JP4158400B2 - Manufacturing method of strength member for automobile - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automotive strength member having a high-rigidity portion that retains its shape during a collision and protects an occupant and a fuel tank portion, and a low-rigidity portion that is crushed and absorbs collision energy. Further, the present invention relates to an automotive strength member that is integrally provided with a portion having an inclined distribution of plate thickness.
[0002]
[Problems to be solved by the invention]
Conventionally, tailored pipes are known as automotive strength members that are integrally provided with parts having different strengths and thicknesses. However, they are made by joining together plate materials having different thicknesses and strengths. Therefore, changes in thickness and strength are gradual and do not result in a continuous inclined structure. On the other hand, spinning or swaging can be considered as a means for inclining the strength and thickness, but in order to rotate the pipe when spinning or swaging is performed on a part of a large-sized pipe, for example, the tip. Large-scale equipment is required.
[0003]
Moreover, when butt welding pipes together, arc welding such as MIG welding and laser welding are conceivable, but when arc welding is used, joining can be performed with stable quality regardless of the shape of the joining end face. However, welding deformation is large and it is difficult to obtain sufficient accuracy as a strength member for automobiles. On the other hand, in laser welding, although welding deformation is small, the welding quality largely depends on the shape of the butt portion.For example, when the gap of the butt portion is large, there is a problem that sufficient joint strength cannot be obtained. It has been a problem in conventional strength members for automobiles to eliminate this problem.
[0004]
OBJECT OF THE INVENTION
The present invention has been made by paying attention to the above-mentioned problems in conventional welded structural members of automobile strength members, and has a portion having a gradient distribution of strength and thickness without requiring large-scale equipment. An object of the present invention is to provide a manufacturing method of a strength member that is integrally provided and that can provide a strength member for automobiles having excellent quality in terms of dimensional accuracy and strength.
[0005]
[Means for Solving the Problems]
The manufacturing method of the strength member for automobiles according to the present invention includes a first cylindrical structure made of a steel material having strain aging, and having a strain and a gradient of plate thickness in the axial direction, and a second cylindrical structure, molded in a state of joining, it is characterized in that to facilities the hardening process further baking, and a means for solving the conventional problems described above such a configuration in a method of manufacturing an automobile strength member.
[0006]
Further, in the manufacturing method of the present invention, when imparting the strain and thickness of the gradient to the first tubular structure, or facilities for spinning or swaging, bonding of the first and second tubular structures at the time of the plate thickness at the joint end of the first tubular structure T, the outer diameter D _1, when the outer diameter at the joint end of the second tubular structure and D _2, D ₁ is D while 5-20% larger in T than _2, the joining end face of the first tubular structure is inclined toward the inside, and welding abutted the joining end of the second tubular structure Is desirable .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the manufacturing method of the strength member for automobiles according to the present invention, the first cylindrical structure and the second cylindrical structure which are made of a steel material having strain aging and have a strain and a gradient of plate thickness in the axial direction. molded in a state of joining the door, because I was further bake hardening treatment facilities Suyo, without depending on a large-scale equipment, the strength and thickness of the tilt (gradient) portion integrally provided, collapse in the portion A deformable automotive strength member can be obtained at low cost.
[0008]
At this time, it is assumed that the second cylindrical structure is joined to the thick side or the high strain side of the first cylindrical structure having the inclined structure, and more preferably, the first cylindrical structure is made of energy. By positioning it on the input side, the strength member for automobiles is preferentially crushed from the front end side of the member in the event of a collision, and the safety at the time of the collision is improved.
[0009]
At this time , at the joint portion of both cylindrical structures, the value of plate thickness x proof stress on the first cylindrical structure side is 1.07 times or more than the value of plate thickness x proof stress on the second cylindrical structure side. As a result, the inclined structure portion of the strength member is preferentially crushed and deformed even with respect to a load in a direction having an angle of, for example, 30 degrees with respect to the axial direction of the member. It will be. The effect of preferentially collapsing the inclined structure portion with respect to such a load input deviating from the axial direction is that the value on the first cylindrical structure side relative to the value of plate thickness x proof stress on the second cylindrical structure side is If it is divided by 1.07, it becomes difficult to obtain, and the buckling deformation of the inclined structure portion tends to propagate to other than the inclined structure portion, that is, the second cylindrical structure side.
[0010]
In the manufacturing method of the strength member for automobiles according to the present invention, by applying spinning or swaging, a strain and a thickness gradient are imparted to the first tubular structure, and a large-scale facility is provided. Without using it, the first cylindrical structure having an inclined structure with thickness and strength can be easily obtained.
[0011]
In joining the first and second cylindrical structures, as shown in FIG. 1A, the plate thickness at the joining end of the first cylindrical structure P1 is T, and the outer diameter is D _1. and then, when the outer diameter at the joint end of the second tubular structure P2 and D _2, D ₁ is 5-20% larger in T than D _2, preferably the angle θ between the outer peripheral surface Welding is performed in a state where the joint end E2 of the _second tubular structure P2 is abutted against the joint end face F1 of the _first tubular structure P1 inclined inward so as to be 30 to 80 degrees. As a result, a welded portion having a satisfactory shape with sufficient penetration and no level difference can be obtained, and an automotive strength member having sufficient joint strength can be obtained. That, or greater than the joint end outer diameter D ₁ of the outer diameter D ₂ first tubular structure P1 at the junction end of the second tubular structure P2, even with a small towards D ₂ As shown in FIG. 1B, when there is almost no difference between D ₁ and D ₂ (that is, when D ₁ -D ₂ is smaller than 5% of T), or cylindrical when the angle θ of the joining end face F ₁ and the outer peripheral surface of the structure P1 is almost a right angle more than 80 degrees, easy gap is generated in the butt I portion of the tubular structure P1 and P2, when welding Since a heat source such as laser light is lost, good bonding cannot be performed. Further, as shown in FIG. 1 (c), the end outer shape D1 of the _first cylindrical structure P1 is too large with respect to the joining end portion outer diameter D2 of the _second cylindrical structure P2. (That is, when D ₁ -D ₂ is larger than 20% of T), the step becomes too large, the desired penetration cannot be obtained, and good bonding cannot be performed.
[0012]
The inclination angle θ of the joining end face of the first tubular structure P1 is preferably in the range of 30 to 80 degrees. When θ is less than 30 degrees, the volume of the molten metal at the time of welding is insufficient. Tends to generate holes in the welded portion, and there is a tendency that sufficient strength cannot be obtained. On the contrary, when it exceeds 80 degrees, as described above, when a gap is formed in the butted portion, it is almost vertical. This is because holes tend to occur, and similarly, sufficient strength cannot be obtained.
[0013]
When forming an inclined surface directed inward at the joint end of the first cylindrical structure, linearly polarized laser light is irradiated in a predetermined direction with respect to the cutting progress direction after spinning or swaging of the cylindrical structure. Irradiation can be performed at an angle, thereby forming a joint end surface that is inclined while being cut without special processing after cutting. That is, as shown in FIGS. 2 (a) and 2 (b), by changing the polarization direction P of the laser light L with respect to the cutting direction C, the absorptance of the laser light with respect to the material to be cut differs, so that the inclination direction Different cuttings are possible.
[0014]
In addition, in order to form the inclined surface at the joint end of the first cylindrical structure, it is possible to perform plastic working on the joint end in addition to the laser cutting. Furthermore, in the manufacturing method of the strength member for automobiles according to the present invention, it is desirable to apply laser welding at the time of joining the first and second cylindrical structures, thereby reducing welding deformation and excellent dimensional accuracy. Thus, a high-quality automotive strength member can be obtained.
[0015]
The steel material having strain aging generally refers to a steel material having an increased yield point, but more preferably a steel material having an increased tensile strength. Moreover, the baking hardening process may use, for example, an electrodeposition coating baking process (170 ° C. × 20 minutes).
[0016]
【Example】
Hereinafter, the present invention will be described more specifically based on examples.
[0017]
(Example 1)
A steel plate having a thickness of 1.6 mm having strain aging properties and a material tensile strength of 440 MPa is rolled, formed into a tapered cylindrical shape having a length of 400 mm, and seam-welded. ), A tapered tube material P0 having a front end diameter of 100 mm and a rear end diameter of 120 mm was obtained. Next, as shown in FIGS. 3 (b) and 3 (c), using the spinning roller R1, the pipe material P0 is subjected to spinning molding so that the tube contraction rate in the length direction changes linearly, and the rear end The diameter of the tube was reduced so that the diameter would be 100 mm, which is almost equal to the front end.
[0018]
Next, as shown in FIG. 3D, an unnecessary portion on the right side of the pipe P0 in the drawing while blowing carbon dioxide with a laser beam L obtained by condensing a 3 kW carbon dioxide laser having linear polarization with a lens having a focal length of 100 mm. At a speed of 7 m / min. To obtain a first cylindrical structure P1 having a length of 300 mm having a strain and a thickness gradient in the axial direction and a rear end diameter of 100.2 mm. At the time of cutting, as shown in FIG. 2 (a), the polarization direction P of the laser light L was irradiated at an angle of 45 degrees toward the front end with respect to the cutting direction C. angle between P1 joining end face F ₁ and the outer circumferential surface of the theta (see Figure 1) was about 70 °. Further, by the above spinning molding, the plate thickness is changed from the original 1.6 mm to 1.9 mm (= T) on the rear end side where the outer diameter is reduced from 120 mm to 100.2 mm (= D ₁ ). It was confirmed that the plate thickness continuously changed from 1.6 mm to 1.9 mm from the front end to the rear end.
[0019]
And as shown in FIG.3 (e), plate | board thickness of 3.0 mm which has a 590 MPa class tensile strength in the rear-end side (thickness side) of the 1st cylindrical structure P1 obtained by the said process. A cylindrical structure P2 (second cylindrical structure) made of a high-tensile steel plate and having a diameter of 100 mm (= D ₂ ) is abutted, and a carbon dioxide laser with an output of 3 kW is condensed by a lens with a focal length of 250 mm, and a welding speed of 5 m / min. The first and second cylindrical structures P1 and P2 were joined together to obtain a joined pipe material P3 as shown in FIG.
[0020]
The joining pipe material P3 welded in this way can be processed into automotive parts by press molding or hydraulic molding. In this example, molding was performed by applying hydraulic molding. That is, the initial atmospheric pressure is set to about 10 MPa, the hydraulic pressure that rises as the punch stroke is pushed in is adjusted by a leak valve, and a hollow rectangular cross-section member having a side of 80 mm and a corner R of 8 mm is formed. By applying a baking and curing treatment at 20 ° C. for 20 minutes, an automotive strength member 1 shown in FIG. 3G was obtained.
[0021]
In accordance with the inclination of the strain applied to the steel material having strain aging by the bake hardening process, the inclination of the proof stress and the tensile strength is imparted. In this embodiment, the first cylindrical structure with the laser welded portion as a boundary. The product of the proof stress and the plate thickness in the body P1 is 1.1 times the product of the proof stress and the plate thickness in the second tubular structure P2 joined thereto, and a sound welded portion is provided. Thus, a lightweight and high-strength automotive strength member 1 was obtained. In addition, the yield strength in the first cylindrical structure P1 is obtained by calculating the equivalent strain amount from the contraction rate and the plate thickness, and converting the yield strength from the strain amount.
[0022]
Using the thus obtained automotive strength member 1, as shown in FIG. 4 (a), a crushing test was performed on a load shifted from the axial direction of the member, as shown in FIG. 4 (b). Even with respect to a load input having a deviation of 30 degrees with respect to the axial direction of the strength member 1, the strength inclined portion located on the distal end side, that is, the portion of the first cylindrical structure P1 is preferentially used. It was confirmed to be deformed.
[0023]
(Example 2)
As in Example 1 above, it is made of a strain-aged steel sheet having a tensile strength of 440 MPa and a thickness of 1.6 mm, and is formed by spinning into a tapered tubular material P0 having a front end diameter of 100 mm, a rear end diameter of 120 mm, and a length of 400 mm. And the tube was reduced so that the rear end had a diameter of 100 mm, which was substantially equal to the front end (see FIGS. 3A to 3C).
[0024]
Next, as shown in FIG. 5 (a), by cutting the unnecessary portion of the tube material P0 using the cutting roller R2 while rotating the tube material P0, as in the above-described embodiment, about 100 mm. A first cylindrical structure P1 having an outer diameter, a length of 300 mm having a plate thickness continuously changing from 1.6 mm to 1.9 mm from the front end to the rear end, and a rear end diameter of 100.2 mm Got. Then, as shown in FIG. 5 (b), it was subjected to plastic working so that the angle of the joining end face F ₁ theta (see FIG. 1) is 45 ° cut end by another spinning roller R3.
[0025]
On the other hand, a tube material having a diameter of 100 mm made from a high-tensile steel plate having a thickness of 3.0 mm having a tensile strength of 590 MPa is bend-formed to form a second cylindrical structure P2, and the first cylindrical structure is added thereto. The thick tube side of P1 is butted and laser welding is performed under the same conditions as in the first embodiment to join the first and second cylindrical structures P1 and P2, and a joined pipe material as shown in FIG. P3 was obtained. Next, hydroforming is performed under the same conditions as in Example 1, forming a member having a hollow square cross section with a side of 80 mm and a corner R of 8 mm, and further subjected to a baking and curing treatment at 170 ° C. for 20 minutes. Thereby, as shown in FIG.5 (d), the automotive strength member 1 provided with the bend part was obtained.
[0026]
In the automotive strength member 1, the proof stress and the tensile strength gradient are imparted according to the strain gradient applied to the steel having strain aging by the bake hardening process, and the first portion is formed with the laser welded portion as the boundary. The product of the proof stress and the plate thickness in the cylindrical structure P1 was 1.1 times the product of the proof stress and the plate thickness in the second cylindrical structure P2 joined thereto.
[0027]
(Example 3)
It consists of a strain-aged steel sheet with a tensile strength of 440 MPa and a plate thickness of 1.6 mm. Spinning is applied to the tapered tube P0 having a front end diameter of 100 mm, a rear end diameter of 150 mm, and a length of 400 mm. The tube was shrunk so as to be 120 mm.
[0028]
Next, the unnecessary part of the tube material P0 is laser-cut under the same conditions as in Example 1, so that the outer diameter of the front end is 100 mm, the outer diameter of the rear end is 120.2 mm, and the plate thickness is from the front end toward the rear end. Thus, a tapered shape continuously changing from 1.6 mm to 1.9 mm was obtained, and a first tubular structure P1 having a length of 300 mm was obtained. In addition, the inclination angle θ of the joining end face is about 70 °.
[0029]
Next, a tubular material having a diameter of 120 mm prepared from a high-tensile steel plate having a thickness of 3.0 mm and having a tensile strength of 590 MPa is bent to form a second cylindrical structure P2, which is obtained by the above process. The cylindrical structure P1 of the cylindrical structure P1 is abutted against the rear end side (thick wall, large diameter side), and a carbon dioxide laser with an output of 3 kW is condensed with a lens having a focal length of 250 mm, and a welding speed of 5 m / min. The first and second cylindrical structures P1 and P2 were joined together to obtain a joined pipe material P3 as shown in FIG.
[0030]
Then, by performing hydraulic forming under the same conditions as in Example 1, as shown in FIG. 5B, the front end side of the first cylindrical structure P1 has a circular cross section with an initial diameter of 100 mm. Then, on the rear end side and the second cylindrical structure P2 side, a member having a square cross section with a side of 85 mm and a corner R of 8 mm is formed, and then subjected to a baking hardening treatment at 170 ° C. for 20 minutes. As shown in FIG. 6B, an automotive strength member 1 having a bend portion was obtained.
[0031]
In the automotive strength member 1 obtained in this way, the gradient of the proof stress and the tensile strength is given according to the inclination of the strain applied to the steel material having strain aging by the bake hardening process, and the first tubular shape The product of the proof stress and the plate thickness in the structure P1 was 1.1 times the product of the proof stress and the plate thickness in the second cylindrical structure P2 bonded thereto.
[0032]
【The invention's effect】
As described above, in the method for manufacturing a strength member for an automobile according to the present invention, the first tubular structure made of a steel material having strain aging and having a strain and a gradient of thickness in the axial direction; molded in a state of bonding the second tubular structure, because the further baking facilities curing treatment Suyo, without using a large-scale equipment, the strength in a part of the vehicle body frame to collapse deformation and plate A thick inclined structure is integrally provided, and an extremely excellent effect that a lightweight and high-strength automotive strength member can be obtained at low cost is brought about.
[0033]
In the preferred embodiment of the manufacturing method, when the strain and thickness gradient are applied to the first cylindrical structure, spinning or swaging is applied to provide an inclined structure with thickness or strength. The provided first cylindrical structure can be easily obtained. When joining the first and second tubular structures, the thickness and outer diameter of the joining ends of the first and second tubular structures are matched within a predetermined numerical range by laser welding, for example. By welding, it is possible to obtain a high-quality welded part that does not melt or have poor fusion, and to produce an automotive strength member having excellent dimensional accuracy and high strength with a small mass. Excellent effect.
[Brief description of the drawings]
FIG. 1A is a cross-sectional explanatory view showing the shape and dimensions of the joining ends of first and second tubular structures in an automotive strength member according to the present invention.
(B) It is sectional explanatory drawing which illustrates the case where the outer diameter difference of the 1st and 2nd cylindrical structure in a junction end is too small.
(C) It is sectional explanatory drawing which illustrates the case where the outer diameter difference of the 1st and 2nd cylindrical structure in a junction end is excessive.
FIGS. 2A and 2B are explanatory views showing a cutting procedure using linearly polarized laser light. FIGS.
FIGS. 3A to 3G are process diagrams sequentially showing a manufacturing procedure of a strength member for an automobile according to Embodiment 1 of the present invention.
FIGS. 4A and 4B are schematic explanatory views showing a crush test procedure and results of a strength member for automobiles. FIGS.
FIGS. 5A to 5D are process diagrams showing a manufacturing procedure of a strength member for an automobile according to Embodiment 2 of the present invention.
FIGS. 6A and 6B are process diagrams showing a manufacturing procedure of a strength member for an automobile according to Embodiment 3 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Automotive strength member P1 1st cylindrical structure P2 2nd cylindrical structure

Claims (9)

This state after joining the first tubular structure (P1) and the second tubular structure (P2) , which are made of a steel material having strain aging and have a strain and thickness gradient in the axial direction. in molding method for an automobile strength member, characterized in that to facilities the hardening process further baking. The method for producing a strength member for an automobile according to claim 1, wherein the second tubular structure (P2) is joined to the thick wall side or the high strain side of the first tubular structure (P1) . Method for producing automobile strength member according to claim 2, wherein the joining the first tubular structure and (P1) to the energy input. The strength for automobiles according to any one of claims 1 to 3 , wherein spinning or swaging is applied to the first tubular structure (P1) to impart a strain and a gradient of plate thickness. Manufacturing method of member. When joining the first tubular structure (P1) and the second tubular structure (P2), the plate thickness at the joining end of the first tubular structure (P1) is T, and the outer diameter is D _1. and then, when the outer diameter at the joint end of the second tubular structure (P2) and D _2, D ₁ together with 5 to 20% larger formation of T than D _2, is inclined toward the inside The welding according to any one of claims 1 to 4, wherein welding is performed in a state where the joining end of the second tubular structure (P2) is abutted against the joining end surface of the first tubular structure (P1) . The manufacturing method of the strength member for motor vehicles described in claim | item. 6. The method for manufacturing a strength member for an automobile according to claim 5, wherein an angle formed between the joining end face of the first tubular structure (P1) and the outer peripheral face is in a range of 30 to 80 degrees. After spinning or swaging, the linearly polarized laser beam is irradiated and cut in a state inclined obliquely with respect to the cutting progress direction, and an inclination is provided at the joint end of the first cylindrical structure (P1). The manufacturing method of the strength member for motor vehicles of Claim 5 or 6 . The strength member for an automobile according to claim 5 or 6, wherein after the spinning or swaging, the joining end is subjected to plastic working to provide an inclination at the joining end of the first cylindrical structure (P1). Manufacturing method. The method for manufacturing a strength member for an automobile according to any one of claims 5 to 8, wherein the joining is performed by laser welding.

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