Manufacturing method for impact absorption component and impact absorption component

Abstract

To provide a manufacturing method for an impact absorption component that achieves both high collision performance and excellent EA performance through local heating, as well as impact absorption components, etc.SOLUTION: A manufacturing method for an impact absorption component according to an aspect has a member formed by processing a steel plate, where at least a portion of the bending ridges generated by the processing is heated to 600°C to AC1 point. An impact absorption component according to an aspect of the present disclosure comprises a member formed by processing a steel plate, where the Vickers hardness of at least a portion of the bending edges generated by the processing is equal to or lower than the Vickers hardness of the planar surface constituting the impact absorption component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a shock-absorbing component and a shock-absorbing component.

Background Art

[0002] Reducing the vehicle weight of automobiles is an important issue for CO2 reduction by increasing the cruising range in BEVs (Battery Electric Vehicles) and improving fuel efficiency in conventional vehicles. Therefore, it is often considered to integrate and thin components using high-strength steel sheets.

[0003] Patent Document 1 discloses a technique for improving collision performance by removing the work-hardened layer of a ridge line by heating the ridge line of a collision member formed by press working at 300 to 600 °C.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although high-strength steel sheets have high strength, they have low toughness and ductility, and cracks occur before sufficient energy can be absorbed during a collision. Therefore, the adoption of high-strength steel sheets for collision components has not progressed.

Means for Solving the Problems

[0006] A method for manufacturing a shock-absorbing component according to an aspect of the present disclosure is a method for manufacturing a shock-absorbing component having a member formed by processing a steel sheet, wherein at least a part of the bent ridge line generated by the processing is heated to 600 °C to the AC1 point.

[0007] The shock-absorbing component according to one aspect of the present disclosure is a shock-absorbing component having a member formed by processing a steel plate, and the Vickers hardness of at least a part of the bending ridge line generated by the processing is equal to or lower than the Vickers hardness of the plane constituting the shock-absorbing component.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a method for manufacturing a shock-absorbing component that achieves both high collision performance and excellent EA performance by local heating, and a shock-absorbing component and the like.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] A weight reduction technique that aims to reduce the thickness by using high-strength steel sheets for the skeletal parts of vehicles is widely adopted. However, in collision parts typified by crash boxes and FR side members, high collision performance and excellent energy absorption characteristics are required at the same time, so the thinning by high-strength steel sheets has not progressed. This is because although high-strength steel sheets have high strength, they have low toughness and ductility, so cracking occurs before sufficient energy can be absorbed during a collision. Therefore, the present disclosure provides a technique that can achieve both high collision performance and excellent EA performance by partially heating a collision part using a high-strength steel sheet after press forming.

[0011] Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings are simplified as appropriate.

[0012] Reducing the vehicle weight of automobiles is an important issue for CO2 reduction by extending the cruising range in BEVs (Battery Electric Vehicles) and improving the fuel efficiency in conventional gasoline vehicles. Therefore, many studies have been conducted to integrate and thin parts using high-strength steel sheets.

[0013] In collision parts represented by a crash box and an FR member, high collision performance and excellent energy absorption characteristics are required at the same time. However, although high-strength steel sheets have high strength, they have low toughness and ductility, and cracks occur before sufficient energy can be absorbed during a collision. Therefore, the adoption of high-strength steel sheets for collision parts has not advanced. In addition, in BEVs, due to the increase in the size of the battery and the shortening of the overhang, the crash box is required to absorb a large amount of energy with a shorter stroke. Therefore, means are used to promote bellows deformation during a collision with a soft material and ensure the maximum load by increasing the plate thickness.

[0014] Generally, since these parts are manufactured by press working, work hardening occurs due to the dislocations generated during (bending) forming at the time of the product. Therefore, after bending forming, a part of the deformability originally possessed by the material has been exhausted during part manufacturing, and energy absorption is achieved with the remaining deformability during (vehicle) collision. In the present disclosure, the purpose is to draw out the original deformability of the material to the limit by recovering the dislocations generated during press forming by local heating.

[0015] A high-strength steel sheet with a tensile strength of 780 MPa or more is used, and a collision safety part is manufactured by press working such as bending or drawing. For the manufactured collision safety part, heating is performed at 600 °C to the AC1 point (about 730 °C depending on the material composition), for 1 to 5 seconds, on the bending ridge line in the direction perpendicular to the main collision direction (in the case of the drop hammer test, the vertical direction). As a result, the work hardened layer generated during press working disappears, and high collision performance and energy absorption performance can be achieved simultaneously.

[0016] FIG. 1 is a diagram for explaining a method of manufacturing an impact absorbing part according to the present disclosure. In the first step, the workpiece 10 is press worked by the upper and lower press dies 11a and 11b. The workpiece 10 can be an automotive structural member made of a high-tensile material with a tensile strength of 780 MPa or more and formed into a product shape by cold press working. The workpiece 10 can be, in particular, an impact absorbing member for which impact absorbing energy is required.

[0017] In the second step, the work 10 is partially welded to another part 12 (a flat plate in FIG. 1) by the spot welding machine 20.

[0018] In the third step, at least a part of the bending ridge line of the work 10 is heated using the heating device 30. At least a part of the bending ridge line of the work 10 may be a part (a part on the bending ridge line) that becomes the starting point of cracking during a collision. The heating is performed at 600°C to the AC1 point (about 730°C) for 1 to 5 seconds. The cooling rate is not particularly limited.

[0019] The heating device 30 shown in the third step of FIG. 1 includes a high-frequency oscillator 31 and a heating coil 32 connected to the high-frequency oscillator 31. The heating coil 32 extends along the bending ridge line of the work 10. The heating coil 32 is arranged in proximity along the bending ridge line of the work 10 using a positioning jig. As this heating method, productivity can be improved by combining high-frequency induction heating and a positioning jig or the like. In other embodiments, other heating methods such as a laser (see FIG. 11) or a heater may be used.

[0020] Next, the relationship between the heating temperature of the work and the hardness of the work after heating is examined. A test piece with a thickness of 1.4 mm having a tensile strength of 1180 MPa was bent at an in-plate R of 7 mm. Heat treatment was performed on the ridge line of the processed test piece at various temperatures from 400°C to 800°C for 5 seconds. FIG. 2 is a view of the bending ridge line of the bent test piece as seen from above. As shown in the broken-line area of FIG. 2, the hardness was measured by a Vickers hardness test at 7 points in the plate thickness direction from the inside of the bending tip portion (the first point is 0.1 mm, and thereafter, at intervals of 0.2 mm). In the Vickers hardness test, a pyramidal indenter made of diamond is pressed against the test piece, the resulting indentation is observed with a microscope, and the length of the diagonal line (surface area) is measured to obtain the hardness.

[0021] Figure 3 shows the measurement results of the Vickers hardness test. In Figure 3, the horizontal axis represents the distance (mm) in the plate thickness direction from the bending inner side. The vertical axis represents the Vickers hardness (HV). As shown in Figure 3, it can be confirmed that softening occurs during heating at 600 - 700 °C, and conversely, the hardness increases at 800 °C. This is presumably because the transformation point is exceeded at 800 °C, resulting in martensite transformation. Therefore, the suitable heating temperature for preventing cracks during impact is considered to be 600 °C to the AC1 point (the temperature at which transformation starts). As shown in Figure 3, overall, the hardness is softened near the center (0.7 mm). This is because compressive stress is applied to the upper side of the measurement site (Figure 2), tensile stress is applied to the lower side, and near the center of these, the compressive stress and tensile stress balance each other, and work hardening hardly acts. In other words, it is considered that a work-hardened layer is formed on the upper or lower side of the bending ridge line, while near the center of these, the work-hardened layer is not formed so much.

[0022] Figure 4 shows a photograph of the specimen when the drop weight test was conducted. The specimen was a hat-shaped specimen using a high-strength steel plate with a tensile strength of 1180 MPa grade, and heating was carried out at 700 °C for 3 seconds on the four ridge lines. As shown on the left side of Figure 4, it can be seen that large cracks occurred along the ridge line of the specimen without heating. On the other hand, as shown on the right side of Figure 4, it can be seen that the heated specimen buckled in a bellows shape without cracking.

[0023] Figure 5 shows the stroke load (FS) diagram at this time. The horizontal axis represents the stroke (mm), and the vertical axis represents the force (kN). It can be confirmed that from the rise after a 2 mm stroke, there is almost no change in the maximum load (135.1 kN and 134.6 kN) between the case without heating and the case with heating (700 °C) (the difference is approximately less than 1%). On the other hand, after a 40 mm stroke (i.e., when 40 mm of crushing occurs), fracture occurs in the case without heating, and fracture does not occur in the case with heating. This is considered to be due to a difference in energy absorption depending on the presence or absence of heating.

[0024] Figure 6 shows the maximum load and EA (Energy Absorption) amount of the test piece when the drop hammer test is performed. As shown in the left figure of Figure 6, there is no change in the maximum load due to the presence or absence of heating. That is, there is no significant decrease in the maximum load due to heating (less than approximately 1%), and high impact performance can be maintained. On the other hand, as shown in the right figure of Figure 6, by heating at 700 °C, an EA amount approximately 2.5 times can be realized. From the above, it can be confirmed that the local heating according to the present embodiment enables both high impact performance and excellent EA performance to be achieved.

[0025] The difference in the maximum load of the impact absorbing component compared to the maximum load of the same-shaped component without heating according to the present embodiment can be less than 3%, preferably less than 1%. Also, the EA (Energy Absorption) amount of the impact absorbing component is 1.5 times or more, preferably 2 times or more, compared to the EA amount of the same-shaped component without heating.

[0026] Figures 7 to 10 show various examples of impact absorbing components according to some embodiments. Figure 7 is a crash box among the structural members for automobiles. Figure 8 is an FR side member among the structural members for automobiles. Figure 9 is an RR floor side member RR among the structural members for automobiles. Figure 10 is an outer rocker among the structural members for automobiles. These are typical impact absorbing components for automobiles, but the present disclosure is not limited thereto.

[0027] In FIGS. 7 to 9, the arrows indicate the generally assumed typical collision directions, specifically, the vehicle longitudinal direction. In FIG. 10, the arrows indicate the generally assumed typical collision directions, which are perpendicular to the vehicle longitudinal direction. Also, the assumed heating regions are indicated by broken lines. The Vickers hardness of at least a part of the bending ridges formed by processing is equal to or lower than the Vickers hardness of the plane constituting the shock absorbing component. In particular, as shown in FIGS. 7 to 9, a plurality of (preferably, all) adjacent bending ridges along the typical collision direction are heated substantially evenly. For example, the heating temperature is 600°C to the AC1 point in all cases. Therefore, a plurality of (preferably, all) adjacent bending ridges along the collision direction have substantially uniform Vickers hardness. As a result, as shown on the right side of FIG. 4, when compressed and deformed during a collision, the planes constituting the shock absorbing component are configured to alternately bend outward in a bellows shape.

[0028] In some embodiments, as shown in FIGS. 1, 7, and 8, after the cross-section of the shock absorbing component is processed into a closed cross-section, a plurality of adjacent bending ridges along the main collision direction may be heated (substantially evenly). In some embodiments, a part of the closed cross-section, that is, at least a part of the bending ridges may be heated.

[0029] FIG. 10 is an example of at least partially heating the bending ridges of the rocker outer. This example utilizes the mode control design technique. The heated part can be assumed to deform during a collision of the automotive structural member, for example, considering the position of the passengers in the vehicle.

[0030] That is, in some embodiments, an impact absorbing component may be provided. When the impact absorbing component is compressed and deformed along the main collision direction, the planes constituting the impact absorbing component are configured to bend outward alternately. Further, in an impact absorbing component having a member formed by processing a steel plate, the Vickers hardness of at least a part of the bending ridges generated by the processing is equal to or lower than the Vickers hardness of the plane constituting the impact absorbing component. Among the bending ridges of the impact absorbing component, at least a part of the work-hardened layer of a plurality of adjacent ridge portions along the main collision direction (the vehicle front-rear direction shown in FIGS. 7 to 9, the vehicle left-right direction shown in FIG. 10) is removed. The impact absorbing component has a member formed by processing a high-strength steel plate with a tensile strength of 1180 MPa or more. Among the bending ridges of the impact absorbing component, the Vickers hardness of a plurality of adjacent ridge portions along the main collision direction (the vehicle front-rear direction shown in FIGS. 7 to 9, the vehicle left-right direction shown in FIG. 10) is equal to or lower than the Vickers hardness of the plane constituting the impact absorbing component, and is substantially uniform with each other. The difference in the maximum load of the impact absorbing component compared to the maximum load of an identical component without heating is less than 1%, and the EA (Energy Absorption) amount of the impact absorbing component is 1.5 times or more compared to the EA amount of an identical component without heating.

[0031] FIG. 11 is a diagram for explaining an example of a heating device according to another embodiment. It is also possible to obtain the same effects as those of the above-described embodiments by laser heating. For example, a laser source 40 is attached to the tip of the arm of a 6-axis robot 50. As described above, the laser source 40 may be moved parallel along the bending ridge line to irradiate the laser.

[0032] Note that the present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the spirit thereof.

Explanation of Reference Numerals

[0033] 10 Workpiece 11a Press die 12 Component 20 Spot Welder 30 Heating Device 31 High-Frequency Oscillator 32 Heating Coil 40 Laser Source 50 Robot

Claims

1. A method for manufacturing a shock-absorbing component having a member formed by processing a steel plate, comprising: heating at least a part of the bending ridge line generated by processing to a temperature between 600°C and the AC1 point; A method for manufacturing a shock-absorbing component.

2. The manufacturing method according to claim 1, wherein heating is performed for 1 to 5 seconds.

3. The manufacturing method according to claim 1, wherein at least a part of the bending ridge line is locally heated by high-frequency induction.

4. The manufacturing method according to claim 1, wherein the steel plate is a high-strength steel plate of 1180 MPa class or higher.

5. After the cross-section of the shock-absorbing component is processed into a closed cross-section, heating is performed substantially evenly on at least a part of a plurality of adjacent bending ridge lines along the main collision direction. The manufacturing method according to claim 1.

6. A shock-absorbing component having a member formed by processing a steel plate, comprising: The Vickers hardness of at least a part of the bending ridge line generated by processing is equal to or lower than the Vickers hardness of the plane constituting the shock-absorbing component. A shock-absorbing component.

7. The shock-absorbing component according to claim 6, wherein at least a part of the work-hardened layer of a plurality of adjacent ridge line portions along the main collision direction among the bending ridge lines of the shock-absorbing component is removed.

8. The shock-absorbing component according to claim 6, having a member formed by processing a high-strength steel plate with a tensile strength of 1180 MPa class or higher.

9. The shock-absorbing component according to claim 6, wherein when the shock-absorbing component is compressed and deformed along the main collision direction, the plane constituting the shock-absorbing component is configured to bend outward alternately.

10. The shock-absorbing component according to claim 6, wherein the Vickers hardness of a plurality of adjacent ridge line portions along the main collision direction among the bending ridge lines of the shock-absorbing component is equal to or lower than the Vickers hardness of the plane constituting the shock-absorbing component and is substantially uniform with each other.

11. The difference in the maximum load of the shock-absorbing component compared to the maximum load of a component of the same shape without heating is less than 1%, and the EA (Energy Absorption) amount of the shock-absorbing component is 1.5 times or more compared to the EA amount of a component of the same shape without heating. The shock-absorbing component according to claim 6.

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