JP4705348B2 - Steel sheet punching tool and punching method using the same - Google Patents

Description

  The present invention mainly relates to a technique for punching a steel sheet into a predetermined contour in order to use a thin steel plate as a part of an automobile or the like.

  When a thin steel sheet is actually used, in many cases, it is first formed into a predetermined shape by punching, and then formed into a predetermined shape by forming and then assembled and used as an automobile part through a welding process. . FIG. 1 shows a deformation state of a material by a conventional punching process. Since a large compressive or tensile strain is applied to the hardened layer shown in the figure, the material there is remarkably hardened and the ductility of the hardened portion is deteriorated. The ductility of the end face deteriorated, and the hole expansibility of the punched hole was remarkably deteriorated. The end face ductility deterioration due to the hardened layer is particularly severe in high-strength steel, and the formability of high-strength steel sheets that have been frequently used in recent years in response to needs for reducing the weight of automobiles has deteriorated significantly. The hole expansion value required for forming an actual part is approximately 65%, and obtaining a hole expansion value exceeding this value in a high-strength steel sheet is an issue for weight reduction.

  As a punching technology to improve the formability of the end face after punching, a technology has been developed in which the shape of the punch tip is shaped as shown in Fig. 2, and the notch shape and work hardening part generated after the first stage punching are scraped off. (Non-Patent Document 1). However, since the punch shape shown in this technology has a complicated shape, it is usually put to practical use in an actual process that is reused after polishing a die such as a punch or die as a countermeasure against wear due to continuous punching. It was difficult.

In addition, as a technique for controlling the end face properties by improving the shape of the punching punch, a technique for reducing a burr on the punching end face by attaching a convex protrusion to the tip of the punching punch has been reported (Patent Document 1).
However, the shape of the convex protrusions of the punching tool according to the art is not preferable in order to greatly improve the hole expanding property. FIG. 3 shows the shape of a punch shown in a gazette explaining the technology. The convex protrusion at the tip of the punch has a shoulder at the tip of about 90 degrees. In this case, particularly when a high-strength steel plate is punched out, as shown in FIG. 4, the steel plate is easily cut by the protrusions themselves, so that sufficient bending stress cannot be applied to the originally cut portion. For this reason, in the said technique, hole expansibility does not improve significantly.
Takeo Nakagawa, Kiyota Yoshida: Cutting-out method-Measures to improve the elongation deformability of sheared surfaces-Plasticity and processing, Vol. 10, no. 10, no. 104, P.I. 665-671 (1696.9) Japanese Patent Laid-Open No. 5-23755

  An object of the present invention is to solve the above-described problems of the prior art and to provide a technique for easily and easily improving the hole expandability in a punched hole of a steel plate.

Invention 1 is a punching tool for making a workpiece into a predetermined shape by cutting a steel plate as a workpiece into a sheared portion and a sheared portion using at least a die and a punch. The punching tool is characterized by having a bending blade having a convex shape at the tip of the cutting blade and having a bending blade shoulder angle of not less than 100 degrees and not more than 170 degrees.
  Invention 2 is a punching tool for making a workpiece into a predetermined shape by cutting a steel plate as a workpiece into a sheared portion and a sheared portion using at least a die and a punch. The tip of the cutting blade has a bending blade having a convex shape, the curvature radius of the bending blade shoulder is 0.2 mm or more, and the bending blade shoulder angle is 100 degrees or more and 170 degrees or less. It is a punching tool characterized by being.

Invention 3 is a punching and / or die cutting blade in a punching process in which a work material is cut into a predetermined shape by cutting a steel plate to be processed into a shearing portion and a shearing portion using at least a die and a punch. A steel plate punching method using a punching tool having a bending blade having a convex shape at a tip end portion of the portion and having a bending blade shoulder portion angle of not less than 100 degrees and not more than 170 degrees.
Invention 4 provides a punching tool and / or a die cutting blade in a punching tool for making a workpiece into a predetermined shape by cutting a steel plate as a workpiece into a sheared portion and a sheared portion using at least a die and a punch. A bending blade having a convex shape at the tip of the part, the radius of curvature of the bending blade shoulder is 0.2 mm or more, and the bending blade shoulder angle is 100 degrees or more and 170 degrees or less. A steel plate punching method using a punching tool characterized by the above.

According to the present invention, a high-strength steel plate can be applied as an automobile part or the like, which contributes to reducing the weight of an automobile and thus saving energy.

In view of the above problems, the present inventors have found that the punch shape can be improved by making the punch shape a two-stage structure of a bending blade A and a cutting blade B shown in FIG.
The reason is considered as follows.
In the usual case, a large tensile or compressive strain is applied to the portion where the punch and die are deformed (hardened layer) as shown in FIG. 1, and this causes significant work hardening, resulting in a deterioration in end face ductility. The hole spreading ability deteriorates. However, the punch shape is bent into a part (material cutting part M) cut by the cutting blade B as shown in FIG. 6 as a two-stage structure consisting of the cutting blade B and the bending blade A as shown in the present invention (FIG. 5). When tensile stress is applied by the blade A, the crack expansion generated from the cutting blade B and the die shoulder is accelerated by the tensile stress, and the material is cut by the cutting blade B without being compressed. Improve.

Furthermore, the present inventors have made further detailed studies on the shape of the bending blade, and have found that a sufficient effect of improving the hole expansibility cannot be obtained unless the bending blade has a predetermined shape.
That is, when the shape of the bending blade A is not a predetermined shape, since the material is cut by the bending blade A, a tensile stress due to sufficient bending cannot be applied to the portion M cut by the cutting blade B, and a good hole is obtained. Expandability cannot be obtained. However, it has been found that good hole expansibility can be obtained by making the bending blade shape into a shape in which the material is not cut by the bending blade itself.

In FIG. 7, the punching punch of FIG. 5 is used, the bending blade height Hp is changed, the radius of curvature Rp = 0 mm of the shoulder of the bending blade A, and the angle θp = 90 degrees of the vertical wall portion of the bending blade A are punched. The result of the expansion test is shown. Here, the material used is a TS780 MPa class hot rolled steel sheet having a thickness of 2.6 mm. The punching conditions are a punch diameter Ap = 10 mm, a punching clearance = 12.5%, and a distance Dp = 1.0 mm between the cutting edge end P and the bending blade rising position D. Also, the hole expansion value is determined by inserting a conical punch with an apex angle of 60 degrees into the initial hole, and then expanding the crack when the crack penetrates in the thickness direction of the end face of the hole. The initial hole diameter (10 mm) of the hole diameter at that time It was calculated as the rate of increase relative to The definition of the punching clearance was 12.5%. The clearance is a distance between the punch and the die C / plate thickness t × 100 (%).
In this case, even if the bending blade height Hp is increased, the hole expansion value is not greatly improved. This is because in this case, since the steel sheet is cut by the bending blade itself as shown in FIG. 4, a sufficient bending stress cannot be applied to the originally cut portion.

In order to solve this problem, it was examined that the bending blade shape does not cut the material by itself. And it discovered that the objective could be achieved by making the angle θp of the bending blade vertical wall an obtuse angle.
FIG. 8 shows the relationship between the angle θp and the hole expansion rate when the predetermined angle θp is attached to the vertical wall portion of the bending blade A. From this, the bending blade vertical wall angle θp is set to 100 degrees or more and 170 degrees or less. It can be seen that the hole expansion rate is remarkably improved.

The present invention has been made on the basis of the above examination, and the following is a requirement thereof.
The punching punch or die used in the present invention needs to have a two-stage structure of a bending blade portion A and a cutting blade portion B. This is because the bending edge A gives a tensile stress to the cut portion M of the workpiece before shearing the workpiece with the cutting edge B, and reduces the distortion of the cut end face of the workpiece after cutting. There is .
The bending blade shoulder angle θp needs to be 100 degrees or more and 170 degrees or less. This is because when the bending blade shoulder angle θp is 100 degrees or less, the material is sheared by the bending blade A, so that sufficient tensile stress cannot be applied to the portion M sheared by the cutting blade B, and the bending is performed. This is because if the blade shoulder angle θp is 170 degrees or more, sufficient tensile stress cannot be applied to the portion sheared by the cutting blade B.

A great effect can be obtained by satisfying the above-mentioned conditions regarding the bending blade shoulder angle θp. However, when both the bending blade shoulder angle θp and the bending blade shoulder radius of curvature Rp are satisfied, the contact surface pressure of the material that contacts the mold This reduces the mold wear. Therefore, it is preferable that both conditions are satisfied in terms of maintenance.
In the punching with this technique, the influence of the punching clearance (interval C in FIG. 5 / thickness t × 100 (%)) on the end face ductility is the same as that in the conventional technique, and special attention is required in comparison with the conventional punching method. There is no need to pay.

In normal punching, a plate press is usually used to fix the material to the die appropriately. However, the plate press may be used as appropriate in the punching method of the present invention. The wrinkle pressing load (the load applied to the material from the plate pressing) does not particularly affect the punching hole expandability, and any amount may be used.
The punch speed does not have a great influence on the punching hole expandability, so any value can be used.
In many cases, in the punching process, lubricating oil is applied to the mold or the material in order to suppress wear of the mold, but in the present invention, lubricating oil may be used as appropriate for this purpose.
In order to give sufficient bending stress to the bending blade A, the bending blade height Hp is preferably set to 10% or more of the plate thickness of the workpiece.
The distance Dp between the cutting edge end P and the rising position Q of the bending blade is preferably 0.1 mm or more. This is because when this interval is less than this, when the workpiece is sheared by the cutting edge B, cracks that normally occur from the vicinity of the shoulder of the cutting edge are less likely to occur, and distortion is applied to the cutting position by the cutting edge. .
In the punch of the present invention, the portion between the cutting edge end P and the rising edge Q of the bending blade, the bottom surface portion of the bending blade A, and the vertical wall portion of the bending blade A preferably have a flat shape for manufacturing the punch. Even if there are slight irregularities, the effect is the same as long as the above requirements are satisfied.

In the present invention, the punching hole expandability is improved by further attaching the bending blade A to the punch of only the conventional cutting blade B. However, the bending blade A is attached and the bending blade height Hp is further increased. As a result, the surface pressure at which the cutting blade B and the workpiece are in contact with each other is lowered, and the amount of wear of the cutting blade end portion P is also reduced. From this viewpoint, the bending blade height Hp is preferably as high as possible. However, if it is too high, depending on the target material, the material may be broken between the bending blade A and the cutting blade B before the cutting blade B and the workpiece are in contact with each other. In such a case, it is preferable that the bending blade height Hp is approximately 10 mm or less.
In the present invention, there is no particular upper limit to the bending blade shoulder radius of curvature Rp. However, depending on the punch size, if the curvature radius Rp is too large, it becomes difficult to increase the bending blade height Hp, and it is preferably 5 mm or less.

  In the above, the effect when the bending blade is attached only to the punch has been described. However, even when the bending blade is attached to both the punch and the die, or when only the die is attached to the bending, only the punch described above is bent. Since it has the effect of giving a tensile stress to the same material as when the blade is attached, the same effect of improving the hole expandability can be obtained. The restrictions on the dimensions of the bending blade in those cases are the same as the restrictions when the bending blade is attached only to the punch described above.

After punching using punches of type X 1 and Y 2 shown in FIG. 9 , a hole expansion test was performed. Two kinds of high-strength hot-rolled steel sheets called A and B were used as test steels. The plate thickness is 1.2 to 5.0 mm. Steel A has TS = 820 MPa, YP = 591 MPa, T.P. El = 32%, Steel B is TS = 740 MPa, YP = 620 MPa, T.P. El = 23%. The size of the test piece used was 150 mm in width and 150 mm in length, and was performed under the conditions shown in Table 2. Lubricating oil was applied to the material at the time of punching.
In the hole expansion test, a 60 ° conical punch was used, and the test piece was set so that the surface of the steel plate that was in contact with the die during punching was on the opposite side of the punch during the hole expansion test. ,went. The punch was pushed into the punched hole, the punch was moved until the crack penetrated on the punched end face, the hole diameter D at that time was measured, and the hole expansion value was obtained from the following formula.
Hole expansion value (%) = (D (mm) −D0 (mm)) / D0 (mm) × 100 (%)
However, the initial hole diameter D0 = 1 to 10 to 50 mm (Table 2 “Punch Diameter Ap”).

The punching clearance was 5 to 20%. The clearance is a distance between the punch and the die C / plate thickness t × 100 (%).
For the levels (1), (11), (19), (38), (39), punching was performed 2000 times with the materials and conditions shown in Table 2, followed by punch cutting edge portions, and The wear situation of the punch bending blade shoulder was investigated. As shown in FIG. 10 , the wear state is processed, embedded, and polished so that the cross-section including the central axis of the punch can be seen, and the cross-sectional shape is compared with the estimated shape before wear. The punch cutting blade end wear amount F1 (mm) and the punch bending blade shoulder wear amount F2 (mm) shown in FIG. 10 were obtained.
Table 2 shows the hole expansion values obtained by the test. Both punching and hole expansion tests were performed at n = 5. The hole expansion value represents the average value.

Levels (1) and (2) are tests using conventional punching punches, and serve as a reference for comparison of hole expansion values by punching according to the present invention. The hole expansion value is 40% for steel A and 50% for steel B.
Levels ( 9 ) to (37) are test results by punching according to the present invention, and a good hole expansion value is obtained as compared with the conventional method.
In the levels (3) and (4), the angle θp of the bending blade shoulder is large, and the bending blade shoulder radius of curvature Rp is small. For this reason, the hole expansion value obtained by this punching is not improved as compared with the conventional method.
In levels (5) and (6), the angle of the bending blade shoulder portion θp is small, and the bending blade shoulder radius of curvature Rp is small. For this reason, the hole expansion value obtained by this punching is not improved as compared with the conventional method.
When comparing the punch cutting edge end wear amount F1 (mm) of the levels (1), (19), and (39), the higher the bending blade height, the smaller the cutting edge end wear amount F1 and the more the wear is suppressed. I understand that

When the bending blade height is the same (levels (19) and (11)), the level (19) is a level where only the bending blade shoulder angle θp satisfies a predetermined condition. The level (11) is a level where both the bending blade shoulder radius of curvature Rp and the bending blade shoulder angle θp satisfy the predetermined condition, but the level (11) where both satisfy the predetermined condition is the amount of wear F2. Is small.
From the above, wear of the cutting edge can be suppressed by attaching a higher bending blade, and the bending blade shoulder can be set by simultaneously setting both the curvature radius Rp of the bending blade shoulder and the angle θp of the bending blade shoulder to predetermined conditions. It was confirmed that the wear of the part was suppressed.

After punching using punches and dies of types X, Z, and W shown in FIGS. 9 and 11 , a hole expansion test was performed. As test steel, TS = 820 MPa, YP = 590 MPa, T.P. A hot-rolled steel sheet (steel C) with El = 30% and a plate thickness of 2.6 mm was used. The size of the test piece used is 150 mm wide and 150 mm long. Punching was performed using the mold shown in FIG. 10 and the conditions shown in Table 3. At the time of punching, lubricating oil was applied to the material.
The hole expansion test uses a conical punch with an apex angle of 60 degrees, and sets the test piece so that the surface of the steel plate that is in contact with the die at the time of punching is the opposite side of the punch during the hole expansion test. went. The punch was pushed into the punched hole, the punch was moved until the crack penetrated on the punched end face, the hole diameter D at that time was measured, and the hole expansion value was obtained from the following formula.
Hole expansion value (%) = (D (mm) −D0 (mm)) / D0 (mm) × 100 (%)
However, initial hole diameter D0 = 20 mm (Table 3 “Punch Diameter Ap”).

The punching clearance was 12.5%. The clearance is a distance between the punch and the die C / plate thickness t × 100 (%).
The test results are shown in Table 3.
Level (1) shows the hole expansion value of the test steel when the punch and die have the conventional shape. In this case, the hole expansion rate is a low value of 40%.
In the level (2), the punch is a normal punch, and the shoulder angle θd and the shoulder curvature radius Rd of the die protrusion do not satisfy the predetermined conditions. That is, neither the punch nor the die satisfies the predetermined condition, and the hole expansion value is not improved.
In the level (9), the shoulder angle θp and shoulder curvature radius Rp of the punch protrusion and the shoulder angle θd and shoulder curvature radius Rd of the die protrusion do not satisfy predetermined conditions. That is, neither the punch nor the die satisfies the predetermined condition, and the hole expansion value is not improved.
In the levels (3) , (5) to (8), and (11) to (15), the die shape is a predetermined shape, or both the punch shape and the die shape are predetermined shapes. As a result, an excellent hole expansion value is obtained as compared with the levels (1), (2), and (9) of the comparative example .

FIG. 1 is a schematic diagram showing a mold used for conventional punching and a state of deformation of a material at the time of punching.
FIG. 2 is a schematic view of a punching punch used for a cutting method.
FIG. 3 is an example of a tool shape used for conventional punching.
FIG. 4 is a schematic view showing a material deformation behavior at the time of conventional punching.
FIG. 5 is a schematic view of a mold used for punching according to the present invention.
FIG. 6 is a schematic diagram showing a material deformation behavior when punching is performed with the mold of the present invention.
FIG. 7 shows the relationship between the bending blade height and the hole expansion value.
FIG. 8 shows the relationship between the bending blade vertical wall angle θp and the hole expansion value.
FIG. 9 is a schematic view of a mold used for punching in the prior art and the present invention.
FIG. 10 is a view showing a measurement position of the wear amount of the mold.
FIG. 11 is a schematic view of a mold used for punching in the prior art and the present invention.

Claims (4)

  In a punching tool for making a workpiece into a predetermined shape by cutting a steel plate as a workpiece into a sheared portion and a sheared portion using at least a die and a punch, a punching tool and / or a die cutting edge portion The tip has a bending blade having a convex shape, the bending blade shoulder angle is not less than 100 degrees and not more than 170 degrees, and the interval between the cutting edge and the rising position of the bending blade is 0.1. A punching tool having a punching clearance of 0.13 to 0.65 mm as well as a punch clearance of 1.0 to 1.0 mm.   In a punching tool for making a workpiece into a predetermined shape by cutting a steel plate as a workpiece into a sheared portion and a sheared portion using at least a die and a punch, a punching tool and / or a die cutting edge portion The tip has a bending blade having a convex shape, the curvature radius of the bending blade shoulder is 0.2 mm or more, and the bending blade shoulder angle is 100 degrees or more and 170 degrees or less; For punching, characterized in that the distance between the rising edge of the cutting edge and the bending blade is 0.1 to 1.0 mm, and the punching clearance that is the distance between the punch and the die is 0.13 to 0.65 mm. tool.   In the punching process for forming a workpiece into a predetermined shape by cutting a steel plate as a workpiece into a sheared portion and a sheared portion using at least a die and a punch, the tip of the punch and / or die cutting edge portion The bending blade has a convex shape, the bending blade shoulder angle is not less than 100 degrees and not more than 170 degrees, and the interval between the cutting edge and the rising edge of the bending blade is 0.1 to 1. A steel plate punching method using a punching tool having a punching clearance of 0.13 to 0.65 mm and a punch clearance of 0.13 to 0.65 mm. In a punching tool for making a workpiece into a predetermined shape by cutting a steel plate as a workpiece into a sheared portion and a sheared portion using at least a die and a punch, the tip of the punch and / or the cutting edge of the die A bending blade having a convex shape, a radius of curvature of the bending blade shoulder is 0.2 mm or more, a bending blade shoulder angle is 100 degrees or more and 170 degrees or less, and the cutting blade It is characterized by using a punching tool in which the interval between the end portion and the rising position of the bending blade is 0.1 to 1.0 mm, and the punching clearance which is the distance between the punch and the die is 0.13 to 0.65 mm. Steel plate punching method to do .

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