JP5618305B2 - Electromagnetic forming method for polygonal cross-section member - Google Patents

Description

  The present invention relates to a method for producing a member (polygonal cross-section member) having a polygonal cross-sectional shape by expanding a tubular aluminum alloy material by electromagnetic forming.

An aluminum alloy material having a cylindrical peripheral wall is disposed inside a mold having an inner circumferential surface having a polygonal cross section, and an electromagnetic forming coil is disposed inside the aluminum alloy material, and in this state, the electromagnetic forming coil An electromagnetic forming method in which the aluminum alloy material is expanded and formed into a cross-sectional shape along the inner peripheral surface and / or end surface of the mold is applied to forming various members.
For example, Patent Document 1 describes that an end portion of an aluminum alloy material is expanded to form a flanged bumper stay. In Patent Document 2, the front part of an aluminum alloy material is inserted into a through-hole formed in a bumper reinforcement, the periphery of the rear part is surrounded by a mold, the entire length of the aluminum alloy material is expanded, and crimped to the bumper reinforcement. It is described that it is concluded. Patent Document 3 discloses a through-hole in which the rear portion of the aluminum alloy material is formed in a large diameter in the first tube expansion molding, and at the same time a flange is formed in the rear end, and in the second tube expansion molding, the front half is formed as a bumper reinforcement. It is described that it is inserted into a tube and expanded to form a tube, and then crimped to a bumper reinforcement. Patent Document 4 describes that an aluminum alloy material having a circular cross section is subjected to tube expansion forming into a deformed cross section such as a polygon.

JP 2004-189062 A JP 2004-237818 A JP 2010-69927 A JP-A-6-31226

  In pipe expansion by electromagnetic forming, a circular cross-sectional coil in which a conductor having a hollow quadrangular cross-section is spirally wound with the same diameter is generally used as an electromagnetic forming coil. This is because the circular cross-section coil is easy to mold, and the insulating resin layer surrounding the conductor is not easily damaged even if the repulsive force at the time of electromagnetic molding is repeatedly applied. Also, since the electromagnetic forming force is inversely proportional to the cube of the distance between the aluminum alloy material and the electromagnetic forming coil, the aluminum alloy material must also have a circular cross section so that the gap between the aluminum alloy material and the electromagnetic forming coil is very small. It is used.

Using such an electromagnetic forming coil and an aluminum alloy material, as shown in Patent Document 4, for example, when attempting to electromagnetically form a rectangular cross-section member, restrictions on electromagnetic forming force, durability of the electromagnetic forming coil, and materials There is a problem that the R (radius) of the corner portion of the quadrangular cross-section member cannot be formed small due to the extension limit of the shape. This point will be described with reference to FIGS.
First, in FIG. 6A, a cylindrical aluminum alloy material 1 is arranged inside a mold 3 whose inner peripheral surface has a square cross section (in this example, a regular square), and a circular shape is formed inside the aluminum alloy material 1. A cross-sectional electromagnetic forming coil 2 is arranged. R of the inner peripheral surface of the corner portion 3a of the mold 3 is formed to be relatively small in accordance with the cross-sectional shape of the target quadrangular cross-section member.

  In the state of FIG. 6A, the electromagnetic forming coil 2 is energized and the aluminum alloy material 1 is expanded. At this time, if the aluminum alloy material 1 is deformed (expanded) until it reaches the corner portion 3a of the inner peripheral surface of the mold 3, the formed quadrangular cross-section member has a target indicated by a two-dot chain line in FIG. The cross-sectional shape is 5. However, it is generally difficult to form a rectangular cross-section member having a small corner R like the target cross-sectional shape 5, and the actually formed quadrangular cross-section member 4 is indicated by a solid line in FIG. Thus, R of corner part 4a will become large compared with R of corner part 5a of target section shape 5 (shape along the inner peripheral surface of metallic mold 3). That is, the aluminum alloy material 1 is not deformed (expanded) enough to reach the corner portion 3 a of the inner peripheral surface of the mold 3.

  In this pipe expansion molding, if the electric energy input to the electromagnetic forming coil 2 is large and a sufficiently large electromagnetic forming force is generated in the aluminum alloy material 1, the aluminum alloy material 1 becomes the inner periphery of the corner portion 3 a of the mold 3. It deforms (expands) until it reaches the surface, and as a result, a rectangular cross-section member with a small R at the corner can be formed. However, if the electric energy to be input is large, the durability of the electromagnetic forming coil 2 is lowered. In addition, the change in the circumferential length of the aluminum alloy material 1 (extension of the material) increases in the vicinity of the corner portion 3a of the mold 3, so that the thickness of the quadrilateral cross-section member is locally reduced at the corner portion and further breaks. Can also occur. Therefore, when actually forming a rectangular cross-section member by electromagnetic forming using the current electromagnetic forming coil and aluminum alloy material, as shown in FIG. Generally difficult.

Next, in FIG. 7, the cylindrical aluminum alloy material 11 is disposed inside the mold 13, and the electromagnetic forming coil 12 having a circular cross section is disposed inside the aluminum alloy material 11. The coil 12 is energized, and the aluminum alloy material 11 is expanded. The mold 13 has a rectangular cross section (in this example, a regular quadrilateral) and has a large cross section 13A and a small cross section 13B along the length direction, and a step 13C is formed therebetween. . By this electromagnetic forming, as shown in FIG. 8, a rectangular cross-section member (bumper stay) 14 composed of a large cross-sectional portion 14A, a small cross-sectional portion 14B, and a stepped portion 14C therebetween is formed.
In this example as well, the target cross-sectional shape (the shape along the inner peripheral surface of the mold 13) cannot be obtained due to restrictions on the electromagnetic forming force, durability of the coil for electromagnetic forming, and the extension of the material. In the square cross-section member 14, the R of all corner portions of the large cross-section portion 14 </ b> A, the small cross-section portion 14 </ b> B, and the striking portion 14 </ b> C is larger than the R of the corner portion of the target cross-sectional shape.

  As shown in FIG. 8, the bumper stay 14 has a small cross section 14B inserted into the cross section of the side member 15 indicated by a two-dot chain line, and the stepped portion 14C abuts against the flange 15A at the tip of the side member 15, The part 14 </ b> B and the side member 15 are bolted, whereby the bumper stay 14 is fixed to the side member 15. The load applied to the bumper stay 14 at the time of the collision is transmitted from the large cross section 14A of the bumper stay 14 to the side member 15 through the flange 15A. Here, the side member generally has a rectangular R-octagon polygonal cross section with a small corner portion R and a clear ridgeline portion. Similarly, the side member 15 has a small R at the corner portion 15a and a ridgeline portion. Has a clear square cross section.

  Therefore, as shown in FIG. 8A, the large cross-sectional portion 14A of the bumper stay 14 and the side member 15 do not coincide with each other at the cross-sectional corner portions 14a and 15a when viewed in the axial direction. For this reason, the collision load related to the bumper stay 14 cannot be transmitted from the corner portion 14a of the large diameter portion 14A to the corner portion 15a of the side member 15, and as a result, the deformation form of the bumper stay 14 becomes unstable. Or a change in load caused by deformation increases, resulting in a problem that a predetermined energy absorption performance cannot be ensured.

  The present invention has been made in view of the above problems of the conventional electromagnetic forming method, and in the case of expanding a tubular aluminum alloy material having a cylindrical peripheral wall by electromagnetic forming and forming a member having a polygonal cross section, The object is to make the corner portion R smaller.

  According to the present invention, an aluminum alloy material having a cylindrical peripheral wall is disposed inside a mold having an inner circumferential surface having a polygonal cross section, and an electromagnetic forming coil is disposed inside the aluminum alloy material. It is an improved electromagnetic forming method for a polygonal cross-section member that energizes the electromagnetic forming coil and expands and forms the aluminum alloy material into a cross-sectional shape along the inner peripheral surface of the mold. It is characterized by a cross-sectional shape and an arrangement form of the aluminum alloy material in the mold. Specifically, the cross section of the peripheral wall of the aluminum alloy material includes a plurality of arc-shaped regions along a circumferential direction of a substantially circular basic cross-section, and a plurality of uneven regions sandwiched between the arc-shaped regions, In the region, the peripheral wall protrudes inwardly and / or outwardly from the basic cross section, and the peripheral length of the peripheral wall of each uneven region is longer than that in the case where the same region is formed in an arc shape along the peripheral direction of the basic cross section. Is formed. The uneven regions are all disposed so as to face the corners of the mold. Here, the substantially circular basic cross section means a virtual cross section obtained by connecting the arc-shaped regions.

In the electromagnetic forming method, the electromagnetic forming coil is a circular cross-sectional coil in which a conductor is spirally wound .
In the electromagnetic forming method, the flange can be formed by expanding one or both ends of the aluminum alloy material outward at the same time that the aluminum alloy material is expanded.
In the electromagnetic forming method, the polygonal cross-sectional member is an energy absorbing member that absorbs energy by being crushed when receiving a compressive load in the axial direction, for example. In this case, the aluminum alloy material can be expanded and formed, and at the same time, a plurality of crush beads (indented because the bulging amount is relatively small) can be formed. This energy absorbing member is particularly suitable for use in automobiles.

In the electromagnetic forming method, the polygonal cross-sectional member is, for example, an automobile bumper stay (a kind of the energy absorbing member).
In the electromagnetic forming method, the aluminum alloy material can be expanded by electromagnetic forming to form a bumper stay having a polygonal cross section, and at the same time, it can be caulked and joined to bumper reinforcement. In this case, a hole penetrating in the front-rear direction is formed in the bumper reinforcement, a part of the aluminum alloy material is inserted into the hole, and a portion protruding backward from the hole of the aluminum alloy material is surrounded by the mold. And electromagnetic forming. When referring to the front-rear direction with respect to the bumper stay, the collision surface side is the front, and the vehicle body side (side member side) is the rear.
The aluminum alloy material preferably has substantially the same cross section along the longitudinal direction, and includes not only extruded materials but also those obtained by forming a plate material into a cylindrical shape.

  In the aluminum alloy material according to the present invention, the circumferential length of the peripheral wall of the concavo-convex region is longer than that when the region has a simple arc-shaped cross section. In the present invention, this is called that the peripheral wall of the uneven region has a surplus line length. In the aluminum alloy material according to the present invention, the peripheral wall of the concavo-convex region has the surplus line length, and the concavo-convex region is arranged to face the corner portion of the inner peripheral surface of the mold. When the tube is expanded by molding, the peripheral wall of the uneven region easily enters deeply by the excess line length toward the inner peripheral surface of the corner portion of the mold, along the inner peripheral surface of the corner portion of the mold. A polygonal cross-section member having a small corner portion R and a clear ridgeline can be formed.

Since the aluminum alloy material has the surplus line length in the concavo-convex region, the change in the circumference of the aluminum alloy material (elongation of the material) is alleviated by the surplus line length, and in particular, the corner of the polygonal cross-section member is reduced. The local thickness reduction in the portion is alleviated and breakage can be prevented.
In addition, the peripheral wall of the aluminum alloy material is composed of a plurality of arc-shaped regions along the circumferential direction of the basic cross section except that the uneven region is partially formed. The gap between the coils for use can be reduced, and a sufficient electromagnetic forming force can be applied to the aluminum alloy material.

  When the method for producing a polygonal cross-section member according to the present invention is applied to molding of an energy absorbing member that absorbs energy by crushing in the axial direction, a corner portion (ridge line portion) that greatly contributes to energy absorption during crushing deformation It is possible to suppress the reduction of the wall thickness, and it is an energy absorbing member that is lightweight and has excellent energy absorption characteristics. In addition, when applied to molding of the bumper stay among the energy absorbing members, the sectional shape of the bumper stay can be made to coincide with the sectional shape of the side member having a generally polygonal section. As a result, the load applied to the bumper stay at the time of collision can be transmitted from the entire circumference of the bumper stay to the entire circumference of the side member. The predetermined energy absorption performance can be secured.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram explaining the electromagnetic forming method concerning this invention, The top view (a) of an aluminum alloy raw material, the top view (b) of the aluminum alloy raw material and electromagnetic forming coil which have been arrange | positioned in a metal mold | die, and The top view (c) of the polygonal cross-section member obtained by electromagnetic forming is shown. It is a schematic diagram explaining another example of the electromagnetic forming method which concerns on this invention, The top view (a) of the aluminum alloy raw material and electromagnetic forming coil which have been arrange | positioned in a metal mold | die, and its cross section (b), And the top view (c) of the polygonal cross-section member (bumper stay) obtained by electromagnetic forming is shown. It is a perspective view explaining the example which applied the electromagnetic forming method concerning the present invention to formation of a bumper stay, and caulking fastening with bumper reinforcement. It is the front view (b) of the aluminum alloy raw material inserted in the hole, and its side view (c). It is a perspective view which shows the bumper stay and bumper reinforcement after electromagnetic forming, and a side member. It is a schematic diagram explaining another example of the electromagnetic forming method which concerns on this invention, The top view (a) of the aluminum alloy raw material arrange | positioned in a metal mold | die and a metal mold | die, and the coil for electromagnetic forming, Its sectional drawing (b) The top view (c) of the polygonal cross-section member (bumper stay) obtained by electromagnetic forming is shown. It is a plane schematic diagram explaining the conventional electromagnetic forming method which shape | molds a square cross-section member, The top view (a) of the aluminum alloy raw material arrange | positioned in a metal mold | die and a metal mold | die, and an electromagnetic forming coil, and obtained by electromagnetic forming A rectangular cross-section member (b) is shown. It is a schematic diagram explaining the conventional electromagnetic forming method which shape | molds a square cross-section member (bumper stay), The top view (a) of the aluminum alloy raw material and electromagnetic forming coil which were arrange | positioned in a metal mold | die, and the same sectional drawing (B) is shown. It is the top view (a) which combined the square cross-section member (bumper stay) and side member which were obtained with the conventional electromagnetic forming method, and sectional drawing (b).

Hereinafter, the electromagnetic forming method according to the present invention will be described more specifically with reference to FIGS.
FIG. 1 is a schematic view for explaining an electromagnetic forming method according to the present invention. The mold 3 and the electromagnetic forming coil 2 are the same as those shown in FIG.
The aluminum alloy material 21 is obtained by cutting an aluminum alloy extruded material having a cylindrical peripheral wall into a predetermined length, and the peripheral wall is sandwiched between a plurality of arc-shaped regions 22 along the circumferential direction and the arc-shaped region 22. It consists of a plurality of uneven regions 23.
The arcuate region 22 is disposed along the circumferential direction of a substantially circular basic cross section 24 (indicated by a two-dot chain line in FIG. 1). In this example, the central angle of the arcuate region 22 (both ends of the arcuate region 22 and the basic cross section). angle) of the center O of 24 is set to theta ₁ none. As described above, the basic cross section 24 is a virtual cross section obtained by connecting the arc-shaped regions 22 and corresponds to a cross section of the conventional aluminum alloy material 1 (see FIG. 6).

In the uneven region 23, the peripheral wall protrudes outwardly from the basic cross section 24. As for the uneven area 23, similarly to the arc-shaped area 22, if the concept of a central angle (an angle formed by both ends of the uneven area 23 and the center O of 24 of the basic cross section) is introduced, in this example, the central angle of the uneven area 23 is both are set to θ _2. When compared with the same central angle θ ₂ , the length (circumferential length) L ₁ of the peripheral wall in the uneven region 23 is compared with the length (peripheral length) L ₀ of the peripheral wall of the arc-shaped region 22 (or the basic cross section 24). It is long as the peripheral wall is curved outward and protrudes. This circumference difference (L ₁ −L ₀ ) is the surplus line length in the uneven region 23. Looking at the whole cross section of the aluminum alloy material 21, the excess line length in this example is _{4 × (L 1 -L 0)} .

In electromagnetic forming, the aluminum alloy material 21 is disposed inside the mold 3, and the electromagnetic forming coil 2 is disposed inside the aluminum alloy material 21. At this time, in the mold 3, the aluminum alloy material 21 is arranged so that each uneven area 23 faces each corner 3 a of the mold 3.
When the electromagnetic forming coil 2 is energized in this state, the aluminum alloy material 21 is expanded and the peripheral wall reaches the inner peripheral surface (including the corner portion 3a) of the mold 3 over the entire periphery, and the expanded tube is finished. In this case, the expansion of the aluminum alloy material 21 is constrained on the entire circumference of the inner peripheral surface of the mold 3.

Since the uneven region 23 having the surplus line length (L ₁ -L ₀ ) is disposed to face the inner peripheral surface of the corner portion 3 a of the mold 3, the peripheral wall of the uneven region 23 is expanded when expanding the tube by electromagnetic forming. Has a small change in the circumferential length, that is, it reaches the back of the inner peripheral surface of the corner portion 3a relatively easily without greatly reducing the wall thickness, and the cross-sectional shape along the inner peripheral surface of the mold 3 as a whole, That is, the rectangular section member 25 having a small R at the corner portion 25a and a clear ridgeline is formed.
The rectangular cross-section member 25 is suitable for use as an energy absorbing member that absorbs energy by being crushed when receiving a compressive load in the axial direction, for example. The rectangular cross-section member 25 is light in weight and has excellent energy absorption characteristics because the thickness reduction of the corner portion (ridge line portion) that greatly contributes to energy absorption during crushing deformation is suppressed.

FIG. 2 is a schematic view for explaining a method of forming a bumper stay using the electromagnetic forming method according to the present invention. The electromagnetic forming coil 12 and the mold 13 are the same as those shown in FIG.
The aluminum alloy material 31 is obtained by cutting an aluminum alloy extruded material having a cylindrical peripheral wall into a predetermined length just like the aluminum alloy material 21, and the peripheral wall has a plurality of arc-shaped regions 32 along the circumferential direction. And a plurality of concave and convex regions 33 sandwiched between the circular arc regions 32. The arc-shaped region 32 is disposed along the circumferential direction of a substantially circular basic cross section 34 (indicated by a two-dot chain line in FIG. 2), and in the uneven region 33, the peripheral wall protrudes outward from the basic cross section 34. Therefore, the peripheral wall of the uneven region 33 has a surplus line length, like the uneven region 23 of the aluminum alloy material 21.

In electromagnetic forming, the aluminum alloy material 31 is disposed inside the mold 13, and the electromagnetic forming coil 12 is disposed inside the aluminum alloy material 31. At this time, in the mold 13, the aluminum alloy material 31 is arranged so that each uneven region 33 faces each corner 13 a of the mold 13.
When the electromagnetic forming coil 12 is energized in this state, the aluminum alloy material 31 is expanded and the peripheral wall reaches the inner peripheral surface (including the corner portion 13a) of the mold 13 over the entire periphery, and the expanded tube is finished. Since the uneven region 33 having a surplus line length is disposed opposite to the inner peripheral surface of the corner portion of the mold 13, when the pipe is expanded by electromagnetic forming, the peripheral wall of the uneven region 23 has little change in the peripheral length, That is, it reaches the back of the corner portion relatively easily without greatly reducing the wall thickness, and the cross-sectional shape along the inner peripheral surface of the mold 13 as a whole, that is, as shown in FIG. A bumper stay 35 having a small R and a clear ridgeline is formed.

  The bumper stay 35 is fixed to the side member 15 (see FIG. 8) in the same manner as the bumper stay 14. In the bumper stay 35, the cross-sectional shape of the large cross-sectional portion 35 </ b> A can be made to substantially match the cross-sectional shape of the side member 15 including the corner portion. Therefore, the load applied to the bumper stay 35 at the time of collision is also transmitted from the corner portion of the large cross section 35A of the bumper stay 35 to the side member 15 via the flange 15A (see FIG. 8), and deformed like the bumper stay 14. There is no problem that the form becomes unstable or the load fluctuation accompanying the deformation becomes large, and the predetermined energy absorption performance cannot be secured. Further, since the bumper stay 35 can suppress a decrease in the thickness of the corner portion (ridge line portion) that greatly contributes to the amount of energy absorption during crushing deformation, the bumper stay 35 is a lightweight bumper stay having excellent energy absorption characteristics.

  On the other hand, the small cross-sectional portion 35B of the bumper stay 35 can have its outer peripheral surface shape substantially identical to the inner peripheral surface shape of the side member 15 (see FIG. 8) including the corner portion. Therefore, the small cross section 35B can be inserted into the cross section of the side member 15 with almost no gap, and then the small cross section 35B and the side member 15 are bolted from the side, so that the bumper stay 35 and the side member 15 are fastened. (Refer to FIG. 8) is more securely fixed.

3 and 4 are schematic diagrams for explaining a method of fixing the bumper stay to the bumper reinforcement at the same time as forming the bumper stay using the electromagnetic forming method according to the present invention.
In FIG. 3, an aluminum alloy material 41 is obtained by cutting an aluminum alloy extruded material having a cylindrical peripheral wall into a predetermined length, and the peripheral wall, like the aluminum alloy material 31, has a plurality of arc-shaped regions along the circumferential direction. 42 and a plurality of concave and convex regions 43 sandwiched between the arc-shaped regions 42, and the arc-shaped regions 42 are arranged along the circumferential direction of the substantially circular basic cross section (not shown) as described above. . However, the aluminum alloy material 41, since the cross-sectional shape of the side member 44 (see FIG. 4) is slightly longer rectangle vertically, accordingly, slightly larger than the lateral distance d ₂ vertically spacing d ₁ of the irregular region 43 doing.

The bumper reinforcement 45 is made of an aluminum alloy extruded material having a mouth-shaped cross section, and rectangular holes 46 and 47 that are slightly long in the vertical direction are formed in the front and rear vertical walls 45a and 45b in the vicinity of the left and right ends. The holes 46 and 47 are formed in substantially the same shape as the inner contour (inner peripheral shape) of the cross section of the side member 44. The aluminum alloy material 41 is inserted into the holes 46 and 47 of the bumper reinforcement 45, and the front end protrudes beyond the hole 46.
The holes 46 and 47 are preferably burring holes. When the front (collision) side hole 46 is a burring hole, the hole flange of the burring hole protrudes toward the rear side (side member 44 side) from the viewpoint of preventing the bumper cover from being broken at the time of collision. It is desirable to form it as described above (see JP 2010-116129 A).

Subsequently, a mold (not shown) is disposed around the rear portion of the aluminum alloy material 41 (portion protruding rearward from the hole 47 of the bumper reinforcement 45), and electromagnetic molding (not shown) is formed inside the aluminum alloy material 41. A coil for use is arranged.
The mold has a rectangular cross section (however, in this example, a rectangle with a slightly long vertical direction), and, like the mold 13, is composed of a small cross section and a large cross section, and a step between the two. The shape of the inner peripheral surface of the large cross section is formed to be substantially the same as the outer contour of the cross section of the side member 44. However, a plurality of protrusions protruding inward are formed in an appropriate arrangement in a planar region (a portion other than the corner portion) of the large cross section of the mold. This protrusion is for forming a crash bead on the bumper stay. The shape of the inner peripheral surface of the small cross section is formed to be substantially the same as the inner contour (inner peripheral shape) of the cross section of the side member 44.
The electromagnetic forming coil is a circular coil similar to the electromagnetic forming coil 12.

Subsequently, in this state, the electromagnetic forming coil is energized, the aluminum alloy material 41 is expanded and formed, and the bumper stay 48 shown in FIG. 4 is formed, and at the same time, it is caulked and fastened to the bumper reinforcement 45.
The rear portion of the aluminum alloy material 41 is expanded inside the mold and is constrained and deformed by the inner peripheral surface of the mold including the corner portion, and includes a large cross section 48A, a small cross section 48B, And the level | step-difference part 48C between both is shape | molded. The large cross section 48A has a rectangular cross section that is substantially the same shape as the outer contour of the cross section of the side member 44 including the corner section 48a, and the small cross section 48B includes the inner contour of the cross section of the side member 44 including the corner section 48b. And has a quadrangular cross section of substantially the same shape. The large cross-sectional portion 48A and the small cross-sectional portion 48B each have a rectangular cross section with a small R at the corner portions 48a and 48b and a clear ridgeline portion. In addition, a recess (crash bead 49) corresponding to the protrusion of the mold is formed in the planar region of the large cross section 48A. In adjacent planar regions, the crush beads 49, 49,... Are formed at different positions in the axial direction, that is, in a staggered arrangement.

On the other hand, the front portion (portion other than the rear portion) of the aluminum alloy material 41 is expanded in the bumper reinforcement 45 and in front of the bumper reinforcement 45, and the vertical walls 45a and 45b include the holes 46, including the corner portions. In close contact with the inner peripheral surface of 47, the space between the vertical walls 45a and 45b expands without restriction of the mold, the front end is expanded, and the flange 51 is formed.
After the electromagnetic forming, bolt holes 52 are formed on both side surfaces of the small cross section 48B of the bumper stay 48. Subsequently, the small cross-sectional portion 84B of the bumper stay 48 is inserted into the cross-section of the side member 44, the stepped portion 48C contacts the flange 44a at the tip of the side member 44, and the small cross-sectional portion 48B and the side member 44 are bolted. As a result, the bumper stay 48 is fixed to the side member 44.

FIG. 5 is a schematic view for explaining a method of forming a flanged bumper stay using the electromagnetic forming method according to the present invention.
The aluminum alloy material 61 is obtained by cutting an aluminum alloy extruded material having a cylindrical peripheral wall into a predetermined length just like the aluminum alloy material 21, and the peripheral wall has a plurality of arc-shaped regions 62 along the circumferential direction. And a plurality of concave and convex regions 63 sandwiched between the arc-shaped regions 62. The arc-shaped region 62 is disposed along the circumferential direction of a substantially circular basic cross section 64 (indicated by a two-dot chain line in FIG. 5), and in the uneven region 63, the peripheral wall protrudes outward from the basic cross section 64. Therefore, the peripheral wall of the uneven region 63 has a surplus line length as with the uneven region 23 of the aluminum alloy material 21.

In electromagnetic forming, the aluminum alloy material 61 is inserted into the mold 66, one end of the aluminum alloy material 61 is protruded from one end surface 66 b of the mold 66, and the electromagnetic forming coil 65 is placed inside the aluminum alloy material 61. To place. At this time, in the mold 66, the aluminum alloy material 61 is arranged so that each uneven area 63 faces each corner 66 a of the mold 66.
When the electromagnetic forming coil 65 is energized in this state, the aluminum alloy material 61 is expanded and the inner wall of the mold 66 reaches the inner peripheral surface (including the corner portion 66a) of the mold 66 over the entire circumference. At the portion protruding from the end surface 66b of the mold 66, the peripheral wall expands and strikes the end surface 66b, and the tube expansion molding is completed.

  As shown in FIG. 5C, the flanged bumper stay 67 obtained by this electromagnetic forming is composed of a quadrangular cross section 68 and a flange 69 at the end. Since the concavo-convex region 63 having a surplus line length is arranged to face the corner portion 66a of the mold 66, when the pipe is expanded by electromagnetic forming, the peripheral wall of the concavo-convex region 63 has little change in the peripheral length, that is, the wall thickness. The corner portion 66a can be reached relatively easily without greatly reducing the cross-sectional shape along the inner peripheral surface of the mold 66, that is, as shown in FIG. A bumper stay 67 having a square cross section 68 with a small ridge line clearly formed is formed. At the same time, due to the presence of the surplus line length, the local thickness reduction of the flange 69 is alleviated and breakage can be prevented.

In the method for manufacturing a polygonal cross-section member according to the present invention, the aluminum alloy material can take, for example, the following embodiments.
(1) In the example described above, one convex portion is formed in each concave and convex region of the aluminum alloy material. In this concave and convex region, a plurality of convex portions, one or a plurality of concave portions ( A portion where the peripheral wall protrudes inwardly from the basic cross section), or both the convex portion and the concave portion may be formed in a wave shape, for example. In any case, the surplus line length must be generated in the uneven region.

(2) When there are a plurality of uneven regions in the aluminum alloy material, the shape of the recesses or protrusions in each uneven region or the length of the extra line length need not be the same, and the polygonal cross section formed by electromagnetic forming It can adjust suitably according to the shape of a member.
In addition, it is desirable to form the same number of uneven regions of the aluminum alloy material corresponding to each corner (ridge line) of the polygonal cross-section member formed by electromagnetic forming. In a portion where the change (elongation of the material) is small (for example, a portion having a relatively large corner angle among the corner portions of the polygonal cross-section member), it is not necessary to form an uneven region corresponding to the same portion.

(3) The aluminum alloy preferably has an electrical conductivity of 20% IACS or more and a proof stress of 150 MPa or less at the time of electromagnetic forming, and is selected from JIS 1000 series, 3000 series, 5000 series, 6000 series, and 7000 series aluminum alloys. In the case of a heat-treatable aluminum alloy, an aluminum alloy material in a T1 or T4 state, or an aluminum alloy material softened by being restored entirely or locally can be used. In this case, an age hardening process (T5, T6 process) may be performed after the electromagnetic forming. In the examples of FIGS. 3 and 4, the age hardening process is performed after the bumper stay 48 and the bumper reinforcement 45 are caulked and fastened.
(4) When the outer peripheral length of the aluminum alloy material is Lb and the peripheral length of the inner peripheral surface of the mold that restrains deformation of the aluminum alloy material during electromagnetic forming is La, 0.9 <La / Lb <1.3 Set. If La / Lb is 0.9 or less, wrinkles are generated in the electromagnetically formed polygonal cross-section member, and if it is 1.3 or more, the material may be broken. It is desirable that La and Lb are substantially equal.

(5) The thickness of the aluminum alloy material need not be constant over the entire circumference, and can be varied along the circumferential direction. For example, (a) a portion where the forming force of the coil for electromagnetic forming is relatively difficult (a portion far from the center O), that is, an uneven region and its vicinity are made relatively thin if necessary, (b) energy absorption When manufacturing a member, conversely, an uneven region corresponding to a corner portion (ridgeline portion) that greatly contributes to energy absorption and, if necessary, the vicinity thereof is made relatively thick. (C) Flange by electromagnetic forming In the case of forming the attached polygonal cross-section member, it is conceivable that the bolt fastening scheduled portion is relatively thick.

(6) In the example described above, the aluminum alloy material used for electromagnetic forming is only cut from the extruded material, but a pre-processed aluminum alloy material can also be used (Japanese Patent Laid-Open No. 2010-116129). FIG. 16). For example, in the example of FIGS. 4 and 5, the flange can be separately formed by, for example, electromagnetic forming or press forming before expanding into a polygonal cross section by electromagnetic forming.
(7) As the aluminum alloy material, it is possible to use a metal plate that is formed by press molding or roll molding into a cylindrical shape.

12, 65 Electromagnetic forming coil 13, 66 Mold 21, 31, 41, 61 Aluminum alloy material 22, 32, 42, 62 Arc-shaped region 23, 33, 43, 63 Uneven region 24, 34, 64 Basic cross section 25, 35, 48, 67 Square section member (bumper stay)
44 Side member 45 Bumper reinforcement

Claims (5)

An aluminum alloy material having a cylindrical peripheral wall is arranged inside a mold having an inner peripheral surface having a polygonal cross section, and an electromagnetic forming coil is arranged inside the aluminum alloy material, and in that state, the electromagnetic forming material In the electromagnetic forming method for a polygonal cross-section member in which a coil is energized and the aluminum alloy material is expanded and formed into a cross-sectional shape along the inner peripheral surface of the mold, the electromagnetic forming coil spirally winds a conductor. The cross section of the peripheral wall of the aluminum alloy material consists of a plurality of arc-shaped regions along the circumferential direction of a substantially circular basic cross-section, and a plurality of uneven regions sandwiched between the arc-shaped regions, In the uneven region, the peripheral wall protrudes inward and / or outwardly from the basic cross section, and the peripheral wall of each uneven region has a circumferential length formed in an arc shape along the circumferential direction of the basic cross section Than Ku, the aluminum alloy material, electromagnetic forming method of polygonal cross-section member, characterized in that the irregular region are disposed to face the corner portion of the mold. 2. The polygonal cross-section member according to claim 1 , wherein at the same time that the aluminum alloy material is expanded and formed, one or both ends of the aluminum alloy material are expanded outward to form a flange. Electromagnetic forming method. The polygonal cross-section member is an energy absorbing member, and at the same time bulge forming said aluminum alloy material according to claim 1 or 2, characterized in that forming a plurality of crush beads recessed inwardly to the peripheral wall Electromagnetic forming method for a polygonal cross-section member. The method for manufacturing a polygonal cross-section member according to claim 3 , wherein the polygonal cross-section member is a bumper stay. A hole penetrating in the front-rear direction is formed in the bumper reinforcement, a part of the aluminum alloy material is inserted into the hole, and a portion protruding backward from the hole of the aluminum alloy material is surrounded by the mold. The method for electromagnetic forming of a polygonal cross-section member according to claim 4 , wherein electromagnetic forming is performed, and the bumper reinforcement is caulked and fastened.

Images