Process for manufacturing bumper reinforcement

Abstract

A process for manufacturing a bumper reinforcement having a length, wherein the bumper reinforcement is disposed in front or rear of an automobile body with the length directed in transverse direction of the automobile body. The process includes joining a central part and lateral parts of unequal thicknesses to form a planar tailored blank. The process further includes press forming the tailored blank by hot pressing to produce a bumper reinforcement having a length and an M-shaped open cross section, the bumper reinforcement being curved at end portions of the length toward the open side of the cross section relative to a central portion.

Claims

1. A process for manufacturing a bumper reinforcement having a length, wherein the bumper reinforcement is disposed in front or rear of an automobile body with the length directed in transverse direction of the automobile body, the process comprising: joining a central part and lateral parts of unequal thicknesses to form a planar tailored blank; and press forming the tailored blank by hot pressing to produce a bumper reinforcement having a length and an M-shaped open cross section, the bumper reinforcement being curved at end portions of the length toward the open side of the cross section relative to a central portion, the bumper reinforcement comprising a central narrower section, end wider sections having a larger width than the central narrower section, and intermediate widening sections gradually widening from the central narrower section to the end wider sections, such that after the hot pressing the joints of unequal thicknesses between the central part and the lateral parts are located within the intermediate widening section.

2. The process of claim 1, further comprising mounting crash boxes between the end wider sections of the bumper reinforcement and the automobile body.

3. The process of claim 1, the thickness of the central part of the tailored blank being larger than the thickness of the lateral parts.

4. The process of claim 1, the central part and the lateral parts of the tailored blank being made of the same material.

5. The process of claim 1, wherein the step of press forming the tailored blank forms a flange at the opening of the M-shaped open cross section, the process further comprising welding a stiffener bracket to the flange.

6. The process of claim 1, the bumper reinforcement of the M-shaped open cross section being open longitudinally inward in the automobile.

7. The process of claim 1, the end portions of the length of the bumper reinforcement being curved toward the automobile body relative to the central portion.

8. The process of claim 4, wherein the step of press forming the tailored blank forms a flange at the opening of the M-shaped open cross section, the process further comprising welding a stiffener bracket to the flange.

9. The process of claim 4, the bumper reinforcement of the M-shaped open cross section being open longitudinally inward in the automobile.

10. The process of claim 4, the end portions of the length of the bumper reinforcement being curved toward the automobile body relative to the central portion.

11. The process of claim 3, the central part and the lateral parts of the tailored blank being made of the same material.

12. The process of claim 3, wherein the step of press forming the tailored blank forms a flange at the opening of the M-shaped open cross section, the process further comprising welding a stiffener bracket to the flange.

13. The process of claim 3, the bumper reinforcement of the M-shaped open cross section being open longitudinally inward in the automobile.

14. The process of claim 3, the end portions of the length of the bumper reinforcement being curved toward the automobile body relative to the central portion.

15. The process of claim 11, wherein the step of press forming the tailored blank forms a flange at the opening of the M-shaped open cross section, the process further comprising welding a stiffener bracket to the flange.

16. The process of claim 11, the bumper reinforcement of the M-shaped open cross section being open longitudinally inward in the automobile.

17. The process of claim 11, the end portions of the length of the bumper reinforcement being curved toward the automobile body relative to the central portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view of the position of a bumper structure within an automobile body.

(2) FIG. 2 is a perspective view of a bumper reinforcement seen from the front of the upper according to an embodiment.

(3) FIG. 3 is a front view of the right half, as seen from the front, of a bumper reinforcement.

(4) FIG. 4 is a sectional view taken along line IV-IV of FIGS. 2 and 3.

(5) FIG. 5 is a sectional view taken along line V-V of FIGS. 2 and 3.

(6) FIG. 6 is a diagram of a manufacturing process for a bumper reinforcement according to an embodiment.

(7) FIG. 7 is an illustration of wrinkles formed in the bumper reinforcement according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(8) Embodiments of the present invention will be described below with reference to the drawings.

(9) FIG. 1 shows the position of a bumper structure 10 within an automobile. The bumper structure 10 is typically disposed in the front and rear of the automobile body 12 in the transverse direction of the automobile body 12. FIG. 1 indicates the front of the automobile body 12 with arrow F and the rear with arrow R. The bumper structure 10 may include a bumper reinforcement 14, a bumper cover 16 and a bumper support structure 18. The bumper reinforcement 14 serves as a core that provides strength to the bumper structure 10. The bumper cover 16 is disposed so as to cover the front side of the bumper reinforcement 14. The bumper cover 16 is positioned outermost in the bumper structure 10, and designed in consideration of appearance. The bumper cover 16 is typically formed of plastic suitable for styling.

(10) The bumper support structure 18 is disposed between a frame member (not shown) of the automobile body 12 and the bumper reinforcement 14 at a location in the end portion of the length of the bumper reinforcement 14 (i.e. the lateral end portion of the bumper reinforcement 14 with respect to the automobile body 12). Impact load received by the bumper reinforcement 14 is transferred by the bumper support structure 18 to the automobile body 12, and then received by the automobile body 12. In a preferred embodiment the bumper support structure 18 comprises an element called a crash box which absorbs collision energy.

(11) It should be noted that embodiments will be described hereafter as having the bumper reinforcement 14 disposed in the front of the automobile body 12 for illustrative purposes. However, the bumper reinforcement may be disposed in the rear of the automobile body.

(12) In one embodiment, in a head-on collision of the automobile where an impact load is applied to the central portion of the bumper structure 10 configured as described above, the bumper structure 10 receives the load through the following process.

(13) The impact load is first applied to the bumper cover 16 and then received by the bumper reinforcement 14. The load acting on the bumper reinforcement 14 is then received by the automobile body 12 through the crash boxes disposed as bumper support structures 18 at the end portions of the bumper reinforcement 14. During this the crash boxes 18 absorb collision energy.

(14) FIGS. 2-5 show the structure of the bumper reinforcement 14 produced by a method in an embodiment. FIG. 2 is a perspective view of a bumper reinforcement as seen from the upper front; FIG. 3 is a front view of the right half, as seen from the front, of a bumper reinforcement; FIG. 4 is a cross-sectional view taken along line IV-IV of FIGS. 2 and 3; and FIG. 5 is a cross-sectional view taken along line V-V of FIGS. 2 and 3. As shown in FIG. 2 the bumper reinforcement 14 has a length and includes three members joined together. That is, the bumper reinforcement 14 is divided into three sections.

(15) As shown in FIG. 2, a central part 14A extending section X1 and lateral parts 14B extending sections X2 are joined by laser welding. The central part 14A and lateral parts 14B have unequal thicknesses; the thickness of the lateral parts 14B may be smaller than that of the central part 14A. In a preferred embodiment, the thickness of the central part 14A may be 2.0 mm, and the thickness of each lateral part 14B may be 1.6 mm, the thickness difference being 0.4 mm. In a preferred embodiment the bumper reinforcement 14 is manufactured using what is called a tailored blank. The joints of unequal thicknesses in the bumper reinforcement 14 originating from the tailored blank are indicated in FIGS. 2 and 3 with reference symbol S.

(16) In a preferred embodiment, the central part 14A and lateral parts 14B may be made of the same material, and typically of steel. However, other materials such as aluminum may also be used. A combination of different materials can be used as far as they can be welded.

(17) In a preferred embodiment the bumper reinforcement 14 may have a generally M-shaped open cross section. This is made because open cross sections can be most effective in strength. The width of the M-shaped open cross section may vary along the longitudinal direction.

(18) As shown in FIG. 2, a central section indicated by Y1 has a relatively narrow constant width. The section Y1 will be called the central narrower section. End sections indicated by Y3 has a relatively wide constant width. The section Y3 will be called the end wider section.

(19) The intermediate section between sections Y1 and Y3 is gradually widened from the width of section Y1 to that of section Y3. This section Y2 will be called an intermediate widening section.

(20) FIG. 4 shows the narrower cross section of the central part 14A within section Y1. FIG. 5 shows a wider cross section of the lateral parts 14B within section Y3. Sections Y2 have a transitional cross section that gradually widens from the narrower cross section of section Y1 to the wider cross section of Y3.

(21) The cross section of the central part 14A within section Y1 shown in FIG. 4, as compared to the cross section of the lateral parts 14B within section Y3 shown in FIG. 5 and described later, has narrower width W1 and larger height H1. This is because in order to allow more air flow to be supplied to the radiator, which is positioned behind the central part 14A to cool the engine. This requires the cross-sectional width W1 to be as narrow as possible while ensuring the required strength.

(22) The elements of the M-shaped open cross section shown in FIG. 4 generally include a front 14a, a top 14b and a bottom 14c. The front 14a has what is called a impact surface in the event of a vehicle collision, which has a recess 14d depressed rearward in the middle in consideration of ensuring strength. Flanges 14e extend vertically from the rear open edges of the top 14b and bottom 14c.

(23) The cross section of the lateral parts 14B shown in FIG. 5, compared to the cross section of the central part 14A shown in FIG. 4 described above, has a larger width W2 and a smaller height H2. That is, the cross-sectional width W2 is wider than the cross-sectional width W1. The width gradually widens from the cross-sectional width W1 and become constant at the cross-sectional width W2. This widening is possible because the lateral parts 14B that do not require so much strength in a collision as the central part 14A described above. In addition, the widening is made to ensure an area enough to mount the crash box 18.

(24) In a preferred embodiment, lateral portions are bent towards the rear relative to the central portion, thereby improving the appearance of the bumper structure. In a preferred embodiment, the cross-sectional width is bent and widened from the boundary of sections Y1 and Y2 toward sections Y2 and Y3. In a preferred embodiment the tailored blank is characterized in that the unequal thickness joints S are located within the intermediate widening sections Y2. This prevents or reduces wrinkles from being formed in the flange 14e in the hot pressing described below.

(25) As shown in FIGS. 2 and 5, at each end there is mounted a crash box that serves as a bumper support structure 18. The mounting position is indicated in phantom lines. Placing the crash box 18 in this position means placing it into the opening of the M-shaped open cross section, as shown in FIG. 5. This provides the crush box 18 with a longer energy absorbing length, which is efficient. However, the bumper support structure 18 does not necessarily comprise a crash box. When some other requirement requires the cross-sectional width of the end portions to be wider, a variety of support structures may be used.

(26) Now a process for manufacturing the bumper reinforcement 14 as described above will be described with reference to FIG. 6. First, in a blank preparation step, blanks for the central part 14A and lateral parts 14B of the bumper reinforcement 14 are provided. The blanks are each made in advance in a predetermined size. Specifically, the blanks are formed such that the joint S of unequal thicknesses comes within the intermediate widening section Y2 when formed in the later hot press step.

(27) In a tailored blank preparation step, the planar blank for the central part 14A and a planar blank for the lateral parts 14B, prepared as above, are then joined together by laser welding. This yields a planar blank having a predetermined shape for forming the bumper reinforcement 14. The welding may also performed by plasma welding.

(28) In a hot pressing step, the planar blank thus prepared in the predetermined shape is then heated to a predetermined temperature suitable for hot forming, and hot pressed between an upper 22 and a lower die 24 into the product form as shown in FIG. 2. It should be noted that the cross-sectional view for the hot pressing step shows the width of the bumper reinforcement 14, which is different from the cross-sectional views for the other steps which show the length of the bumper reinforcement 14.

(29) FIG. 7 indicates wrinkles formed in the flange 14e when forming the bumper reinforcement 14 in the hot press step described above. The hot press step in the embodiments described above eliminates low strength regions, preventing the wrinkle concentration in low strength regions as is the case in the prior art that uses cold press forming.

(30) Further, as shown in FIG. 7, the joint S of unequal thicknesses provides a ridge which separates wrinkles being formed in the curved portion and the intermediate widening section Y2, and disperses the wrinkles into the central section X1 and the end sections X2, thereby preventing or reducing wrinkles.

(31) In order to improve the strength of the bumper reinforcement 14 in the embodiment described above, a bracket such as a stiffener plate may be mounted to the flange 14e. This allows the welding to be performed by spot welding, resulting in a lower cost.

(32) While specific embodiments of the present invention have been described, those skilled in the art can make various modifications and substitutions without departing from the purpose and spirit of the present invention.