Method and device for evaluating the forgeability of a barrel rifling swaging processing material

Abstract

The application discloses a kind of barrel rifling rotary swaging processing material forgeability evaluation method and device, evaluation method uses specially designed lower die and press test material for barrel rotary swaging processing forgeability, test process retains the characteristics of interaction between hammer head, tubular blank and core rod when barrel rotary swaging processing, process plate-shaped sample experiences similar plastic deformation process with rotary swaging.The maximum extrusion depth of sample after loading, filling rate and the attenuation rate of the two indicators from the middle to both sides along the longitudinal direction are used as the forgeability evaluation index, and the forgeability of the material is quantified according to the surface crack of the sample after loading and the above-mentioned forgeability evaluation index.The application can reduce the cost of forgeability test, improve the test efficiency and shorten the time of material forgeability evaluation.The obtained evaluation results can reflect the forgeability of barrel material during rotary swaging processing, and provide reliable reference for selecting suitable material.

Description

Technical Field

[0001] This invention relates to the field of barrel rifling processing, and in particular to a method and apparatus for evaluating the forgeability of barrel rifling rotary forging materials. Background Technology

[0002] Rotary forging is an advanced machining process for rotating parts such as tubes and shafts. It involves high-frequency synchronous forging of a blank using multiple hammers evenly distributed circumferentially. Rotary forging produces forgings with a uniform and dense microstructure, excellent mechanical properties, and good durability, and is widely used in important fields such as automobiles, aerospace, and the military. The barrel is a crucial component of weapons such as artillery, with a complex and precise rifling pattern on its inner wall. The application of rotary forging can significantly improve the strength, service life, and other performance indicators of the barrel. During rotary forging, a mandrel (i.e., a die) is installed inside the tubular blank. The mandrel's surface is machined with the corresponding rifling structure. During forging, the combined action of the hammers and the mandrel causes the blank to undergo directional plastic deformation, thus forming the barrel rifling. The forgeability of a material includes two main aspects: the material's tendency to undergo plastic deformation during forging, and the risk of defects such as cracks and wrinkles during processing. Materials with good forgeability should be able to undergo significant plastic deformation without defects or with a low risk of defects. In the field of rotary forging, material forgeability assessment is a quantitative evaluation of the machinability of candidate materials based on experimental schemes, and it is an important reference indicator for processing feasibility.

[0003] Currently, existing methods for evaluating the forgeability of materials in the steel tube forging industry require specialized rotary forging equipment and dies (i.e., mandrels and hammers). These methods necessitate the pre-processing of tubular blanks from different materials, followed by actual rotary forging tests. This process is costly, inefficient, and makes it difficult to conduct rotary forging experiments on multiple materials, thus limiting its reference value. Furthermore, the forming precision technology for rotary forging of steel tubes in China is not yet mature, and there is a lack of specific methods for testing and evaluating the forgeability of steel tube materials, especially for those based on rotary forging processes. Evaluating the forgeability of steel tube materials is a crucial verification step in the rotary forging process. To address these issues, an efficient and low-cost method for testing and evaluating the forgeability of steel tube materials is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for evaluating the forgeability of barrel rifling rotary forging materials, so as to obtain the evaluation results of the rotary forging forgeability of barrel materials and solve the problems mentioned in the background art.

[0005] The technical solution to achieve the purpose of this invention is as follows:

[0006] A device for evaluating the forgeability of rifling forging materials, used to obtain the forgeability coefficient of the material to be evaluated, includes a lower die, an upper die, and a lower die base; the lower die is fixed on the lower die base;

[0007] The testing device obtains the rifling by equating the rotary forging process of the barrel with the die forging process, that is, equating the radial reciprocating motion of the hammer in the rotary forging process with the vertical motion of the upper die; the radial thickness is The 1 / 4 tubular blank, when unfolded along its inner cylindrical surface, is equivalent to a thickness of Width is The plate-shaped blank; the radial direction of the tubular blank corresponds to the thickness direction of the plate-shaped blank, the unfolding direction corresponds to the transverse direction of the lower die, and the axial direction corresponds to the longitudinal direction of the lower die; the hammer head is equivalent to the upper die, and the mandrel is equivalent to the lower die. The negative and positive lines on the surface of the lower die are designed according to the rifling parameters of the tube. A V-shaped groove is opened on the positive line of the lower die, so that the plate-shaped sample after loading produces measurable indicators that can characterize the forgeability of the material, namely the material extrusion depth on a series of cross sections perpendicular to the longitudinal direction of the plate-shaped sample and the cross-sectional area in the V-shaped groove.

[0008] A method for testing the forgeability of rifling forging materials, using the aforementioned testing device, includes further obtaining the constitutive model of the material to be evaluated through mechanical property testing, using finite element simulation software to numerically simulate the forging process, estimating the maximum load required during actual forging, and adjusting the longitudinal length of the plate-shaped specimen and the amount of thickness reduction during loading based on the results.

[0009] Based on the adjusted plate-shaped specimen size and the thickness reduction during loading, actual die forging tests are conducted on the materials to be evaluated. The test process for each material to be evaluated should be repeated multiple times. The surface of the plate-shaped specimen after loading is observed, and the extrusion depth and cross-sectional area at different cross-sectional positions perpendicular to the longitudinal direction in the V-shaped groove are measured to obtain the forgeability coefficient of each specimen. The forgeability of each material to be evaluated is compared by taking the average value of the forgeability coefficient.

[0010] The significant advantages of this invention compared to existing technologies are:

[0011] (1) The test method is based on the equivalence and transformation of the tube rotation forging process. The tube rotation forging material forging test process does not require the use of rotation forging equipment, which reduces the test cost and can complete the forging test of multiple materials in a short time, thus improving the efficiency of tube rotation forging material forging evaluation.

[0012] (2) The lower die retains the main geometric dimensions of the mandrel through equivalent or transformation during the design process, namely the main design parameters of the barrel rifling. The forgeability test results and rifling parameters have a clear correlation. Compared with the forgeability test results of existing studies, it is more accurate and reliable and has higher reference value.

[0013] (3) It can meet the material forgeability test requirements when different types of barrel rifling and rifling design parameters are changed. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the forgeability testing device in an embodiment of the present invention;

[0015] Figure 2 This is a schematic diagram of the rifling structure in an embodiment of the present invention;

[0016] Figure 3 This is a schematic diagram of the core rod and body tube in an embodiment of the present invention;

[0017] Figure 4 This is a schematic diagram of the equivalent process of tube rotation forging in an embodiment of the present invention;

[0018] Figure 5 This is a schematic diagram of the mold design in an embodiment of the present invention;

[0019] Figure 6 This is a schematic diagram of the mold in an embodiment of the present invention;

[0020] Figure 7 This is a diagram showing the actual stress-strain curve of material A in an embodiment of the present invention;

[0021] Figure 8 This is a diagram showing the actual stress-strain curve of material B in an embodiment of the present invention;

[0022] Figure 9 This is a schematic diagram of the finite element simulation model for forgeability testing in an embodiment of the present invention;

[0023] Figure 10 This is a schematic diagram of the plate-shaped sample before and after loading in an embodiment of the present invention;

[0024] Figure 11 This is a simulation load curve of forgeability testing in an embodiment of the present invention;

[0025] Figure 12 This is a schematic diagram illustrating the specific measurement parameters of the plate-shaped sample in an embodiment of the present invention;

[0026] Figure 13 This is a flowchart of an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1-Lower mold, 2-Clamping fixture, 3-Lower mold base. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] The forgeability testing device for tube rotation forging materials of the present invention, such as Figure 1 As shown, it includes a lower mold, a fixture, and a lower mold base. There are cylindrical pin holes at the center of the bottom surface of the lower mold and the top surface of the lower mold base. The lower mold is positioned by cylindrical pins. The lower mold is fastened to the lower mold base by fixtures on both sides by screws. The lower mold base is connected to the worktable of the forging equipment by bolts.

[0031] To improve the performance of the weapon barrel, a rotary forging process is considered for machining its rifling section. The forgeability of materials A and B for rotary forging needs to be evaluated. The weapon barrel employs left-handed trapezoidal rifling, with the rifling pattern as shown below. Figure 2 As shown, the specific parameters are shown in Table 1 below. The mandrel used for the rotary forging of this artillery barrel and the corresponding rifling portion of the finished barrel forging are shown below. Figure 3 As shown, Figure 3 The mandrel is on the left and the rifling section of the finished barrel forging is on the right.

[0032] Table 1 Rifling parameters

[0033]

[0034] The wrap angle is calculated using the following formula:

[0035]

[0036] This embodiment provides a method for evaluating the forgeability of materials for rifling in rotary forging, comprising the following steps:

[0037] Step 1: Design a forgeability testing device for barrel rotation forging materials based on rifling parameters

[0038] The rotary forging of the barrel is equated to a die forging method, that is, one radial reciprocating motion of a single hammerhead is equated to a molding process, based on Figure 4 In the equivalent method described above, the radial reciprocating motion of the hammer in rotary forging is equivalent to the vertical motion of the upper die, with a radial thickness of... The 1 / 4 portion of the tubular blank (the main part that comes into contact with the single hammerhead), after being unfolded along the inner cylindrical surface (rifling side), is equivalent to a thickness of Width is The plate-shaped blank (ignoring the difference in arc length between the inner and outer circles of the 1 / 4 tubular blank), the mandrel is equivalent to the lower die, and the rifling on the mandrel corresponds to the "rifling" on the lower die. In rotary forging, the radial direction of the tubular blank corresponds to the thickness direction of the plate-shaped blank. Figure 4 (As shown in the Z-axis direction), the circumferential direction corresponds to the transverse direction of the mold ( Figure 4 The X-axis direction shown is the unfolding direction of the tubular blank, and the axial direction corresponds to the longitudinal direction of the mold. Figure 5 The Y-axis direction shown is the horizontal direction perpendicular to the unfolding direction of the tubular blank. The outer surface of the mandrel is unfolded along the cylindrical surface containing the mandrel's incised line. The surface shape of the lower mold is designed according to the parameters given in Table 1. The radii of the "incised line edge" and "raised line edge" on the lower mold are taken as the median value of their respective allowable ranges. The height of the lower mold is equal to the radius of the incised line. The width of the "positive line" on the lower die is taken as the arc length of the positive line of the rifling profile. (Ignoring rounded corners), the calculation formula is as follows:

[0039]

[0040] In the formula The value represents the arc length of the positive line; the meanings of the other parameters are shown in Table 1. The geometry of the unfolded lower mold is as follows: Figure 5 As shown. To ensure that the plate-shaped specimen generates measurable indices after loading for forgeability testing, planes are respectively opened on the two "positive lines" of the lower die geometry after unfolding, with respect to the midpoint of the positive lines and perpendicular to the XOY plane (e.g., ...). Figure 5 (As shown) symmetrical V-shaped grooves, the width of the grooves The rounded corners of the raised line should be preserved, and the depth should be maintained. The selection should be based on the range of reduction in the outer surface radius of the tubular blank when the barrel is fully forged (forging refers to the complete formation of the barrel rifling). In this example... , The radius of the fillet at the junction of the groove side and the raised line is consistent with the edge of the raised line. To reduce mold processing costs, only two "raised lines" and one "closed line" (located between the two V-grooves) are retained. The lower mold is as follows: Figure 6 As shown, the forgeability testing device for tube rotation forging materials is as follows: Figure 1 As shown.

[0041] Step 2: Obtain the constitutive model of the material through mechanical property tests.

[0042] Materials A and B are widely used gun steel materials, and their chemical compositions (mass fraction, %) are shown in Tables 2 and 3, respectively.

[0043] Table 2 Chemical composition of material A

[0044]

[0045] Table 3 Chemical composition of material B

[0046]

[0047] According to GB / T 228.1-2021, samples were taken from appropriate locations in the raw material and processed into smooth round bar specimens. The test was conducted on a 300kN universal testing machine (model ETM305D). During the test, three sets of round bar specimens prepared for each material were loaded until fracture at a strain rate of [missing information]. The results are shown in Tables 4 and 5 below. The actual stress-strain curves of materials A and B are shown in Tables 4 and 5 respectively. Figure 7 , 8 As shown.

[0048] Table 4 Measurement data for Material A

[0049]

[0050] Table 5 Measurement data for Material B

[0051]

[0052] Step 3: Determine process parameters using finite element simulation

[0053] The material constitutive model (true stress-strain curve) is obtained from the data in step 2. A simulation model of the equivalent forgeability testing device is established in finite element software, and the maximum load on the upper die during the test is estimated through numerical simulation. The thickness of the plate specimen should be selected according to the thickness range of the tubular blank in actual rotary forging (in this embodiment, the thickness of the plate specimen is taken as 13mm). The transverse width of the plate specimen is taken as 1 / 4 arc length of the inner circumference of the tubular blank (rifling forming side), corresponding to the interaction between a single hammer, tubular blank, and mandrel in rotary forging. The longitudinal length of the plate specimen can be initially set to be equal to its transverse width. The reduction in plate specimen thickness caused by the movement of the upper die should be within the range of the reduction in the radius of the tubular blank when the rifling can be fully formed in rotary forging (in this embodiment, the reduction in plate specimen thickness is taken as 2mm). The finite element simulation model established using Deform V11 in this example is as follows: Figure 9 As shown, the device includes an upper mold, a plate-shaped specimen, and a lower mold. The lower mold is fixed, and the plate-shaped specimen is placed on the plane of the "negative line" of the lower mold. The plate-shaped specimen is symmetrical about the longitudinal and transverse mid-planes of the lower mold. During loading, the upper mold moves downward along the thickness direction of the plate-shaped specimen. Figure 9 The negative Z-axis direction (as shown) reduces the thickness of the plate-shaped specimen by 2 mm. Simulation results of the plate-shaped specimen deformation before and after loading are as follows: Figure 10As shown. If the maximum pressure exceeds the allowable range of the press equipment, the longitudinal length and thickness of the plate-shaped specimen can be appropriately reduced, but the thickness reduction in the thickness direction of the plate-shaped specimen caused by the movement of the upper die should not exceed [a certain value]. Finite element simulation results show that the dimensions of the plate-shaped sample are... (Transverse dimension × Longitudinal dimension × Thickness direction dimension), when the thickness reduction of the plate-shaped sample is 2 mm, the maximum pressure of material A is approximately 360 kN, and the maximum pressure of material B is approximately 335 kN. Figure 11 As shown.

[0054] Step 4: Conduct material forgeability testing

[0055] Based on the finite element simulation results, the geometric dimensions of the plate-shaped specimen and the reduction in its thickness during the testing process are determined. The upper die stroke of the press is then adjusted according to this reduction in thickness. In this example, the dimensions of the plate-shaped specimen are: The thickness reduction was 2 mm. Based on the above results, forgeability tests were conducted on the materials to be evaluated. The molding process was repeated three times for each material, and the process parameters for all tests were kept consistent.

[0056] Step 5: Measure the sample data after loading.

[0057] First, observe the surface of the plate-shaped specimen after loading. If obvious cracks, wrinkles, or other defects are present, the material is considered to have poor forgeability. If cracks, wrinkles, or other defects appear in all specimens, the process parameters selected during loading may be unreasonable, and the thickness reduction of the plate-shaped specimen should be reduced. For plate-shaped specimens without significant defects, mark the midpoint of the "positive line edge" of the loaded plate-shaped specimen at equal intervals from both ends (in the direction of the V-groove length) with a marker pen (the marking method should be consistent for all plate-shaped specimens). Cut open the plate-shaped specimen along a cross-section perpendicular to the Y-axis passing through the marked position, and measure the distance from the extruded portion of the plate-shaped specimen in the V-groove at different cross-sections along the thickness direction of the plate-shaped specimen to the contact surface between the plate-shaped specimen and the lower die (the plane where the "negative line" of the lower die is located). Figure 12 The maximum distance along the Z-axis (as shown) The cross-sectional area of ​​the extruded portion within the V-groove of the plate-shaped specimen after loading. , of which area The measurement can be performed using image recognition technology, or by measuring the longitudinal length of the portion of the plate-shaped sample that is in contact with the two sides of the V-groove, the distance from the tangent point of the plate-shaped sample and the side of the V-groove to the positive line of the plate-shaped sample along the thickness direction of the sample, and the area. With the area of ​​the trapezoid and the area of ​​a triangle The approximate calculation of the sum is given by the following formula:

[0058]

[0059] In the formula The width of the V-groove. Let be the transverse width of the portion of the plate-shaped specimen that is completely in contact with the side of the V-groove within the V-groove on the i-th cross-section perpendicular to the longitudinal direction (hereinafter referred to as the cross-section). The distance along the thickness direction from the plate-like portion of the V-groove within the i-th cross-section that is completely in contact with the side of the V-groove of the sample to the plane containing the lower mold's positive line. This represents the distance in the thickness direction from the bottom of the plate-shaped specimen at the bottom of the V-groove within the i-th cross-section, where the portion of the plate-shaped specimen completely adheres to the side of the V-groove. A schematic diagram of the measurement parameters at the i-th cross-section is shown below. Figure 12 As shown in Table 6, the measurement results in this example are as follows: A1-A3 represent the sample numbers of the three samples made of material A, and B1-B3 represent the sample numbers of the three samples made of material B.

[0060] Table 6 Measurement Data

[0061]

[0062] Step 6: Calculate the relevant indicators of material forgeability

[0063] Let the number of all cross sections from the middle to both ends be . (Including a symmetrical cross-section, in this embodiment) At the i-th cross-section, the maximum distance between the extruded portion of the plate-shaped specimen within the V-groove and the contact surface between the plate-shaped specimen and the lower die along the blank thickness direction after loading is... ( The area of ​​the extruded portion within the V-groove of the plate-shaped specimen after loading on the i-th cross-section is... The fill ratio at different cross-sectional locations is calculated using the following formula:

[0064]

[0065] In the formula Let i be the fill rate at the i-th cross-sectional position. Let V be the area of ​​the cross-section of the cavity portion below the male line of the lower mold. In this example, we approximate it as (ignoring the fillet at the transition between the V-groove and the male line of the lower mold). .

[0066] The fill rate reflects the material's ability to fill the cavity. During the rotary forging process of the barrel, under the action of the die, the inner surface of the blank first contacts the groove on the mandrel. As the total forging ratio (the ratio of the reduction in the area of ​​the blank's axial cross-section to its initial area, often used to represent the degree of plastic deformation of the material) increases, the material located above the mandrel cavity gradually fills the cavity structure on the mandrel, successively contacting the cavity walls on both sides and the midpoint of the mandrel's raised groove, and then filling from the midpoint of the raised groove towards the edges of the raised grooves at both ends. The rifling is designed with transition radii (such as...) at the junctions of the raised and recessed groove edges with the cavity walls. Figure 2 As shown in the figure, theoretically, the smaller the transition fillet radius, the more difficult it is for the material to completely fill it. The higher the total forging ratio required for complete filling, and the higher the total forging ratio, the greater the possibility of defects such as cracking, over-forging, and wrinkling in the forging. Therefore, the stronger the material's ability to fill the fillet, the lower the forging ratio level at which the rifling can be fully formed (rifling forged through), and the lower the possibility of forging defects such as cracking, over-forging, and wrinkling, resulting in better forgeability. In forgeability testing, the V-groove can be considered a cavity structure that is extremely difficult to completely fill. Under the same loading conditions, the plate-shaped specimen undergoes the same plastic deformation process, which is equivalent to maintaining a consistent forging ratio. Therefore, the material with a higher filling rate has a stronger ability to fill the cavity. Considering the influence of different rifling fillet sizes on the accuracy of the filling rate results, relevant weighting coefficients are defined based on the allowable values ​​of the fillet radius sizes of the positive and negative rifling edges, as shown in Table 7.

[0067] Table 7 Relevant Weight Coefficients

[0068]

[0069] In this example , .

[0070] For rotary forging of barrel rifling, the attenuation of the material's cavity filling capacity along the cavity contour direction is also an important indicator of the material's forgeability. The extrusion depth attenuation rate is calculated using the following formula:

[0071]

[0072] In the formula The material extrusion depth of the plate-shaped specimen after loading is defined on a symmetrical cross-section perpendicular to the longitudinal direction (the plate-shaped specimen before loading is symmetrical about this cross-section). Let be the material extrusion depth at the i-th cross-section. Let be the extrusion depth decay rate at the i-th cross-section. The equivalent fill rate decay rate at the i-th cross-section is calculated using the following formula:

[0073]

[0074] In the formula The filling rate of the plate-shaped specimen on the symmetrical cross-section after loading.

[0075] The calculation results for plate-shaped specimen A1 in this example are shown in Table 8.

[0076] Table 8 Calculation results of plate-shaped specimen A1

[0077]

[0078] The forgeability coefficient is calculated according to the following formula:

[0079]

[0080] Substituting the calculation results from Table 8 into the above formula, the forgeability coefficient of the plate specimen A1 is calculated as follows:

[0081]

[0082] Similarly, we can obtain

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] Then the forgeability coefficient of material A The forgeability coefficient of material B The higher the forgeability coefficient, the better the forgeability of the material. Therefore, material B is more forgeable than material A.

Claims

1. A device for evaluating the forgeability of rifling forged materials, used to obtain the forgeability coefficient of the material to be evaluated, characterized in that, It includes a lower mold, an upper mold, and a lower mold base; the lower mold is fixed on the lower mold base; The testing device obtains the rifling by equating the rotary forging process of the barrel with the die forging process, that is, equating the radial reciprocating motion of the hammer in the rotary forging process with the vertical motion of the upper die; the radial thickness is The 1 / 4 tubular blank, when unfolded along its inner cylindrical surface, is equivalent to a thickness of Width is The plate-shaped sample; the radial direction of the tubular blank corresponds to the thickness direction of the plate-shaped sample, the unfolding direction corresponds to the transverse direction of the lower die, and the axial direction corresponds to the longitudinal direction of the lower die; the hammer head is equivalent to the upper die, and the mandrel is equivalent to the lower die. The negative and positive lines on the surface of the lower die are designed according to the rifling parameters of the tube. A V-shaped groove is opened on the positive line of the lower die, so that the plate-shaped sample after loading produces measurable indicators that can characterize the forgeability of the material, namely the material extrusion depth on a series of cross sections perpendicular to the longitudinal direction of the plate-shaped sample and the cross-sectional area in the V-shaped groove.

2. The testing device according to claim 1, characterized in that, The fillets of the upper concave and convex edges of the lower mold are taken as the midpoint of their respective allowable ranges, and the height of the lower mold is equal to the radius of the concave edge. The width of the raised line on the lower die is taken as the arc length of the raised line of the rifling profile. .

3. The testing device according to claim 1, characterized in that, The lower mold has two positive lines and one negative line.

4. A method for testing the forgeability of rifling forged materials, using the testing apparatus described in any one of claims 1-3, characterized in that, This includes obtaining the constitutive model of the material to be evaluated through mechanical property tests, using finite element simulation software to numerically simulate the forging process, estimating the maximum load required during actual forging, and adjusting the longitudinal length of the plate specimen and the amount of thickness reduction during loading based on the results. Based on the adjusted plate-shaped specimen size and the thickness reduction during loading, actual die forging tests are conducted on the materials to be evaluated. The test process for each material to be evaluated should be repeated multiple times. The surface of the plate-shaped specimen after loading is observed, and the extrusion depth and cross-sectional area at different cross-sectional positions perpendicular to the longitudinal direction in the V-shaped groove are measured to obtain the forgeability coefficient of each specimen. The forgeability of each material to be evaluated is compared by taking the average value of the forgeability coefficient.

5. The test method according to claim 4, characterized in that, The forgeability coefficient is calculated using the following formula: ； in , , ; In the formula The extrusion depth of the plate-shaped specimen on a symmetrical cross-section perpendicular to the longitudinal direction after loading. Let be the material extrusion depth at the i-th cross-section perpendicular to the longitudinal direction. Let be the extrusion depth decay rate at the i-th cross-sectional position. Let i be the fill rate at the i-th cross-sectional position. The depth of the V-shaped groove. and These are the weighting coefficients for the bearish and bullish candlesticks, respectively. The value represents the filling ratio of the plate-shaped specimen on the symmetrical cross-section after loading, and n represents the number of single-sided sections during the process of moving from the middle to the two equidistant sections. Let be the area of ​​the extruded portion within the V-groove of the plate-shaped specimen after loading on the i-th cross-section. This refers to the area of ​​the cross-section of the cavity portion below the positive line where the V-groove is located.

6. The test method according to claim 4, characterized in that, During the numerical simulation, the plate-shaped specimen is placed on the plane of the lower die's indentation, symmetrical about the longitudinal and transverse mid-planes of the lower die. During loading, the upper die moves, causing a decrease in the thickness of the plate-shaped specimen. If the maximum load exceeds the allowable range of the press equipment, the longitudinal length of the plate-shaped specimen and the amount of thickness reduction during loading should be reduced, but the thickness reduction in the thickness direction of the plate-shaped specimen should not exceed [a certain value]. Where d1 and d2 are the diameters of the bearish and bullish lines, respectively.

Images