JP3450076B2 - Method for manufacturing tubular member for vehicle body structure - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a tubular structural member constituting a vehicle body of an automobile, and more particularly to a method of manufacturing a tubular member having a three-dimensionally curved shape. The present invention relates to a method for manufacturing a member without causing wrinkles or cracks on the wall surface. 2. Description of the Related Art Conventionally, automobile bodies have been manufactured by combining members having various shapes obtained by press-forming steel plates by spot welding or the like. In order to reduce the weight of steel, studies are being made to use aluminum instead of steel. For example, a front side frame member extending rearward from a lower portion of the engine room in front of the vehicle body and connected to a structural member of the passenger compartment front floor, a rear side frame member extending rearward from a structural member of the passenger compartment rear floor and reaching the lower portion of the trunk room, etc. Since it is a cylindrical member with a rectangular cross section that is almost constant over its entire length in the longitudinal direction, it has been a candidate for a target part for weight reduction of a vehicle body as a member that can be efficiently formed from an extruded aluminum square tube. Has been raised. However, as shown in FIG. 1, of the pair of front side frame members 10R and 10L of the vehicle 1, the front side frame member 1 on the front right side of the vehicle body is provided.
Explaining about 0R, the front end portion 10c and the rear end portion 10a are linear, but the portion 10b connecting these linear portions 10c and 10a is rearward to avoid hitting the front wheel 2. It is bent three-dimensionally downward and outward while extending. The front side frame member 10R is integrally provided with a vertically extending flange 10d for connection with a panel member such as a front wheel apron. Similarly, of a pair of rear side frame members of the vehicle 1, a front end portion 20c and a rear end portion 20a of a rear right side frame member 20 shown in FIG.
Are linear, but the linear portions 20c
The part 20b connecting the front and rear sides of the vehicle body extends upward toward the inside of the vehicle body while extending rearward in order to avoid contact with the rear wheel 3.
It is bent in dimension. Further, a pair of flanges 20d extending in the horizontal direction for connecting to a trunk floor or the like.
20e is integrally erected, and a portion 20f adjacent to the rear wheel 3 of the flange 20d extends vertically upward to connect with the rear wheel apron. Accordingly, the front side frame member 10R and the rear side frame member 20
The most efficient method for forming the aluminum pipe by using an aluminum material is to bend an aluminum square pipe extruded into a rectangular cross section having a flange by press working or the like. However, aluminum square pipes have low strength and rigidity unlike steel square pipes, so if an extruded aluminum square pipe is bent by pressing or the like, wrinkles or wrinkles will be formed on the wall surface of the aluminum square pipe. Defects such as cracks occur, which is unsuitable as a method of manufacturing a vehicle body structural member. Accordingly, the applicant of the present invention has previously filed an application for a method of manufacturing a tubular member for a vehicle body structure suitable for manufacturing such a member for a vehicle body structure. (Japanese Patent Application No. 5-1783
75) In the method of manufacturing a tubular member for a vehicle body structure according to the earlier application of the present applicant, a tubular member having a substantially annular cross-section is extruded, and the tubular member is subjected to a bending process to bend. A pressure is applied to the inside of the cylindrical member while the cylindrical member thus held is held inside a mold, and the wall surface of the cylindrical member is overhanged, and the cylindrical member is subjected to an overhanging process to adhere to the mold. The cross-sectional shape of the member is changed to a rectangular shape. [0006] However, using the method for manufacturing a tubular member for vehicle body structure according to the above-mentioned prior application,
When processing a structural member having a more complicated bent shape, cracks may occur on the wall surface of the tubular member in the bending process and the overhanging process. Accordingly, the present invention has been made in view of such circumstances, and an improved method for manufacturing a tubular member for a vehicle body structure according to the above-mentioned prior application has been proposed to provide a vehicle body having a more complicated bent shape. It is an object of the present invention to provide a method of manufacturing a structural tubular member without causing cracks on a wall surface. [0008] In order to solve the above problems, the present invention employs the following method for manufacturing a tubular member for a vehicle body structure. That is, in the method for manufacturing a tubular member for a vehicle body structure according to claim 1, the tubular member having a substantially annular cross section is extruded, and the tubular member is bent to be bent. A vehicle body having a desired cross-sectional shape by applying a pressure to the inside of the cylindrical member while holding the cylindrical member inside the mold, and performing an overhanging process in which a wall surface of the cylindrical member is overhanged and adheres to the mold. In the method of manufacturing a structural tubular member, the metal structure of the tubular member is a fibrous structure extending in the extrusion direction when performing the extrusion molding, and the metal of the tubular member is formed before the overhanging process is performed. The heat treatment is performed to make the structure an equiaxed recrystallized grain structure. According to the first aspect of the present invention, in the method of manufacturing a tubular member for a vehicle body structure, when the tubular member is bent, the sectional shape of the tubular member is substantially annular. Since it has almost the same bending rigidity in any direction, not only the bending direction can be set in any direction, but also the wall surface is curved and the surface rigidity is high, so that the bending process is performed. Also,
Wrinkles are hardly generated on the wall. When the cylindrical member is extruded, its metal structure is formed into a fibrous structure extending in the extrusion direction, thereby improving the workability. Therefore, the tensile force and the compressive force in the extrusion direction due to the bending are reduced. Even if it works, there is no crack on the wall. Further, before performing the overhanging process on the bent tubular member, the tubular member is subjected to a heat treatment so that the metal structure thereof becomes equiaxed crystal grains, so that an internal pressure is applied during the overhanging process. The cylindrical member can be deformed equally in any direction, so that the wall surface does not crack during overhanging. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a tubular member for a vehicle body structure according to the present invention will be described.
Examples applied to the front side frame member and the rear side frame member will be described in detail below with reference to the drawings. Embodiment 1 First, a method of manufacturing the front side frame member will be described. As shown in FIG. 1, the front side frame members 10 are provided in a pair symmetrically with respect to the center line of the vehicle body of the vehicle 1. Here, a front side frame member 10R provided on the front right side of the vehicle body is described. explain. The side frame member 10R includes cylindrical portions 10a, 10b, and 10c having a rectangular cross section extending vertically in the vertical direction, and a flange 10d extending vertically upward along the outer wall surface of the cylindrical portion of the vehicle body. are doing. The portions 10a and 10c at both ends of the cylindrical portion are linear, and extend in the front-rear direction of the vehicle body in parallel with each other. And
Curved cylindrical portion 1 connecting both end portions 10a and 10c
0b is curved in a three-dimensional direction downward and outward of the vehicle body from the front to the rear of the vehicle body.
The radius of curvature of the curve is small in the vertical direction and large in the horizontal direction. Next, the production of the front side frame member 10R will be described in the order of each step with reference to FIG. First, the first step shown in FIG. 2A is a step of extruding and forming a cylindrical member 11 made of an aluminum material.
The cylindrical member 11 has a cylindrical portion 11a having a constant thickness annular cross section, and a constant thickness flange 11d which is integrally erected on the outer surface and extends radially outward. Extruded. In this embodiment, the cylindrical member 11
The sectional shape of a is an annular ring having a constant thickness, and the flange 11
d also extends outward in the radial direction, but in accordance with the required characteristics of the vehicle body structural member, its thickness is changed depending on the region, the cross-sectional shape is, for example, an oval ring, or a flange. 11d may be inclined with respect to the radial direction. In the first step, the cylindrical member 11
When extrusion molding is performed, the metal structure is a fibrous structure in which crystal grains extend in the extrusion direction. This can be achieved by changing the extrusion conditions such as addition of a transition element such as Zr or rapid cooling after extrusion. The second step shown in FIG. 2B is a step of bending the straight cylindrical member 11 extruded in the first step into a vertical plane. This bending process is shown in FIG.
And a bending device 30 as shown in FIG. 4 is used to perform bending while applying a tensile force to the extruded cylindrical member 11, and one end of the cylindrical member 11 has a semicircular shape. The clamping type lower half 32 fixed to the wheel-shaped rotary bending die 31 provided with the groove 31a and the clamping type upper half 33 are fixed to the rotary bending die 31. The cylindrical member 11 extends in the horizontal direction, and its flange 11d is gripped by a movable holding die 34 that moves from the left side to the right side in the drawing during the bending. Furthermore, the cylindrical portion 11 of the cylindrical member 11
A core (not shown) is inserted through
In the bending in the process, the sectional shape is prevented from being deformed. Then, in this state, the rotary bending die 31 is slowly rotated clockwise around the center C so that the cylindrical member 11 has a curvature at the center of the semicircular groove 31a of the rotary bending die 31. It is bent upward in the vertical plane in accordance with the radius. Also, the bent portion of the tubular member 11 that is made to project downward in the vertical plane is bent using the same device as described above. As a result, the cylindrical member 11 extending linearly has linear portions 12a and 12c at both ends.
And a curved portion 1 connecting these straight portions 12a and 12c.
2b and a substantially S-shaped tubular member 12 in side view
Molded into In the present embodiment, the cylindrical member 11 is bent by pulling using a rotary bending die. However, the present invention is not limited to this, and any other bending method may be used. It may be bent. At this time, since the metal structure of the cylindrical member 11 is formed into a fibrous structure extending in the extrusion direction at the time of extrusion forming as described above, the workability is improved. Even when a force or a compressive force is applied, the wall surface does not easily crack, so that it is possible to bend into a curved shape having a smaller bending radius. In the third step shown in FIG. 2C, the wall surface of the cylindrical member 12 that has been bent in the second step is pressed vertically and horizontally using a mold. The cross-sectional shape is changed from an annular shape to a substantially rectangular shape to form a cylindrical member 1.
3 is a pressing step. In the third step, press molding is performed using a mold that is formed in accordance with the curved shape of the cylindrical member 12 that has been bent in the second step. As shown in FIG. 5, the mold 40 includes a fixed mold 41 that holds the tubular member 12, a movable mold 42 that is displaced vertically downward, and a displaceable horizontal direction from right to left in the drawing. And a moving mold 43. Then, the cylindrical member 1 is
2, the cylindrical portions 12a, 12b, and 12c having an annular cross section,
Press and deform in the vertical and horizontal directions respectively,
As shown in FIG. 5, it is formed into a cylindrical member 13 having a substantially rectangular cross-sectional shape composed of curved wall surfaces. at the same time,
The flange 12d of the cylindrical member 12 is bent and deformed by being pinched and pressed by the molds 42 and 43, and becomes a flange 13d extending upward in the vertical direction. In the case where the cylindrical member 12 has either a locally protruded portion or a pushed-in portion, a processing step of crushing or extending the portion is performed in a product shape. It may be additionally added as needed. Next, a heat treatment is applied to the cylindrical member 13 pressed so as to have a substantially rectangular cross-sectional shape as described above. As a result, the metal structure of the cylindrical member 13 where the internal strain has been generated by the bending process and the pressing process is replaced by the recrystallized grains having released the internal strain. At this time, it is preferable to select processing conditions such as annealing temperature and annealing time so that the recrystallized grains become as fine as possible equiaxed grains. Due to this heat treatment step, the portion to be overhanged preferentially has a recrystallized structure having excellent workability. The fourth step shown in FIG. 2D is an overhanging step of deforming the cross-sectional shape of the cylindrical member 13 having a substantially rectangular cross section in the third step into a rectangular shape. In Example 1, at the same time as the overhanging process, the second bending process for gently bending the tubular member 13 in the horizontal direction is performed at the same time. First, the second bending process in the fourth step is press forming performed by using a mold 50 whose cross section is shown in FIG. 6, and the cylindrical shape whose cross section is deformed to be substantially rectangular in the third step. This is performed by pressing the member 13 with the fixed mold 51 and the movable molds 52 and 53. At this time, hydraulic pressure is applied to the inside of the tubular member 13 to prevent deformation of the cross-sectional shape, and in addition, the tubular member 1
Since the wall surface of the cylindrical member 3 is curved and has a high rigidity, no wrinkles or cracks are generated on the wall surface even if the second bending process for gently bending the cylindrical member 3 is performed. . Further, since the cylindrical member 13 is molded by using the mold 50, the straightening process for improving the accuracy of the curved state is performed at the same time. Further, the cylindrical member 1
Since the third flange 13d is sandwiched and pressed by the movable dies 52 and 53 and press-formed, the shape accuracy of the flange 14d can also be improved. Then, at the time when the respective dies of the dies 50 come into close contact with each other to complete the second bending, the pressure of the hydraulic pressure applied to the inside of the cylindrical member 13 is further increased to expand the wall surface thereof. Let mold 5
An overhanging process is carried out so as to be in close contact with the inner surface of 0 and to change the cross-sectional shape from a substantially rectangular shape to a rectangular shape. As a result, the cylindrical member 13 is moved to the position shown in FIG.
Is formed into a cylindrical member 14 having a rectangular cross section as shown in FIG. 1, and if both ends are cut to a predetermined length, the forming of the front side frame member 10R is completed. Also, the front side frame member 10L, which is symmetrical to the front side frame member 10R, can be manufactured by exactly the same manufacturing method. At this time, as described above, the tubular member 13 is subjected to a heat treatment prior to the second bending process and the overhanging process, so that the metal structure is made into fine and equiaxed recrystallized grains. Even if the degree of curvature in the second bending process is increased and the degree of close contact with the die surface in the overhanging process is increased, cracks do not occur on the wall surface of the cylindrical member 13. As described above, according to the first aspect of the present invention,
According to the method of manufacturing a tubular member for a vehicle body structure according to the above, when performing extrusion molding, the metallic structure of the tubular member is a fibrous structure extending in the extrusion direction, and the tubular structure is formed before performing the overhanging process. Since the heat treatment is performed to make the metal structure of the member an equiaxed recrystallized grain structure, the following excellent effects can be obtained. That is, since the metal structure of the cylindrical member is formed into a fibrous structure extending in the extrusion direction at the time of extrusion molding, a tensile force or a compressive force in the extrusion direction is applied to the wall surface when the cylindrical member is subjected to bending. Even if it acts, the wall surface is not easily cracked, so that it can be bent into a curved shape having a smaller bending radius. Further, the tubular member is subjected to a heat treatment prior to the overhanging process, and its metal structure is made into fine and equiaxed recrystallized grains, so that the wall surface of the tubular member adheres to the die surface in the overhanging process. Even if the degree is increased, cracks do not occur on the wall surface of the tubular member. Therefore, for example, a cylindrical structural member that is greatly curved in a three-dimensional direction, such as a side frame member of an automobile body, is formed from a cylindrical member formed by extruding an aluminum material without causing defects such as cracks on its wall surface. It can be manufactured, and the degree of freedom in designing the vehicle body increases, which can greatly contribute to reducing the weight of the vehicle body. [0030]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an automobile showing a mounting portion of a body structure tubular member manufactured by the method for manufacturing a body structure tubular member of the present invention. FIG. 2 is a process diagram showing one embodiment of a method for manufacturing a tubular member for a vehicle body structure according to the present invention. FIG. 3 is a side view of the bending machine used in the first step shown in FIG. FIG. 4 is a front view of the bending machine used in the first step shown in FIG. FIG. 5 is a sectional view showing a pressing step in a third step shown in FIG. 2; FIG. 6 is a cross-sectional view showing a second bending and overhanging step in a fourth step shown in FIG. 2; DESCRIPTION OF SYMBOLS 1 Vehicle 10 Front side frame member 11 Extruded cylindrical member 12 Bent cylindrical member 13 Pressed cylindrical member 14 Overhanged cylindrical member 20 Rear side frame member 30 Bending Processing device 40 Pressing die 50 Overhanging die

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kenji Kanamori 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-6-292929 (JP, A) JP-A-6-226339 (JP, A) JP-A-61-17323 (JP, A) JP-A-7-11399 (JP, A) JP-A-7-32076 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) B21D 53/86 B21C 23/14 B21D 26/02 B21D 53/88 B62D 21/00

Claims (1)

(57) [Claim 1] A cylindrical member having a substantially annular cross section is extruded and subjected to a bending process for bending the cylindrical member.
A pressure is applied to the inside of the cylindrical member while the bent cylindrical member is held inside the mold, and the wall surface of the member is stretched to perform an overhanging process of bringing the wall into close contact with the mold. In the method for manufacturing a tubular member for a vehicle body structure having a cross-sectional shape of, in the extrusion, the metal structure of the tubular member to a fibrous structure extending in the extrusion direction, and before performing the overhanging process, A method for producing a tubular member for a vehicle body structure, wherein a heat treatment is performed to make the metallic structure of the tubular member an equiaxed recrystallized grain structure.