JPH04118118A - Method for bending steel sheet - Google Patents

Abstract

PURPOSE:To prevent the generation of wrinkles or bent on the working time of the high tensile steel sheet by bending while pressurizing the blank holder with the pressing force to increase corresponding to the stroke of the punch for pressing by using the pressure adjusting component. CONSTITUTION:By beginning the working, lowering the upper die 52, further lowering it from the lowered state, the bottom of punch 57 is made in contact with the surface of web 82, then the bending work is began. At the same time, the moving cam 54 is moved by being pushed with the fixed cam 58 of the upper die 52, the blank holder 56 is pressurized to the flange surface 83 while compressing the pressure adjusting component 55. Then, the upper die 52 lowers further, executes bending to the web surface 82, and the flange surface 83 receives the shrink-deformation, but the blank holder 56 gives an orthogonal pressure to the flange surface 83 with the pressure adjusting component 55 following to lowering of the upper die 52, so wrinkles or bent is not generated on the flange surface 83.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for bending a steel plate, and more specifically, when manufacturing a U-shaped cross-sectional product with a curved web surface by press working, the present invention relates to a method for bending a steel plate. The present invention relates to a method for preventing surface quality defects such as wrinkles and warpage from occurring.

[Conventional technology]

Pressed steel plate products having a U-shaped cross section with a curved web surface as shown in FIG. 1 are widely used as structural members of mechanical products such as automobile bumper reinforcing members.

As a recent trend, these components are increasingly using high-tensile steel plates to improve strength and reduce weight. In particular, in the case of automobile bumper reinforcement members, there is a strong demand for weight reduction and improved crash strength. (Steel plates with a tensile strength of 80 kg/mm" or more are being adopted.

However, as the tensile strength of the copper plate increases, the elongation of the material decreases and the folding point increases, so when high-tensile steel plates are press-formed, wrinkles are more likely to occur, and the springback is also thicker. Defects are more likely to occur.

Conventionally, as a method for forming a member as shown in FIG. 1 by bending a steel plate, a processing method using a press mold as shown in FIGS. 2(A) to 2(C) is known. (No. 3, 1982)
3rd Spring Conference on Plastic Working, pp. 277-280) However, in the member 1 shown in FIG. 1, the web surface 2 is curved, and the flange surface 3
is subject to shrinkage deformation, so when using high-tensile steel plates,
In particular, defects such as wrinkles are likely to occur on the flange surface 3. For this reason, when the processing method shown in FIGS. 2(A) and 2(B) is used, wrinkles occur on the flange surface 3 because the flange surface 3 is not restrained by the bunch 4 and the die 5 during processing, resulting in poor surface quality. can't get a good product. In addition, in FIG. 2(C), forming is performed while restraining the flange surface 3 with the blank holder 6, but the flange surface 3 is
Since the product is bent once and then unbended, there is a problem in that the flange surface 3 of the product is warped as shown in FIG. To prevent this, measures have been taken to absorb wrinkles by providing beads 9 on the flange surface 3 as shown in Figure 4, and at the same time increase the rigidity of the flange surface 3 in the height direction. Because the material slides on the bead, mold wear and product galling are likely to occur, especially when high-tensile steel plates are used, causing problems in terms of mold durability and product quality.

In addition, in order to prevent wrinkles on the flange surface 3, gripping parts (lock beads) are provided at both longitudinal ends of the member, and the so-called stretch forming method involves gripping these parts and bending the member while applying tension in the longitudinal direction. (Special Public Interest Publication No. 55-18409
However, as mentioned above, with high-strength steel plates, the elongation of the material is low, so stress concentrates near the lock beads at both ends of the member and cracks occur, making it impossible to apply sufficient tension in the longitudinal direction of the member. Wrinkling of the flange surface 3 may not be prevented in some cases.

Furthermore, since the lock bead portion is cut and scrapped after the member is formed, there is a problem in that the retention of material is poor.

In addition to the above method, a method of forming a member as shown in FIG. 1 from a steel plate using a roll forming method is also used. (Nissan Technical Review No. 14 (1972-1) pp. 145-14
(Page 8) However, the roll forming method basically uses bending lines (Fig. 1, 13).
Since this is a technique suitable for obtaining a straight member, the curvature of the web surface 2 obtained by adjusting the clearance between rolls, etc. is extremely small, and the desired shape cannot be obtained in many cases. Moreover, since the equipment for roll forming is dedicated equipment, there is a problem that the product cost increases.

The applicant of the present application has disclosed in Japanese Patent Laid-Open No. 60-12223 that defects such as wrinkles and warpage occur on the flange surface 3 when a member 1 whose web surface 2 changes in shape is formed by press working as shown in FIG. We are proposing a bending method that prevents this. The bending method proposed in the above publication is basically shown in Figure 2 (B
) but die 5 (Fig. 2(B)
) is formed into an appropriate shape to form an intermediate molded product with a U-shaped cross section in which the shape of the web surface 2 is minimally changed during the downward movement of the bunch 4 when processing the final product from a flat plate. Then, by further lowering the bunch, the web surface of this intermediate molded product is bent to obtain the final product shape.In the above-mentioned method, the member first passes through the shape of the intermediate molded product, and then bends the web surface of this intermediate molded product to obtain the final product shape. Therefore, when the flange surface 3 undergoes shrinkage deformation, deformation in the direction perpendicular to the surface between the bunch side surface and the die can be restricted, and wrinkles and warpage of the flange surface can be prevented.

[Problem to be solved by the invention]

The processing method disclosed in JP-A-60-12223 is such that when the flange surface undergoes shrinkage deformation and the plate thickness increases, deformation in the direction perpendicular to the flange surface is restricted between the bunch and the die. This prevents wrinkles and warpage from occurring on the flange surface. However, in the above method, the die 5 is subjected to a large reaction force directed outward from the member flange surface 3 caused by the shrinkage deformation of the member flange surface 3. In particular, since the yield stress of high-tensile steel plates is high, this reaction force is also large. ing. For this reason, when processing a high-tensile steel plate using the above method, if the rigidity of the die 5 is low, the die 5 itself will be elastically deformed by the reaction force and the clearance between the bunch 4 and the die 5 will be expanded, and the flange Occasionally, it may not be possible to prevent wrinkles from forming on the surface 3. Moreover, even if the rigidity of the die 5 is increased to prevent elastic deformation, the thickness of the material steel plate has fluctuations within the tolerance, so it is difficult to completely prevent the occurrence of wrinkles.

In view of the above problems, it is an object of the present invention to provide a bending method that can prevent the occurrence of wrinkles and warps when processing a member whose flange surface undergoes shrinkage deformation as shown in FIG.

[Means to solve the problem]

As shown in Fig. 1, the bending method of the present invention applies a wrinkle pressing pressure of sufficient magnitude to restrict deformation of the flange surface in the direction perpendicular to the surface when forming a member whose flange surface is compressed and deformed during processing. It is characterized by making it possible to form the web surface without adding anything, and preventing the occurrence of wrinkles and warpage on the flange surface.

That is, according to the present invention, a preformed product having a U-shaped cross section consisting of a web and a flange is made by bending a flat plate linearly, and then the web surface of the preformed product is bent into a predetermined shape by press working. In the method for bending a steel plate to obtain a final product, when pressing the web surface, a pressure adjusting means that generates a predetermined pressing force that increases in accordance with the stroke of a press punch is used to move the wrinkle pressing member to the flange. There is provided a method for bending a steel plate, characterized in that the web surface is pressed while applying a wrinkle pressing force to the flange surface in accordance with the pressing force.

〔Example〕

Embodiments of the method for bending a steel plate according to the present invention will be described below with reference to the accompanying drawings.

FIG. 5 shows an apparatus for carrying out the bending method of the present invention. In the figure, 51 is a lower mold, and 52 is an upper mold that is moved up and down by a hydraulic ram (not shown).

A mold member 53 is fixed to the lower mold 51, and a movable cam 54 is attached so as to be movable in the left-right direction in the figure.

A wrinkle suppressing member 56 is attached to the movable cam 54 via a pressure adjusting member 55 made of an elastic body such as urethane rubber, a spring, or a gas cylinder, and the wrinkle suppressing member 56 is attached to the flange surface 83 of the member 81 during bending as described later. It is designed to press with uniform pressure. - Member 81 for sumo wrestler type 52
a convex punch 5 for curve-forming the web surface 82 of the
7, and a fixed cam 58 that engages with the movable cam 54 and horizontally moves the movable cam 54 toward the punch 57 by the lowering movement of the upper die 52. In addition, °
This device has a symmetrical structure with respect to the center line A--A, and although FIG. 5 shows only the right half thereof, the structure of the side not shown is also the same as that described above.

In this embodiment, the component is pre-processed into a preform 81 as shown in FIG. 8 and then fed to the apparatus shown in FIG. As shown in FIG. 8, the preform 81 has the shape of a U-shaped cross-sectional channel with a bend line 84 bent into a straight line, and both the web surface 82 and the flange surface 83 remain flat.

The step of bending the preformed product 81 having the above shape from a steel plate is performed by a known press method (for example, the method shown in FIG. 2(A)), but in this process, only the portion along the bending line 84 is plastically deformed. Therefore, no wrinkles or warpage occur on the flange surface 83.

Next, the operation of the above device will be explained. FIG. 5 shows a state in which the preformed product 81 is set on the mold member 53 before the start of processing. In this state, the movable cam 54 and the wrinkle presser member 56 are at the right end position of the lower die 51 in the figure.
and the flange surface 83 of the preform 81 are not in contact with each other.

FIG. 6 shows a state in which the upper mold 52 has been lowered after starting machining. When the upper mold 52 descends, the fixed cam 58 engages with the movable cam 54 of the lower mold, and the movable cam 54 is pressed against the wrinkle pressing member 5.
6, the wrinkle pressing member 5 is moved to the left in the figure.
6 comes into contact with the flange surface 83 of the preform 81, but at this time, as shown in FIG. has not been added.

When the upper die 52 is further lowered from this state, the bottom of the punch 57 comes into contact with the web surface 82 and the bending process begins.
At the same time, the movable cam 54 is moved by the fixed cam 58 of the upper mold 52, compressing the pressure adjusting member 55 and pressing the wrinkle pressing member 56 against the flange surface 83. After this, the upper die 52 further descends to bend the web surface 82 and flange surface 82.
3 undergoes shrinkage deformation, but since the wrinkle pressing member 56 applies pressure perpendicularly to the flange surface 83 by the pressure adjusting member 55 as the upper die 52 descends, no wrinkles or warpage occur on the flange surface 83. FIG. 7 shows a state in which the upper mold 52 has descended to the bottom dead center and the pressure adjustment member 55 has been compressed to the maximum. As can be seen from the above description, as the punch 57 descends and the amount of shrinkage deformation of the flange surface 83 increases, the amount of compression of the pressure adjusting member 55 increases, and the wrinkle pressing member 56
The pressure with which the flange surface 83 is pressed also increases, and the clearance between the wrinkle pressing member 56 and the side surface of the punch 57 is not enlarged due to the reaction force caused by the shrinkage deformation of the flange surface 83, and the flange surface 83 is pressed against the punch 57. It is always in close contact with the side surface and the wrinkle pressing member 56 and receives compressive force in the thickness direction. Furthermore, since the pressure applied to the flange surface by the wrinkle pressing member 56 can be easily adjusted by changing the thickness and elastic modulus of the elastic body constituting the pressure adjusting member 55, the member 8
The pressure applied to the flange surface can be appropriately set depending on the shape and material of the flange.

Next, the pressing force required when performing the bending process according to the present invention (the value obtained by dividing the initial pressing force of the wrinkle pressing member 56 by the contact area of the flange surface 83).

kg, expressed as /+w+2. ) will be explained.

FIG. 10 is a diagram showing the relationship between the yield point stress of the material and the occurrence of wrinkles when the processing method of the present invention is used. 1st
Figure 0 shows a product with a flange surface height (h) of 85 mm+ shown in Figure 9 made from a copper plate with a thickness (t) of 1.6 am, when formed using a punch with a web surface curvature radius of 2100R111, with a constant wrinkle pressing pressure ( These are the results of actual measurements using a steel plate with a yield point stress of 60 to 110 kg/av2. A value obtained by averaging the height of wrinkles with respect to the number of wrinkles (average height Hm) is shown.

As can be seen from the figure, under these conditions the yield point stress is 75 kg.
/l! No wrinkles occur in materials with a yield point or yield stress of 1+" or less, and in materials with a yield point or yield stress higher than that, the average height of peaks increases almost in proportion to the yield stress, and the occurrence of wrinkles and material yield. A correlation with stress has become clear.

Next, Fig. 11 shows the actual measurement results of the pressing pressure required to prevent the occurrence of wrinkles when the product shown in Fig. 9 is molded by the processing method of the present invention using materials with different yield stresses. This is what is shown. As can be seen from the figure, the required wrinkle pressing pressure is approximately proportional to the yield stress of the material, and the yield stress is 90 to 1.
0.5 when processing 10kg/++v+” material
A pressing pressure of ~0.6 kg/i11" or more is required.

As described above, the bending method according to the present invention is particularly suitable for processing high-strength steel plates having a high yield stress (for example, a yield stress of 50 kg/w+s2 or more). However, according to the bending method of the present invention, it is possible to generate wrinkle pressing pressure according to the product shape and material. A product with good properties can be obtained.

〔Effect of the invention〕

The bending method according to the present invention processes a high-tensile steel plate by performing bending while pressing a wrinkle pressing member with a pressing force that increases according to the stroke of a press punch using a pressure adjustment member. It is possible to reliably prevent the occurrence of wrinkles and warps. Further, unlike the stretch molding method, there is no need to provide a lock bead portion, so there is an advantage that the material yield is good. Further, the bending method according to the present invention does not require special equipment unlike roll forming, and can use conventional press equipment, thereby suppressing increases in product costs.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the shape of a final product produced by the bending method of the present invention, Figs. 2 (A) to (C) are diagrams showing an example of a conventional bending method, and Fig. 3 is a diagram showing an example of a conventional bending method. FIG. 4 is a diagram showing a bead section provided to improve the surface quality using the conventional bending method, and FIGS. FIG. 8 is a diagram showing the shape of a preform used in the bending method according to the present invention, and FIG.
Figure 1 shows the product shape used for the actual measurements in Figures and Figure 11.
Figure 0 shows the correlation between the yield stress of the material and the occurrence of wrinkles.
FIG. 11 is a diagram showing the relationship between the yield stress of the material and the required wrinkle pressing pressure. 1... Product component, 2... Web surface, 3...
...Flange surface, 51...Lower mold, 52...
Upper mold, 53... Mold member, 54... Movable cam, 55... Pressure adjustment member, 56... Wrinkle pressing member, 57... Punch, 58... Fixed cam,
81... Preformed product. 1st... Product 2... Web 3... Flange 2 Fig. 4... Punch 5... Die 6... Blank holder Fig. y4 Fig. 1... Product 2... Web 3...Flange 9...Bead construction 5 51...Lower Mold 52...Upper mold 53...Mold member 54...Movable cam 55...Pressure adjustment mechanism 56...Wrinkle presser Part diagram 57...Punch 58...Fixed cam 81...Preformed product 82...Web 83...Flange B-B cross section (B) Fig. 6 53...Mold member 56... - Wrinkle holding member 57... Punch 81... Preformed product 82... Web Fig. 7 54... Movable cam 55... Pressure adjustment mechanism 56... Wrinkle holding member 57... Punch 58 ...Fixed cam Figure 9 Fig. 81... Preformed product 82... Web 83... Flange yield stress Yp (kg/■-2) Fig. 10

Claims (1)

[Claims] 1. A steel plate by bending a flat plate in a straight line to make a preformed product with a U-shaped cross section consisting of a web and a flange, and then bending the web surface of the preformed product into a predetermined shape by press working to obtain a final product. In the bending method,
When pressing the web surface, a wrinkle pressing member is pressed against the flange surface using a pressure adjusting means that generates a predetermined pressing force that increases in accordance with the stroke of a press punch, and the pressing force is applied to the flange surface. A method for bending a steel plate, characterized in that the web surface is press-formed while applying a wrinkle-pressing pressure depending on the pressure.