Special-shaped die for evaluating forming performance of thin plate under nonlinear strain path

Abstract

The invention relates to a special-shaped die for evaluating the forming performance of a thin plate under a nonlinear strain path, which belongs to the technical field of metal plastic processing and dies, and comprises a plurality of special-shaped concave dies, a special-shaped convex die 2, a blank holder 4, a screw 3 and a support rod 5, the multiple special-shaped female dies and the special-shaped male dies 2 are combined for use according to the test requirements of the test pieces, and the fracture limits of the metal test pieces of the same size under multiple non-linear strain paths are obtained; the prepared metal bulging part is suitable for forming performance evaluation under a non-linear strain path, various strain paths and forming limit points under the continuous and non-linear strain path are generated by means of cooperation of the special-shaped male die and the female die, the strain paths are more diversified, and by comparing forming limit curves of a plate under the linear strain path, the forming performance of the metal bulging part is evaluated. Therefore, the influence rule of the nonlinear strain path on the forming limit of the metal test piece is researched and verified, and the test cost is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of metal plastic processing and die technology, and particularly relates to a special-shaped die for evaluating the forming performance of thin plates under non-linear strain paths. Background Art

[0002] The complexity of the sheet metal stamping process and the diversity of influencing factors have always been the key points and difficulties in the field of thin sheet stamping. With the development of industrial scale effect, the optimization control of stamping becomes increasingly important. The forming limit curve is the criterion for the forming limit of sheet metal stamping and an important reference for formulating the forming process flow. However, its strain path correlation severely restricts the development of the forming limit curve. At present, the experimental research on the influence of non-linear strain paths on the forming limit curve of sheet metal is quite limited, mainly because the experimental difficulty is large and the cost is high.

[0003] Currently, for the fracture prediction of local profiles with complex strain paths in actual production, there is a large deviation between the forming limit diagram (FLD) under linear strain paths and the experimental results, that is, the FLD under linear strain paths cannot predict the forming limit of sheet metal under non-linear strain paths. Research shows that FLD is linear path-dependent.

[0004] At present, the research on the forming limit of metal sheet under non-linear strain paths mainly includes two parts: theoretical and experimental research. In the theoretical research part, scholars have derived the forming limits under different strain paths based on instability criteria such as Swift, Hill, M-K, C-H, and MMFC according to the stress and strain states during the sheet metal stamping process, and certain results have been obtained. However, the theoretical derivation is based on various assumptions, and there is currently no generally recognized method, and the accuracy of theoretical prediction cannot be guaranteed. In the experimental research part, generally, the sheet metal is pre-strained first, and then a rigid die bulging test is carried out, or a multi-pass stamping is achieved by nesting the punch and die, etc. However, this experimental method has an unloading process, and the strain path is discontinuous, which does not conform to the engineering reality. Whether using three-dimensional laser cutting or nesting the punch and die to achieve the non-linear strain path of the sheet metal, the development cost and experimental cost are relatively high.

[0005] Currently, Chinese Utility Model with publication number CN 211528095U provides a test platform for realizing the forming limits of thin sheets under non-linear and linear strain paths. The test platform uses an upper punch in the form of a quasi-flat punch and an ellipsoidal lower punch to punch the specimen to obtain the complex strain path of the fracture point on the specimen surface.

[0006] The Chinese patent with the publication number CN 106825118B provides a forming limit test device and its test method for measuring under non-linear strain paths. The punch and the die of this test device are both hollow-shaped, and a certain degree of forming operation is performed on the test specimen by moving the die. By matching different initial specimen sizes and the working positions of the laser cutting head, the forming limit test under different strain paths is achieved.

[0007] For the experimental platform in the above patent, its invention purpose is to change the strain path of the specimen rupture point. The die structure and dimensions are modified based on the die size standard in "G / T 15825.3-1995 Metallic materials - Sheet - Forming properties and test methods - Forming-limit diagram (FLD) test", and it can be directly used in general sheet metal forming testing machines. While standardizing the experimental steps, it can also reduce the experimental cost. Summary of the Invention

[0008] In view of the above problems, the present invention provides a special-shaped die for evaluating the forming performance of thin plates under non-linear strain paths. Relying on the cooperation of the special-shaped punch and the die, metal bulging parts with various rupture shapes are obtained, as well as the strain paths and forming limit points under various continuous non-linear strain paths. The prepared metal bulging parts are suitable for evaluating the forming performance under non-linear strain paths. By comparing the forming limits of the sheet under linear strain paths, the influence law of non-linear strain paths on the forming limits of metal specimens is studied and verified, significantly reducing the test cost.

[0009] The present invention provides a special-shaped die for evaluating the forming performance of thin plates under non-linear strain paths, including:

[0010] Multiple special-shaped dies 1, special-shaped punch 2, blank holder 4, support rod 5; The multiple special-shaped dies are combined with the special-shaped punch 2 to obtain various ruptured metal bulging parts of the metal sheet and the corresponding forming limits under various non-linear strain paths.

[0011] The special-shaped punch 2 is arranged inside the blank holder 4, and the special-shaped punch 2 is connected to the support rod 5 through a screw 3;

[0012] In an embodiment of the present invention, any special-shaped die 1 is selected, and the special-shaped die 1 is connected to the blank holder 4;

[0013] The metal sheet is placed between the special-shaped die and the blank holder 4; The special-shaped punch is arranged inside the blank holder 4 along the z-axis, and the special-shaped punch 2 is connected to the testing machine through the support rod 5; The support rod 5 provides a longitudinal supporting force to the special-shaped punch 2; The special-shaped punch 2 moves upward under the longitudinal supporting force inside the blank holder 4, and the metal sheet is rigidly bulged inside the corresponding special-shaped die.

[0014] Further, the metal sheet complies with the requirements of GBT 24171.2-2009 "Determination of Forming Limit Curves for Thin Metal Sheets and Strips - Part 2: Determination of Laboratory Forming Limit Curves".

[0015] In an embodiment of the present invention, the special-shaped punch 2 includes a punch head 2-1 and a punch base 2-2; the punch head 2-1 is semi-cylindrical, including an arc-shaped top surface 2-11, a semi-circular side surface one 2-12, a semi-circular side surface two, and a bottom surface one;

[0016] The punch base 2-2 includes an outer peripheral wall one 2-21, a top surface, a bottom surface two, and an inner cavity 2-22;

[0017] The bottom surface one of the punch head 2-1 is arranged at the middle position of the top surface of the punch base 2-2, and the semi-circular side surface one 2-12 and the semi-circular side surface two are respectively perpendicular to the top surface of the punch base 2-2 along the positive z-axis; both ends of the arc-shaped top surface 2-11 are respectively connected to the semi-circular side surface one 2-12 and the semi-circular side surface two;

[0018] The outer peripheral wall is respectively connected to the top surface and the bottom surface two; the bottom surface one of the punch head 2-1 is connected to the top surface of the punch base 2-2; the inner cavity 2-22 penetrates the bottom surface two and is arranged inside the punch base 2-2 for connecting the support rod 5; the support rod 5 is also connected to the testing machine, and the testing machine provides an upward support force along the z-axis to the punch base;

[0019] Further, the height ratio of the punch base 2-2 to the inner cavity 2-22 of the punch head 2-1 is: 4:3;

[0020] Exemplarily, the height of the punch base 2-2 is 40 mm, and the height of the inner cavity 2-22 is 30 mm; it can be understood that during the rigid bulging test, the special-shaped punch receives an upward support force along the z-axis, the arc-shaped top surface 2-11 contacts the metal sheet, and the metal sheet is pushed upward in the shape of the arc-shaped top surface, and rigid bulging is completed in the corresponding special-shaped die cavity to obtain a ruptured metal bulging part;

[0021] In an embodiment of the present invention, the multiple special-shaped die cavities are all die cavity parts with elliptical grooves;

[0022] Further, the multiple special-shaped die cavities 1 include a special-shaped die cavity one 1-1, a special-shaped die cavity two 1-2, a special-shaped die cavity three 1-3, and a special-shaped die cavity four 1-4; each special-shaped die cavity 1 includes an elliptical groove, and by changing the short radius of the elliptical groove, elliptical grooves with different diameters are obtained, and the metal sheet realizes different degrees of non-linear strain paths based on the elliptical grooves with different diameters;

[0023] It can be understood that when the short radius of the elliptical groove is equal to the long radius, it is a circular groove;

[0024] Furthermore, the special-shaped female die 1-1 includes a first end face, a second end face, an elliptical groove 1-11, and a first reinforcing rib 1-12;

[0025] The elliptical groove 1-11 penetrates through the first end face and the second end face and is located at the middle position of the special-shaped female die 1-1; the first reinforcing rib is arranged on the first end face and is used for connecting the groove of the blank holder 4 to play a role in fixing the blank holding;

[0026] The special-shaped female die 1 is connected to the blank holder 4 and the metal sheet through an annular reinforcing rib, which is used for strengthening the blank holding force and increasing the binding force on the metal sheet;

[0027] Furthermore, the elliptical groove 1-11 includes a first major diameter 1-101 and a first minor diameter 1-102;

[0028] Furthermore, the special-shaped female die 1-2 includes a third end face, a fourth end face, an elliptical groove 1-21, and a second reinforcing rib;

[0029] The elliptical groove 1-21 penetrates through the third end face and the fourth end face and is located at the middle position of the special-shaped female die 1-2; the second reinforcing rib is arranged on the third end face and is used for connecting the groove of the blank holder to play a role in fixing the blank holding;

[0030] Furthermore, the elliptical groove 1-21 includes a second major diameter 1-201 and a second minor diameter 1-202;

[0031] Furthermore, the special-shaped female die 1-3 includes a fifth end face, a sixth end face, an elliptical groove 1-31, and a third reinforcing rib;

[0032] The elliptical groove 1-31 penetrates through the fifth end face and the sixth end face and is located at the middle position of the special-shaped female die 1-3; the third reinforcing rib is arranged on the fifth end face and is used for connecting the groove of the blank holder to play a role in fixing the blank holding;

[0033] Furthermore, the elliptical groove 1-3 includes a third major diameter 1-301 and a third minor diameter 1-302;

[0034] Furthermore, the special-shaped female die 1-4 includes a seventh end face, an eighth end face, an elliptical groove 1-401, and a fourth reinforcing rib;

[0035] The elliptical groove 1-41 penetrates through the seventh end face and the eighth end face and is located at the middle position of the special-shaped female die 1-4; the fourth reinforcing rib is arranged on the seventh end face and is used for connecting the groove of the blank holder to play a role in fixing the blank holding;

[0036] Furthermore, the elliptical groove 1-41 includes a major diameter 1-401 and a minor diameter 1-402;

[0037] Exemplarily,

[0038] Exemplarily, the length ratio relationship of the major diameter 1-101, the major diameter 1-201, the major diameter 1-301, and the major diameter 1-401 is: 1:1:1:1;

[0039] The expression of the relationship between the minor diameter and the major diameter is:

[0040] D l = αDx

[0041] where D l represents the major diameter of the elliptical groove, Dx represents the minor diameter of the elliptical groove, and α represents the formability coefficient.

[0042] The length ratio relationship of the minor diameter 1-102, the minor diameter 1-202, the minor diameter 1-302, and the minor diameter 1-402 is: 45:65:85:105;

[0043] Further, the lengths of the major diameter 1, the major diameter 2, the major diameter 3, and the major diameter 4 are 105 mm;

[0044] Further, the lengths of the minor diameter 1, the minor diameter 2, the minor diameter 3, and the minor diameter 4 are respectively: 45 mm, 65 mm, 85 mm, 105 mm; the outer diameter of the special-shaped punch 2 is 100 mm, and the inner diameter of the blank holder 2 is 100.2 mm.

[0045] In the present invention, the special-shaped die is used to conduct a forming limit test on the sheet metal under a continuous non-linear strain path. At a lower test cost, for different deformation characteristics, the influence of various continuous non-linear strain paths on the forming limit of the metal sheet is studied, providing test data for the scientific research problem of the strain path correlation of the forming limit criterion of the metal sheet under complex stamping conditions. Especially, it provides guidance for the optimization process of difficult-to-process metal materials such as ultra-high strength steel widely used in the future, and has important theoretical and practical values.

[0046] Another object of the present invention also provides a method for using a special-shaped die for evaluating the forming performance of a thin sheet under a non-linear strain path, including:

[0047] When conducting a steel die bulging test, each special-shaped female die 1 is sequentially connected to the blank holder 4 through the annular reinforcing rib 6 and the reinforcing rib;

[0048] Place the metal sheet to be tested between the special-shaped female die 1 and the blank holder 4; arrange the special-shaped male die 1 along the z-axis inside the blank holder 4, and connect the special-shaped male die 2 to the testing machine through the support rod 5; the testing machine provides an upward supporting force along the z-axis to the special-shaped male die 2 through the support rod 5;

[0049] The special-shaped male die 2 is supported upward in the blank holder 4, and the arc-shaped top surface of the special-shaped male die contacts the metal sheet to be tested, pushing the metal sheet to be tested upward in the shape of the arc-shaped top surface, and completing rigid bulging in the elliptical groove of the corresponding special-shaped female die to obtain metal bulging parts of multiple shapes;

[0050] Measure the strain of the metal bulging parts of each shape through the DIC strain system or grid measurement technology to obtain the forming limit data of the metal sheet under various non-linear strain paths;

[0051] Evaluate the forming performance of the metal sheet under loading conditions based on the forming limit data of the metal sheet under various non-linear strain paths.

[0052] It also includes: obtaining the forming limit data of the metal sheet under the linear strain path under the test conditions;

[0053] Compare the forming limit data of the metal sheet under the linear strain path with the forming limit data under various non-linear strain paths to obtain the influence law of the non-linear strain path on the forming limit of the metal sheet;

[0054] Predict the deformation limit during the forming process of the metal sheet under loading conditions based on the influence law of the non-linear strain path on the forming limit of the metal sheet.

[0055] Compared with the prior art, the present invention has at least the following beneficial effects:

[0056] (1) Through the cooperation of one male die and four female dies, the forming limit points of the sheet under four continuous non-linear strain paths can be directly obtained with the mold of the present invention. The test is easy to implement and the cost is relatively low;

[0057] (2) Based on the standard experimental specimens of the standard forming limit test, the mold of the present invention uses specimens with different width specifications and different angles with the rolling direction, and the forming limit points and their experimental strain paths of the sheet under various complex non-linear strain paths can be obtained. By comparing with the forming limit curve under the linear strain path, the influence of the strain path on the forming limit of the sheet can be quantitatively analyzed. Description of the Drawings

[0058] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention.

[0059] Figure 1Cross-sectional view of the rigid die bulging test die for metal specimens of the present invention;

[0060] Figure 2 (a)-(d) Schematic diagrams of the top view, front view, side view and physical diagram of the special-shaped punch in the embodiment of the present invention;

[0061] Figure 3 Schematic diagram of the top view of the special-shaped female die 1 in the embodiment of the present invention;

[0062] Figure 4 Schematic diagram of the top view of the special-shaped female die 2 in the embodiment of the present invention;

[0063] Figure 5 Schematic diagram of the top view of the special-shaped female die 3 in the embodiment of the present invention;

[0064] Figure 6 Schematic diagram of the top view of the special-shaped female die 4 in the embodiment of the present invention;

[0065] Figure 7 Schematic diagram of the physical diagram of the special-shaped punch and multiple special-shaped female dies in the embodiment of the present invention;

[0066] Figure 8 Schematic diagram of the specimen after the rigid die bulging test of the rigid die bulging test die for metal specimens in the embodiment of the present invention;

[0067] Figure 9 Schematic diagram of the comparison between the test and simulation results of the rigid die bulging test die for metal specimens and the DP980 test FLC in the embodiment of the present invention.

[0068] Reference numerals:

[0069] Special-shaped female die 1, special-shaped punch 2, screw 3, blank holder 4, support rod 5, special-shaped female die 1-1, special-shaped female die 1-2, special-shaped female die 1-3, special-shaped female die 1-4, elliptical groove 1-11, reinforcing rib 1-12, major diameter 1-101, minor diameter 1-102, elliptical groove 1-21, major diameter 1-201 and minor diameter 1-202, elliptical groove 1-31, straight radius 1-301, minor diameter 1-302, elliptical groove 1-401, major diameter 1-401, minor diameter 1-402 punch head 2-1, punch holder 2-2, arc top surface 2-11, semi-circular side surface 2-12, outer peripheral wall 2-21, inner cavity 2-22. Detailed implementation manners

[0070] In order to more clearly understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. In addition, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0071] A specific embodiment of the present invention, such as Figures 1-9 , discloses a rigid die bulging test die for metal specimens;

[0072] In order to illustrate the effectiveness of the method proposed by the present invention, the above technical solutions of the present invention will be described in detail through a specific embodiment as follows, specifically including:

[0073] The present invention provides a special-shaped die for evaluating the forming performance of thin plates under non-linear strain paths, including:

[0074] Multiple special-shaped female dies 1, special-shaped male dies 2, blank holders 4, and support rods 5; the multiple special-shaped female dies and the special-shaped male dies 2 are used in combination to obtain various cracked metal bulging parts of the metal sheet and the corresponding forming limits under various non-linear strain paths;

[0075] The special-shaped male die 2 is arranged inside the blank holder 4, and the special-shaped male die 2 is connected to the support rod 5 through screws 3;

[0076] In an embodiment of the present invention, any special-shaped female die 1 is selected, and the special-shaped female die 1 is connected to the blank holder 4;

[0077] The metal sheet is placed between the special-shaped female die and the blank holder 4; the special-shaped male die is arranged inside the blank holder 4 along the z-axis, and the special-shaped male die 2 is connected to the testing machine through the support rod 5; the support rod 5 provides a longitudinal supporting force to the special-shaped male die 2; the special-shaped male die 2 is upward under the longitudinal supporting force inside the blank holder 4, and the metal sheet is rigidly bulged inside the corresponding special-shaped female die;

[0078] Further, the metal sheet meets the requirements of GBT 24171.2-2009 "Determination of Forming Limit Curves for Thin Metal Sheets and Strips - Part 2: Determination of Laboratory Forming Limit Curves".

[0079] In an embodiment of the present invention, the special-shaped male die 2 includes a male die head 2-1 and a male die seat 2-2; the male die head 2-1 is semi-cylindrical, including an arc-shaped top surface 2-11, a semi-circular side surface one 2-12, a semi-circular side surface two, and a bottom surface one;

[0080] The punch holder 2-2 includes an outer peripheral wall 2-21, a top surface, a bottom surface 2, and an inner cavity 2-22;

[0081] The bottom surface 1 of the punch head 2-1 is arranged at the middle position of the top surface of the punch holder 2-2, and the semi-circular side surface 1 2-12 and the semi-circular side surface 2 are respectively perpendicular to the top surface of the punch holder 2-2 along the positive z-axis; both ends of the arc-shaped top surface 2-11 are respectively connected to the semi-circular side surface 1 2-12 and the semi-circular side surface 2;

[0082] The outer peripheral wall is respectively connected to the top surface and the bottom surface 2; the bottom surface 1 of the punch head 2-1 is connected to the top surface of the punch holder 2-2; the inner cavity 2-22 penetrates the bottom surface 2 and is arranged inside the punch holder 2-2 for connecting the support rod 5; the support rod 5 is also connected to a testing machine, and the testing machine provides an upward support force along the z-axis to the punch holder;

[0083] Further, the height ratio of the punch holder 2-2 to the inner cavity 2-22 of the punch head 2-1 is: 4:3;

[0084] Exemplarily, the height of the punch holder 2-2 is 40 mm, and the height of the inner cavity 2-22 is 30 mm; it can be understood that during the rigid bulging test, the special-shaped punch receives an upward support force along the z-axis, the arc-shaped top surface 2-11 contacts the metal sheet, and the metal sheet is pushed upward in the shape of the arc-shaped top surface, and rigid bulging is completed in the corresponding special-shaped die cavity to obtain a ruptured metal bulging part;

[0085] In an embodiment of the present invention, the multiple special-shaped die cavities are all die cavity parts with elliptical grooves;

[0086] Further, the multiple special-shaped die cavities 1 include a special-shaped die cavity 1 1-1, a special-shaped die cavity 2 1-2, a special-shaped die cavity 3 1-3, and a special-shaped die cavity 4 1-4; each special-shaped die cavity 1 includes an elliptical groove, and by changing the short radius of the elliptical groove, elliptical grooves with different diameters are obtained, and the metal sheet realizes different degrees of non-linear strain paths based on the elliptical grooves with different diameters;

[0087] It can be understood that when the short radius of the elliptical groove is equal to the long radius, it is a circular groove;

[0088] Further, the special-shaped die cavity 1 1-1 includes an end surface 1, an end surface 2, an elliptical groove 1 1-11, and a reinforcing rib 1 1-12;

[0089] The elliptical groove 1 1-11 penetrates the end surface 1 and the end surface 2 and is located at the middle position of the special-shaped die cavity 1 1-1; the reinforcing rib 1 is arranged on the end surface 1 for connecting the groove of the blank holder 4 to play a role in fixing the blank holder;

[0090] The special-shaped female die 1 is connected to the blank holder 4 and the metal sheet through an annular reinforcing rib, which is used to strengthen the blank holding force and increase the binding force on the metal sheet;

[0091] Furthermore, the first elliptical groove 1-11 includes a first major diameter 1-101 and a first minor diameter 1-102;

[0092] Further, the second special-shaped female die 1-2 includes a third end face, a fourth end face, a second elliptical groove 1-21 and a second reinforcing rib;

[0093] The second elliptical groove 1-21 penetrates through the third end face and the fourth end face and is located at the middle position of the second special-shaped female die 1-2; the second reinforcing rib is arranged on the third end face and is used to connect the groove of the blank holder to play a role in fixing the blank holder;

[0094] Furthermore, the second elliptical groove 1-21 includes a second major diameter 1-201 and a second minor diameter 1-202;

[0095] Further, the third special-shaped female die 1-3 includes a fifth end face, a sixth end face, a third elliptical groove 1-31 and a third reinforcing rib;

[0096] The third elliptical groove 1-31 penetrates through the fifth end face and the sixth end face and is located at the middle position of the third special-shaped female die 1-3; the third reinforcing rib is arranged on the fifth end face and is used to connect the groove of the blank holder to play a role in fixing the blank holder;

[0097] Furthermore, the third elliptical groove 1-3 includes a third major radius 1-301 and a third minor diameter 1-302;

[0098] Further, the fourth special-shaped female die 1-4 includes a seventh end face, an eighth end face, a fourth elliptical groove 1-401 and a fourth reinforcing rib;

[0099] The fourth elliptical groove 1-41 penetrates through the seventh end face and the eighth end face and is located at the middle position of the fourth special-shaped female die 1-4; the fourth reinforcing rib is arranged on the seventh end face and is used to connect the groove of the blank holder to play a role in fixing the blank holder;

[0100] Furthermore, the fourth elliptical groove 1-41 includes a fourth major diameter 1-401 and a fourth minor diameter 1-402;

[0101] Exemplarily, the length ratio relationship of the first major diameter 1-101, the second major diameter 1-201, the third major diameter 1-301 and the fourth major diameter 1-401 is: 1:1:1:1;

[0102] The expression of the relationship between the minor diameter and the major diameter is:

[0103] D l = αDx

[0104] Among them, D l represents the long diameter of the elliptical groove, Dx represents the short diameter of the elliptical groove, and α represents the formability coefficient.

[0105] The length ratio relationships of the short diameter one 1-102, the short diameter two 1-202, the short diameter three 1-302, and the short diameter four 1-402 are: 45:65:85:105;

[0106] Furthermore, the lengths of the long diameter one, the long diameter two, the long diameter three, and the long diameter four are 105 mm;

[0107] Furthermore, the lengths of the short diameter one, the short diameter two, the short diameter three, and the short diameter four are respectively: 45 mm, 65 mm, 85 mm, 105 mm; the outer diameter of the special-shaped punch 2 is 100 mm, and the inner diameter of the blank holder 2 is 100.2 mm.

[0108] In the present invention, the special-shaped die is used to conduct a forming limit test on a sheet under a continuous non-linear strain path. At a relatively low test cost, for different deformation characteristics, the influence of various continuous non-linear strain paths on the forming limit of metal sheets is studied, providing test data for the scientific research problem of the strain path correlation of the forming limit criterion of metal sheets under complex stamping conditions. In particular, it provides guidance for the optimization process of difficult-to-process metal materials such as ultra-high-strength steel that will be widely used in the future, and has important theoretical and practical value.

[0109] Another object of the present invention also provides a method for using a special-shaped die for evaluating the forming performance of a thin sheet under a non-linear strain path, including:

[0110] When conducting a steel die bulging test, each special-shaped female die 1 is sequentially connected to the blank holder 4 through the annular reinforcing rib 6 and the reinforcing rib;

[0111] Place the metal sheet to be tested between the special-shaped female die 1 and the blank holder 4; arrange the special-shaped punch 1 inside the blank holder 4 along the z-axis, and connect the special-shaped punch 2 to the testing machine through the support rod 5; the testing machine provides an upward support force along the z-axis to the special-shaped punch 2 through the support rod 5;

[0112] The special-shaped punch 2 is supported upward inside the blank holder 4, and the arc-shaped top surface of the special-shaped punch contacts the metal sheet to be tested, and the metal sheet to be tested is pushed upward in the shape of the arc-shaped top surface, and rigid bulging is completed in the elliptical groove of the corresponding special-shaped female die to obtain metal bulging parts of multiple shapes;

[0113] Strain measurements are carried out on metal bulging parts of various shapes through a DIC strain system or grid measurement technology to obtain the forming limit data of metal sheets under various non-linear strain paths;

[0114] Based on the forming limit data of the metal sheet under various non-linear strain paths, the forming performance of the metal sheet under loading conditions is evaluated.

[0115] It also includes: obtaining the forming limit data of the metal sheet under the linear strain path under test conditions;

[0116] The forming limit data of the metal sheet under the linear strain path and the forming limit data under various non-linear strain paths are compared to obtain the influence law of the non-linear strain path on the forming limit of the metal sheet;

[0117] Based on the influence law of the non-linear strain path on the forming limit of the metal sheet, the deformation limit during the forming process of the metal sheet under loading conditions is predicted.

[0118] As mentioned above, it is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A special-shaped die for evaluating the forming performance of a thin plate under nonlinear strain path, characterized in that: include: A plurality of special-shaped concave dies (1), special-shaped convex dies (2), blank holders (4) and support rods (5); A plurality of special-shaped concave dies and a special-shaped convex die (2) are used in combination to obtain a plurality of cracked metal bulged parts of the metal sheet and corresponding forming limits under a plurality of nonlinear strain paths; The special-shaped punch (2) is arranged in the pressure ring (4), and the special-shaped punch (2) is connected to the support rod (5).

2. The special-shaped mold according to claim 1, characterized in that: The plurality of special-shaped dies are all die parts with elliptical grooves; the plurality of special-shaped dies include special-shaped die one (1-1), special-shaped die two (1-2), special-shaped die three (1-3) and special-shaped die four (1-4).

3. The special-shaped mold according to claim 2, characterized in that: The special-shaped concave mold 1 (1-1) includes an elliptical groove 1 (1-11); The oval groove 1 is located in the middle of the special-shaped concave mold 1; The elliptical groove (1-11) includes a long diameter (1-10) 1 and a short diameter (1-102).

4. The special-shaped mold according to claim 1, characterized in that: The special-shaped concave mold 2 (1-2) comprises an elliptical groove 2 (1-21); The second elliptical groove is located in the middle of the second special-shaped concave mold; the second elliptical groove (1-21) includes a second long diameter (1-201) and a second short diameter (1-202).

5. The special-shaped mold according to claim 4, characterized in that: The special-shaped concave mold three (1-3) includes an elliptical groove three (1-31); The oval groove is located in the middle of the special-shaped concave mold three; The elliptical groove three (1-3) includes a straight radius three (1-301) and a short diameter three (1-302).

6. The special-shaped mold according to claim 5, characterized in that: The special-shaped concave mold 4 1-4 includes an elliptical groove 4 (1-401); The oval groove four is located in the middle of the special-shaped concave mold four; The elliptical groove four (1-41) includes a long diameter four (1-401) and a short diameter four (1-402).

7. The special-shaped mold according to claim 6, characterized in that: The length ratio relationship among the long diameter one (1-11), the long diameter two, the long diameter three and the long diameter four is 1:1:1:

1.

8. A method for using a special-shaped die for evaluating the forming performance of a thin plate under a nonlinear strain path, using the special-shaped die according to any one of claims 1 to 7, characterized in that: include: When conducting a steel die bulging test, each of the special-shaped concave dies (1) is sequentially connected to the blank holder (4); The metal plate to be tested is placed between the special-shaped concave die (1) and the blank holder (4); the special-shaped convex die is arranged inside the blank holder (4) along the z-axis, and the special-shaped convex die (2) is connected to the testing machine via a support rod (5); the testing machine provides an upward support force along the z-axis to the special-shaped convex die (2) via the support rod (5); The special-shaped punch (2) is supported upward in the blank holder (4), and the arc-shaped top surface of the special-shaped punch contacts the metal sheet to be tested, so that the metal sheet to be tested is pushed upward in the shape of the arc-shaped top surface, and rigid bulging is completed in the elliptical groove of the corresponding special-shaped concave die (1), thereby obtaining metal bulged parts of multiple shapes; Strain measurements are performed on metal bulging parts of various shapes to obtain the forming limit data of metal sheets under various nonlinear strain paths; The forming performance of the metal sheet under loading conditions is evaluated based on the forming limit data of the metal sheet under various nonlinear strain paths.

9. The method for using a special-shaped die for evaluating the forming performance of a thin plate under a nonlinear strain path according to claim 8, characterized in that: Also includes: The forming limit data of metal sheets under linear strain path are compared with the forming limit data under various nonlinear strain paths, and the influence of nonlinear strain path on the forming limit of metal sheets is obtained. Based on the influence of the nonlinear strain path on the forming limit of the metal sheet, the deformation limit of the metal sheet during the forming process under loading conditions is predicted.

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