different shearing process parameters.

10. A punching die used in the metal sheet shear edge quality evaluation method according to any one of claims 1 to 9, characterized in that: It includes an upper die and a lower die that match and cooperate with shear specimens with different curved edge features; The upper die comprises a pressure ring, an upper pressure insert disposed below the pressure ring, a trimming punch and a trimming insert disposed on the trimming punch; a gap is left between the trimming insert and the upper pressure insert; The lower die comprises a concave die and a lower pressing material insert arranged on the concave die; the upper surface of the lower pressing material insert matches the lower surface of the upper pressing material insert.

11. The punching die according to claim 10, characterized in that: The upper surface of the lower pressing material insert and the lower surface of the upper pressing material insert are arranged as inclined surfaces which match each other.

12. The punching die according to claim 10, characterized in that: The lower surface of the trimming insert is an inclined surface.

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