Vehicle body frame members and their manufacturing method

Abstract

The present invention provides a vehicle body frame member capable of mitigating stress concentration at the periphery of an opening during bending deformation, and a method for manufacturing the same. [Solution] A vehicle body frame member according to one aspect of the present disclosure is a cylindrical vehicle body frame member formed by welding together a first steel plate and a second steel plate having an opening, wherein a burring portion is formed on the peripheral edge of the opening of the first steel plate, rising toward the second steel plate.

Description

Technical Field

[0001] The present disclosure relates to a vehicle body frame member and a method for manufacturing the same.

Background Art

[0002] As disclosed in Patent Document 1, the inventors have developed a method of removing strain from the peripheral edge of a through-hole formed in a steel plate by punching and then performing flanging on the peripheral edge by induction heating. Flanging is also called stretch flange processing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in vehicle body frame members such as pillars, side members, and rocker panels (also called side sills), relatively large openings may be formed for attaching other parts or for the passage of wire harnesses. In vehicle body frame members having such openings, there is a problem that stress concentrates on the peripheral edge of the opening during bending deformation, resulting in a decrease in strength. Note that such a problem becomes more prominent as the steel plate constituting the vehicle body frame member has higher strength.

[0005] The present disclosure has been made in view of such circumstances, and provides a vehicle body frame member and a method for manufacturing the same that can relieve stress concentration at the peripheral edge of an opening during bending deformation.

Means for Solving the Problems

[0006] A vehicle body frame member according to an aspect of the present disclosure is a cylindrical vehicle body frame member in which a first steel plate having an opening and a second steel plate are welded, A burring portion is formed on the periphery of the opening of the first steel plate, rising toward the second steel plate.

[0007] In one aspect of the present invention, a burring portion is formed on the periphery of the opening of the first steel plate, rising toward the second steel plate. This reduces stress concentration at the periphery of the opening.

[0008] A method for manufacturing a vehicle body frame member according to one aspect of this disclosure is: The process involves inductively heating the periphery of an opening formed in a first steel plate to remove strain, and then burring the periphery to form a burred portion. The process includes the step of welding the first steel plate to the second steel plate with the burring portion facing inward to form a cylindrical vehicle body frame member.

[0009] In a method for manufacturing a vehicle body frame member according to one aspect of the present invention, the peripheral edge of an opening formed in a first steel plate is induction heated to remove strain, and then the peripheral edge is burred to form a burred portion. This makes it possible to alleviate stress concentration at the peripheral edge of the opening. [Effects of the Invention]

[0010] This disclosure provides a vehicle body frame member and a method for manufacturing the same that can alleviate stress concentration at the periphery of an opening during bending deformation. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic perspective view of a vehicle body frame member according to the first embodiment. [Figure 2] This is a schematic cross-sectional view of a vehicle body frame member according to the first embodiment. [Figure 3] This is a partial plan view showing an example of an opening 11 in the first steel plate 10. [Figure 4] This graph shows the change in maximum load and fracture stroke with respect to the height H of the burring section. [Figure 5]This is a flowchart showing a method for manufacturing a vehicle body frame member according to the first embodiment. [Modes for carrying out the invention]

[0012] The following describes specific embodiments of this disclosure in detail with reference to the drawings. However, this disclosure is not limited to the following embodiments. Also, for clarity, the following descriptions and drawings have been simplified as appropriate.

[0013] (First Embodiment) <Structure of the vehicle body frame components> First, the configuration of the vehicle body frame members according to the first embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic perspective view of the vehicle body frame member according to the first embodiment. Figure 2 is a schematic cross-sectional view of the vehicle body frame member according to the first embodiment. The vehicle body frame members shown in Figures 1 and 2 are not particularly limited, but include pillars, side members, rocker panels, etc.

[0014] It should be noted that the right-handed XYZ Cartesian coordinate system shown in Figures 1 and 2 is merely a convenient representation for explaining the positional relationships of the constituent elements. In Figure 1, etc., the positive Z-axis is vertically upward, and the XY plane is horizontal; this is consistent across all drawings.

[0015] The vehicle body frame member shown in Figures 1 and 2 comprises two steel plates, namely a first steel plate 10 and a second steel plate 20, extending in the Y-axis direction. As shown in Figure 1, the vehicle body frame member is a rectangular tubular member in which the first steel plate 10 and the second steel plate 20 are welded at both ends in the width direction (X-axis direction). As shown in Figure 2, an opening 11 is formed in the flat first steel plate 10, and a burring portion 12 rises upward (in the positive Z-axis direction) from the periphery of the opening 11 toward the second steel plate 20.

[0016] The opening 11 shown in FIG. 2 is formed, for example, by punching a first steel plate 10. The burring portion 12 is formed by subjecting the peripheral portion of the opening 11 to induction heating to remove strain and then performing burring on the peripheral portion. Further, the burring portion 12 can be stretched by repeating induction heating and burring on the peripheral portion of the opening 11. That is, the height H of the burring portion 12 shown in FIG. 2 can be increased.

[0017] For example, by inserting an induction heating coil into the opening 11, the peripheral portion of the opening 11 is induction heated. With such a simple configuration, the peripheral portion of the opening 11 can be effectively heated. The heating conditions are, for example, a heating temperature of about 500 to 830°C and a heating time of 10 seconds or less. However, the heating time may exceed 10 seconds.

[0018] Here, FIG. 3 is a partial plan view showing an example of the opening 11 of the first steel plate 10. The first steel plate 10 shown in FIG. 3 is an inner pillar of a center pillar and has a polygonal opening 11. In this case, the second steel plate 20 is an outer pillar.

[0019] The opening 11 is used, for example, for attaching other components or as a passage for a wire harness. The width of the opening 11 in the X-axis direction is, for example, 50% or more, and may be 70% or more, of the width of the first steel plate 10 in the X-axis direction. Further, although the opening 11 shown in FIG. 3 has a complex and asymmetric polygonal shape, it may have a simple shape such as a circular shape, an elliptical shape, a rectangular shape (including a square shape).

[0020] Here, FIG. 4 is a graph showing changes in the maximum load and the breaking stroke during a bending test according to the height H of the burring portion. In FIG. 4, the maximum load (kN) and the breaking stroke (mm) for the height H = 0 mm, 6 mm, and 8 mm of the burring portion 12 are shown. The height H = 0 mm of the burring portion 12 means that no burring has been performed.

[0021] As shown in Figure 4, the maximum load and fracture stroke during the bending test increase as the height H of the burring portion 12 increases. In this way, by forming the burring portion 12 on the periphery of the opening 11 of the first steel plate 10, stress concentration at the periphery of the opening 11 can be alleviated during the bending deformation of the vehicle body frame member.

[0022] Here, the larger the height H of the burring portion 12, the more the stress concentration at the periphery of the opening 11 can be alleviated, but the burring process becomes more difficult, and productivity decreases. For this reason, the height H of the burring portion 12 is, for example, 2 to 15 mm, and preferably 4 to 10 mm. If the height H of the burring portion 12 is 2 mm or more, the stress concentration at the periphery of the opening 11 can be alleviated during bending deformation. On the other hand, if the height H of the burring portion 12 is 15 mm or less, the burring portion 12 is easier to form, resulting in excellent productivity.

[0023] As shown in Figures 1 and 2, the second steel plate 20 is a steel plate with a hat-shaped cross-section positioned opposite the burring portion 12 side of the first steel plate 10. More specifically, the second steel plate 20 comprises a top plate 21 extending in the Y-axis direction, side walls 22, and flange portions 23. A pair of side walls 22 are formed downward from the widthwise (X-axis direction) end of the top plate 21 that extends in the Y-axis direction. Furthermore, flange portions 23 protrude outward from the lower (negative Z-axis direction) end of each side wall 22. The flange portions 23 are welded to the first steel plate 10.

[0024] The first steel plate 10 and the second steel plate 20 are not particularly limited, but for example, they have a thickness of about 1 to 3 mm and a tensile strength of 440 MPa or more. The first steel plate 10 and the second steel plate 20 may also be high-strength steel plates with a tensile strength of 590 MPa or more, or even 780 MPa or more. By using high-strength steel plates, the thickness of the steel plates can be reduced, and the vehicle body can be made lighter.

[0025] As described above, the higher the strength of the first steel plate 10, the more pronounced the stress concentration at the periphery of the opening 11 becomes during bending deformation. Therefore, until now, it has been difficult to use high-strength steel plates for the first steel plate 10 that has an opening 11. However, by forming a burring portion 12 at the periphery of the opening 11, it is now possible to use high-strength steel plates for the first steel plate 10 as well.

[0026] As described above, in the vehicle body frame member according to this embodiment, a burring portion 12 is formed on the peripheral edge of the opening 11 of the first steel plate 10, rising toward the second steel plate 20. Therefore, stress concentration at the peripheral edge of the opening 11 of the first steel plate 10 can be alleviated when the vehicle body frame member undergoes bending deformation.

[0027] If a first steel plate 10 and a second steel plate 20, both having an opening 11, are welded together to form a cylindrical vehicle body frame member, the shapes of the first steel plate 10 and the second steel plate 20 are not particularly limited. For example, the first steel plate 10 may have a hat-shaped cross-section with the opening 11 formed in the top plate. In that case, the second steel plate 20 may have either a hat-shaped cross-section or a flat plate shape.

[0028] <Manufacturing method for vehicle body frame components> Next, with reference to Figure 5, a method for manufacturing a vehicle body frame member according to the first embodiment will be described. Figure 5 is a flowchart showing the method for manufacturing a vehicle body frame member according to the first embodiment.

[0029] First, as shown in Figure 5, the peripheral edge of the opening 11 formed in the first steel plate 10 is induction heated, and then burring is performed to form a burred portion 12 (step ST1). For example, an induction heating coil is inserted into the opening 11, the peripheral edge of the opening 11 is induction heated to remove strain, and then the peripheral edge is burred. Step ST1 may be repeated to stretch the burred portion 12. As shown in the bending test results in Figure 4 above, stretching the burred portion 12 can further alleviate stress concentration at the peripheral edge of the opening 11.

[0030] Then, as shown in Figure 5, with the burring portion 12 facing inward, the first steel plate 10 and the second steel plate 20 are welded to each other (step ST2). More specifically, as shown in Figure 2, both ends in the width direction of the first steel plate 10 and the second steel plate 20 are welded together to form a rectangular tubular vehicle frame member.

[0031] As described above, in the manufacturing method of the vehicle body frame member according to this embodiment, the peripheral edge of the opening 11 formed in the first steel plate 10 is induction heated and then burred to form a burred portion 12. Therefore, stress concentration at the peripheral edge of the opening 11 can be alleviated when the manufactured vehicle body frame member undergoes bending deformation.

[0032] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its intent. [Explanation of Symbols]

[0033] 10 First steel plate 11 Aperture 12 Burring section 20 Second steel plate 21 Top plate 22 Side wall 23 Flange section

Claims

1. A cylindrical vehicle body frame member formed by welding together a first steel plate and a second steel plate having an opening, A burring portion is formed on the periphery of the opening of the first steel plate, rising toward the second steel plate. Vehicle body frame components.

2. The first steel plate is flat, The second steel plate has a hat-shaped cross-section. The vehicle body frame member according to claim 1.

3. The opening has a polygonal shape. The vehicle body frame member according to claim 1 or 2.

4. The process involves inductively heating the periphery of an opening formed in a first steel plate to remove strain, and then burring the periphery to form a burred portion. The process includes the step of welding the first steel plate to the second steel plate with the burring portion facing inward to form a cylindrical vehicle body frame member, A method for manufacturing vehicle body frame components.

5. In the process of forming the burring portion, The burred portion is stretched by repeatedly inductively heating the peripheral portion and performing burring. A method for manufacturing a vehicle body frame member according to claim 4.

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