1. Field of Invention
The present invention relates to an outer panel for a pillar of a vehicle, and an apparatus and a method for manufacturing the same. More particularly, it relates to an outer panel for a center pillar which can enhance energy absorption efficiency during collision, and a rolling apparatus and a rolling method for manufacturing the same.
2. Description of Related Art
In general, a shape of a vehicle is formed by assembling pressed panels such that the pressed panels correspond to various parts of a vehicle body frame, and a center pillar of the vehicle also is formed by assembling a plurality of panels.
A general center pillar is formed by assembling an outer panel and an inner panel, and a space between the outer panel and the inner panel has a closed cross-section. A reinforcing panel is installed in the space or a filling material for preventing introduction or transfer of noise is filled.
FIGS. 1 and 2 are views showing an outer panel of a center pillar. FIG. 1 shows an outer panel 2 manufactured through a hot stamping method, and FIG. 2 shows an outer panel 2 manufactured by applying a TRB method.
According to the related art, a center pillar outer panel 2 is manufactured through a hot stamping method to reduce weight while improving strength, and a reinforcing panel is installed inside the outer panel to reinforce strength.
However, since a panel manufactured through a hot stamping method has too high a strength, a deformation of the pillar becomes excessive due to a fracture during a side collision. Thus, a technology of manufacturing a panel by applying a tailor rolled blank (TRB) method is known.
The TRB is a rolling technology for producing materials with difference in thickness by changing a gap between rollers during rolling. Since the TRB allows a high strength and a light weight at a part of a product, reduces the number of production processes, and improves structural strength, it is widely used in producing vehicle body parts having different thicknesses.
When the TRB technology is applied to manufacturing of a panel, a panel (outer panel) can be manufactured with a plurality of sections having different thicknesses along a lengthwise direction (a longitudinal direction, that is, a heightwise direction with respect to the vehicle body).
When the variable longitudinal thickness shape is applied, a thickness of a portion requiring a high strength can be relatively large. Thus, an existing reinforcing panel can be deleted and light weight can be achieved as the reinforcing panel is deleted.
A prior technical document applying the TRB technology in manufacturing a vehicle body panel includes Korean Patent Application Publication No. 10-2009-0024880 (published on Mar. 10, 2009). A technology of overlapping two steel plates between a work roll at an upper end of a rolling machine and a work roll at a lower end thereof is well known in the prior document, but one panel is generally TRB rolled to manufacture a panel having a variable thickness structure.
International Publication No. WO 2012/126697 discloses a technology of manufacturing a panel for a center pillar having a thickness difference with respect to a longitudinal cross-sectional thereof by applying the TRB technology.
FIG. 3 is a view showing a thickness change of a cross-section taken along line A-A of FIG. 2, and shows that the thickness of a panel 2 is varied (graded) according to locations of the panel 2 along a lengthwise direction thereof when the TRB method is applied.
Referring to FIG. 3, a thickness of a vertically intermediate portion (portion ‘c’) of the panel 2 to which a door supporting force is applied is made large to locally reinforce the panel 2, and a thickness of a portion (portion ‘d’) where a reinforcing panel is located is made larger on the upper side of portion ‘c’.
FIG. 4 is a view showing a rolling apparatus to which the TRB method is applied. In order to manufacture an outer panel having a variable thickness structure, a steel plate 1 that is a panel material passes between upper and lower rolling rollers 11 and 12 to perform TRB rolling to grade a thickness of the steel plate, and an outer panel having a desired shape is finished through a press process including drawing and trimming and a succeeding process such as hole processing.
Here, the TRB rolling process, a thickness of the rolled steel plate 1 is varied by controlling vertical locations of the two upper and lower rolling rollers 11 and 12.
However, since a panel manufactured through the TRB method has a thickness difference along a longitudinal direction (heightwise direction) of the panel, it may be fractured and may cope with absorption of collision energy only in a longitudinal direction thereof.
As shown in FIG. 5, in the center pillar according to the related art, opposite side surfaces 2b of an outer panel 2 may be fractured or a welding point of a flange 2c may be fractured due to strong collision energy in a cross-section where the outer panel 2 and an inner panel 3 are bonded to each other during a side collision thereof.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.