JP2012111356A - Method for manufacturing energy absorbing structure, and energy absorbing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an energy absorbing structure that reduces production cost and a difference between an initial load and an average load.SOLUTION: The method is includes: a preparation step of preparing a hyper reinforcement 12, a pair of energy absorbing members 2, and a pair of stays 14, the energy absorbing members having an outer wall shaping a closed cross section on an axially vertical cross section and axially plastically-deforming to absorb energy; a first mold tube-expansion joining step of joining each of the pair of energy absorbing members 2 with each of the right/left ends of the hyper reinforcement 12, using mold tube-expansion; and a joint step of joining each of the pair of stays 14 with each of the other ends of the pair of energy absorbing members 2.

Description

  The present invention relates to a method for manufacturing an energy absorbing structure used in a vehicle or the like and an energy absorbing structure.

  Conventionally, in a vehicle such as an automobile, impact energy is generated by repeatedly repeating plastic deformation in a bellows shape between a bumper reinforcement and a pair of side members arranged on both sides in the width direction of the vehicle and extending in the front-rear direction. A crash box to absorb is arranged. In recent years, there has been a demand for weight reduction of the vehicle body from the viewpoint of reducing fuel consumption and improving vehicle motion performance. Since the aluminum alloy extruded material can make the cross section orthogonal to the extrusion direction a closed cross section and has a large light weight effect, an aluminum hollow extruded material is also used for energy absorbing members such as a crash box.

  When an axial load is applied to an energy absorbing member such as a crash box to cause plastic deformation, if the initial load is excessively high, impact energy due to vehicle collision cannot be absorbed by the plastic deformation of the energy absorbing member. Other members such as side members may be damaged.

  Therefore, there is an energy absorbing member in which the initial load is prevented from becoming excessively high by providing a weak portion as a starting point of plastic deformation. That is, Patent Document 1 discloses an energy absorbing member in which a wall surface of a hollow shape member is bent to an outer surface or an inner surface to form an uneven portion that becomes a starting point of bellows-like deformation of the shape member. Further, Patent Document 2 discloses an energy absorbing member in which a soft portion serving as a starting point of bellows-like deformation of a shape member is formed by locally heating the wall surface of the hollow shape member. Patent Document 3 discloses an energy absorbing member in which one or two or more partial cutouts are formed on the wall surface of a hollow shape member. Patent Document 4 discloses a method for manufacturing a bumper structure in which a tubular aluminum alloy extruded material is expanded by electromagnetic forming and fixed to a bumper reinforcement.

JP 2005-29064 A Japanese Patent Laid-Open No. 7-145843 JP 2005-162061 A JP 2008-308170 A

  However, in order to join the energy absorbing member described in each of the above-mentioned patent documents to the bumper reinforcement constituting the bumper used in the vehicle, the joining is separate from the step of providing the weak part that becomes the starting point of plastic deformation. The process was necessary and the production cost was high.

  An object of the present invention is to provide a method for manufacturing an energy absorbing structure and an energy absorbing structure with a small difference between an initial load and an average load while suppressing production costs.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, it attaches | subjects and demonstrates the code | symbol corresponding to embodiment of this invention, but this invention is not limited to this.

  The manufacturing method of the energy absorption structure according to claim 1 includes a pair of energy that has bumper reinforcement 12 and an outer wall portion having a closed cross-sectional shape in a cross section perpendicular to the axial direction and absorbs energy by plastic deformation in the axial direction. A preparation step of preparing the absorbing member 2 and the pair of stays 14, and a first mold expanding and bonding step of expanding and bonding the pair of energy absorbing members 2 to the left and right ends of the bumper reinforcement 12 respectively. And a joining step of joining each of the pair of stays 14 to the other end of each of the pair of energy absorbing members 2.

  The method for manufacturing an energy absorbing structure according to claim 2 is the method for manufacturing the energy absorbing structure according to claim 1, wherein the joining step is performed at the other end of each of the pair of energy absorbing members 2. This is a second mold pipe expansion joining step in which each of the pair of stays 14 is joined by mold pipe expansion joining.

  Moreover, the manufacturing method of the energy absorption structure of Claim 3 WHEREIN: The manufacturing method of the energy absorption structure of Claim 2 WHEREIN: The said 1st mold pipe expansion joining process and the said 2nd mold pipe expansion joining process are the same processes. It is characterized by being.

  Moreover, the manufacturing method of the energy absorption structure of Claim 4 is a manufacturing method of the energy absorption structure as described in any one of Claims 1-3, The said outer wall part 4 of the said energy absorption member 2 is an axis | shaft. The cross-section perpendicular to the direction forms a closed cross-sectional shape having a polygonal shape, and has the same number of middle ribs 6 as the number of sides constituting the polygon inside the outer wall portion. One end portion is connected to a substantially central portion of each wall portion 4a constituting the outer wall portion, and the other end portion is connected to each other at a central portion in the outer wall portion.

  Moreover, the manufacturing method of the energy absorption structure of Claim 5 is a manufacturing method of the energy absorption structure as described in any one of Claims 2-4. WHEREIN: The said 1st metal mold | die pipe expansion joining process and said 2nd. The expanded pipe portion 8 formed in the mold expanded joint process is formed in a region including the ridge line portion 4b formed by the two wall portions 4a constituting the outer wall portion 4.

  The method for manufacturing an energy absorbing structure according to claim 6 is the method for manufacturing an energy absorbing structure according to claim 4 or 5, wherein the polygon is a pentagon, hexagon, heptagon, or octagon. It is either.

  The energy absorption structure according to claim 7 has a bumper reinforcement 12 and an outer wall portion having a closed cross-sectional shape in a cross section perpendicular to the axial direction, and absorbs energy by plastic deformation in the axial direction. A pair of energy absorbing members 2 having a mold expansion joint portion 8 for joining one end portion to each of the left and right end portions of the bumper reinforcement, and the other end portion of each of the pair of energy absorbing members. It is characterized by comprising a pair of stays 14 joined together.

  The energy absorbing structure according to claim 8 is the energy absorbing structure according to claim 7, wherein each of the pair of energy absorbing members 2 is a mold for joining the stay 14 to the other end. It has a pipe expansion joint 8.

  The energy absorbing structure according to claim 9 is the energy absorbing structure according to claim 7 or 8, wherein the outer wall portion 4 of the energy absorbing member 2 has a polygonal outer shape in a cross section perpendicular to the axial direction. It has a closed cross-sectional shape, and has the same number of middle ribs 6 as the number of sides constituting the polygon provided inside the outer wall portion, and each of the middle ribs has one end portion on the outer wall portion. Are connected to a substantially central portion of each wall portion 4a, and the other end portions are connected to each other at the central portion in the outer wall portion.

  The energy absorbing structure according to claim 10 is the energy absorbing structure according to any one of claims 7 to 9, wherein the mold expanding joint 8 constitutes the two outer walls 4. It is formed in the area | region containing the ridgeline part 4b formed of the wall part 4a.

  An energy absorbing structure according to claim 11 is the energy absorbing structure according to claim 9 or 10, wherein the polygon is any one of a pentagon, a hexagon, a heptagon, and an octagon. Features.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and energy absorption structure of the energy absorption structure with a small difference of an initial load and an average load which suppressed production cost can be provided.

It is a perspective view of the crush box concerning an embodiment. It is a top view of the crush box concerning an embodiment. It is a perspective view of the bumper beam concerning an embodiment. It is the rear view, top view, and front view of the bumper beam which concern on embodiment. It is a figure for demonstrating the mold expansion by the mandrel which concerns on embodiment. It is sectional drawing (AA sectional drawing of FIG.4 (C)) which shows the joining state to the bumper reinforcement of the crash box which concerns on embodiment. It is a top view of the crush box at the time of applying load to an axial direction concerning an embodiment, and carrying out plastic deformation. It is a load-displacement diagram at the time of carrying out the plastic deformation of the crash box which concerns on embodiment to an axial direction. It is a figure for demonstrating the ideal energy absorption amount (ideal EA amount). It is a figure which shows the other cross-sectional shape of the crash box which concerns on embodiment.

  Hereinafter, a method for manufacturing a bumper beam which is an energy absorbing structure according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a crash box constituting a bumper beam according to the embodiment, and FIG. 2 is a plan view of the crash box according to the embodiment.

  The crash box 2 shown in FIGS. 1 and 2 is formed of an aluminum alloy extruded material having a predetermined length in which the vehicle longitudinal direction and the extrusion direction are substantially parallel. The crush box 2 has an outer wall part 4 having a closed hexagonal outer shape in a cross section perpendicular to the extrusion direction, and six inner parts that are the same as the number of sides constituting the regular hexagon provided inside the outer wall part 4. Ribs 6 are provided. Here, each of the middle ribs 6 is connected along the longitudinal direction to the substantially central portion in the inner surface width direction of the six wall portions 4 a constituting the outer wall portion 4, and the other end portion is inside the outer wall portion 4. Are connected to each other at the center of each other. At the position corresponding to the position where the outer rib 6 of the wall 4a constituting the outer wall 4 is connected, the thickness of the wall 4a in the connecting portion 4c to which the inner rib 6 is connected is made constant. In order to reduce the weight of the crash box 2, a recess extending in the longitudinal direction of the wall 4a is formed.

  The outer wall portion 4 of the crash box 2 is provided with a tube expansion portion 8 in a region including a ridge line portion 4b formed by two wall portions 4a constituting the outer wall portion 4. As will be described later, the expanded pipe portion 8 is formed when the crush box 2 is joined to the bumper reinforcement 12 by a mold expansion joint when the bumper beam 10 (see FIG. 3) disposed in the bumper of the vehicle is manufactured. Here, the expanded pipe portion 8 has a ridgeline portion 4b formed by two wall portions 4a having a high fastening strength in the axial direction, that is, a high fastening strength in the axial direction when the crush box 2 is joined to the bumper reinforcement 12 by mold expansion. It is provided in each of the included areas. That is, six expanded pipe portions 8 are provided in the circumferential direction of the outer wall portion 4. In addition, the pipe expansion part 8 functions as a weak part when a load is applied in the axial direction to plastically deform the crash box 2, and the crush box 2 is plastically deformed starting from the pipe expansion part 8. Further, the ridge line portion 4b is formed with a predetermined curved surface in order to improve the formability when the tube expansion portion 8 is formed and to prevent the ridge line portion 4b from being broken when the tube expansion portion 8 is formed.

  FIG. 3 is a perspective view of a bumper beam that is an energy absorbing structure according to the embodiment, and FIG. 4 is a diagram illustrating a configuration of the bumper beam according to the embodiment (a rear view (a), a plan view (b), and a front view). (C)). The bumper beam 10 includes a bumper reinforcement 12 disposed in the bumper, a pair of crash boxes 2 (see FIGS. 1 and 2) in which one end is joined at each of the left and right ends thereof, and And a stay 14 joined to the other end of the crash box 2. As will be described later, the crash box 2 is provided with a mold expansion joint 8 for joining the bumper reinforcement 12 and a mold expansion joint 8 for joining the stay 14. The bumper beam 10 is joined to the front end portion of a side member (not shown) that is disposed on both sides in the width direction of the vehicle via the stay 14 and extends in the front-rear direction.

  Here, a method for manufacturing the bumper beam 10 will be described. First, a bumper reinforcement 12, a pair of crash boxes 2 and a pair of stays 14 provided in the bumper are prepared. Next, one end portion of the crash box 2 is inserted into each of the through holes provided in the left and right end portions of the bumper reinforcement 12 and penetrating from the front surface to the back surface of the bumper reinforcement 12. A predetermined length is exposed from the front surface of the bumper reinforcement 12. Further, the other end portion of the crush box 2 is inserted into a hole provided in the center portion of the stay 14, and the other end portion is exposed from the stay 14 for a predetermined length.

  In this state, as shown in FIG. 5 (a), the expanded pipe portion 8 is attached to the outer wall portion 4 of the crash box 2 using a mold 20 having a shape corresponding to the shape of the expanded pipe portion 8 and a mandrel 22 having a wedge portion. Form. That is, the mold 20 is disposed in each of the six spaces formed by the outer wall portion 4 and the middle rib 6 of the crash box 2, and the wedge portion of the mandrel 22 is disposed. And as shown in FIG.5 (b), the type | mold 20 is moved to the direction of the outer wall part 4 by moving the mandrel 22 to the axial direction (left direction of FIG. 5) of the crush box 2. As shown in FIG. As a result, as shown in the cross-sectional view of FIG. 6, a tube expansion portion (die expansion tube joint portion) 8 is formed at a position in contact with the front surface of the bumper reinforcement 12 and a position in contact with the back surface. The mold is expanded. Further, a tube expansion portion (die expansion tube joint portion) 8 is formed at a position in contact with the front surface of the stay 14 and a position in contact with the back surface, and the stay 14 is bonded to the crush box 2 by metal tube expansion. As described above, when the crash box 2 and the stay 14 are joined to the bumper reinforcement 12 by the die expansion joint, the expanded portion 8 that functions as a weak portion of plastic deformation is formed, so that the weak portion is formed in the crash box 2. Therefore, it is not necessary to provide a special process for reducing the manufacturing cost of the bumper beam 10.

  1 shows only six expanded pipe portions 8 formed in the vicinity of the upper end (near the contact surface) of the outer wall 4 of the crash box 2. However, the bumper reinforcement 12 and the stay 14 are attached to the crash box 2 by a mold. At the time of pipe expansion joining, the mold pipe expansion portion 8 is formed at the same position shown in FIG. 6 at the same time, and the crash box 2, the bumper reinforcement 12 and the stay 14 are mold pipe expansion joined.

  Here, in the diameter expansion by electromagnetic forming of the aluminum alloy extruded material disclosed in Patent Document 4, an electromagnetic forming coil body is inserted into the aluminum alloy extruded material, and an instantaneous large current is passed through the electromagnetic forming coil body. The diameter has been expanded. Therefore, the diameter expansion by this electromagnetic forming cannot be used when the rib 6 is provided in the outer wall part 4 like the crush box 2. On the other hand, as described above, the die expansion joint can be used even when the rib 6 is provided in the outer wall portion 4 of the crash box 2.

  FIG. 7 is a plan view of the crash box 2 when the crash box 2 is plastically deformed by applying a load in the axial direction. As shown in FIG. 7, the crush box 2 has a side between the connecting part 4 c where the ridge line part 4 b and the middle rib 6 are connected, the side next to the crushed side swells, and the side next to the side collapses. The sides of 12 are crushed or swelled, and the plastic deformation is repeated in a bellows-like cross section. Therefore, the crush box 2 is plastically deformed smoothly into a bellows shape with a regular shape because the number of sides when plastic deforming is large and the length of one side is short.

  FIG. 8 is a load-displacement diagram obtained from an analysis performed when the crash box 2 is plastically deformed in the axial direction using FEM analysis. As shown in this load-displacement diagram, the load-displacement curve of the crash box 2 has a fast initial rise, and the difference between the initial load value and the average load value after the second peak of the load-displacement curve is small.

  FIG. 9 is a diagram for explaining an actual energy absorption amount (EA amount) and an ideal energy absorption amount (ideal EA amount). The ideal EA amount is represented by an area indicated by hatching in the drawing, and the EA amount is represented by an area below the load-displacement curve in a region indicated by hatching.

Table 1 shows the EA amount, the ideal EA amount, the ideal EA value (EA amount / ideal EA amount), the ideal EA value per unit weight, the second peak of the load-displacement curve to the displacement of 60 mm. The standard deviation of load fluctuation (hereinafter referred to as standard deviation of load fluctuation) and the average load (hereinafter referred to as average load) between the second peak and the displacement of the load-displacement curve of 60 mm are shown. The values shown in Table 1 are calculated based on the load-displacement curve of the crash box 2 shown in FIG.

  As shown in Table 1, the anti-ideal EA value of the crash box 2 is 85.2%, which is a value close to the ideal EA amount, and thus has extremely excellent energy absorption characteristics. Further, as is clear from the fact that the standard deviation of the load fluctuation of the crash box 2 is 2.88, the load fluctuation after the initial load is small and the load stability is excellent.

  Further, the outer wall portion 4 of the crash box 2 includes a pipe expanding portion 8 provided in the circumferential direction. Since the pipe expanding portion 8 is a starting point and the crash box 2 is plastically deformed in a bellows shape, the initial load becomes excessively high. The difference between the initial load value and the average load value is small. That is, as apparent from 93.9 kN which is the average load of the crash box 2 shown in FIG. 8 and Table 1, the crash box 2 has a small difference between the initial load value and the average load value. Moreover, since the ideal EA value per unit weight of the crash box 2 is 2.196, the crash box 2 has extremely excellent energy absorption characteristics.

  In addition, the crash box 2 according to this embodiment has a closed hexagonal closed cross-sectional shape in which the outer wall portion 4 is perpendicular to the extrusion direction, and has six medium ribs 6 equal in number to the sides constituting the regular hexagon. It has. Therefore, since the space formed by the outer wall portion 4 and the middle rib 6 is large, good workability can be obtained when the bumper beam 10 is assembled.

  In the bumper beam according to this embodiment, it is not necessary to provide a special step for providing the crash box 2 with a weak portion that becomes a starting point of plastic deformation, and the manufacturing cost is reduced. In addition, since the mold tube expansion joint portion for joining the crash box 2 to the bumper reinforcement 12 of the bumper beam 10 functions as a weak portion from which plastic deformation starts, the initial stage when the crash box 2 of the bumper beam 10 undergoes plastic deformation. The difference between the load and the average load can be reduced. Further, it is not affected by heat unlike the case where the crash box is joined to the bumper reinforcement by welding. Also, there is no dead stroke as in the case where the crash box is fastened to the bumper reinforcement with bolts and nuts.

  Moreover, in the bumper beam manufacturing method according to this embodiment, the tube expansion portion 8 that joins the crash box 2 to the bumper reinforcement 12 of the bumper beam 10 functions as a weak portion from which plastic deformation starts. It is not necessary to provide a special step for providing a weak portion as a starting point of plastic deformation in FIG. 2, so that the manufacturing cost can be reduced, and the initial load and the average load when the crash box 2 of the bumper beam 10 is plastically deformed. The bumper beam 10 with a small difference can be manufactured.

  In addition, in the bumper beam manufacturing method according to the above-described embodiment, when the stay 14 is joined to the bumper reinforcement 12, the mold tube expansion joining is used, but the stay is joined to the bumper reinforcement by welding, Alternatively, the stay may be fastened to the bumper reinforcement with bolts and nuts.

  Further, the crash box 2 according to the above-described embodiment has a regular hexagonal cross-sectional shape. However, the present invention is not limited to this, and as shown in FIG. 10, any one of a regular pentagon, a regular heptagon, and a regular octagon. It may be a cross-sectional shape. That is, as shown in FIG. 10 (a), an outer wall portion having a regular pentagonal closed cross-sectional shape and five ribs provided inside the outer wall portion are provided, and one end of each middle rib constitutes the outer wall portion. A structure in which the other end portions are connected to each other at the central portion in the outer wall portion, and the outer wall portion and the outer wall having a regular heptagonal closed cross-sectional shape as shown in FIG. Each of the middle ribs is connected to a substantially central portion of each wall portion constituting the outer wall portion, and the other end portion is mutually connected at the central portion in the outer wall portion. As shown in FIG. 10 (c), the outer wall portion has a regular octagonal closed cross-sectional shape and eight ribs provided inside the outer wall portion, and each middle rib has one end portion. Is connected to the substantially central part of each wall part constituting the outer wall part, and the other end part is in the central part in the outer wall part It may be configured to be connected are.

  Further, the cross-sectional shapes are not limited to regular pentagons, regular hexagons, regular heptagons, and regular octagons, but may be pentagonal, hexagonal, heptagonal, and octagonal sectional shapes having non-uniform side lengths.

  In the above-described embodiment, an aluminum extruded material is used for the energy absorbing member having the outer wall portion 4 and the inner rib 6. However, the outer wall portion and the inner rib are separately formed by aluminum extrusion, and then the inner wall portion is formed in the outer wall portion. An energy absorbing member in which ribs are arranged and joined may be used, or an energy absorbing member in which an outer wall portion and an intermediate rib are formed by bending a metal plate may be used.

2 ... Crash box, 4 ... Outer wall part, 4a ... Wall part, 4b ... Ridge line part, 4c ... Connection part, 6 ... Middle rib, 8 ... Tube expansion part, 10 ... Bumper beam, 12 ... Bumper reinforcement, 14 ... Stay, 20 ... mold, 22 ... mandrel

Claims (11)

Preparing a bumper reinforcement and a pair of energy absorbing members and a pair of stays having an outer wall portion having a closed cross-sectional shape in a cross section perpendicular to the axial direction and absorbing energy by plastic deformation in the axial direction;
A first mold tube expansion joining step of mold expanding and joining each of the pair of energy absorbing members to left and right ends of the bumper reinforcement; and
A joining step of joining each of the pair of stays to the other end of each of the pair of energy absorbing members;
The manufacturing method of the energy absorption structure characterized by including.   2. The joining step is a second die expansion joint step for joining each of the pair of stays to each other end portion of the pair of energy absorbing members by die expansion joining. The manufacturing method of the energy absorption structure of description.   The method for manufacturing an energy absorbing structure according to claim 2, wherein the first mold tube expansion joining step and the second mold tube expansion joining step are the same step. The outer wall portion of the energy absorbing member forms a closed cross-sectional shape having a polygonal outer shape in a cross section perpendicular to the axial direction,
The inner wall has the same number of medium ribs as the number of sides constituting the polygon,
Each of the middle ribs has one end connected to a substantially central part of each wall part constituting the outer wall part, and the other end part connected to each other at a central part in the outer wall part. The manufacturing method of the energy absorption structure as described in any one of Claims 1-3 to do.   The expanded portion formed in the first mold expanded pipe joining step and the second mold expanded tube joining process is formed in a region including a ridge line portion formed by the two wall portions constituting the outer wall portion. The manufacturing method of the energy absorption structure as described in any one of Claims 2-4 characterized by the above-mentioned.   The method for manufacturing an energy absorbing structure according to claim 4 or 5, wherein the polygon is any one of a pentagon, a hexagon, a heptagon, and an octagon. Bumper reinforcement,
The outer wall has a closed cross-sectional shape in a cross section perpendicular to the axial direction, absorbs energy by plastic deformation in the axial direction, and one end is joined to the left and right ends of the bumper reinforcement on the outer wall. A pair of energy absorbing members having a mold tube expansion joint to be
A pair of stays joined to the other end of each of the pair of energy absorbing members;
An energy absorbing structure comprising:   8. The energy absorbing structure according to claim 7, wherein each of the pair of energy absorbing members has a mold tube expansion joint portion that joins the stay to the other end portion. The outer wall portion of the energy absorbing member forms a closed cross-sectional shape having a polygonal outer shape in a cross section perpendicular to the axial direction,
The inner wall has the same number of medium ribs as the number of sides constituting the polygon,
Each of the middle ribs has one end connected to a substantially central part of each wall part constituting the outer wall part, and the other end part connected to each other at a central part in the outer wall part. The energy absorbing structure according to claim 7 or 8.   The said mold pipe expansion joint part is formed in the area | region containing the ridgeline part formed of the two said wall parts which comprise the said outer wall part, It is any one of Claims 7-9 characterized by the above-mentioned. Energy absorption structure.   The energy absorbing structure according to claim 9 or 10, wherein the polygon is any one of a pentagon, a hexagon, a heptagon, and an octagon.

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