JP2010172912A - Method of bending steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture parts having the bent part of a small shoulder radius at the tip of a bent part without generating cracks in a bent shoulder part even when using a steel sheet having high strength and small stretch as a workpiece. <P>SOLUTION: After forming a preliminarily bent article having a bent part which has larger shoulder radius than the target shoulder radius by applying preliminary bending to the steel sheet, in the state where the outside of unworked parts on both sides of the preliminarily bent article is brought into contact with two fixed walls forming a predetermined angle, the unworked part on one side end of the preliminarily bent article is restrained and the other side end of the preliminarily bent article is pressed in the bending direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of bending a steel plate, and more particularly to a method of bending a high strength steel plate suitable for manufacturing various fasteners that require high strength.

  In various fields such as architecture, home appliances, automobiles, and communication devices, fasteners having a V-shaped portion and an L-shaped portion made of high-strength steel plates are used for the purpose of positioning and positioning various members. These high-strength steel plate fasteners are widely used as joining aids for workpieces in welding and caulking.

As the characteristics of these fasteners, a high elastic limit and a high fracture limit are required from the viewpoint of safety and performance, and a high-strength steel plate having a high elastic limit and a high fracture limit is used for the applicable material. Furthermore, when used in an environment where weather resistance and corrosion resistance are required, a high-strength stainless steel plate having excellent weather resistance and corrosion resistance is used.
In addition, as shown in FIG. 1, for example, as shown in FIG. 1, when attaching to a member having a small corner portion R, the fastening member 1 is required to have a small R. There are many cases in which a bending shoulder radius R is required due to such problems.

  Generally, in order to obtain a product having a V-shaped part and an L-shaped part from a high-strength steel plate, as shown in FIGS. 2 (a) and 2 (b), upper and lower V molds are used for the V-shaped part. For bending (V-bending) and L-shaped parts, bending in the shearing direction (L-bending) is performed by the upper and lower molds. In these processes, tensile deformation in the circumferential direction occurs outside the bending neutral axis, and the amount of deformation becomes maximum at the outer periphery of the bending. Therefore, when a material with small elongation is applied, if the bending shoulder radius is small, a large line length difference is generated between the neutral shaft and the bending outer peripheral portion, so that the amount of strain in the tensile direction is excessive in the bending outer peripheral portion, leading to cracks.

  For this reason, a material having a large elongation is generally used for manufacturing a part having a small shoulder radius bending portion, and a spring material such as SUS304 is used for a member that requires high strength ( JIS G 4313 spring stainless steel strip). However, since SUS304 material contains a large amount of alloy components such as Ni in order to stabilize the austenite structure, the material cost is very high compared to general materials.

  In addition, as a low cost material, a quench hardening type special steel is used which is soft and has a large elongation at the time of processing and ensures strength by heat treatment after the processing. However, the use of quench-hardening type special steel requires a heat treatment step in addition to the bending step, which causes problems such as time loss and cost increase due to the use of a heat source. In addition, the use of a spring material of 13Cr type stainless steel as a low-cost material is also being studied, but these materials have a remarkably small elongation, so that they are used only for large shoulder radius bending.

  For example, Patent Literature 1 proposes a method for improving the bending workability of a low-elongation material by using a warm die and softening the workpiece by heating to improve the elongation. However, in this method, in addition to the cost of introducing a heating device, a time loss for increasing the temperature, an increase in cost due to the use of a heat source, and a deterioration in corrosion resistance due to an increase in temperature are caused.

JP 2004-34074 A

  As described above, when manufacturing a part having a small shoulder radius bend using a high-strength steel plate, such as a fastener having a V-shaped part or an L-shaped part, a material having a large elongation such as a spring material of SUS304 is used. It was used. However, these high-strength steel sheets having a large elongation have a high material cost, and when a low-cost high-strength steel sheet is used, a bending shoulder is cracked, and bending to a small shoulder radius is difficult. In addition, attempts have been made to use quench-hardening steel plates and warm dies, but it has been unavoidable that time loss and cost increase due to the use of heat sources are unavoidable.

  The present invention has been devised to solve such problems, and even when a steel plate having high strength and low elongation is used as a work material, it is processed using an existing bending machine. It is an object of the present invention to provide a bending method capable of manufacturing a part having a small shoulder radius bending portion at the tip of a bending portion without causing a crack in a bending shoulder portion of a product.

In order to achieve the object, the method of bending a steel sheet according to the present invention forms a pre-bending product having a bent portion with a shoulder radius larger than the target shoulder radius when forming a bent portion with a small shoulder radius on the steel plate. Then, in a state where the outer surfaces of the unmachined parts on both sides of the pre-bending product are brought into contact with the fixed two walls forming a predetermined angle, the both-side ends of the pre-bending product are pressed in the bending part direction to form the bending part. A target small shoulder radius is given.
Instead of pressing both side ends of the pre-bending product in the direction of the bending part, restraining one side unprocessed part of the pre-bending product and pressing the other side end in the direction of the bending part, The form which provides the target small shoulder radius may be sufficient.

The bending process for obtaining the pre-bending product is performed under the condition of r _p ^′ / t> r _p / t, and the step of giving the small shoulder radius in the subsequent stage is performed by d = L _{a′−b ′} −L _ab It is preferable to carry out under these conditions.
The bending method of the present invention can be applied to a high-strength low-stretch steel sheet that is difficult to bend with a small shoulder radius where r _p / t> 0 when V bending or L bending is performed.
Here, r _p ^' / t is the punch shoulder radius of the first step, r _p / t is the bending shoulder radius at which cracking occurs, t is the base plate thickness, d is the indentation amount of the second step, _{La'- b 'is} the line length of the bent portion of the final product, L _ab is a line length of the bent portion of the pre-bending the workpiece.

According to the steel sheet bending method of the present invention, a low-strength, high-strength steel sheet that has been impossible to use until now is used, and a part having a high-strength, small-shoulder radius bending portion such as a fastener. Can be manufactured.
Therefore, the material cost can be reduced as compared with the existing technology. In addition, since there is no need for post-processing and the use of a heat source, the manufacturing time can be shortened and the manufacturing cost can be reduced.

The figure explaining the shape of a fastener and its usage The figure explaining the aspect of general V bending process (a) and L bending process (b) The figure explaining the deformation situation of the material board at the time of bending The figure explaining the process aspect of the 1st process of this invention The figure explaining the processing aspect of the 2nd process of this invention The figure explaining the processing aspect of the 2nd process for providing an acute angle The figure explaining the processing aspect of the 2nd process for providing an obtuse angle The figure which shows V bending process conditions of the 1st process in a comparative example and an Example The figure which shows the L bending process conditions of the 1st process in a comparative example and an Example The figure which shows the processing conditions of the 2nd process in an Example

When a steel sheet is bent using a die and a punch, for example, as shown in FIG. 3, compressive stress acts on the inner shoulder radius portion of the bending shoulder portion, and tensile stress acts on the outer shoulder radius portion. Then, bend the shoulder as the radius becomes smaller, the line length L ₂ of the curved portion of the outer shoulder radius portion is increased bending for bend line length L ₁ of the neutral axis C, the strain amount of the tensile stress is increased. For this reason, when a material with small elongation is used for bending with a small shoulder radius, a crack tends to occur at the tip of the bent portion.
As fasteners used for building materials, there are many cases where high-strength materials are used from the viewpoint of safety. However, for the above processing reasons, expensive materials with large elongation are used. Has become almost.

Accordingly, the present inventors have made extensive studies to perform bending with a small shoulder radius without generating cracks on an inexpensive high-strength steel sheet with small elongation.
In that process, after pre-bending the steel plate to a large shoulder radius approximating the desired shape, the outer surfaces of the unmachined parts on both sides of the pre-bending product are brought into contact with the fixed two walls forming a predetermined angle. By bending both sides of the pre-bending product in the direction of the bending part, bending of the steel sheet that can suppress the tensile strain that occurs when forming the small shoulder radius bending part and can form the small shoulder radius bending part in the processed product It came to invent the processing method.
As a form other than pressing both ends of the pre-bending product in the direction of the bending part, the unprocessed part of one side end of the pre-bending product is constrained and the other side end of the pre-bending product is pressed in the direction of the bending part. By doing so, a form using reaction force can be used.

In the present specification, a steel plate having a small elongation means that a bending shoulder radius r _{p at} which cracking per base plate thickness t occurs when V bending or L bending is performed among steel plates is larger than 0, that is, r. _It refers to a low-stretched steel sheet in which _{p 1} / t> 0 (a crack occurs when bending is performed using a mold having a bending shoulder radius r _{p of} 0 mm). Note that r _p / t is a general index of bending workability defined for the purpose of qualitatively defining the bending limit value by making the numerical dimension non-dimensional by dividing the bending shoulder radius by the plate thickness. In such a low-strength steel sheet, cracks are generated in the bent portion, and it is difficult to form a small shoulder radius bent portion by a normal bending process.
Here, r _p is the shoulder radius given to the tip of the punch die, and cracking with r _p > 0 mm means that cracking occurs when bending is performed using a die with a punch shoulder radius of 0 mm. Means that The r _p of the used mold is confirmed by a contour shape measuring instrument.

The method of the present invention will be described with reference to FIGS.
First, in the first step, preliminary bending is performed on a steel sheet having a small elongation using the upper and lower molds shown in FIG. The upper and lower molds used in this step are the same as the normal bending mold shown in FIG. 2B, and the base plate 3 is pressed against the base plate 4, the punch 5 having the punch shoulder radius r _p ^′ , and the die shoulder. Bending is performed with a die 6 having a radius r _d ^' . The bending process in this step is performed under the condition that the punch shoulder radius r _p ^′ per base plate thickness t is larger than the bending shoulder radius r _p where cracks occur per base plate thickness t, that is, r _p ^′ / t. It is necessary to carry out under the condition of> r _p / t. By this pre-bending process, the pre-bending product 7 having a shoulder radius bending portion larger than the shoulder radius bending portion of the final product, which is a desired product, is formed.

In the subsequent second step, the pre-bending product 7 formed by the pre-bending process in the first step is bent by the apparatus shown in FIG. This is a form in which a reaction force is utilized by restraining an unprocessed portion at one end of the pre-bending product and pressing the other end of the pre-bending product in the direction of the bending portion.
In this apparatus, a lower plate presser 8 and a side plate presser 9 are attached to a lower base, and an upper plate presser 10 is directly attached to an upper base via a buffering mechanism such as a spring and a shaping punch 11 is directly connected. It is attached, and the upper base can be moved downward by a driving device (not shown). In this apparatus, the lower base and the upper base are opposed to each other, and the side surface presser 9 attached to the lower base and the upper plate presser 10 attached to the upper base slightly exceed the processed plate thickness. It arrange | positions with clearance and the shaping punch 11 is attached in the positional relationship in which the side surface contacts the side surface of the upper board retainer 10. FIG. Further, the lower plate presser 8 is formed with a recess having the same depth as the raw plate thickness t of the pre-bending product 7 and the same length as the long side portion to be obtained. That is, a convex portion serving as a stopper is formed at the end of the lower plate presser 8. Moreover, it is preferable that the shaping punch 11 has a recess having the same width as the base plate thickness t of the pre-bending product 7 on the side in contact with the upper plate presser 10.

In the second step, the unprocessed portion at one side end of the pre-bending product 7 is constrained, and the other side end of the pre-bending product 7 is pressed in the direction of the bending portion, thereby giving a target small shoulder radius to the bending portion. .
In this step, the pre-bending product 7 is placed so that the outer surface of the longer unmachined portion is placed so that the outer surface of the shorter unmachined portion of the both-side unmachined portions of the pre-bending product is in contact with the side plate retainer 9. After placing in the recess of the plate retainer 8, the upper base is lowered. By lowering the upper base downward, an unprocessed portion at one end of the pre-bending product 7 is first fixed between the lower plate presser 8 and the upper plate presser 10. The end portion of the unprocessed portion is configured to be prevented from moving outward by the concave portion of the lower plate presser 8.

Thereafter, the upper base is further lowered, so that the shaping punch 11 comes into contact with the other end of the pre-bending product 7 and presses it. When the other side end of the pre-bending product 7 is pressed downward, both side portions of the bending portion having a large bending radius are pressed against the lower plate presser 8 and the side plate presser 9 to be flattened, and the bending The substantially central portion of the bending portion having a large radius is deformed so that the bending radius becomes small. That is, a bent portion having a small shoulder radius is formed at a substantially central portion of a bent portion having a large bending radius.
The corner R of the upper plate presser 10 is preferably larger than the shoulder radius of the bent product to be obtained.
Push-in amount of 2 steps first, as shown in FIG. 5 (b), bend line length of the final bending workpieces (line AA ^'+ line ^A' B ^'+ line ^B' B) - preliminary bending The bent part line length (line segment AB) of the product. This indentation amount is the numerical value d described in claim 3.

  The above description with reference to FIGS. 4 and 5 is for L bending, but the same is true for V bending. A conventional bending mold with an adjusted punch angle is used as the upper and lower molds in the first process, and one end of the unprocessed portion of the pre-bending product 7 is formed on a die as a lower mold, for example, In addition to disposing a concave portion for housing the plate, a plate presser is disposed, and a shaping punch is disposed above the die that is the upper die, and one end of both unmachined portions of the prebending product 7 is constrained while preliminarily bending. An L-bending product having a desired shoulder radius can be obtained by pressing the other end of the workpiece 7 in the direction of the bending portion.

4 and 5 are for the case where the bending angle is 90 °, the method of the present invention can be applied even if the angle is an acute angle or an obtuse angle other than 90 °.
FIG. 6 illustrates a second embodiment of the processing mode when the bending angle is an acute angle and FIG. 7 illustrates the case where the bending angle is an obtuse angle.
That is, when the bending angle is an acute angle or an obtuse angle, after performing V-bending using a conventional bending die whose punch angle is adjusted as the upper and lower dies in the first step, a die as shown in FIGS. By performing the second process using the apparatus, a bent product having a desired bending angle can be obtained.

In the mold apparatus shown in FIGS. 6 and 7, a plate presser 12 and a shaping punch 13 which are attached to a side wall erected on the upper surface of the mold apparatus via a buffer mechanism such as a spring on the lower base. The pressing rod 14 is erected on the lower surface of the upper base. The rear wall of the shaping punch 13 and the tip wall of the pressing rod 14 form a cam slide 15 to change the vertical movement of the pressing rod 14 to the horizontal movement of the shaping punch 13. Further, the front surface of the plate presser 12 and the pressing surface of the processing punch 13 are inclined at a predetermined angle so as to have a bending angle to be processed. Furthermore, a concave portion having the same depth as the preliminary bent product 16 base plate thickness t is formed on the front surface of the plate presser 12 and the pressing surface of the processing punch 13.
Therefore, after placing the pre-bending product 16 on the front side of the plate presser 12, the shaping punch 13 is pressed, and then the upper base is moved downward to press the processing punch 13 toward the plate presser 12. Thus, the target small shoulder radius can be given to the bent portion.

  As described above, the present invention divides the bending process into two steps. First, in the first step, as a preliminary bending process, a crack is generated in a normal bending process part that generates tensile strain outside the bending neutral axis. After giving a shoulder radius larger than the generated shoulder radius, a step of applying a pressing force in the direction of the bending portion to both ends of the pre-bending product is adopted as the second step. In particular, by pushing the difference in line length between the first and second processes in the second process, the tensile stress and tensile strain generated in the outer shoulder radius of the bent product do not occur. Since the processing form in which only the compressive stress and the compressive strain are generated in the inner shoulder radius, it is possible to bend the small shoulder radius even in a steel plate having a small elongation.

Comparative example;
As the test material, two types of stainless steel plates having the composition shown in Table 1 and the mechanical properties shown in Table 2 were used, and V bending was performed under the conditions shown in FIG. 8, and L bending was performed under the conditions shown in FIG. Was given. The bending process was performed three times under each condition. Then, the occurrence of cracks was visually observed. The results are shown in Tables 3 and 4. In the table, those where cracks occurred are indicated by ×, and those where no cracks were observed are indicated by ○.
As shown in Tables 3 and 4, the specimen A having a large elongation for both the V-bending and the L-bending did not crack even when the punch shoulder radius was 0, but the specimen B (spring steel plate) having a small elongation was a punch shoulder. Cracks occurred as the radius decreased.

Example;
Using the component composition shown in Table 1 and the stainless steel plate for spring material of Test Material B having the mechanical properties shown in Table 2, bending was performed under the processing conditions of FIG. The processing was performed according to FIG. 9 for the mold and processing conditions in the first step. In addition, it is assumed that the push amount in the second step is a bending of a shoulder radius of 3.0 mm on the temporarily bent product in the first step, and the shoulder radius R is set to 0 mm, 1.0 mm, and 1.5 mm, respectively. The difference in line length from the first step required for.
The results are shown in Table 5. It was possible to obtain a processed product without cracking under the bending condition of the small shoulder radius in which cracking occurred in the V bending and L bending processes described above.

1: Fastener 2: Fastening material 3: Workpiece base plate 4: Plate retainer
5: Punch 6: Die 7: Pre-bending product 8: Lower plate presser
9: Side plate presser 10: Upper plate presser 11: Shaping punch 12: Plate presser 13: Processing punch 14: Press rod 15: Cam slide
16: Pre-bending product

Claims (4)

  In forming a bent portion having a small shoulder radius on a steel plate, after forming a pre-bending product having a bending portion having a shoulder radius larger than the target shoulder radius, the pre-bending product is formed on a fixed two wall having a predetermined angle. Bending of a steel sheet, characterized in that a target small shoulder radius is given to the bent portion by pressing both side ends of the pre-bending product in the direction of the bent portion in a state where the outer surfaces of the unmachined portions on both sides are in contact with each other. Method.   In forming a bent portion having a small shoulder radius on a steel plate, after forming a pre-bending product having a bending portion having a shoulder radius larger than the target shoulder radius, the pre-bending product is formed on a fixed two wall having a predetermined angle. With the outer surfaces of both side unmachined parts in contact with each other, the unfinished part on one side of the pre-bending product is constrained and the other end is pressed in the direction of the bent part to give the target shoulder a small shoulder radius. A method for bending a steel sheet, comprising: The bending process for obtaining the pre-bending product is performed under the condition of r _p ^′ / t> r _p / t, and the step of giving the small shoulder radius in the subsequent stage is performed by d = L _{a′−b ′} −L _ab The bending method of the steel plate of Claim 1 or 2 performed on condition of this.
However, r _p ^' / t; punch shoulder radius in the first step, r _p / t; bending shoulder radius in which cracking occurs, t: base plate thickness, d: indentation amount in the second step, _{La'-b '} : Bending part line length of final product, _Lab : Bending part line length of pre-bending product The method for bending a steel sheet according to any one of claims 1 to 3, wherein a material satisfying r _p / t> 0 is used as the steel sheet when V bending or L bending is performed.
Where r _p / t; bending shoulder radius at which cracking occurs, t: base plate thickness

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