JPH09141327A - Manufacture of reinforcing member for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of the delayed breakdown of the beam part of a side impact beam. SOLUTION: The beam part 3 made of a high tension steel plate, of a side impact beam 2 with mounting bracket parts 4 and 5 formed by pressing at both ends as one body, is pressed into a circular shape in cross-section by using a press die whose dimension of an inner periphery is smaller than the expanded width of a material. Consequently, a compressive force is uniformly applied over the whole area of the plate thickness of the beam part 3, and the absolute values of tensile residual stresses in the inside and the outside of the plate, are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a reinforcing member for a vehicle such as a side impact beam attached to the inside of a door of an automobile for protecting an occupant.

[0002]

2. Description of the Related Art In an automobile, a side impact beam is generally provided inside a door to reinforce the door itself in order to prevent the door from entering into the cabin and protect an occupant caused by a side collision. Is installed. A side impact beam as a vehicle reinforcing member is required to be lightweight and inexpensive as long as a required quality standard is satisfied in order to improve fuel efficiency.

Conventionally, in order to reduce the weight and cost, a flat strip made of a high-tensile steel plate is used to form a beam portion having a circular cross section, and mounting bracket portions for the doors at both ends of the beam portion are attached to the beam portion. Japanese Patent Laid-Open No. 4-23872 discloses a side impact beam press-molded integrally with a portion.
No. 5 discloses this.

[0004]

However, the high-tensile steel sheet has a property that a high tensile residual stress is generated during forming, and there is a case where delayed fracture occurs on the steel sheet surface or the like after forming. Therefore, even in the side impact beam using the above high-tensile steel plate, a high tensile residual stress is generated in the beam portion, which may cause delayed fracture in the beam portion after a lapse of a predetermined time of molding.

The present invention has been proposed in order to solve the above-mentioned problems in the vehicle reinforcing member such as the side impact beam. The high-tensile steel plate is used as a material and the beam portion is formed into a circular cross section. In this regard, it is an object of the present invention to uniformly apply a compressive force to the beam portion to prevent the occurrence of delayed fracture after molding.

[0006]

In order to achieve the above-mentioned object, a method for manufacturing a vehicle reinforcing member according to the present invention uses a high-strength steel plate as a material, and a cross section integrally formed with a mounting bracket portion for a vehicle body. The surface circular beam portion is formed by applying a compressive force in the circumferential direction in the forming step so that the tensile residual stress after forming is reduced.

The beam section uses a press die having an inner peripheral dimension smaller than the material development width, and a compressive force is applied in the circumferential direction by the reduction of the material development width dimension to the inner peripheral dimension of the die. Is preferably molded.

[0008]

In the method of manufacturing a vehicle reinforcing member according to the present invention, when a beam portion having a circular cross section is formed, a compressive force is applied in the circumferential direction of the cross section, so that plastic deformation occurs in the entire plate thickness. As a result, the absolute value of the tensile residual stress in the beam portion is reduced, and delayed fracture is prevented from occurring.

In press-molding the beam part,
When a press die with an inner diameter smaller than the material development width is used and a compressive force is applied to the beam due to the reduction from the material development width to the inner circumference of the die, the entire plate thickness of the beam The compressive force can be evenly applied to.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to a side impact beam attached to the inside of an automobile door will be described below with reference to the drawings. FIG. 1 is a view showing a mounting state of the side impact beam. The side impact beam 2 is mounted in a substantially central portion inside the door 1 in parallel with the ground, and is resistant to an impact from a side surface of the door 1.
Prevents the car from invading inside the vehicle.

FIG. 2 is an external view of the side impact beam 2. The side impact beam 2 includes a central beam portion 3 and mounting bracket portions 4 and 5 for the door 1 which are formed at both ends of the beam portion 3. Are integrally press-molded, and the mounting bracket portions 4 and 5 are fixed to the front end portion and the rear end portion of the door 1, respectively. The beam portion 3 is made of a material whose width dimension is larger than that of a molding die, which will be described later, and is press-molded into a circular cross section as shown in FIG. Then, the abutting portion 6 of the beam portion 3 does not require welding and is attached facing the indoor side. Hereinafter, a description will be given assuming that the radius of the cross section of the beam portion 3 is R and the diameter is D.

Next, the forming process of the beam portion 3 will be described with reference to FIG. First, as shown in FIG. 4A, a strip 3 ′ of a high-tensile steel plate is prepared as a material. This strip 3 '
Is set to be longer than the dimension of a mold described later. For example, when the plate thickness of the side impact beam 2 is t and the diameter of the beam portion 3 is D, according to the conventional example, the width dimension L of the strip plate is L = (D−t) π. In the claims and the detailed description of the invention, this L is referred to as the inner peripheral dimension of the mold. However, according to the present invention, the width dimension L'of the strip 3'is set to L '=
L ((100 + α) / 100), the beam unit 3 is α%
Mold by adding compression. The width dimension L ′ of the material in the sample described later is L ′ = L × 1.03, and compression of 3% is applied.

Next, as shown in FIG. 4B, the band plate 3'is bent into a U-shaped cross section by pressing using a U-bending die 11. This is a preliminary bending step for the next step, and uses the following mold 11. That is, the die 11 has a bent portion 12 ″ at the tip end that has a radius smaller than the radius R as a finished product, and when the strip plate 3 ′ is bent into a U-shaped cross section, a projection having a dimension larger than the material width dimension thereof. It consists of an upper mold 12 with a part 12 'and a lower mold 13 with a recess 13' which substantially matches the bend 12 ".

Then, as shown in FIG. 4 (c), the U-shaped band plate 3 "formed by the pre-bending process is inserted into the cavity 14 'of the molding die 14 here.
Molding mold 14 composed of half-shaped upper mold 15 and lower mold 16
In press molding, the dimensions of the cavity 14 'are formed such that the dimensions of the beam portion 3 having a circular cross section have a diameter D. In this case, the strip 3 ″ is composed of the upper die 15 and the lower die 16.
U-shaped in the press direction between the and.

Next, as shown in FIG. 4D, the upper mold 15 and the lower mold 16 as the molding mold 14 are closed. The figure shows a state in which the strip 3 ″ is formed along the inner surface of the cavity 14 ′, and the upper part is formed by the difference between the width L ′ of the strip 3 ′ and the inner circumference L of the cavity 14 ′. The figure shows a state in which a gap s is formed between the mold 15 and the lower mold 16. Here, the dimension S of the gap s is S = (L'-L) / 2,
The length S is compressed.

Then, as shown in FIG. 4 (e), the upper die 15 and the lower die 16 as the molding die 14 are closed to form a U-shaped strip 3 "having a circular cross section. And press-molding into the cavity 1. Here, the width dimension of the strip 3 ′ is the cavity 1
Since L 'is larger than the inner peripheral dimension L of 4', the beam portion 3 is press-formed with a compressive force applied over the entire circumference. Thereby, in the entire circumference of the beam portion 3 having a circular cross section, plastic deformation occurs in the entire thickness range from the plate surface to the plate inner surface, so that the difference in stress generated between the plate surface and the plate inner surface is reduced, The absolute value of the tensile residual stress is reduced.

Next, the results of comparison between the sample manufactured according to the conventional example and the sample manufactured according to this embodiment will be described. As a sample, a high-strength steel plate having a tensile strength of 140 kg / mm ² and a plate thickness of 2.3 mm and having a cross-sectional diameter D of 35 mm is used. The measuring method is a method in which the amount of strain is measured by a strain gauge after molding and the residual stress is calculated from the amount of strain.

5 to 7 are diagrams showing the measurement results, FIG. 5 is a diagram showing a conventional sample, and FIGS. 6 and 7 are diagrams showing the distribution of residual stress with respect to the distance from the plate surface in the sample according to this example. Is. Here, the unsigned value of the residual stress represents the tensile stress, and the value with the minus (-) sign represents the compressive stress. The measurement points P are, as shown in the same figure, respectively, a position rotated 180 degrees clockwise from the abutment portion 6, a position rotated θ = 15 degrees from the abutment portion 6, and θ ′ clockwise from the abutment portion 6. = 180 ° rotated position. The triangular mark represents the stress in the circumferential direction as the residual stress, and the square mark represents the stress in the axial direction as the residual stress.

It is recognized from FIG. 5 that, in the sample according to the conventional example, the circumferential stress and the axial stress as the tensile residual stress exist at positions apart from the line showing the tensile residual stress 0, and in particular, Distance 1.0m from board surface
The presence of a large tensile residual stress is recognized at a position near m.

It is recognized from FIGS. 6 and 7 that, in the sample according to this example, the circumferential stress and the axial stress as the tensile residual stress exist near the line showing the tensile residual stress 0, and the tensile stress It can be seen that there is almost no residual stress. This is the same both in FIG. 6 showing the position of 15 degrees from the abutting portion 6 and in FIG. 7 showing the position of 180 degrees.

As described above, when the beam portion 3 is press-formed into a circular cross section by using a material having a material width dimension for forming a circular cross section larger than the theoretical dimension of the mold, the beam section 3 is formed in the circumferential direction. A compressive force is applied, and plastic deformation occurs due to the compressive force over the entire plate thickness. As a result, the difference in the tensile residual stress generated between the plate surface portion and the plate inner surface portion decreases, and the absolute value decreases. This prevents the occurrence of delayed fracture due to tensile residual stress.

In the embodiment, the beam section 3 is
Although the one formed by the two press dies 11 and 14 has been exemplified, after forming into a circular cross section by roll forming using a forging roll, a compressive force is applied in the circumferential direction of the beam portion 3 by the die. Can also. Further, although the butt portion 6 in the beam portion 3 is not welded as an example, even if the butt portion 6 is welded, the same result as the above measurement result can be obtained.

[0023]

As described above, according to the method for manufacturing a vehicle reinforcing member according to the present invention, a beam portion having a circular cross section is formed by applying a compressive force in the circumferential direction at the forming step. Therefore, the plastic deformation due to the compressive force occurs over the entire plate thickness of the beam portion, the difference in the tensile stress generated between the inside and the outside of the plate becomes small, and the absolute value of the tensile residual stress decreases. This makes it possible to prevent delayed fracture due to residual stress even when a high-tensile steel plate is used.

In particular, when press-forming the above-mentioned beam portion, a press die having an inner peripheral dimension smaller than the material development width is used, and the beam is reduced by reducing the material development width dimension to the inner peripheral dimension of the die. By applying compressive force to the part, it is possible to mold and press the cross section with a single press die,
Easy to manufacture.

[Brief description of the drawings]

FIG. 1 is a diagram showing an attached state of a side impact beam according to an embodiment of the present invention.

FIG. 2 is an external view of a side impact beam.

FIG. 3 is a cross-sectional view of a beam portion of a side impact beam.

FIG. 4 is a diagram showing a forming process of a beam portion of a side impact beam.

FIG. 5 is a diagram showing residual stress of a sample according to a conventional example.

FIG. 6 is a diagram showing residual stress of a sample according to an example.

FIG. 7 is a diagram showing residual stress of a sample according to an example.

[Explanation of symbols]

 1 Door 2 Side Impact Beam 3 Beam Part 3'Strip Plate 4, 5 Mounting Bracket Part 6 Butt Part 11 U Bending Mold 14 Molding Mold

Claims (2)

[Claims] 1. A method of manufacturing a vehicle reinforcing member, comprising a beam portion having a circular cross section and made of high-strength steel sheet, and mounting bracket portions for vehicle bodies provided at both ends of the beam portion. A method of manufacturing a reinforcing member for a vehicle, which comprises applying a compressive force in a circumferential direction of the transverse section in a step of forming a beam portion to obtain a reinforcing member having a beam portion in which tensile residual stress after forming is reduced. . 2. The step of forming the beam portion includes forming a region corresponding to the beam portion between the mounting bracket portions,
It consists of a step of making a circular cross section where the width edges are abutted by press molding using a mold whose inner peripheral dimension is smaller than the material development width, and depending on the reduction from the material development width dimension to the inner peripheral dimension of the mold. A method of manufacturing a reinforcing member for a vehicle, wherein the compressive force is applied.