JP7555868B2 - Method for manufacturing a vehicle structural member - Google Patents

Description

The present invention relates to structural components for vehicles.

Various technologies related to vehicle structural members have been proposed in the past. For example, in the method of hardening a metal sheet by hot stamping described in the following Patent Document 1, a hat beam formed into a generally hat-shaped cross section by hot press forming has a soft area perpendicular to the longitudinal direction, which has a lower strength than the majority of the beam. In this soft area, multiple soft band areas and narrow band areas formed between the band areas and having a higher strength than the band areas are provided perpendicular to the longitudinal direction. It is described that by providing a gap between the forming die and the formed body, the cooling rate in hot press forming is slowed down in each band area, and the strength of the band areas is lower than that of the majority of the beam areas.

Special Publication No. 2008-516080

However, in the method of hardening a metal sheet by hot stamping as described in Patent Document 1, in order to provide a flexible zone in the hat beam, hot press forming is required, and there is a problem that a flexible zone cannot be formed by cold press forming. In addition, since a gap must be provided between the forming die and the formed body, the area in which the flexible zone can be set is limited, resulting in a problem of reduced design freedom.

The present invention was conceived in light of these points, and aims to provide a vehicle structural member in which a flexible area with reduced strength compared to the majority of the elongated press-formed body formed by cold press forming or hot press forming can be provided perpendicular to the longitudinal direction.

To solve the above problems, the first invention is a vehicle structural component comprising a long press-formed body made of high-tensile steel plate and press-formed into a hat-shaped cross-section, and a flexible area formed at a predetermined position in the longitudinal direction of the press-formed body by continuously arranging a plurality of heat-affected softened portions along a direction perpendicular to the longitudinal direction, the heat-affected softened portions being formed by sandwiching the press-formed body between a pair of electrodes of a spot welding machine and passing electricity through the press-formed body while applying pressure.

The second invention is a vehicle structural member according to the first invention, in which the heat-affected softened portion has an indentation with a thickness thinner than the plate thickness of the press-formed body, formed by the pressure applied by the pair of electrodes when electricity is passed through them.

The third invention is a vehicle structural component according to the second invention, in which the heat-affected softened portion has a pair of raised portions formed around the dent so as to rise outward on both sides in the plate thickness direction.

The fourth invention is a vehicle structural component according to the second or third invention, in which the heat-affected softened portions are arranged so as to overlap each other in parts outside the dents, forming the soft area.

The fifth invention is a vehicle structural component according to any one of the first to fourth inventions, in which the heat-affected softened portions are arranged so that the melted and solidified nuggets are positioned in a straight line.

The sixth invention is a vehicle structural component according to any one of the first to fourth inventions, in which the heat-affected softened portions are arranged such that the melt-solidified nuggets are positioned in a staggered pattern.

The seventh invention is a vehicle structural member according to the fifth or sixth invention, in which the press-formed body has a pair of ridges formed by a pair of vertical wall portions and a connecting wall portion connecting one end of the pair of vertical wall portions, and the heat-affected softened portions are arranged only near each of the pair of ridges to form a pair of flexible regions arranged along the orthogonal direction.

The eighth invention is a vehicle structural member according to any one of the first to seventh inventions, in which the press-formed body includes a center pillar reinforcement, and the flexible area is provided below the belt line of the center pillar reinforcement in the vertical direction of the vehicle.

The ninth invention is a vehicle structural member according to any one of the first to seventh inventions, in which the press-formed body includes a body portion formed in an elongated shape like a bumper reinforcement, and the flexible region is formed at the predetermined position in the longitudinal direction of the body portion.

By adopting the configurations of the above-mentioned inventions, the present invention can provide a flexible area, the strength of which is reduced compared to the majority of the elongated press-formed body, formed into a hat-shaped cross section by cold press forming or hot press forming, perpendicular to the longitudinal direction.

1 is a perspective view showing an example of a vehicle structural member according to a first embodiment. FIG. 2 is a plan view of the vehicle structural member shown in FIG. 1 taken along the line II. 1A to 1C are diagrams illustrating a method for forming a heat-affected softened portion in a high-tensile steel plate. FIG. 4 is a cross-sectional view illustrating a heat-affected softened portion. FIG. 4 is a plan view illustrating a heat-affected softening portion. FIG. 2 is a diagram illustrating the configuration of the flexible section of FIG. 1. FIG. 2 is an explanatory diagram of a three-point bending strength test of Example 1 of the present invention. FIG. 2 is a side view showing an example of an analysis result of a three-point bending strength test of Example 1 of the present invention. FIG. 1 is an explanatory diagram of a three-point bending strength test of Comparative Example 1. FIG. 1 is a side view showing an example of an analysis result of a three-point bending strength test of Comparative Example 1. FIG. 13 is a diagram showing an example in which a flexible region is provided in a center pillar reinforcement. 1 is a diagram showing an example in which a flexible region is provided in the main body portion of a bumper reinforcement. FIG. FIG. 11 is a perspective view showing an example of a vehicle structural member according to a second embodiment. FIG. 14 is a diagram illustrating the configuration of the flexible region of FIG. 13. FIG. 11 is a perspective view showing an example of a vehicle structural member according to a third embodiment.

The following will describe in detail the first to third embodiments of the vehicle structural member according to the present invention with reference to the drawings. First, the vehicle structural member 1 according to the first embodiment will be described with reference to Figs. 1 to 12. The present invention can also be applied to side sills, roof side rails, front pillar reinforcements, center pillar reinforcements, bumper reinforcements, door beams, etc.

[First Prevailing Form]
1 and 2 show a schematic configuration of a vehicle structural member 1 according to the first embodiment. As shown in Fig. 1 and 2, the vehicle structural member 1 is composed of a long press-formed body 11 made of high-tensile steel plate and formed into a hat-shaped cross-sectional shape by cold press forming or hot press forming, and a flexible region 12 formed at a predetermined position in the longitudinal direction of the press-formed body 11 (for example, a position spaced a distance L1 from the longitudinal center position).

The press-formed body 11 is a cold-press steel plate with a thickness of about 0.6 mm to 2.6 mm and a tensile strength of 1180 MPa or more, and is formed into an approximately hat-shaped cross-section by cold press forming. Alternatively, the press-formed body 11 is a hot-press steel plate with a thickness of about 0.6 mm to 2.6 mm and a tensile strength of 1500 MPa or more, and is formed into an approximately hat-shaped cross-section by hot press forming.

Specifically, the press molded body 11 has a pair of opposing vertical wall portions 11A, 11B, a connecting wall portion 11C that connects one side edge of the pair of vertical wall portions 11A, 11B and has a generally vertically elongated rectangular shape in a plan view, a pair of ridge portions 11D, 11E formed by the pair of vertical wall portions 11A, 11B and the connecting wall portion 11C, and a pair of flange portions 11F, 11G that are bent outwardly from the other side edge of the pair of vertical wall portions 11A, 11B, i.e., the side edge on the opening side, generally parallel to the connecting wall portion 11C.

The soft zone 12 is arranged in a linear, continuous band of approximately constant width (e.g., about 8 mm to 16 mm) from the outer side edge of one flange portion 11F to the outer side edge of the other flange portion 11G along a direction perpendicular to the longitudinal direction of the press-formed body 11. This soft zone 12 is arranged in a straight line so that a portion of a plurality of heat-affected softened zones (hereinafter referred to as "HAZ softened zones") 22 formed in a generally circular shape in a plan view as described below overlap each other (see FIG. 6), forming a band-like portion with reduced strength compared to the majority of the press-formed body 11 (base material).

Here, an example of a method for forming the HAZ softened portion 22 will be described with reference to Figures 3 to 5. As shown in Figure 3, first, the press-formed body 11 is sandwiched between a pair of electrodes 15, and while being pressurized with a predetermined load P, electricity is passed through the spot welder 16 to melt the inside of the base material of the press-formed body 11 by resistance heating. Next, the passage of electricity through the spot welder 16 is stopped, pressure is continued, and after cooling, the pressure is released and each electrode 15 is separated from the press-formed body 11.

The pair of electrodes 15 are flat electrodes in which the contact surface 15A that contacts the press-formed body 11 is a circular flat surface with a diameter D1 (for example, D1 = 6 mm to 12 mm). The spot welder 16 can be, for example, a current inverter type spot welder with a power supply frequency of 50 Hz or 60 Hz.

As a result, as shown in Figures 4 and 5, a molten and solidified nugget 21 is formed inside the base material of the press-formed body 11. The diameter (nugget diameter) of the nugget 21 is formed to be, for example, a diameter (for example, a diameter of 4 mm to 10 mm) slightly smaller than the diameter D1 of the contact surface 15A of the electrode 15. The Vickers hardness of the nugget 21 is approximately the same as that of the base material of the press-formed body 11. In addition, a HAZ softened portion 22 that is softer than the base material of the press-formed body 11 due to thermal influence is formed around the nugget 21. The diameter (outer diameter) D2 of the HAZ softened portion 22 is formed to be, for example, a diameter (for example, a diameter of 8 mm to 16 mm) larger than the diameter of the nugget 21 by about 4 mm.

In addition, at approximately the center of both sides of the HAZ softened portion 22 where the electrodes 15 are in contact, dents 23 are formed by the pressure applied by the pair of electrodes 15 when electricity is applied. The plate thickness of the portion where the dents 23 are formed is approximately 10% to 30% thinner than the plate thickness of the base material of the press-formed body 11. The diameter of each dent 23 is, for example, approximately equal to the diameter D1 of the contact surface 15A of the electrode 15. A pair of raised portions 25 are formed on the outer periphery of each dent 23, which are raised higher than the surface of the base material of the press-formed body 11, that is, raised outward on both sides in the plate thickness direction.

Here, an example of the Vickers hardness of the nugget 21 and the HAZ softened portion 22 is shown. When the base material of the press-formed body 11 is a steel plate for cold pressing with a tensile strength of 1180 MPa or more, the Vickers hardness of the nugget 21 is approximately HV370 to HV420, which is almost the same hardness as the base material, and the Vickers hardness of the softest part of the HAZ softened portion 22 has decreased to approximately HV300. When the base material of the press-formed body 11 is a steel plate for hot pressing with a tensile strength of 1500 MPa or more, the Vickers hardness of the nugget 21 is approximately HV450, which is almost the same hardness as the base material after hot press forming, and the Vickers hardness of the softest part of the HAZ softened portion 22 has decreased to approximately HV300.

Next, the arrangement of the nuggets 21 and HAZ softened portions 22 in the soft region 12 will be described with reference to Figure 6. As shown in Figure 6, in the soft region 12, the approximate center of each dent 23 formed by the pressure applied by the pair of electrodes 15 when electricity is passed through them, i.e., the approximate center of the nugget 21, is located on a straight line 27 perpendicular to the longitudinal direction of the press-formed body 11, and the parts of the HAZ softened portions 22 radially outward of the dents 23 are arranged at an approximately equal pitch H1 so that they overlap each other.

Specifically, each HAZ softened portion 22 is arranged continuously on a straight line 27 at a substantially equal pitch H1, forming an overlapping portion A1 where the portion radially outward from the dent 23 overlaps with each other by, for example, about 30% to 70%, preferably about 50%. Therefore, the width of the soft zone 12 is formed to a width dimension substantially equal to the diameter D2 of the HAZ softened portion 22. In addition, in Figures 1 and 2, the position of each dent 23 formed by the pressure force of the pair of electrodes 15 when electricity is applied is shown diagrammatically by an x mark in the soft zone 12.

Next, the effects of the vehicle structural member 1 according to the first embodiment will be described with reference to Figures 7 to 10. As shown in Figures 7 and 9, a first analytical model 31 was prepared as invention example 1, and a second analytical model 32 was prepared as comparative example 1, and the load-displacement characteristics of each analytical model 31, 32 were analyzed by CAE (Computer Aided Engineering) analysis. Note that the same reference numerals as those of the vehicle structural member 1 according to the first embodiment indicate the same or equivalent parts as those of the vehicle structural member 1 according to the first embodiment.

As shown in FIG. 7, the first analysis model 31 has the same configuration as the vehicle structural member 1, and is composed of a long press-formed body 11 formed in a hat-shaped cross section, and a soft area 12 formed at a position a distance L1 away from the longitudinal center position of the press-formed body 11. The soft area 12 is provided in a continuous band shape from the outer side edge of one flange portion 11F to the side edge of the other flange portion 11G along a direction perpendicular to the longitudinal direction of the press-formed body 11. The soft area 12 has each dent 23 (indicated by an x mark in FIG. 7) formed by the pressure force when electricity is applied by a pair of electrodes 15, and is a model in which the HAZ softened portions 22 are arranged in a straight line so that parts of them overlap each other.

As shown in FIG. 9, the second analytical model 32 as Comparative Example 1 is a model in which the flexible region 12 is omitted from the configuration of the first analytical model 31. Next, as shown in FIG. 7 and FIG. 9, both ends of the first analytical model 31 and the second analytical model 32 are supported horizontally by supporting members 33 with semicircular cross sections. Then, a downward load W1 is applied to the longitudinal center position of each analytical model 31, 32 by an impactor 35 with a semicircular cross section of radius R1 and a length longer than the width of the connecting wall portion 11C, and the amount of displacement of each analytical model 31, 32 in response to the load is analyzed.

Figure 8 shows the analysis results of the first analytical model 31 by CAE. Figure 10 shows the analysis results of the second analytical model 32. As shown in Figure 8, in the first analytical model 31, the deflection is greatest in the part where the flexible region 12 is formed, and is greater than the deflection in the longitudinal center, i.e., the deflection at the position where the impactor 35 is in contact. On the other hand, as shown in Figure 10, in the second analytical model 32, the flexible region 12 is omitted, so the deflection is greatest in the longitudinal center, i.e., the deflection at the position where the impactor 35 is in contact.

Therefore, it is believed that the buckling position of the press-formed body 11 can be controlled by providing a flexible region 12 perpendicular to the longitudinal direction at the desired buckling position of the press-formed body 11. In addition, by changing the size of the contact surface 15A of the electrode 15, i.e., the diameter D1, or the current value or pressure applied to the pair of electrodes 15, the plate thickness of the portion where the dent 23 is formed and the size of the HAZ softened portion 22, i.e., the diameter D2, can be changed. As a result, it is believed that the bending strength and buckling timing of the press-formed body 11 can be controlled by changing the width and strength of the flexible region 12.

As described above in detail, in the vehicle structural member 1 according to the first embodiment, the flexible region 12 in which the multiple HAZ softened portions 22 are arranged in succession can be formed at a predetermined position in the longitudinal direction of the press-formed body 11 formed into a substantially hat-shaped cross-section by cold press forming or hot press forming, so as to be perpendicular to the longitudinal direction. This allows the vehicle structural member 1 to be set so that it bends at the position where the flexible region 12 is formed when a high load is applied to the vehicle structural member 1 from outside the vehicle. In addition, the bending strength and buckling timing of the vehicle structural member 1 can be controlled by adjusting the location where the flexible region 12 is arranged.

In addition, by controlling the shape of the pair of electrodes 15, the pressure and current applied when the pair of electrodes 15 are pressed against the press-formed body 11, the size of the dent 23 and the plate thickness of the portion where the dent 23 is formed can be adjusted, making it easy to control the bending strength and buckling timing of the vehicle structural member 1. In addition, by forming a raised portion 25 around the dent 23, it is possible to absorb dimensional changes in the vehicle structural member 1 caused by changes in the plate thickness of the portion where the dent 23 is formed, thereby improving dimensional accuracy.

The multiple HAZ softened portions 22 are arranged so that they overlap each other in parts outside the dents 23 to form the soft zone 12. This allows the multiple HAZ softened portions 22 to be arranged so that they are reliably continuous, and the number of dents 23 and HAZ softened portions 22 that form the soft zone 12 can be reduced, improving work efficiency. The multiple HAZ softened portions 22 are arranged so that the melted and solidified nuggets 21 are positioned in a straight line. This allows the soft zone 12 to be formed in a straight line, and the bending position, bending strength, and buckling timing of the vehicle structural member 1 can be easily set.

Here, an example of applying the vehicle structural member 1 according to the first embodiment to a center pillar reinforcement will be described with reference to FIG. 11. As shown in FIG. 11, the center pillar reinforcement 41, which is disposed on the vehicle widthwise outer side of the center pillar (not shown), is formed in a predetermined hat-shaped cross-sectional shape that opens inward in the vehicle width direction, and flange portions 42 bent outward at approximately right angles are provided on both ends of the opening side of the groove-shaped cross section. The upper end edge of this center pillar reinforcement 41 is connected to the roof side rail 46 via an attachment portion 45. The lower end edge of the center pillar reinforcement 41 is connected to the side sill 48 via an attachment portion 47, and is disposed in the vehicle up-down direction.

In addition, at a position about 1/3 of the overall height of the center pillar reinforcement 41 from the lower end, a flexible region 12 (see FIG. 6) is provided in a band shape along a direction perpendicular to the longitudinal direction, from the outer side edge of one flange portion 42 to the outer side edge of the other flange portion 42. Therefore, the flexible region 12 is provided so as to be located below the belt line 49. This makes it easy to set the bending position, bending strength, and buckling timing so that the center pillar reinforcement 41 is bent from the flexible region 12 during a side collision from the outside of the vehicle, and reduces the amount of penetration of the colliding object into the inside of the vehicle cabin.

Next, an example in which the vehicle structural member 1 according to the first embodiment is applied to a bumper reinforcement will be described with reference to FIG. 12. As shown in FIG. 12, the bumper reinforcement 51 has both longitudinal ends, i.e., both vehicle width ends, attached to a frame member (not shown) via bumper support members 52. The bumper reinforcement 51 forms a closed cross-sectional structure with a main body portion 53 formed in a predetermined hat-shaped cross-sectional shape that opens toward the inside in the vehicle longitudinal direction, and a long lid portion (not shown) attached to cover the opening side of the main body portion 53.

The bumper reinforcement 51 may have an open cross-sectional structure without blocking the opening side of the hat-shaped main body 53. The bumper reinforcement 51 may be attached to a frame member (not shown) via bumper support members 52 at both longitudinal ends of the main body 53, i.e., both transverse ends of the vehicle.

The body 53 has flanges 53A (only the upper side is shown in FIG. 12) bent outward at approximately right angles at both ends of the opening of the groove-shaped cross section. In addition, at two positions that divide the entire length of the body 53 into three equal parts in the longitudinal direction, flexible regions 12 (see FIG. 6) are provided in a strip shape from the outer edge of one flange 53A to the outer edge of the other flange 53A along a direction perpendicular to the longitudinal direction. This makes it easy to set the bending position, bending strength, and buckling timing so that the bumper reinforcement 51 is bent from each flexible region 12 during a vehicle collision.

[Second embodiment]
Next, a vehicle structural member 61 according to a second embodiment will be described with reference to Figures 13 and 14. Note that the same reference numerals as those in the vehicle structural member 1 according to the first embodiment indicate the same or corresponding parts as those in the vehicle structural member 1 according to the first embodiment.

The vehicle structural member 61 according to the second embodiment has substantially the same configuration as the vehicle structural member 1 according to the first embodiment. However, as shown in FIG. 13, the vehicle structural member 61 differs in that a flexible region 62 is provided in place of the flexible region 12 at a predetermined position in the longitudinal direction of the press-formed body 11 (e.g., a position distance L1 away from the longitudinal center position) of the press-formed body 11. The flexible region 62 is provided in a continuous zigzag strip of substantially constant width (e.g., a width of about 8 mm to 16 mm) from the outer side edge of one flange portion 11F to the outer side edge of the other flange portion 11G along the orthogonal direction perpendicular to the longitudinal direction of the press-formed body 11.

Specifically, as shown in FIG. 14, in the soft region 62, the approximate centers of the dents 23 formed by the pressure applied by the pair of electrodes 15 when electricity is applied, i.e., the approximate centers of the nuggets 21, are positioned in a staggered pattern along a direction perpendicular to the longitudinal direction of the press-formed body 11, and are arranged at an approximately equal pitch H2 so that the radially outer portions of the HAZ softened portions 22 from the dents 23 overlap each other. The radially outer portions of the HAZ softened portions 22 from the dents 23 form overlapping portions A1, for example, by about 30% to 70%, preferably about 50%. In FIG. 13, the positions of the dents 23 formed by the pressure applied by the pair of electrodes 15 when electricity is applied are typically indicated by cross marks in the soft region 62.

In this way, in the vehicle structural member 61 according to the second embodiment, the flexible region 62 can be formed to bend in a zigzag pattern, and the width of the flexible region 62 in the longitudinal direction of the press-formed body 11 can be increased in appearance. As a result, when a high load acts on the vehicle structural member 61 from outside the vehicle, it can be set to bend at the position where the flexible region 62 is formed. In addition, by adjusting the location where the flexible region 62 is disposed, the bending strength and buckling timing of the vehicle structural member 61 can be controlled. Therefore, the flexible region 62 can be formed to bend in a zigzag pattern, and the bending position, bending strength, and buckling timing of the vehicle structural member 61 can be easily set.

[Third embodiment]
Next, a vehicle structural member 71 according to a third embodiment will be described with reference to Fig. 15. Note that the same reference numerals as those in the vehicle structural member 1 according to the first embodiment indicate the same or corresponding parts as those in the vehicle structural member 1 according to the first embodiment.

The vehicle structural member 71 according to the third embodiment has a configuration substantially the same as that of the vehicle structural member 1 according to the first embodiment. However, as shown in FIG. 15, the vehicle structural member 71 differs in that a pair of flexible regions 72A, 72B are provided in place of the flexible region 12 at a predetermined position in the longitudinal direction of the press-formed body 11 (e.g., a position spaced a distance L1 from the longitudinal center position).

Specifically, the pair of flexible regions 72A, 72B are arranged in a linear band shape along a direction perpendicular to the longitudinal direction of the press-molded body 11, straddling each of the ridges 11D, 11E, and only in the vicinity of each of the ridges 11D, 11E. In FIG. 15, the x marks in each of the flexible regions 72A, 72B show the positions of the dents 23 formed by the pressure applied by the pair of electrodes 15 when electricity is applied.

Therefore, in the vehicle structural member 71 according to the third embodiment, a pair of flexible regions 72A, 72B can be formed only near each of a pair of ridges 11D, 11E, in which multiple HAZ softened portions 22 are arranged continuously along a direction perpendicular to the longitudinal direction of the press-formed body 11. This allows the vehicle structural member 71 to be set to bend at the position where the pair of flexible regions 72A, 72B are formed when a high load is applied to the vehicle structural member 71 from outside the vehicle. In addition, the bending strength and buckling timing of the vehicle structural member 71 can be controlled by adjusting the location where the pair of flexible regions 72A, 72B are arranged.

The present invention is not limited to the first to third embodiments, and various improvements, modifications, additions, and deletions are possible without departing from the scope of the present invention. For example, the following may be done. In the following description, the same reference numerals as those of the vehicle structural members 1, 61, and 71 according to the first to third embodiments indicate the same or equivalent parts as those of the vehicle structural members 1, 61, and 71 according to the first to third embodiments.

(A) For example, in each vehicle structural member 1, 61, 71, the multiple rows of flexible regions 12, 62, 72A, 72B may be arranged adjacent to each other in the longitudinal direction of the press-formed body 11, along a direction perpendicular to the longitudinal direction of the press-formed body 11. In addition, the adjacent multiple rows of flexible regions 12, 62, 72A, 72B may be arranged such that the radially outer portions of the impact marks 23 of the HAZ-softened portions 22 adjacent to each other in the longitudinal direction of the press-formed body 11 overlap each other.

This allows the width of each flexible region 12, 62, 72A, 72B, which has a lower strength than the majority of the press-formed body 11 formed by cold press forming or hot press forming, to be made appear larger. As a result, when a high load acts on each vehicle structural member 1, 61, 71 from outside the vehicle, each flexible region 12, 62, 72A, 72B can be set to bend at the position where it is formed, making it even easier to set the bending position, bending strength, and buckling timing of each vehicle structural member 1, 61, 71.

(B) For example, in the vehicle structural member 1, the flexible regions 12, 62, 72A, 72B may be combined in any manner and arranged adjacent to each other in the longitudinal direction of the press-formed body 11 along a direction perpendicular to the longitudinal direction of the press-formed body 11. Also, adjacent flexible regions 12, 62, 72A, 72B may be arranged such that the radially outer portions of the impact marks 23 of the HAZ-softened portions 22 adjacent to each other in the longitudinal direction of the press-formed body 11 overlap each other.

This allows the apparent longitudinal width of the press-formed body 11 formed by cold press forming or hot press forming to be increased in the portion (flexible region) that has a lower strength than the majority of the press-formed body 11. As a result, when a high load is applied to the vehicle structural member 1 from outside the vehicle, it can be set to bend at the positions where the flexible regions 12, 62, 72A, and 72B are formed, making it even easier to set the bending position, bending strength, and buckling timing of the vehicle structural member 1.

(C) For example, in the vehicle structural member 71, the pair of soft regions 72A, 72B may be provided in a zigzag continuous band shape only in the vicinity of each of the ridges 11D, 11E along the orthogonal direction perpendicular to the longitudinal direction of the press-formed body 11, straddling the ridges 11D, 11E. Specifically, in the pair of soft regions 72A, 72B, the approximate centers of the dents 23 formed by the pressure applied by the pair of electrodes 15 when electricity is applied, that is, the approximate centers of the nuggets 21, may be positioned in a staggered manner along the orthogonal direction perpendicular to the longitudinal direction of the press-formed body 11, and the radially outer portions of the HAZ softened portions 22 beyond the dents 23 may be arranged at an approximately equal pitch H2 so as to overlap each other.

In this way, in the vehicle structural member 71, the pair of flexible regions 72A, 72B can be formed to bend in a zigzag pattern, and the width of the pair of flexible regions 72A, 72B in the longitudinal direction of the press-formed body 11 can be increased in appearance. As a result, when a high load acts on the vehicle structural member 71 from outside the vehicle, it can be set to bend at the position where the pair of flexible regions 72A, 72B are formed. In addition, by adjusting the location where the pair of flexible regions 72A, 72B are arranged, the bending strength and buckling timing of the vehicle structural member 71 can be controlled. Therefore, the pair of flexible regions 72A, 72B can be formed to bend in a zigzag pattern, and the bending position, bending strength, and buckling timing of the vehicle structural member 71 can be easily set.

(D) For example, the contact surface 15A of the electrode 15 that contacts the press-formed body 11 is not limited to a circular flat surface, but may be a polygonal flat surface such as a triangle, a rectangle, a pentagon, or a hexagon. This allows the shape of the dent 23 in the HAZ softened portion 22, i.e., the shape of the raised portion 25, to be a triangle, a rectangle, a pentagon, or a hexagon. As a result, the area of the overlapping portion A1 of the HAZ softened portion 22 that constitutes each flexible region 12, 62, 72A, and 72B can be increased, and the bending position, bending strength, and buckling timing of each vehicle structural member 1, 61, and 71 can be set more easily.

(E) For example, instead of the flexible region 12 of the center pillar reinforcement 41 shown in FIG. 11, a flexible region 62 (see FIG. 13) may be disposed along an orthogonal direction perpendicular to the longitudinal direction of the center pillar reinforcement 41. Also, instead of the flexible region 12 of the center pillar reinforcement 41 shown in FIG. 11, a pair of flexible regions 72A, 72B may be disposed on each ridge of the center pillar reinforcement 41 along an orthogonal direction perpendicular to the longitudinal direction of the center pillar reinforcement 41.

This makes it easy to set the bending position, bending strength, and buckling timing so that the center pillar reinforcement 41 can bend from each flexible section 62, 72A, and 72B during a side collision from the outside of the vehicle, thereby reducing the amount of penetration of the colliding object into the interior of the vehicle.

(F) For example, in the main body portion 53 of the bumper reinforcement 51 shown in FIG. 12, instead of the flexible regions 12 provided at two locations, flexible regions 62 (see FIG. 13) may be arranged at two locations on the main body portion 53 along an orthogonal direction perpendicular to the longitudinal direction of the main body portion 53. In addition, in the main body portion 53 of the bumper reinforcement 51 shown in FIG. 12, instead of the flexible regions 12 provided at two locations, a pair of flexible regions 72A, 72B may be arranged at each of the ridge portions at two locations on the main body portion 53 along an orthogonal direction perpendicular to the longitudinal direction of the main body portion 53.

This allows the bending position, bending strength, and buckling timing to be easily set so that the bumper reinforcement 51 is bent from each of the flexible regions 62 provided at two locations on the main body 53 during a vehicle collision. Also, the bending position, bending strength, and buckling timing to be easily set so that the bumper reinforcement 51 is bent from a pair of flexible regions 72A, 72B provided on each of the two ridges of the main body 53.

(G) For example, the press-formed body 11 is not limited to a substantially hat-shaped cross-sectional shape, and may also have a groove-shaped cross-sectional shape. That is, the press-formed body 11 may be configured with a pair of vertical wall portions 11A, 11B and a connecting wall portion 11C that connects one end of the pair of vertical wall portions 11A, 11B. Each flexible region 12, 62 may be provided in a linear band shape or a zigzag band shape that continues from the outer side edge of one vertical wall portion 11A to the outer side edge of the other vertical wall portion 11B along a direction perpendicular to the longitudinal direction of the press-formed body 11.

This allows the press-formed body 11 to be set so that it bends at the positions where each flexible area 12, 62 is formed when a high load is applied from outside the vehicle. Therefore, by adjusting the locations where each flexible area 12, 62 is positioned, it is possible to control the bending strength and buckling timing of the vehicle structural member formed by the press-formed body 11.

(H) The first to ninth inventions also provide the following effects. For example, according to the vehicle structural member of the first invention, a flexible region in which a plurality of heat-affected softened portions are arranged in succession can be provided at a predetermined position in the longitudinal direction of a long press-formed body formed into a hat cross-sectional shape by press forming, so as to be perpendicular to the longitudinal direction. This allows the vehicle structural member to be set so as to bend at the predetermined position when a high load acts on the vehicle structural member from outside the vehicle. Furthermore, by adjusting the length of the flexible region and the location where it is arranged, the bending strength and buckling timing of the vehicle structural member can be controlled.

In addition, according to the vehicle structural member of the second invention, by controlling the shape of the pair of electrodes, the pressure and current used to press the pair of electrodes against the press-formed body, etc., the size and thickness of the dent and the size of the heat-affected softened zone (HAZ softened zone) can be adjusted, making it easy to control the bending strength and buckling timing of the vehicle structural member. In addition, according to the vehicle structural member of the third invention, a raised portion is formed around the dent, which makes it possible to absorb dimensional changes in the vehicle structural member due to changes in the thickness of the dent, thereby improving dimensional accuracy.

The vehicle structural member according to the fourth aspect of the invention allows multiple heat-affected softened sections to be arranged so that they are reliably continuous, and the number of heat-affected softened sections that form the flexible zone can be reduced, improving work efficiency. The vehicle structural member according to the fifth aspect of the invention allows the flexible zone to be formed in a straight line, making it easy to set the bending position, bending strength, and buckling timing of the vehicle structural member.

Furthermore, according to the vehicle structural member of the sixth invention, the flexible region can be formed so as to bend in a zigzag pattern, and the bending position, bending strength, and buckling timing of the vehicle structural member can be easily set. Furthermore, according to the vehicle structural member of the seventh invention, by arranging multiple heat-affected softening portions along the orthogonal direction only near each of a pair of ridges, and forming a pair of flexible regions to straddle each of the ridges, the bending position, bending strength, and buckling timing of the vehicle structural member can be easily set.

Furthermore, with the vehicle structural member according to the eighth aspect of the invention, the bending position, bending strength, and buckling timing of the center pillar reinforcement can be easily set during a side impact from the outside of the vehicle. Furthermore, with the vehicle structural member according to the ninth aspect of the invention, the bending position, bending strength, and buckling timing of the bumper reinforcement can be easily set during a vehicle collision.

REFERENCE SIGNS LIST 1, 61, 71 Vehicle structural member 11 Press-formed body 11A, 11B Vertical wall portion 11C Connecting wall portion 11D, 11E Ridge line portion 11F, 11G Flange portion 12, 62, 72A, 72B Soft area 15 Electrode 16 Spot welder 21 Nugget 22 Heat-affected zone (HAZ)
23 Dent 25 Raised portion 41 Center pillar reinforcement 51 Bumper reinforcement 53 Main body

Claims (9)

A method for manufacturing a vehicle structural member, comprising the steps of:
A step of forming a long press-formed body having a hat cross-sectional shape by press-forming a high-tensile steel plate;
and a step of sandwiching the press-formed body between a pair of electrodes of a spot welding machine and passing an electric current through the press-formed body while applying pressure to form a soft area at a predetermined position in the longitudinal direction of the press-formed body, the soft area having a plurality of heat-affected softened portions arranged continuously along a direction perpendicular to the longitudinal direction. 2. The method of claim 1 ,
the heat-affected softened portion has an indentation having a thickness thinner than a plate thickness of the press-formed body formed by a pressure force applied by the pair of electrodes when a current is passed through the electrodes. 3. The method of claim 2,
The heat-affected softened portion has a pair of raised portions formed around the impact mark so as to rise outward on both sides in the plate thickness direction. 4. The method according to claim 2 or claim 3,
The method of claim 1, wherein the heat-affected softened portions are arranged to overlap each other in a portion outside the impact mark to form the soft region. 5. The method according to any one of claims 1 to 4, comprising:
A method according to claim 1, wherein a plurality of said heat-affected softened zones are arranged such that the solidified nuggets are aligned in a straight line. 5. The method according to any one of claims 1 to 4, comprising:
The method of claim 1, wherein a plurality of the heat-affected softened zones are arranged such that the melt-solidified nuggets are staggered. 7. The method of claim 5 or claim 6,
The press-formed body has a pair of ridge lines formed by a pair of vertical wall portions and a connecting wall portion connecting one ends of the pair of vertical wall portions,
The method , wherein the plurality of heat-affected softened portions are disposed only adjacent to each of a pair of the ridge portions to form a pair of the soft regions disposed along the orthogonal direction. 8. The method according to any one of claims 1 to 7, comprising:
The press-formed body includes a center pillar reinforcement,
The method , wherein the flexible region is provided below a belt line in a vehicle vertical direction of the center pillar reinforcement. 8. The method according to any one of claims 1 to 7, comprising:
The press-formed body includes a main body portion formed in a long shape of a bumper reinforcement,
The method of claim 1, wherein the flexible section is formed at the predetermined location along the length of the body portion.

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