Shearing method, press-molded product manufacturing method, and shearing device

Abstract

The present invention provides a shearing technique that reduces unevenness of the sheared edge, thereby suppressing the promotion of delayed fracture, particularly in blank regions that are at high risk of delayed fracture. [Solution] This is a shearing method for shearing a metal plate for press molding before press molding, in which shearing conditions that will not cause non-uniformity on the sheared end surface after shearing are determined in advance, and shearing is performed under the determined shearing conditions, and the sheared end surface having the non-uniformity has unevenness along the extension direction of the sheared end surface, and the change between the concave and convex parts is in a region that is 5% or more of the thickness of the metal plate along the extension direction, or 3% or more of the thickness of the metal plate in the direction along the shear direction.

Description

[Technical Field]

[0001] The present invention relates to a technology for improving the delayed fracture resistance of a sheared end surface of a metal plate used in press forming, and to a technology relating to a press-formed product using the metal plate. A steel sheet having a tensile strength of 980 MPa or more is referred to as a high-strength steel sheet. The present invention is a suitable technique for shearing a metal sheet having a tensile strength of 980 MPa or more. [Background technology]

[0002] Currently, automobiles are required to improve fuel efficiency and crashworthiness through weight reduction. Therefore, there is a trend toward using high-strength steel sheets in automobile bodies in order to achieve both weight reduction and occupant protection in the event of a collision. In particular, high-strength steel sheets with a tensile strength of 980 MPa or more have been used in automobile bodies in recent years. One of the issues when using high-strength steel sheets in automobile bodies is delayed fracture after press forming. One of the major issues, particularly with steel sheets with a tensile strength of 980 MPa or more, is delayed fracture that occurs at the edge after shearing. The edge after shearing is also called the sheared edge.

[0003] It is known that large tensile stress remains at the sheared edge. Therefore, there is concern about delayed fracture at the sheared edge of press-formed products after press forming. It is also known that delayed fracture at the sheared edge is further accelerated by applying external stress to the press-formed product. An example of external stress application occurs when a press-formed product is assembled with another part.

[0004] Test methods for evaluating delayed fracture include those described in Patent Documents 1 to 3, for example. Patent Documents 1 and 2 propose a test in which stress is applied by constant displacement restraint due to bending deformation. Patent Document 3 proposes a test in which stress is applied by applying a constant load due to uniaxial deformation.

[0005] It is also known that the critical stress for delayed fracture changes due to the influence of forming strain, as in Patent Document 4. In particular, when excessive strain is introduced into the sheared edge, the critical stress for delayed fracture may decrease due to damage to the sheared edge (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-142086 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-70927 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-57163 [Patent Document 4] Japanese Patent Publication No. 2022-14784 [Non-patent literature]

[0007] [Non-Patent Document 1] Influence of Sheared Edge on Hydrogen Embrittlement Resistance: ISIJ International, Vol. 54 (2014), No. 6, pp. 1416-1425 Summary of the Invention [Problem to be solved by the invention]

[0008] Here, the inventors have studied the properties of the sheared end surface and have come to the following findings. In other words, when shearing is performed in a laboratory test evaluation, the sheared edge has ideal properties. However, compared to this ideal sheared edge, the sheared edge produced during shearing on an actual mass production line has been found to have non-uniformity. For example, in the actual production of automobile parts, the sheared edge produced during blanking has uneven edge shapes due to chipped areas caused by dents and raised areas such as stepped bumps. These chipped areas and stepped bumps occur intermittently along the extension direction (horizontal direction) of the edge. It was also found that the tendency for non-uniformity becomes more pronounced as the material strength increases, and as the material becomes more brittle and the shear surface ratio at the sheared edge decreases.

[0009] Non-uniformity in the edge shape appears as chips or step-like protrusions along the extension direction. Therefore, at the sheared edge, non-uniformity leads to the concentration of forming strain and forming residual stress, which are caused by shape factors. As a result, excessive strain promotes the reduction of the delayed fracture critical stress. Furthermore, it was found that even without the influence of forming strain, the delayed fracture critical stress is reduced due to stress concentration caused by non-uniformity.

[0010] Therefore, in order to prevent delayed fracture at the sheared end faces of actual automobile parts (press-formed products), the following measures are required. In particular, the following measures are required for blank areas that are at high risk of delayed fracture. In other words, the inventors have come to the realization that it is necessary to establish a shearing method that reduces the non-uniformity of the end face shape in the mass production process. The inventors then considered it important to identify the factors that cause non-uniformity in the sheared end surface in mass production processes using high-strength steel, and to develop an effective shearing method to improve this.

[0011] It is easy to infer that such non-uniformity of the sheared edge also promotes stretch flange cracking. Therefore, suppressing such non-uniformity is effective from the viewpoint of preventing stretch flange cracking. It is also easy to infer that such non-uniformity of the sheared edge also promotes a decrease in fatigue strength. Therefore, suppressing such non-uniformity is effective from the viewpoint of preventing fatigue fracture.

[0012] As described above, in the actual mass production process of high-strength steel, highly non-uniform shear edges are generated compared to ideal shear edges. This can sometimes promote delayed fracture. It is also easy to infer that such non-uniform areas promote stretch flange cracking and fatigue fracture.

[0013] The present invention has been made in light of these points and has been devised to solve the above-mentioned problems. The present invention aims to provide a shearing technique that can reduce the non-uniformity by focusing on the mechanism by which highly non-uniform sheared edges are generated in shearing. As a result, the present invention aims to suppress the promotion of delayed fracture, particularly in areas where the risk of delayed fracture is high. [Means for solving the problem]

[0014] The inventors have found that even if a critical stress for delayed fracture, at which delayed fracture does not occur, is determined through laboratory testing and press forming is designed based on the critical stress, the following problem still exists: that is, delayed fracture may be accelerated due to a decrease in the critical stress caused by non-uniformity of the sheared edge. The present invention is based on this finding.

[0015] In order to solve the problem, one aspect of the present invention is a shearing method for shearing a metal plate for press molding before press molding, which includes determining in advance shearing conditions that will not cause non-uniformity on the sheared end surface after shearing, and performing shearing under the determined shearing conditions, so that the sheared end surface having the non-uniformity has unevenness along the extension direction of the sheared end surface, and the change between the concave and convex portions is in a region that is 5% or more of the thickness of the metal plate along the extension direction, or 3% or more of the thickness of the metal plate in the direction along the shearing direction. [Effects of the Invention]

[0016] According to the present invention, it is possible to suppress the non-uniformity of the sheared edge, which increases the risk of delayed fracture in a delayed fracture-prone region. As a result, according to the present invention, it is possible to manufacture, for example, automobile parts made of high-strength steel plate with better delayed fracture resistance, which can contribute to improving the collision performance and reducing the weight of automobiles. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram illustrating the shape of a sheared end surface in ideal shearing processing, based on laboratory tests, etc. [Figure 2] This is a diagram explaining the shape of the sheared end surface in ideal shearing on the punched-out side. The sheared end surface on the punched-out side is the sheared end surface on the product side, and is the sheared end surface on the side that is restrained by the lower blade and the sheet metal holder. (a) is a schematic cross-sectional view of the sheared end surface. (b) is a schematic plan view of the sheared end surface. The plan view is a view seen from the opposing direction of the end surface. [Figure 3] FIG. 2 is a schematic plan view illustrating a sheared surface having non-uniformity (first non-uniformity) due to a chipped portion consisting of a recessed portion. [Figure 4] 4 is a schematic cross-sectional view of the sheared surface of FIG. 3. (a) is a diagram showing a normal sheared end surface. (b) is a cross-sectional view of a part with a concave chip. (c) is a cross-sectional view of a convex part. [Figure 5]FIG. 2 is a schematic plan view illustrating a shear surface having non-uniformity (second non-uniformity) due to stepped protrusions. [Figure 6] Schematic cross-sectional views of the sheared surface in Figure 5. (a) is the sheared surface of the non-protruding part, and (b) is the sheared surface of the region where the sheared end face is protruding long toward the convex side (the direction protruding from the end face) in the extension direction. [Figure 7] 1A to 1C are diagrams illustrating steps in a method for manufacturing a press-formed product according to an embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram of a die structure (shearing device) that can limit the effective clearance between the upper and lower blades so that it does not become too small. [Figure 9] 1A and 1B are schematic diagrams showing an example of a mechanism for a shear plane device capable of adjusting the penetration depth, in which (a) is a side view showing the device configuration incorporating a height adjustment mechanism, and (b) is a diagram for explaining an example of the height adjustment mechanism. [Figure 10] FIG. 10 is a diagram showing the change in cutting edge R due to wear in each blade material when the initial cutting edge R under shearing conditions is set to 0 mm in an example. [Figure 11] FIG. 1 is a perspective view showing a press-formed product (automobile part) having a delayed fracture risk portion after press-forming in an example. [Figure 12] 1A and 1B are diagrams showing examples of the shape of the plate holder and the arrangement of gas springs that restrain the plate holder in the embodiment. (a) is an example with four gas springs, (b) is an example with three gas springs, (c) is an example with two gas springs, and (d) is an example with one gas spring. DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, an embodiment based on the present invention will be described with reference to the drawings. (Inventor's knowledge) As a result of studying the properties of the sheared edge as described above, the inventors have come to the following finding: that is, compared to the sheared edge formed in a laboratory test, which has ideal properties, the sheared edge formed by shearing in an actual mass production line has non-uniformity. Furthermore, the inventors have focused on the mechanism of occurrence of unevenness in the sheared edge, which is specific to mass production blanking of high-strength steel, and have found that suppressing the unevenness in the sheared edge in the mass production process in which multiple shearing processes are repeated can suppress an increase in the risk of delayed fracture.

[0019] Next, we will explain the mechanism behind the occurrence of non-uniformity in the sheared edge, which is specific to mass production blanking of high-strength steel. <Ideal sheared edge> First, we will describe the ideal sheared edge generated in laboratory testing. An initial crack occurs on the sheared edge 1A when the upper blade 3 and lower blade 2, both of which have sufficiently sharp cutting edges, approach each other as shown in Figure 1 during shearing. As the blades continue to be pressed, the two blades 2, 3 advance and meet, completing the shearing process. At this time, on the product side (the side that remains uncut), which is the fixed lower blade 2 side, a glossy sheared edge is formed on the upper upper blade 3 side, and a fractured edge with a rough surface is formed on the lower lower blade 2 side, as shown in Figure 2. Even if a shear angle is set to reduce shear load and noise, this fractured edge will have a similar shape if the shearing process is performed appropriately. Furthermore, an ideal sheared edge has minimal irregularities along the extension direction of the edge.

[0020] In Fig. 1, reference numeral 4 denotes a sheet holder. Reference numeral 1 denotes a metal sheet to be sheared. Reference numeral 2A denotes a top surface of a lower blade 2 that contacts the bottom surface of the metal sheet 1. The height of the top surface 2A of the lower blade 2 is synonymous with the height of the tip of the lower blade 2.

[0021] However, if the clearance between the upper and lower blades 2 and 3 is too small, the cracks from the upper and lower blades 3 and 2 may not meet cleanly, resulting in the formation of a secondary shear surface. On the other hand, if the clearance between the upper and lower blades 2 and 3 is too large, the bending deformation becomes strong, increasing the compressive stress at the tip of the lower blade 2 and potentially causing burrs. The ideal clearance between the upper and lower blades 2 and 3 is considered to be approximately 10% to 20%. However, in mass production, unevenness in the sheared edge 1A occurs even with this ideal clearance.

[0022] In this embodiment, a sheared edge having non-uniformity is defined as a region having irregularities along the extension direction of the sheared edge, where the change between the concave and convex portions is 5% or more of the thickness of the metal sheet 1 along the extension direction of the sheared edge, or 3% or more of the thickness of the metal sheet 1 along the shearing direction. The change is either a change in the protruding or concave direction of the edge (the normal direction of the edge) (a change along the extension direction of the sheared edge), or a change in the direction along the shearing direction, as described below. A region where any of the changes due to irregularities satisfies the above condition is defined as a sheared edge region having non-uniformity. Here, the non-uniformity of the sheared end surface 1A can be quantitatively observed by visual observation, observation with a microscope, laser microscope, or microscopic observation of the cross section.

[0023] <Example of unevenness on sheared edge 1A> As examples of the non-uniformity of the sheared end surface 1A, the following first and second examples of non-uniformity will be described.

[0024] [First non-uniformity (non-uniformity due to chipping caused by recesses)] Fig. 3 is a schematic plan view of a sheared edge 1A having intermittent chipped portions consisting of recesses along the extending direction of the edge. Fig. 3 is a schematic diagram showing chipped portions consisting of recesses that occur on the sheared edge 1A of mass-produced blanking of high-strength steel and are the cause of the non-uniformity of the sheared edge 1A. Figure 4 is a cross-sectional view of each part of Figure 3. Figure 4(a) is a cross-sectional view of a normal sheared end surface 1A. Figure 4(b) is a cross-sectional view of a sheared end surface 1A of a chipped portion of a recessed portion. Figure 4(c) is a cross-sectional view of a sheared end surface 1A of a convex portion.

[0025] The concave part (Fig. 4(b)) is a rough fracture surface that has been torn off completely, including the chipped part, and is a part with a chip that is recessed from the reference sheared edge. The convex part (Fig. 4(c)) is a convex part that has been ground down and includes a shiny sheared surface. The reference sheared edge is the position of the target sheared edge. In the example shown in Figure 3, the concave portions (Figure 4(b)) and convex portions (Figure 4(c)) are shown to be intermittently repeated along the direction of shear extension between normal shear end faces 1A.

[0026] In this example, a sheared edge having a non-uniformity is defined as a sheared edge where the amount of change between the recessed portion (FIG. 4(b)) and the protruding portion (FIG. 4(c)) is 5% or more of the thickness of the metal plate 1. The direction of change is the protruding direction (normal direction) of the edge. In other words, a sheared edge having a first non-uniformity is defined as a sheared edge where the amount of depression of the recessed portion (FIG. 4(b)) relative to a reference sheared edge along the extension direction is 5% or more of the thickness of the metal plate 1.

[0027] [Second non-uniformity (non-uniformity due to step-like ridges)] FIG. 5 is a schematic plan view of a sheared end surface 1A having a stepped protrusion. Figure 6 is a cross-sectional view of each part of Figure 5. Figure 6(a) is a cross-sectional view of the sheared end surface 1A in the non-protruding part. Figure 6(b) is a cross-sectional view of the sheared end surface 1A in the region where it is protruding long to the convex side. In the example shown in Figure 5, the seam (boundary) between the non-protruding area (Figure 6(a)) and the protruding area on the convex side (Figure 6(b)) has a sharp step shape that is parallel to and almost perpendicular to the shear direction (the up-and-down direction in Figure 5).

[0028] The sheared edge having the second non-uniformity is a region having a protruding portion that protrudes relatively from the reference sheared edge along the extension direction of the sheared edge. Furthermore, the sheared edge having the second non-uniformity has a step-like boundary between the region connected to the protruding portion in the extension direction of the edge and the protruding portion region, which is a step-like boundary along the shear direction (see FIG. 5). The sheared edge having the second non-uniformity is a region where the step at the boundary between the two regions is 3% or more of the thickness of the metal plate 1.

[0029] <Causes of heterogeneity> The inventors have found that the following factors (a) to (c) contribute to the cause of such non-uniformity. (a) First, high-strength steel plates are more brittle than low-strength steel plates and have a lower shear surface ratio at the sheared edge 1A. Therefore, the depth of penetration of the upper and lower blades 2 into the blank when cracks initiate and propagate is small. In such a state, cracks tend to propagate easily and unstably. The shear surface ratio refers to the proportion of the sheared surface in the cross section, as shown in Figure 2.

[0030] (b) Second, the shearing of high-strength steel plates significantly affects the upper and lower blades 2 with wear and chipping. Therefore, in mass production processes involving hundreds of thousands of shearing shots, the sharpness of the cutting edges is easily lost. This causes the cutting edges to become rounded or chipped, reducing stress concentration at the tip of the cutting edge. As a result, crack initiation is delayed. The degree of wear and chipping of the cutting edges varies across the entire shearing die, depending on the load on each part of the die during shearing.

[0031] (c) Thirdly, extremely high loads are applied when high-strength steel plates are sheared. This makes it easy for the mold to deflect, resulting in variations in clearance and lifting of the plate clamp 4. This can cause deviations from the ideal clearance between the upper and lower blades in different parts of the mold. Furthermore, if the plate clamp 4 unintentionally lifts during shearing, the plate may be sheared in an unstable, lifted state. The above-mentioned non-uniformity of the sheared end surface 1A arises from factors (a) to (c).

[0032] Furthermore, the inventors have found the following experimental facts regarding shear conditions. (1) When a shear angle is set, or when a shear angle occurs unintentionally due to deflection of the mold, unevenness (first unevenness) due to chipping caused by recesses in the sheared end surface 1A is likely to occur.

[0033] (2) On the other hand, when the shear angle is 0 degrees or close to 0 degrees, unevenness (second unevenness) due to a step-like protrusion is likely to occur on the sheared end surface 1A. However, in reality, (1) and (2) may occur in combination. For example, when the shear angle or clearance changes partially due to mold deflection, when the state of wear differs partially, or when the cutting edge is severely worn, these two factors may occur in combination.

[0034] The inventors also studied the mechanism by which chipped portions (depressed portions) that become uneven on the sheared end surface 1A as shown in FIG. 3 are generated in shearing processing with a shear angle. As a result of the investigation, for the reason (a), in high-strength steel plates, cracks occur in the upper and lower blades 2 when the shear surface ratio is low. Similarly, for the reason (a), cracks tend to easily propagate not only in the vertical direction (shear direction) connecting the upper and lower blades 2 and 3, but also in the perpendicular horizontal direction (extension direction of the end faces perpendicular to the shear direction).

[0035] Furthermore, for reason (b), if the shear blades are worn, the upper and lower blades 2 and 3 must be pressed in deeper before a crack occurs than when the cutting edges are sharp. As a result, the force tearing the crack laterally acts more prominently, and the crack propagates not only vertically but also horizontally.

[0036] When the degree of the above-mentioned (a) to (c) is significant and the crack propagates beyond the area where both the upper and lower blades 2 and 3 are embedded in the metal sheet 1, the crack begins to propagate laterally without the constraint of the upper and lower blades 2 and 3. In this case, the crack propagating laterally first snakes away from the upper blade 3, forming a concave portion. The crack then snakes back toward the upper blade 3, forming a convex portion, at which point its lateral propagation stops. Furthermore, when the upper blade 3 again contacts the convex portion, a shear plane is formed, restoring the shear state to normal longitudinal crack propagation and convergence. The following characteristics of the chipping caused by the concave portion on the sheared edge 1A were identified. Based on the above mechanism, it was found that discontinuous portions of the shear plane appear intermittently along the extension direction of the edge. It was also found that there are regions where the height difference between the intermittent concave portions and the convex portions is 5% or more of the material sheet thickness.

[0037] The inventors also investigated the mechanism by which step-like protrusions as shown in FIG. 5 occur intermittently along the extending direction of the end face when the shear angle is 0 degrees or close to 0 degrees.

[0038] If the shear angle is sufficiently small, no force is generated to tear the crack laterally. Therefore, the unevenness caused by the lateral propagation of the crack does not occur. However, due to reason (b), the worn shear blades with rounded edges penetrate a wide area of ​​the plate surface simultaneously. Furthermore, due to reason (a), the brittleness of the material causes differences in the timing and location of crack initiation within the upper blade 3. As a result, cracks that originate at shallower penetration depths of the upper blade 3 retreat toward the lower blade 2. On the other hand, cracks that originate at deeper penetration depths of the upper blade 3 advance further toward the upper blade 3. Furthermore, when the shear angle is 0 degrees, the cutting edges simultaneously contact the plate surface, resulting in an extremely high shear load. This can easily cause the mold deflection (c), which can result in the actual effective clearance being smaller than the specified value. If the clearance is too small, the stress state of the cutting edges of the upper and lower blades 2 and 3 becomes unstable, which tends to promote the formation of bumps and unevenness. The researchers then identified the following characteristics of the sheared edge 1A, which has step-like protrusions intermittently along the extension direction of the edge. Specifically, the sheared surface is continuous because there is no lateral crack propagation. However, there are relatively concave areas on the lower blade 2 side and protruding areas (protruding areas) on the upper blade 3 side. The sheared surface ratio is higher in the latter than in the former, and the boundary between these areas is sharp and intermittent. Furthermore, the researchers found that the difference in height in the vertical direction (along the shearing direction) is relatively small, amounting to more than 3% of the material thickness, due to differences in the location of crack initiation within the cutting edge R.

[0039] Furthermore, the inventors have found that the non-uniformity of the sheared edge 1A caused by the above-mentioned multiple causes increases the risk of delayed fracture due to the following reasons.

[0040] (3) Due to the non-uniformity, tensile stress is concentrated in the recessed portion of the sheared edge 1A or in the corners of the stepped protrusions that are close to a right angle. This increases the tensile stress that causes delayed fracture. The recessed portion or stepped protrusions are formed intermittently along the extension direction of the edge.

[0041] (4) Plastic deformation during press forming is concentrated at the recessed portion of the sheared edge 1A or at the corners of the stepped protrusions that are close to right angles. This increases the plastic strain that promotes delayed fracture.

[0042] From these findings, the inventors have found the following, particularly with regard to high-strength steel sheets: That is, when a portion where the residual tensile stress after press forming is 600 MPa or more, or where the equivalent plastic strain is 0.06 or more and the residual tensile stress is 400 MPa or more, overlaps with an uneven portion of the sheared edge 1A, the risk of delayed fracture increases locally. In this specification, such a risk portion is defined as a delayed-fracture risk portion in the following description.

[0043] (Configuration of this embodiment) Based on the above findings, in this embodiment, in order to prevent delayed fracture at a portion that is at risk of delayed fracture, shearing is performed under shearing conditions that can suppress non-uniformity in forming the sheared end surface that will become the portion at risk of delayed fracture. This embodiment is a manufacturing method for manufacturing a press-formed product. As shown in FIG. 7, the manufacturing method of this embodiment includes a shearing step S10 and a pressing step S20. In this example, the metal plate 1 is made of a high-strength steel plate, but the metal plate 1 may be made of a metal plate other than a high-strength steel plate.

[0044] <Shearing S10> The shearing step S10 is a step in which the metal plate 1 is sheared to produce a blank (metal plate 1) for pressing. In this embodiment, when a metal plate 1 is sheared under standard shearing conditions set in the mass production process, the region of the sheared edge 1A where non-uniformity occurs is determined among the sheared edge 1A generated. The region of the sheared edge 1A where non-uniformity occurs is called the non-uniform part. The uneven portion is found, for example, by observing the sheared end surface 1A generated by the shearing process up to now.

[0045] In this specification, the definition of the non-uniformity of the sheared end surface 1A that needs to be addressed is as follows. As shown in Fig. 3, the sheared surface having the first non-uniformity (sheared edge 1A having a chipped portion due to a recessed portion) is discontinuous in at least a part of the sheared edge 1A along the extending direction of the edge. The sheared surface having the first non-uniformity is an edge in which there is a region where the difference in height between the recessed portions and the protruding portions intermittently occurring along the extending direction is 5% or more of the thickness of the metal plate 1. That is, the sheared edge 1A has a chipped portion due to a recessed portion, and is a sheared edge 1A in a region where the difference in height between the recessed portions and the protruding portions intermittently occurring along the extending direction (lateral direction) of the edge is 5% or more of the thickness of the metal plate 1.

[0046] As shown in Fig. 5, the sheared surface having the second non-uniformity (sheared end surface 1A having stepped protrusions) is continuous along the extension direction of the end surface, but has a region that is relatively recessed toward the lower blade 2 and a region (protruding region) that protrudes toward the upper blade 3. The boundaries between these regions exist intermittently along the extension direction of the end surface, and this end surface has a region where the difference in height of the steps along the shear direction is 3% or more of the thickness of the metal sheet 1. In other words, this is a sheared end surface 1A having protrusions, and is a sheared end surface 1A in a region where the difference in height in the vertical direction caused by the protrusions that occur intermittently along the extension direction is 5% or more of the thickness of the metal sheet 1.

[0047] In this embodiment, for the portion that will become the non-uniform portion, shearing conditions that will not cause non-uniformity on the sheared end face 1A after shearing are determined in advance, and shearing is performed under the determined shearing conditions. Here, while non-uniformity occurs under normal shearing conditions, the shearing conditions that do not cause non-uniformity on the sheared end surface 1A after shearing are also called improved shearing conditions. Specific examples of improved shearing conditions will be described later.

[0048] It is also possible to apply shear processing under the improved shear conditions to the entire region of the non-uniform part. However, it is assumed that areas other than the delayed fracture risk areas in the press-formed product will pose fewer problems even if they are non-uniform parts. Therefore, it is sufficient to apply shear processing under the improved shear conditions only to the areas that are the delayed fracture risk areas.

[0049] In the following embodiment, an example will be given in which a portion determined to be at risk of delayed fracture is subjected to shearing under improved shearing conditions regardless of whether it is an uneven portion or not. The delayed fracture risk portion is detected by, for example, a laboratory test using a known method such as that described in prior art documents, to evaluate delayed fracture and obtain evaluation values ​​for critical stress, etc. Then, a forming analysis (CAE analysis) is performed to press-form the metal plate 1 having the sheared end surface 1A into a target part shape, and the delayed fracture risk portion is determined by referring to the evaluation values.

[0050] In this embodiment, a portion at risk of delayed fracture is defined as a portion where the residual tensile stress after press forming is 600 MPa or more, or where the equivalent plastic strain is 0.06 or more and the residual tensile stress is 400 MPa or more. That is, a CAE analysis is performed on the press forming to obtain the target part shape, and a portion where the residual tensile stress after press forming is 600 MPa or more, or where the equivalent plastic strain is 0.06 or more and the residual tensile stress is 400 MPa or more is extracted as a portion at risk of delayed fracture.

[0051] In the shearing step S10 of this embodiment, the shearing is performed under the improved shearing conditions for the portion including the delayed fracture risk portion. The shearing is performed under the standard shearing conditions (existing shearing conditions) for the other portions. This allows the region to be sheared under the improved shearing conditions to be limited. In the shearing process S10, for example, shearing is performed under standard shearing conditions (existing shearing conditions), and then shearing is performed under improved shearing conditions.

[0052] <Pressing process S20> In the pressing step S20, the blank (metal plate 1) produced in the shearing step S10 is press-formed into a target part shape.

[0053] <Improved shear conditions> In this embodiment, the cutting edge condition, shear angle, management of effective clearance, and constraint conditions of the plate holder 4 will be described as examples of shear conditions for uneven portions. The improved shear conditions are set as shear conditions that include one or more of the following conditions:

[0054] "A: Conditions of cutting edge (maintaining cutting edge R by selecting material)" The cutting edge R of one or both of the upper blade 3 and the lower blade 2 is kept sufficiently sharp, and is set to a cutting edge condition that can prevent chipping of the cutting edge. This prevents chipping of the sheared edge 1A when a shear angle is present. In other words, the upper blade 3 easily bites in, causing cracks to occur early, which means that the propagation of cracks in the vertical direction between the upper and lower blades 2 and 3 is more dominant than the propagation of cracks in the horizontal direction. As a result, the propagation of cracks in the horizontal direction is suppressed.

[0055] Similarly, the occurrence of step-like ridges, which occurs when there is no shear angle, is also suppressed. This is because the sharp cutting edge R concentrates stress, stabilizing the amount of indentation that causes cracks. In addition, because the blade is not rounded, even if there is some variation in the depth of the crack, there is no difference in the distance from the lower blade 2 where the crack occurs.

[0056] Therefore, when forming the sheared edge 1A in the range corresponding to the delayed fracture risk portion, a hard blade material that can maintain the sharpness of the cutting edge even in mass production is used for either or both of the upper blade 3 and the lower blade 2. This prevents unevenness on the sheared edge 1A in the delayed fracture risk portion and makes it possible to suppress the occurrence of delayed fracture.

[0057] For example, the majority of the shearing die (the part that is sheared under the standard shearing conditions) is made of SKD11, which is a standard shearing die material. On the other hand, by using a higher hardness high-speed steel such as SKH51 in the area at risk of delayed fracture, it is possible to partially suppress wear of the shear blade. Such high-speed steel is generally expensive, and it is difficult to use it for the entire die from a cost perspective. In contrast, in this embodiment, by limiting its application to the area at risk of delayed fracture, it is possible to alleviate this problem.

[0058] The material of the shear blades in the delayed fracture risk area is made to have a Rockwell hardness that is at least 3 higher than that of the shear blades in other areas.Instead of using a material with high hardness, it is also possible to apply a highly wear-resistant coating. In this way, the shear blade material for improved shearing conditions is a high-speed steel with higher hardness, such as SKH51, or a material with a Rockwell hardness of 3 or more higher than that of the shear blades other than those at risk of delayed fracture.In addition, instead of using a hard material, a highly wear-resistant coating is applied to partially suppress the wear of the shear blades.

[0059] That is, for at least a portion of the area at risk of delayed fracture, a die is used that is designed to manufacture the upper blade 3, preferably the upper blade 3 and lower blade 2, using a high-hardness steel that can prevent wear of the cutting edge. Specifically, SKD11, a standard material for shear dies, is used for the majority of the shear die. On the other hand, high-speed steel such as various SKH steels is used for the area at risk of delayed fracture, thereby partially suppressing wear of the shear blades. In reality, it is effective to use a shearing die characterized in that the material of the shearing blades in the delayed fracture-prone areas is higher in Rockwell hardness by 3 or more than that of the shearing blades in the areas other than the delayed fracture-prone areas.

[0060] If the limit value of the cutting edge R that can suppress non-uniformity of the sheared edge 1A can be determined in advance by delayed fracture testing, it is preferable to select and use a shear blade material with a hardness that can maintain the desired cutting edge R within the number of manufacturing shots. In this case, it is possible to use a shear blade with a higher hardness depending on the number of manufacturing shots. The limit of the cutting edge R and the hardness of the shear blade may vary depending on the strength and thickness of the material being sheared.

[0061] Furthermore, if the occurrence of the aforementioned uneven sheared end surface 1A is found in the area at risk of delayed fracture during the mass production process, measures such as replacing the upper and lower shear blades, changing to a harder material to maintain the end surface quality, or applying an abrasion-resistant coating will be implemented.

[0062] [B: Selection of shear angle 0 degrees and effective clearance management, die structure, constraint of plate holder 4] As shown in (b), when the cutting edge is worn, it is difficult to suppress the propagation of cracks in the lateral direction when there is a shear angle. Therefore, as an example of improved shear conditions, for the area at risk of delayed fracture, the shear angle is set to 0 degrees or close to 0 degrees and the mold is fabricated. Furthermore, in order to prevent the occurrence of steps due to the protrusions in this state (second non-uniformity), the mold is controlled so that the effective clearance does not become too small.

[0063] For this reason, it is effective to observe the sheared edge 1A actually created in the shearing die and adjust the die's effective clearance so that it is 10% or more of the plate thickness at any position on the sheared edge 1A. However, if the clearance exceeds 25% of the plate thickness, significant burrs will occur. Therefore, taking into consideration the prevention of burrs, it is desirable for the clearance to be 10% to 25% of the plate thickness.

[0064] It is also preferable to design the shearing device so that the clearance of the upper blade 3 does not become too small due to mold deflection. For example, as shown in FIG. 8, a guide portion 3A is provided on the side of the upper blade 3 above the blank contact surface, protruding toward the sheet holder 4. By making this guide portion 3A contactable with the sheet holder 4, it is effective to maintain the clearance between the upper and lower blades 2, 3 at a predetermined level or greater. In this case, it is desirable to form a relief 4A at the bottom of the sheet holder 4 so that it is not cut by the positioning contact portion of the upper blade 3. The guide portion 4 may be provided so as to protrude from the sheet holder side toward the side of the upper blade 3.

[0065] The configuration of Figure 8 shows an example of a shearing device that shears a metal sheet 1 by relatively moving the upper blade 3 toward the lower blade 2 while the metal sheet 1 is constrained by the top surface 2A of the lower blade 2 and the sheet holder 4. A guide portion 3A is provided between the side surface of the upper blade 3 and the sheet holder 4. The guide portion 3A maintains a certain value or greater of clearance between the upper blade 3 and the lower blade 2 during shearing. In Figure 8, the guide portion 3A is a portion that protrudes from the side surface of the upper blade 3 toward the sheet holder 4. The protrusion amount D (thickness) of the guide portion 3A is set so that the clearance between the upper blade 3 and the lower blade 2 during shearing is 10% or greater of the thickness of the metal sheet 1. In Figure 8, a recess that forms a relief 4A is provided at the bottom of the sheet holder 4. Furthermore, the reference numeral 5 denotes a positioning slide guide between the sheet holder 4 and the lower blade 2.

[0066] In addition, the shear load increases in such areas. Therefore, it is effective to partially and strongly restrain the sheet clamp 4. Specifically, it is desirable to locally increase the sheet clamp force per shear line length compared to areas that are not at risk of delayed fracture.

[0067] A more specific embodiment will now be described. First, for the area at risk of delayed fracture, a die is prepared with the shear angle set to 0 degrees. To prevent the occurrence of step-like protrusions in this state, the die structure of the shearing device is controlled so that the effective clearance is not too small. To achieve this, it is effective to observe the sheared end surface 1A actually created in the shearing die and adjust the die so that the effective clearance of the die is 10% or more of the plate thickness at any position on the sheared end surface 1A. Furthermore, it is effective to adjust the effective clearance so that it is 20% or less of the plate thickness to prevent the occurrence of burrs.

[0068] To prevent the clearance of the upper blade 3 from becoming too small, it is effective to provide a guide portion 3A that protrudes toward the sheet holder 4 above and to the side of the upper blade 3's contact surface with the metal sheet, as shown in Figure 8. This guide portion 3A comes into contact with the sheet holder 4, creating a mold structure that maintains the clearance between the upper and lower blades 2, 3. However, the guide portion 3A is configured so that it can move in the shearing direction even when it comes into contact with the sheet holder 4. It is also desirable to provide a relief 4A in the lower part of the sheet holder 4 so that it is not cut by the positioning contact portion of the upper blade 3.

[0069] Furthermore, since the shear load increases in such areas, it is also effective to partially and strongly restrain the sheet clamp 4. Specifically, it is desirable to set the sheet clamp force per unit shear line length to 7.8 kgf / mm or more in an area 300 mm wide and 400 mm in the blank direction centered on the area at risk of delayed fracture, compared to areas not at risk of delayed fracture.

[0070] [C: Shear rate] The inventors have found that even under conditions where non-uniformity of the sheared edge 1A occurs when the shear rate is set to a high rate in consideration of mass production, the non-uniformity may be reduced or eliminated at a certain shear rate. Specifically, the inventors have found that when the shear rate is sufficiently reduced, that is, at a low rate, the non-uniformity of the sheared edge 1A may be reduced or eliminated.

[0071] Based on this, in this embodiment, the shear rate at which non-uniformity is suppressed is calculated, and the range of the calculated shear rate is set as the shear rate during shearing as the improved shearing condition. Note that the stroke speed until the upper blade 3 contacts the plate does not need to be slow. Here, the non-uniformity of the sheared edge 1A described above is due to (a) the brittleness of the material and (c) instability due to the load on the die. Therefore, by slowing the shear rate, the material deformation slows down. As a result, the impact force when the upper blade 3 contacts the die is alleviated, and the unstable generation and propagation of cracks (a) is suppressed. Furthermore, by slowing the shear rate, the instantaneous processing force and the impact force when the upper blade 3 contacts the die are reduced. As a result, (c) deflection of the die and (b) wear are suppressed, resulting in a stabilized edge.

[0072] On the other hand, reducing the shear rate may reduce the productivity of the blanking process. This is a trade-off between productivity and the shear rate. Therefore, the inventors devised the following method to instantly reduce the shear rate during shearing of the portion at risk of delayed fracture while maintaining productivity.

[0073] For example, in a servo press with variable shear rate, the shear rate is instantaneously reduced in a portion at risk of delayed fracture from the start of shearing when the upper blade 3 begins to contact the material until the end of shearing, which results in separation of the metal sheet 1. Specifically, the upper blade 3 is stroked at a high speed from before the upper blade 3 comes into contact with the metal sheet 1 until it contacts the metal sheet 1, then at a low speed from when it contacts the metal sheet 1 until the material separates, and further at a high speed from when the material separates until it reaches the bottom dead center and returns to the standby position.

[0074] In a servo press, the speed can be controlled. Therefore, the shear speed at which the non-uniformity of the sheared edge 1A disappears is first determined. Then, it is desirable to set the stroke speed during shearing of the metal sheet 1 within that range.

[0075] Furthermore, in the case of various mechanical presses widely used in shearing, the press load capacity increases as the bottom dead center is approached. However, mechanical presses have the characteristic of extremely slowing down near the bottom dead center. Therefore, as an improved shearing condition for areas at risk of delayed fracture, the depth of penetration of the upper blade 3 into the top surface 2A of the lower blade 2 is set to 1 mm or less, preferably less than 0 mm, in areas of the metal plate 1 at risk of delayed fracture.

[0076] In this embodiment, the stroke when shearing the delayed fracture risk portion is brought as close as possible to the bottom dead center. This enables shearing in a stroke region with an extremely low shear rate. Even when the penetration depth is less than 0 mm, the material can be separated by pressing the upper blade 3 in by an amount calculated by multiplying the plate thickness by the ratio of the sag region to the sheared surface region. Therefore, shearing with a negative penetration depth is also possible. In other words, even when the penetration depth is less than 0 mm, the material can be separated by pressing the upper blade 3 in by an amount calculated by multiplying the ratio of the sag region to the sheared surface region in the plate thickness direction. Therefore, since processing with a negative penetration depth is also possible, it is desirable to adjust the penetration depth in the delayed fracture risk portion within a range of -1 multiplied by the minimum value of the plate thickness x (fracture surface ratio) within the sheared edge 1A.

[0077] In addition, in normal shearing, taking into consideration the deflection of the mold, the depth of penetration of the upper blade 3 into the top surface 2A of the lower blade 2 is set to 2 to 3 mm or more. Note that the penetration depth is the minimum distance in the shearing direction from the tip of the upper blade 3 to the top surface 2A of the lower blade 2 at the bottom dead center. In this embodiment, if the cutting depth of the die is adjusted to the limit at which the workpiece can be sheared, the following may occur: The cutting depth of the upper blade 3 may become smaller or larger than expected due to deflection of the die, etc. In this case, the stroke for shearing must be finely adjusted.

[0078] Also, for example, blanking is performed in an earlier process of the transfer press. Therefore, it may not be easy to adjust the stroke due to the relationship with the later process. In this case, as shown in Figure 9, it is recommended to introduce a height adjustment mechanism 6 that can adjust the height of either the upper blade 3 or the lower blade 2 using a shim 6B or a block 6A. In this case, it is possible to address this issue by adjusting the relative positions of the cutting edges of the upper and lower blades 2 and 3 in the shearing direction at the bottom dead center.

[0079] The example shown in Figure 9 shows a configuration example in which the cutting depth is adjusted using a shearing device mechanism that can finely adjust the cutting depth when the stroke amount of the upper blade 3 is constant. In the shearing device shown in Figure 9, a bottom dead center position adjustment mechanism (height adjustment mechanism 6) for the upper blade 3 and the lower blade 2 is provided above the upper blade 3 or below the lower blade 2, or both. An example of such a bottom dead center position adjustment mechanism (height adjustment mechanism 6) is a mechanism that inserts a combination of a block 6A and a shim plate 6B with high dimensional accuracy.

[0080] In this shearing state, where non-uniformity is observed at the sheared edge 1A, the shear rate setting, SPM, is reduced to an SPM where non-uniformity at the sheared edge 1A is no longer observed. SPM stands for Shots Per Minute. In a mechanical press, the average stroke speed can be calculated from the SPM and stroke. For example, for ultra-high strength steel with a tensile strength of 1470 MPa, it is desirable to set the average stroke speed to 200 mm / s or less.

[0081] (others) The present disclosure may also be configured as follows. (1) Disclosure 1 is a shearing method for shearing a metal plate for press molding before press molding, Determine the shearing conditions that will not cause unevenness on the sheared end surface after shearing in advance. Shearing is carried out under the determined shearing conditions, The non-uniform sheared end surface has irregularities along the extension direction of the sheared end surface, and the change between the concave and convex portions is 5% or more of the thickness of the metal plate along the extension direction, or 3% or more of the thickness of the metal plate in the shear direction along the shear direction. Shearing method. (2) Disclosure 2 states that the non-uniform sheared edge is a region having a recessed portion that is recessed relatively to the reference sheared edge along the extension direction of the sheared edge, and the recessed amount of the recessed portion is 5% or more of the thickness of the metal plate. Shearing method. (3) Disclosure 3 discloses that the non-uniform sheared end surface has a protruding portion that protrudes relatively from the reference sheared end surface along the extension direction of the sheared end surface, and the boundary between the region connected to the protruding portion in the extension direction and the region of the protruding portion is a stepped boundary in the direction along the shearing direction, and the step at the boundary between the two regions is 3% or more of the thickness of the metal plate. Shearing method. (4) Disclosure 4 discloses a method for manufacturing a press-formed product having a target part shape by press-forming the metal plate, and determining in advance, among the sheared end faces of the press-formed product, the sheared end faces that are at risk of delayed fracture, The formation of the sheared end surface of the portion of the metal plate corresponding to the delayed fracture risk portion is carried out by the shearing method described in claim 1. Shearing method. (5) Disclosure 5 states that the delayed fracture risk area is a location where the residual tensile stress after press forming is 600 MPa or more, or where the equivalent plastic strain is 0.06 or more and the residual tensile stress is 400 MPa or more. Shearing method. (6) Disclosure 6 provides a coating with superior wear resistance to either or both of the upper blade and the lower blade used to shear the portion corresponding to the portion at risk of delayed fracture, compared to the shear blade used to shear the portion other than the portion at risk of delayed fracture. Shearing method. (7) Disclosure 7 uses a material with a Rockwell hardness of 3 or more higher for either or both of the upper blade and lower blade used to shear the portion corresponding to the portion at risk of delayed fracture than the shear blade used to shear the portion other than the portion at risk of delayed fracture. Shearing method. (8) Disclosure 8 performs cutting processing using multiple cutting edges with different cutting edge R to determine the range of cutting edge R in which unevenness does not occur on the sheared end surface, and sets the determined range of cutting edge R as the shearing condition in which the above-mentioned unevenness does not occur. Shearing method. (9) Disclosure 9 sets the absolute value of the shear angle to 0.2 degrees or less as shearing conditions that prevent the above-mentioned non-uniformity from occurring, and sets the clearance between the upper blade and the lower blade to 10% or more of the thickness of the metal plate. Shearing method. (10) Disclosure 10 sets the clearance to 20% or less of the thickness of the metal plate. Shearing method. (11) Disclosure 11 involves shearing a metal plate with an upper blade and a lower blade while the metal plate is restrained with a lower blade and a plate holder. By providing a guide portion that protrudes from the upper blade toward the sheet pressing side, the clearance between the upper blade and the lower blade during shearing is maintained at 10% or more of the thickness of the metal sheet. Shearing method. (12) Disclosure 12 sets the absolute value of the shear angle to 0.2 degrees or less as shearing conditions that prevent the above-mentioned non-uniformity from occurring, and sets the clearance between the upper blade and the lower blade to 10% or more of the thickness of the metal plate. Shearing method. (13) Disclosure 13 performs shear processing under a plurality of different shear rate conditions to determine a range of shear rate conditions under which non-uniformity does not occur on the sheared end surface, and the determined range of shear rate conditions under which non-uniformity does not occur is set as the shear condition under which non-uniformity does not occur. Shearing method. (14) Disclosure 14 performs shear processing under a plurality of different shear rate conditions to determine a range of shear rate conditions under which non-uniformity does not occur on the sheared end surface, and defines the determined range of shear rate conditions under which non-uniformity does not occur as the shear condition under which non-uniformity does not occur. Shearing method. (15) Disclosure 15 defines the distance in the shearing direction from the top surface of the lower blade at the bottom dead center of the tip of the upper blade that contacts the metal plate to be sheared as the biting depth. By performing shearing at a plurality of different penetration depths, a range of penetration depths in which non-uniformity does not occur on the sheared end surface is determined, and the determined range of penetration depths is set as the shearing condition in which the non-uniformity does not occur. Shearing method. (16) Disclosure 16 defines the distance in the shearing direction from the top surface of the lower blade at the bottom dead center of the tip of the upper blade that contacts the metal plate to be sheared as the biting depth. As a shearing condition for shearing at least a part of the delayed fracture risk portion, the penetration depth is set to less than 1.5 mm and to a penetration amount that can cut the workpiece. Shearing method. (17) Disclosure 17 provides a shearing device that performs shearing under shearing conditions that do not cause unevenness, and provides a height adjustment mechanism above the upper blade or below the lower blade that can adjust the bottom dead center position of the upper blade or the bottom dead center position of the lower blade, or both, and adjusts the relative positions of the upper blade and the lower blade at the bottom dead center using the height adjustment mechanism. Shearing method. (18) Disclosure 18 states that the height adjustment mechanism is implemented by placing a block and a shim plate above the upper blade or below the lower blade. Shearing method. (19) Disclosure 19 states that the metal plate is a high-strength steel plate having a tensile strength of 980 MPa or more. Shearing method. (20) Disclosure 20 is a method for producing a press-formed product having a target part shape by press-forming a metal plate sheared by a shearing method described in any one of the disclosures. Manufacturing method for press-molded products. (21) Disclosure 21 is a shearing device that shears a metal plate with the upper blade and the lower blade by relatively moving the upper blade toward the lower blade while the metal plate is restrained by the top surface of the lower blade and the plate holder, a guide portion interposed between the side surface of the upper blade and the plate holder, for maintaining a clearance between the upper blade and the lower blade at a certain value or more during shearing; The thickness of the guide portion is set so that the clearance between the upper blade and the lower blade during the shearing process is 10% or more of the thickness of the metal plate. Shearing equipment. [Example]

[0082] Next, an example based on this embodiment will be described. In this example, the description will be made on specimen A, which is a steel sheet with a thickness of 1.4 mm and a tensile strength of 1470 MPa. However, the present invention is not limited to this specimen, and can be suitably applied to metal materials, including high-strength steel sheets with a tensile strength of 980 MPa or more, which are susceptible to delayed fracture at the sheared edge 1A.

[0083] (First Example) A: We considered how to maintain the cutting edge R by selecting the right material. In this example, upper and lower blades 2 and 3 (shear blades) with different tip radii were used to simulate wear during mass production. The shear angle was selected from a range of 0 to 3 degrees, and shearing was performed. The cutting edge radii of each of the upper and lower blades 2 and 3 were selected from 0 mm, 0.1 mm, 0.2 mm, 0.3 mm, and 0.5 mm. The shearing was performed by linearly shearing a length of 200 mm of the test material. The set shear clearance was set to 10% of the plate thickness.

[0084] The results are shown in Table 1. This is an evaluation of the presence or absence of unevenness in the sheared end surface 1A on the remaining part due to different cutting edge R and shear angle of the upper and lower blades 2 and 3.

[0085] [Table 1]

[0086] According to Table 1, when the cutting edge R of the upper and lower blades is 0.2 mm or less, it is expected that unevenness in the sheared edge 1A will not occur even if the shear angle changes. Such cutting edge R of the upper and lower blades may be applied to either the upper blade 3 or the lower blade 2, depending on the actual wear state. Furthermore, as shown in Table 2, we investigated conditions with different blade materials and coating conditions.

[0087] [Table 2]

[0088] The results are shown in Figure 10. Figure 10 shows the change in cutting edge R due to wear at a shear angle of 0° for each blade material, assuming the initial cutting edge R to be 0 mm under the same shearing conditions. The cutting edge R was determined to be the R that most closely approximates the shape of the most worn part of the upper and lower shear blades.

[0089] Here, for example, the target is set to obtain a stable sheared edge 1A after 30,000 shearing shots. Under this target, under conditions C and D, the cutting edge R is below 0.20 mm at 30,000 shots. It can be seen that under conditions C and D, the sheared edge 1A is uniform. Therefore, if the shearing die is primarily made of uncoated SKD11, it is preferable to do the following: Apply a coating to improve wear resistance, or replace the base material with SKH51, which has a hardness 3 HRC higher. This makes it possible to partially maintain the cutting edge R up to the target number of shots. The threshold value of the cutting edge R that can suppress the target number of shots, the degree of wear, and unevenness of the end surface can vary depending on the strength and thickness of the material being sheared.

[0090] Next, the upper and lower blades 2 and 3 made of each material and having the cutting edge R at 30,000 shots were used. Then, a delayed fracture test was carried out on each metal plate 1 after shearing. The shear conditions were a set shear clearance of 10% of the plate thickness and a shear angle of 0 or 2 degrees. A length of 200 mm was sheared in a straight line.

[0091] In addition, the method of Patent Document 4 was used to control the equivalent pre-strain and applied stress to the sheared edge 1A in the delayed fracture test. Then, stress was applied to each test specimen by four-point bending to the sheared edge 1A, either as sheared or after uniaxial compressive deformation. Then, each test specimen was immersed in a hydrochloric acid solution of pH 2.7 for 96 hours while under stress. In the delayed fracture test, if a crack initiated from the sheared edge 1A and penetrated the plate thickness, the delayed fracture was judged to be NG. Otherwise, the delayed fracture was judged to be OK. Note that areas other than the sheared edge 1A, which was the subject of the evaluation, were ground to prevent delayed fracture.

[0092] Here, evaluation was carried out under the following four conditions, Condition α to Condition δ, which simulate areas at risk of delayed fracture. Conditions γ and δ are conditions that simulate areas at a relatively low risk of delayed fracture. Condition α: Equivalent pre-strain 0.00, load stress 800 MPa Condition β: Equivalent pre-strain 0.06, load stress 500 MPa Condition γ: Equivalent pre-strain 0.00, load stress 500 MPa Condition δ: Equivalent pre-strain 0.03, load stress 500 MPa

[0093] The evaluation results of the delayed fracture test are shown in Table 3.

[0094] [Table 3]

[0095] Table 3 shows the shearing conditions (cutting edge R, shear angle) and sheared edge condition (edge ​​nonuniformity) of each delayed fracture test piece. Figure 3 also shows the equivalent pre-strain and applied stress of the test piece, as well as the OK / NG delayed fracture result for each equivalent pre-strain and applied stress condition.

[0096] The test results revealed the following. Assume that the target cutting edge R for preventing unevenness on the sheared edge 1A is 0.20. In this case, under the conditions of a C cutting edge classification with an abrasion-resistant coating and a D cutting edge classification with a relatively high hardness, it is possible to suppress the amount of wear to below the target cutting edge R for the target number of cutting shots of 30,000. As a result, it was found that by suppressing the unevenness on the sheared edge 1A, delayed fracture can be suppressed in areas at risk of delayed fracture.

[0097] Using the same 1.4 mm thick steel specimen A as in the above evaluation, which is a 1470 MPa tensile strength steel, the specimen A was press-formed into a press-formed product 10 as shown in Figure 11 and evaluated. After press forming, a similar evaluation was carried out using the press-formed product 10 having the following delayed fracture risk region ε and delayed fracture risk region ζ. Delayed fracture risk area ε: equivalent pre-strain due to forming 0.08, residual tensile stress 700MPa Delayed fracture risk area ζ: Equivalent pre-strain due to forming 0.00, residual tensile stress 1000MPa

[0098] Here, the equivalent pre-strain and residual tensile stress of the delayed fracture risk regions ε and ζ were calculated using CAE analysis by FEM of press forming. Additionally, CAE was used to estimate stress-strain this time due to its simplicity, but strain can also be estimated by applying an equally spaced grid to the metal plate 1 before processing and directly measuring the amount of deformation before and after forming, or by measurement using a strain gauge. Stress can also be estimated by X-ray stress measurement, or by attaching a strain gauge to the stress measurement area, cutting out the measurement area, and releasing the stress, and measuring the change in strain at that time.

[0099] The test results were then obtained for each cutting edge material with a wear-simulated cutting edge R for the target number of machining rounds of 30,000 shots. Specifically, the unevenness of the end surface and the delayed fracture test results were obtained when the part at risk of delayed fracture was locally sheared with a shear angle of 0 degrees or 2 degrees. The results are shown in Table 4.

[0100] [Table 4]

[0101] According to Table 4, this was effective under the conditions of the C cutting edge classification with a wear-resistant coating and the D cutting edge classification with a relatively high hardness. In other words, it was found that it was possible to suppress the amount of wear to below the target cutting edge R after the target number of cutting shots of 30,000. In addition, in this case, it became possible to manufacture automotive parts with excellent delayed fracture resistance.

[0102] (Second Example) B: Selection of partial shear angle 0 degrees and effective clearance management, die structure, plate clamp 4 Shearing was performed using upper and lower blades 2 and 3 made of SKD11 with a cutting edge radius (0.2 mm) simulating wear during mass production, with a shear angle selected from a range of 0 to 4 degrees. Additionally, a 230 mm square metal plate 1 was sheared linearly over a length of 230 mm with a punching allowance of 15 mm. The presence or absence of non-uniformity on the sheared edge 1A on the remaining side was then investigated. The shear clearance setting was 5%, 10%, 15%, 20%, and 25% of the plate thickness.

[0103] In addition, the sheet pressure was measured by placing four gas cylinders evenly across the width of the sheet as shown in Figure B (left), which provided a sheet pressure of 900 kgf at the start of shearing. The results are shown in Table 5. Table 1 shows the state of unevenness of the sheared edge 1A due to different shear angles and clearances. In addition, if burrs were generated, they were also noted.

[0104] [Table 5]

[0105] According to Table 5, it is expected that unevenness of the sheared edge 1A will not occur if the shear angle is 0.2 degrees or less. Furthermore, it can be seen that by setting the clearance to 10% or more of the plate thickness, it is possible to suppress the occurrence of steps due to protrusions. It can also be seen that by setting the clearance to 20% or less of the plate thickness, it is possible to suppress the occurrence of burrs.

[0106] Furthermore, Table 6 shows the state of unevenness of the end surface when the number of gas cylinders evenly arranged within the shear length range is reduced from a maximum of four to one when the clearance relative to the plate thickness is set to 10% for shear angles of 0 degrees and 0.2 degrees. FIG. 12 shows the shape of the plate holder 4 and the arrangement of the gas spring 7. Table 6 shows the change in the end surface non-uniformity due to the sheet pressing force when the shear angle is 0 degrees or 0.2 degrees.

[0107] [Table 6]

[0108] When the shear angle is close to 0 degrees, the upper blade 3 comes into contact with various points of the metal sheet 1 almost simultaneously. For this reason, according to Table 6, it can be seen that a large load is placed on the sheet holder 4. However, it was found that if the sheet holder force per cross-sectional length is set to 7.8 kgf / mm or more in the area of ​​the sheet holder 4,300 mm x 400 mm for a shear length of 230 mm, the unevenness of the sheared edge 1A can be suppressed.

[0109] On the other hand, the clearance in the shearing die is sometimes controlled to be narrower by 10 to 15% to improve shape accuracy and prevent burrs. However, in this case, the deflection of the die due to the shear load can cause the dynamic clearance during shearing to fall below 5% in some areas, which can result in steps.

[0110] Therefore, an example will be described in which a mechanism is employed to limit the clearance between the upper blade 3 and the plate holder 4 so that it does not become too small, as shown in FIG.

[0111] In this die structure, a guide portion 3A is installed at a position between the shear clearances above the upper blade 3. By adjusting the width D of this guide portion 3A, the minimum value of the effective clearance is set to 10% or more of the plate thickness. In this example, it is assumed that the width D of the guide portion 3A is set to be the minimum value of the effective clearance. In this case, if the width D of the guide portion 3A is 10% of the plate thickness, and the effective clearance attempts to fall below 10% due to mold deflection, the plate holder 4 and the guide portion 3A of the upper blade 3 will come into contact. As a result, as long as the positional relationship between the lower blade 2 and the plate holder 4 is fixed by a positioning mechanism such as the slide guide 5, the effective clearance will be corrected to 10% of the plate thickness. By introducing such a mechanism, it is possible to maintain a minimum amount of clearance at each point on the metal plate 1, even with the complex outline of the metal plate 1 of an actual part.

[0112] Furthermore, if the tip of the guide portion 3A of the upper blade 3 comes into contact with the sheet holder 4, and the corner of the guide portion 3A of the upper blade 3 comes into contact with the sheet holder 4, the sheet holder 4 will be scraped off. For this reason, a relief 4A is formed in the sheet holder 4. Also, if the cutting edge is made too deep and the guide portion 3A comes into contact with the metal sheet 1, unintended deformation will occur at the end face. For this reason, the guide portion 3A needs to be positioned at the bottom dead center of the shearing process so that it does not come into contact with the metal sheet 1.

[0113] Next, under the conditions in Table 5, delayed fracture tests were carried out for the following four patterns A to D. A: No unevenness (shear angle 0 degrees, clearance to plate thickness 10%) B: Step (shear angle 0 degrees, clearance against plate thickness 5%) C: Chipping (shear angle 1 degree, clearance to plate thickness 10%) D: Burr (shear angle 0 degrees, clearance to plate thickness 25%)

[0114] In the test, the equivalent pre-strain and applied stress to the sheared end surface 1A were controlled using the method described in Patent Document 4. In addition, stress was applied by four-point bending to the sheared end surface 1A of the test specimen, either in shear or after uniaxial compressive deformation. The test pieces were then immersed in a pH 2.7 hydrochloric acid solution for 96 hours while stress was applied. The test was evaluated as NG for delayed fracture if a crack initiated from the sheared edge 1A and penetrated through the plate thickness. Otherwise, it was evaluated as OK for delayed fracture. Note that areas other than the sheared edge 1A, which was the subject of evaluation, were ground to prevent delayed fracture.

[0115] Here, evaluation was carried out under the following four conditions, α to δ, as conditions simulating parts at risk of delayed fracture: Conditions γ and δ are conditions simulating parts at a relatively low risk of delayed fracture. Condition α: Equivalent pre-strain 0.00, load stress 800 MPa Condition β: Equivalent pre-strain 0.06, load stress 500 MPa Condition γ: Equivalent pre-strain 0.00, load stress 500 MPa Condition δ: Equivalent pre-strain 0.03, load stress 500 MPa

[0116] Table 7 shows the shear end surface condition of each delayed fracture test specimen (A, B, C, D above), the equivalent pre-strain and applied stress of the test specimen, and the delayed fracture OK / NG for each equivalent pre-strain and applied stress condition. That is, Table 7 shows the shear end surface conditions (A, B, C, and D above) of each delayed fracture test piece and the delayed fracture test results.

[0117] [Table 7]

[0118] From the test results, it was found that in the case of an edge that does not have shear edge 1A nonuniformity, delayed fracture can be suppressed in the delayed fracture risk region.

[0119] In addition, the same 1.4 mm thick, 1470 MPa strength steel specimen A as used in the above evaluation was used to press-form the prototype shown in Figure B3, and then a similar evaluation was carried out using the prototype automobile part that had the following delayed fracture risk regions ε and ζ. Delayed fracture risk area ε: equivalent pre-strain due to forming 0.08, residual tensile stress 700MPa Delayed fracture risk area ζ: Equivalent pre-strain due to forming 0.00, residual tensile stress 1000MPa

[0120] The equivalent pre-strain and residual tensile stress of the delayed fracture risk regions ε and ζ were calculated using CAE analysis with FEM for press forming. CAE was used to estimate stress-strain this time due to its simplicity, but strain can also be estimated by applying an equally spaced grid to the metal plate 1 before processing and directly measuring the amount of deformation before and after forming, or by using a strain gauge. Stress can also be estimated by X-ray stress measurement, or by attaching a strain gauge to the stress measurement section, cutting out the measurement section, and then releasing the stress and measuring the change in strain.

[0121] This part was fitted with upper and lower blades 2 and 3 made of SKD11 with a cutting edge radius (0.2 mm) and a local shear angle of 0 or 1 degree at the area at risk of delayed fracture. The target clearance was set to 12, 20 or 25% of the plate thickness, and the mechanism shown in Figure B2 above was used to ensure a minimum clearance of 10% of the plate thickness. Table 4 shows the results of the end surface unevenness and delayed fracture test when the part was sheared. However, the plate pressure applied to the plate holder 4 was set to 10 kgf / mm per cross-sectional length within a 200 mm x 400 mm range from the area at risk of delayed fracture. Table 8 shows the shear edge 1A nonuniformity and delayed fracture test results for each shear angle and clearance.

[0122] [Table 8]

[0123] According to the results in Table 8, by shearing with a shear angle close to 0 degrees, an appropriate sheet pressure, and an appropriate shearing device with an appropriate clearance, it is possible to suppress the non-uniformity of the sheared edge 1A in the delayed fracture risk area and the resulting occurrence of delayed fracture. As a result, it is possible to manufacture automotive parts with excellent delayed fracture resistance.

[0124] (Third Example) "C: Shear rate" was examined. In this example, shear blades with a cutting edge radius of 0.2 mm for the upper and lower blades 2 and 3 made of SKD11 were used to simulate wear during mass production. The shearing process was performed with a shear angle selected from the range of 0 to 2.0 degrees. A linear shear was performed over a length of 200 mm, and the presence or absence of non-uniformity in the sheared edge surface 1A within a 40 mm central region on the remaining side due to differences in SPM was evaluated. The shear clearance was set to 10% of the plate thickness. The stroke of the upper blade 3 for shearing was set to 900 mm using a mechanical press. The shearing process was carried out with the minimum penetration depth of the upper blade 3 into the lower blade 2 at the center of the width of the metal plate 1 set to 6 mm. The minimum penetration depth indicates how far below the plate surface of the lower blade 2 the tip of the upper blade 3 reaches. The results are shown in Table 9. Table 9 shows the state of sheared edge 1A nonuniformity with different SPM and shear angle.

[0125] [Table 9]

[0126] According to Table 9, in shearing at a low speed with an average stroke speed of 210 mm / s or less, an improvement effect on the non-uniformity of the sheared end surface 1A was observed.

[0127] Next, an embodiment using a speed-controllable servo press will be described. The stroke of the servo press was set to 130 mm, and the maximum stroke speed was set to 400 mm / s. All other conditions were the same as those in Table 1.

[0128] The results are shown in Table 10. Table 10 shows the state of shear end surface 1A nonuniformity at each control stroke speed.

[0129] [Table 10]

[0130] In this example, it was found that the non-uniformity of the sheared end surface 1A could be suppressed when the control stroke speed was 150 mm / s or less.

[0131] Therefore, we investigated how to maximize SPM while keeping the shearing speed sufficiently low. Specifically, we evaluated shearing under the following shear conditions A, B, and C. Shearing condition A (partially low speed): The control stroke speed was set to 100 mm / s only for a 10 mm stroke centered on the center of the thickness of metal plate 1 during shearing. Furthermore, the control stroke speed was set to 400 mm / s for the rest of the stroke. · Shear condition B (high speed): Always set the control stroke speed to 400 mm / s. · Shear condition C (low speed): Always set the control stroke speed to 100 mm / s. The superiority of SPM calculated from the nonuniformity of the sheared edge 1A, stroke, and shear rate was then confirmed. The shear angle was set to 0 degrees or 0.5 degrees. The results are shown in Table 11. Table 11 shows the relationship between sheared edge 1A nonuniformity and SPM under shear condition A (partially low speed), shear condition B (high speed), and shear condition C (low speed).

[0132] [Table 11]

[0133] According to Table 11, under shearing condition B (high speed), SPM is maximized, but non-uniformity occurs at the sheared edge 1A. Under shearing condition C (low speed), non-uniformity at the sheared edge 1A is suppressed, but SPM drops to 25% of the maximum value. On the other hand, under shearing condition A (partially low speed), non-uniformity at the sheared edge 1A can be suppressed while maintaining shear SPM at 90% of the maximum speed. As a result, it is possible to improve the uniformity of the sheared edge 1A without reducing productivity.

[0134] Next, an example of a technique for improving the uniformity of the sheared end surface 1A by reducing the shear rate by controlling the distance from the bottom dead center during shearing in a mechanical press will be described. Here, various types of mechanical presses widely used for shearing can take on a higher press load capacity as they approach the bottom dead center, but they also have the characteristic of decelerating extremely near the bottom dead center because the stroke direction starts to reverse. An example using a crank press, which is a type of mechanical press, will be described below. In this example, the stroke was set to 175 mm, the set SPM was 55, and the average stroke speed was 320 mm / s, which were conditions closer to actual production. Here, the cutting edge depth was defined as the distance between the tip of the upper blade 3 and the top surface 2A of the lower blade 2 at the bottom dead center in the center of the width when linearly shearing a length of 200 mm.

[0135] In this example, the stroke was constant. The cutting depth was adjusted using a shearing device mechanism capable of finely adjusting the cutting depth, as shown in Figure 9. This shearing device is provided with a bottom dead center position adjustment mechanism (height adjustment mechanism 6) for the upper blade 3 and the lower blade 2, either above the upper blade 3 or below the lower blade 2, or both.

[0136] The average stroke speed was set to 320 mm / s, and shearing was performed at shear angles of 0 and 0.5 degrees. The cutting edge penetration depth was varied to check the state of non-uniformity within a range of 40 mm from the center of the sheared edge 1A. The results are shown in Table 12. In other words, Table 12 shows the relationship between the penetration depth and the non-uniformity of the sheared edge 1A. However, with a shear width of 200 mm and a shear angle of 0.5 degrees, the amount of penetration at one end was approximately 0.9 mm shallower than in the center. This meant that there were cases where the metal sheet 1 could not be cut all the way through. For this reason, this was noted in the cases. Also, if the amount of penetration into the workpiece was insufficient even with a shear angle of 0 degrees and the metal sheet 1 could not be cut, this was noted in the cases. The amount of penetration was adjusted as follows: That is, taking into account the deflection of the mold, the length of the part of the red iron oxide pigment applied to the metal sheet 1 that was attached to the upper blade 3 was measured and checked while making the adjustment.

[0137] [Table 12]

[0138] According to Table 12, if the cutting depth of the blade is adjusted to 1.5 mm or less, it is expected that the unevenness of the sheared edge 1A in that area can be suppressed. Because the cutting length was 200 mm, if the cutting depth was -0.2 mm or less, the end of punching could not be cut when the shear angle was 0.5 degrees. However, this is a defect that can be avoided in actual production by setting only the areas at risk of delayed fracture to a shear angle of 0 degrees. Alternatively, it is a defect that can be avoided by ingeniously designing the mold so that the areas at risk of delayed fracture are located closer to the end of punching.

[0139] As representatives of the properties of the sheared edge 1A obtained under the various shearing conditions described above, the following edge surfaces A to D in Table 12 were evaluated for delayed fracture. These edge surfaces are not limited to those in Table 12, but are representative of the delayed fracture properties when there is heterogeneity in the edge surface under each condition. End face A: End face with a step at a shear angle of 0 degrees and a penetration depth of 6 mm End surface B: End surface with no unevenness and penetration depth of 0 mm End face C: End face with chipping at a shear angle of 0.5 degrees and a depth of 6 mm End surface D: End surface with no unevenness at a penetration depth of 0 mm

[0140] The equivalent pre-strain and applied stress to the sheared edge 1A for delayed fracture evaluation were controlled using the method described in Patent Document 4. That is, stress was applied by four-point bending to the sheared edge 1A of the test specimen, either as sheared or after uniaxial compressive deformation. The test pieces were then immersed in a pH 2.7 hydrochloric acid solution for 96 hours while stress was applied. The evaluation was based on whether a crack initiated from the sheared edge 1A and penetrated the plate thickness, in which case it was judged to be NG for delayed fracture. Otherwise, it was judged to be OK for delayed fracture. Note that areas other than the sheared edge 1A, which was the subject of evaluation, were ground to prevent delayed fracture.

[0141] Here, evaluation was carried out under the following four conditions, conditions α to δ, as conditions simulating regions at risk of delayed fracture: Conditions γ and δ are conditions simulating regions at a relatively low risk of delayed fracture. Condition α: Equivalent pre-strain 0.00, load stress 800 MPa Condition β: Equivalent pre-strain 0.06, load stress 500 MPa Condition γ: Equivalent pre-strain 0.00, Load stress 500MPa Condition δ: Equivalent pre-strain 0.03, load stress 500 MPa

[0142] Table 13 shows the shear edge condition (edge ​​non-uniformity) of each delayed fracture test specimen, as well as the equivalent pre-strain and applied stress of the test specimen. Also, Figure 13 shows the delayed fracture OK / NG result for each equivalent pre-strain and applied stress condition. In other words, Table 13 shows the shear edge condition (edge ​​non-uniformity) of each delayed fracture test specimen and the delayed fracture test results.

[0143] [Table 13]

[0144] These test results showed that delayed fracture can be suppressed in areas at risk of delayed fracture by using a shearing method and shearing equipment that can achieve a sheared end surface condition that does not cause non-uniformity at the sheared end surface 1A.

[0145] Test material A, the same 1.4 mm thick, 1470 MPa strength steel as used in the above evaluation, was press-formed into a press-formed product as shown in Figure 11. After that, a similar evaluation was carried out using a prototype automobile part that had the following delayed fracture risk regions ε and ζ. Delayed fracture risk area ε: equivalent pre-strain due to forming 0.08, residual tensile stress 700MPa Delayed fracture risk area ζ: equivalent pre-strain due to forming 0.00, residual tensile stress 1000MPa

[0146] The equivalent pre-strain and residual tensile stress of the delayed fracture risk areas ε and ζ were calculated using CAE analysis with FEM for press forming. CAE was used to estimate stress-strain this time due to its simplicity, but strain can also be estimated by applying an equally spaced grid to the metal plate 1 before processing and directly measuring the amount of deformation before and after forming, or by measurement using a strain gauge. Stress can also be estimated using X-ray stress measurement, or by attaching a strain gauge to the stress measurement area, cutting out the measurement area, and releasing the stress, and measuring the change in strain during this process.

[0147] To shear the area of ​​metal plate 1 corresponding to the delayed fracture risk region of this part, the stroke was set to 175 mm, the set SPM was 55, and the average stroke speed was set to 320 mm / s. The cutting edge material was SKD11, and the cutting edges of upper and lower blades 2 and 3 were set to R0.2 to simulate wear. The shear angle was then locally set to 0 degrees or 0.5 degrees in the delayed fracture risk region, and the cutting depth was adjusted to either 6 mm or 0 mm using the device shown in Figure 9 above. Table 14 shows the conditions, the unevenness of the edge when sheared, and the delayed fracture test results. That is, Table 14 shows the shear angle / penetration depth, the unevenness of the edge, and the delayed fracture test results.

[0148] [Table 14]

[0149] According to Table 14, by using the shearing method according to the present invention that suppresses the non-uniformity of the sheared edge 1A, it is possible to manufacture automobile parts that are excellent in delayed fracture resistance. [Explanation of symbols]

[0150] 1 metal plate 1A Sheared end face 2 Lower blade 2A Top 3 Upper blade 3A Guide section 4 Board holder 6 Height adjustment mechanism 10 Press-molded products S10 Shearing process S20 Press Process

Claims

1. A shearing method for shearing a metal plate for press molding before press molding, comprising: Determine the shearing conditions that will not cause unevenness on the sheared end surface after shearing in advance. Shearing is carried out under the determined shearing conditions, The non-uniform sheared end surface has irregularities along the extension direction of the sheared end surface, and the change between the concave and convex portions is 5% or more of the thickness of the metal plate along the extension direction, or 3% or more of the thickness of the metal plate in the direction along the shear direction. Shearing method.

2. The non-uniform sheared end surface is a region having a recessed portion that is recessed relatively to a reference sheared end surface along the extension direction of the sheared end surface, and the recessed amount of the recessed portion is 5% or more of the plate thickness of the metal plate. The shearing method according to claim 1.

3. The non-uniform sheared end surface has a protruding portion that protrudes relatively from a reference sheared end surface along the extension direction of the sheared end surface, and the boundary between the region connected to the protruding portion in the extension direction and the region of the protruding portion is a stepped boundary in the direction along the shearing direction, and the step at the boundary between the two regions is 3% or more of the plate thickness of the metal plate. The shearing method according to claim 1.

4. When the metal plate is press-formed to produce a press-formed product having a target part shape, a shear end surface that becomes a delayed fracture risk portion among the shear end surfaces of the press-formed product is determined in advance, The formation of the sheared end surface of the portion of the metal plate corresponding to the delayed fracture risk portion is carried out by the shearing method described in claim 1. The shearing method according to claim 1.

5. The delayed fracture risk portion is a portion where the residual tensile stress after press forming is 600 MPa or more, or where the equivalent plastic strain is 0.06 or more and the residual tensile stress is 400 MPa or more. The shearing method according to claim 4.

6. A coating having superior wear resistance to either or both of the upper blade and the lower blade used for shearing the portion corresponding to the portion at risk of delayed fracture is applied compared to the shear blade used for shearing the portion other than the portion at risk of delayed fracture. The shearing method according to claim 4.

7. For either or both of the upper blade and lower blade used for shearing the portion corresponding to the portion at risk of delayed fracture, a material with a Rockwell hardness that is 3 or more higher than that of the shear blade used for shearing other than the portion at risk of delayed fracture is used. The shearing method according to claim 4.

8. By performing cutting processing with a plurality of cutting edges having different cutting edge R for shearing, a range of cutting edge R in which unevenness does not occur on the sheared end surface is determined, and the determined range of cutting edge R is set as the shearing condition in which the above-mentioned unevenness does not occur. The shearing method according to any one of claims 1 to 7.

9. As shearing conditions that prevent the non-uniformity, the absolute value of the shear angle is set to 0.2 degrees or less, and the clearance between the upper blade and the lower blade is set to 10% or more of the thickness of the metal plate. The shearing method according to any one of claims 1 to 7.

10. The clearance is set to 20% or less of the thickness of the metal plate. The shearing method according to claim 9.

11. With the metal plate restrained by the lower blade and plate holder, the upper and lower blades shear it. By providing a guide portion that protrudes from the upper blade toward the sheet pressing side, the clearance between the upper blade and the lower blade during shearing is maintained at 10% or more of the thickness of the metal sheet. The shearing method according to claim 9.

12. As shearing conditions that prevent the non-uniformity, the absolute value of the shear angle is set to 0.2 degrees or less, and the clearance between the upper blade and the lower blade is set to 10% or more of the thickness of the metal plate. The shearing method according to claim 8.

13. By performing shear processing under a plurality of different shear rate conditions, a range of shear rate conditions under which non-uniformity does not occur on the sheared end surface is determined, and the determined range of shear rate conditions under which non-uniformity does not occur is set as the shear condition under which non-uniformity does not occur. The shearing method according to any one of claims 1 to 7.

14. By performing shear processing under a plurality of different shear rate conditions, a range of shear rate conditions under which non-uniformity does not occur on the sheared end surface is determined, and the determined range of shear rate conditions under which non-uniformity does not occur is set as the shear condition under which non-uniformity does not occur. The shearing method according to claim 8.

15. When the distance in the shearing direction from the top surface of the lower blade at the bottom dead center of the tip of the upper blade that contacts the metal plate to be sheared is defined as the biting depth, By performing shearing at a plurality of different penetration depths, a range of penetration depths in which non-uniformity does not occur on the sheared end surface is determined, and the determined range of penetration depths is set as the shearing condition in which the non-uniformity does not occur. The shearing method according to any one of claims 1 to 7.

16. When the distance in the shearing direction from the top surface of the lower blade at the bottom dead center of the tip of the upper blade that contacts the metal plate to be sheared is defined as the biting depth, As a shearing condition for shearing at least a part of the delayed fracture risk portion, a penetration depth is set to less than 1.5 mm and to a penetration amount that can cut the workpiece. The shearing method according to any one of claims 4 to 7.

17. A shearing device that performs shearing under shearing conditions that do not cause unevenness is provided with a height adjustment mechanism above the upper blade or below the lower blade that can adjust the bottom dead center position of the upper blade or the bottom dead center position of the lower blade, or both, and the relative positions of the upper blade and the lower blade at the bottom dead center are adjusted by the height adjustment mechanism. The shearing method according to claim 15.

18. The height adjustment mechanism is implemented by placing a block and a shim above the upper blade or below the lower blade. The shearing method according to claim 17.

19. The metal plate is a high-strength steel plate having a tensile strength of 980 MPa or more. The shearing method according to any one of claims 1 to 7.

20. The metal plate sheared by the shearing method according to any one of claims 1 to 7 is press-formed to produce a press-formed product having a target part shape. Manufacturing method for press-molded products.

21. A shearing device that shears a metal plate with the upper blade and the lower blade by relatively moving the upper blade toward the lower blade while the metal plate is restrained by the top surface of the lower blade and the plate holder, a guide portion interposed between the side surface of the upper blade and the plate holder, for maintaining a clearance between the upper blade and the lower blade at a certain value or more during shearing; The thickness of the guide portion is set so that the clearance between the upper blade and the lower blade during the shearing process is 10% or more of the thickness of the metal plate. Shearing equipment.

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