Patent Publication Number: US-2022219759-A1

Title: Reinforcement for a vehicle structural member and method for manufacturing the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. National Phase entry of, and claims priority to, PCT Application No. PCT/JP2019/025876, filed Jun. 28, 2019, which claims priority to Japanese Patent Application No. 2018-127705, filed Jul. 4, 2018, both of which are incorporated herein by reference in their entireties for all purposes. 
    
    
     BACKGROUND 
     The present disclosure relates to a reinforcement for a vehicle structural member and a method for manufacturing the same. 
     A vehicle, such as an automobile, typically includes pillars on its sides, serving as structural members, Such pillars include a front pillar, commonly referred to as an A-pillar, a. center pillar, commonly referred to as a B-pillar, and a rear pillar, commonly referred to as a. C-pillar, arranged from the front to the rear of the automobile. Among these pillars, the center pillar is particularly required to have a structural strength to resist a side collision with an automobile. The center pillar is therefore provided with a reinforcement, which may be called a hinge reinforcement, to reinforce its strength. 
     The pillar may be provided with a mounting portion for attaching an additional vehicle part situated near the pillar, and therefore need strength for this attachment purpose. For example, a lock striker that keeps a side door in the closed position may be attached to the center pillar. The hinge reinforcement, which is a reinforcement of the center pillar, is provided with a flat surface portion for attaching the striker. 
     The center pillar is elongated and has a closed cross section comprising an outer panel having a hat-shaped cross section and a planar inner panel. The hinge reinforcement is arranged within the closed cross section of the center pillar and is joined to the outer panel by welding, or other means, to reinforce the center pillar. 
     Since placed inside the closed cross section of the center pillar, the hinge reinforcement is elongated and has a U--shaped cross section, in accordance with the inner surfaces of the outer panel of the hat-shaped cross section. The configuration of U-shaped cross section comprises a top wall in the middle in the width direction (vehicle front-rear direction) and opposite lateral walls extending from the opposite edges of the top wall, bent to form ridges. The hinge reinforcement includes, in one of the lateral walls, a flat surface portion for mounting the lock striker, which is an additionally attached part mentioned above. 
     Hinge reinforcements are formed by pressing. A single steel sheet is bent by pressing into a U-shaped cross section (see Japanese Patent Application Publication No. 2013-220807). The press forming process typically employs two kinds of press forming dies, one for drawing and the other for unbending. 
     Another technique in this field is described in Japanese Patent Application Publication Nos. 2002-254114 and 2015-066584. 
     SUMMARY 
     The material used for the hinge reinforcement tends to have a higher strength, due to the recent demand for improved performance against side impact. Wrinkles, once formed during a press forming process when a high-strength material is used, are difficult to be smoothed and flattened within the same press forming process. In other words, when the material strength is not high, any wrinkles formed during the forming process can be smoothed and flattened at the final pressing step of the forming process. However, in the case of a high-strength material, wrinkles once formed are difficult to be flattened in the subsequent pressing step because of the high strength of the material. Moreover, it is difficult to remove wrinkles by other means after the press forming process. It should be noted that the wrinkles considered a problem herein are undulation formed. during the press forming process. 
     It is therefore needed to prevent formation of wrinkles when press forming the striker mounting flat surface portion of the lateral wall of the hinge reinforcement described above, or any other portions where a highly accurate flatness without wrinkles or undulation is required after press forming. 
     When press forming a reinforcement having a flat surface portion for attaching an additional part, it is thus desired to prevent or suppress formation of undulation or wrinkles in the flat surface portion, even when using a high-strength material. 
     One aspect of the present disclosure provides a reinforcement for a vehicle structural member, comprising a top wall, and opposite lateral walls extending from opposite edges of the top wall. At least one of the lateral walls includes a flat surface portion for mounting an additional vehicle part. The flat surface portion has an edge forward in a press direction in which the reinforcement is pressed, the edge being curved and convex in the press direction. 
     In some embodiments, the vehicle structural member is a pillar installed on a side of the vehicle, and the reinforcement is a hinge reinforcement for reinforcing the pillar. 
     In some embodiments, the additional vehicle part is a striker for)cking a vehicle door, and the striker is attached to the flat surface portion. 
     Another aspect of the present disclosure provides a method of manufacturing a reinforcement for a vehicle structural member according to any of claims  1  to  3 . The method comprises press forming the reinforcement with a press forming die. The press forming die includes a first die face corresponding to the flat surface portion of the lateral wall and a second die face corresponding to a portion of the lateral wall adjacent to the flat surface portion. The first die face is curved and convex forward in the press direction relative to the second die face. 
     In some embodiments, the step of press forming comprises drawing the reinforcement with a drawing die, and unbending the drawn reinforcement with an unbending die. The drawing die and the unbending die each include the first die face that is curved and convex. 
     In some embodiments, when press forming a vehicle reinforcement having a flat surface portion for mounting an additionally attached part, it is possible to prevent or suppress the formation of undulating wrinkles during press forming, even when using a high-strength material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall view of an exemplary center pillar arranged in a side of a vehicle, such as an automobile. 
         FIG. 2  is a cross-sectional view of the center pillar of  FIG. 1  taken along line II-II. 
         FIG. 3  is a front view of the top wall of the hinge reinforcement after the second step (in its final form) as seen from the outside of the vehicle, 
         FIG. 4  is a side view of the lateral wall on the vehicle rearward side of the hinge reinforcement of  FIG. 3  as seen from the direction of arrow IV. 
         FIG. 5  is a side view of the lateral wall on the vehicle forward side of the hinge reinforcement of  FIG. 3  as seen from the direction of arrow V. 
         FIG. 6  is an enlarged view of a flat surface portion of the hinge reinforcement for mounting a lock striker, in circle VI defined in  FIG. 5 , 
         FIG. 7  is an enlarged perspective view of a welding projection formed in a lateral wall of a hinge reinforcement. 
         FIG. 8  is a conceptual sketch of a general configuration of a drawing process of a hinge reinforcement. 
         FIG. 9  is a conceptual sketch of a general configuration of an unbending process of a reinforcement, 
         FIG. 10  is a cross-sectional view of a lock striker attached to a center pillar. 
         FIG. 11  is a front view of the top wall of a hinge reinforcement after the first step (after the drawing step) as seen from the outside of the vehicle. 
         FIG. 12  is a side view of the lateral wall on the vehicle rearward side of the hinge reinforcement of  FIG. 11  as seen from the direction of arrow XII 
         FIG. 13  is a side view of the lateral wall on the vehicle forward side of the hinge reinforcement of  FIG. 11  as seen from the direction of arrow XIII 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described below with reference to the drawings. in one embodiment, the vehicle structural member is a center pillar, which is one of the pillars of a side of an automobile or other vehicle, and the reinforcement is a hinge reinforcement that reinforces the center pillar. The directional terms used in the following descriptions basically refers to the direction based on the vehicle in the normal position, In each figure, arrow FR indicates the vehicle forward direction, arrow UP the vehicle upward direction, and arrow IN the vehicle inward direction. 
       FIG. 1  shows the exterior of the center pillar  10  for an automobile or other vehicle, and  FIG. 2  shows a cross section of the center pillar  10  of  FIG. 1  taken along line II-II. The center pillar  10  shown in  FIG. 1  is that of the left side of the vehicle. In addition to the center pillar  10 , a front pillar (not shown) and a rear pillar (not shown) may be arranged in the side of the vehicle, as vehicle structural members. The strength of the center pillar  10 , among these pillars, is considered important because of the need for countermeasures against a side collision with an automobile. Therefore, as shown in  FIG. 2 , the center pillar  10  is provided with a hinge reinforcement  20  to reinforce its strength. In one embodiment, a high-strength steel sheet may be used, as will be further described later, to satisfy the recent demand for even higher strength. 
     As shown in  FIGS. 1 and 2 , the center pillar  10  includes an elongated outer panel  12  that forms the vehicle outer side of the center pillar  10  and an elongated inner panel  14  that forms the vehicle inner side of the center pillar  10 . The center pillar  10  further includes a hinge reinforcement  20  arranged inside the outer panel  12 . 
     The outer panel  12  has a hat-shaped cross section, open toward the inside of the vehicle, and includes a top wall  12 A, lateral walls  12 B, and flanges  12 C. The top wall  12 A is situated on the vehicle outer side (lower side as seen in  FIG. 2 ), and the left and right lateral walls  12 B extend toward the vehicle inner side (upward as seen in  FIG. 2 ) from the opposite edges of the top wall  12 A. The left and right lateral walls  12 B are inclined such that the distance between them increases toward the inside of the vehicle (upward as seen in  FIG. 2 ). The flanges  12 C extend in opposite directions from the inward edges (upward edges in  FIG. 2 ) of the lateral walls  121 . The flanges  12 C extends parallel to the top wall  12 A. 
     When it is needed to distinguish between the symmetrically arranged lateral walls  12 B and flanges  12 C in the following descriptions, those on the vehicle rearward side (right side as seen in  FIG. 2 ) will be denoted by their reference symbols followed by an “r,” and those on the vehicle forward side (left side) by their reference symbols followed by an “f.” 
     As shown in  FIG. 2 , the inner panel  14  is generally planar, and the flanges  14 C extends outward from the opposite side edges on the vehicle forward and rearward sides (left and right ends as seen in  FIG. 2 ) The flanges  14 C of the inner panel  14  are held against the flanges  12 C of the outer panel  12  in the vehicle width direction and joined thereto by spot welding to firm a closed cross section. The welding spots are indicated by dots in  FIG. 1  and crosses in  FIG. 2 . The welding method is not limited to spot welding, but may instead be other welding methods, such as laser welding. 
     As shown in  FIG. 1 , the center pillar  10  is arranged in a vertical position in the vehicle. The center pillar  10  is gently curved, such that it is convex toward the vehicle outside in the middle of its length. The center pillar  10  is inclined rearward of the vehicle at the upper end relative to the lower end. 
     As shown in  FIGS. 1 and 2 , the elongated center pillar  10  has a closed cross section, and thus defines an interior space. The center pillar  10  is joined to the roof side rail  18  via a generally T-shaped attachment portion  16  at the upper end of the outer panel  12 . The center pillar  10  is also joined to the side sill  19  via a generally T-shaped attachment portion  17  at the lower end of the outer panel  12 . 
     The outer panel  12  may be made of a sheet of steel having a tensile strength of 1180 MPa or more. In one embodiment, a sheet of 1470 MPa high-strength steel may be used. The outer panel  12  may be formed by a room temperature pressing, a cold pressing, or a hot stamping. The inner panel  14  may be made of a sheet of steel having a tensile strength equal to or lower than the tensile strength of the outer panel  12 . In a particular embodiment, a 590 MPa steel sheet may be used. The inner panel  14  is formed by a room temperature press, 
     The hinge reinforcement  20  arranged in the interior space of the center pillar  10  will now be described. As best shown in  FIG. 2 , the hinge reinforcement  20  is disposed along the inner surface of the outer panel  12  of the center pillar  10 . The hinge reinforcement  20  includes a top wall  20 A and lateral walls  20 B. 
     To be arranged along the inner surface of the outer panel  12  of the center pillar  10  as described above, the hinge reinforcement  20  has a generally U-shaped cross section. The top wall  20 A is positioned along the inner side of the top wall  12 A of the outer panel  12 . The two lateral walls  205  as seen in  FIG. 2  are positioned along the inner sides of the lateral walls  125  of the outer panel  12 . The two lateral walls  20 B extend continuously from the opposite edges of the top wall  20 A toward the vehicle inside (upward as seen in  FIG. 2 ), forming the ridge lines L 1 . The lateral walls  205  of the hinge reinforcement  20 , like the lateral walls  125  of the outer panel  12 , are inclined in a direction in which the distance between them increases toward the vehicle inside (upward as seen in  FIG. 2 ). 
     As with the outer panel  12 , when it is needed to distinguish the symmetrically arranged left and right lateral walls  20 B of the hinge reinfbrcement  20 , that on the vehicle rearward side (right side as seen in  FIG. 2 ) will be denoted by its reference symbol followed by an “r,” and that on the vehicle forward side (left side as seen in  FIG. 2 ) by its reference symbol followed by an 
     The vehicle doors (not shown) are arranged on the forward and rearward sides of the center pillar  10  shown in  FIG. 1 . (left and right sides as seen in  FIG. 1 ). A front door is arranged on the forward side of the center pillar  10 , and a rear door is arranged on the rearward side of the center pillar  10 . The front door is opened and closed by one or more door hinges secured to the front pillar, and is locked onto the center pillar  10  by a lock striker  30  secured to the center pillar  10 . As shown in  FIG. 1 , the lock striker  30  is positioned on the forward side of the center pillar  10 , near the lower end. Although the position of taking the cross section of the center pillar shown in  FIG. 2  differs from the position of the lock striker  30 , the lock striker  30  is shown in  FIG. 2  by two-dot chain lines for an image of where in the forward lateral wall  125   f  and  205   f  the lock striker  30  is located. 
       FIG. 10  shows a lock striker  30  mounted to the center pillar  10  in a specific embodiment, In this figure, the outer panel  12 , the inner panel  14 , and the hinge reinforcement  20  are drawn with thickness omitted. As can be seen from  FIG. 10 , the lock striker  30  is arranged. on the forward lateral walls  12 B f  and  205 f of the outer panel  12  and hinge reinforcement  20 , The lock striker  30  is mounted to the lateral walls  125 f and  20 B f  on the lock striker base  31  by a fastener  36 , such as bolt and nut. An exterior panel  38  covers the outer side of the outer panel  12 , 
       FIGS. 3 to 5  show the overall configuration of the hinge reinforcement  20 . The hinge reinforcement  20  shown is in a form as a final product of the press forming process, which will be described later,  FIG. 3  is a view of the top wall  20 A of the hinge reinforcement  20  as seen from the vehicle outside.  FIG. 4  shows a lateral wall  20 B r  on the vehicle rearward side of the hinge reinfbrcement  20  of  FIG. 3  as viewed from the direction of arrow IV.  FIG. 5  shows a lateral wall  20 B f  on the vehicle forward side of the hinge reinforcement  20  shown in  FIG. 3  as viewed from the direction of arrow V. As shown in these drawings, the hinge reinforcement  20  is elongated, and, as shown in  FIGS. 4 and 5 , the hinge reinforcement  20  is gently curved such that it is convex toward the vehicle outside. 
     The hinge reinforcement  20  is formed by pressing, As the material for the press forming, a sheet of high-strength steel may be used to enhance the performance against lateral collision. The tensile strength of the steel may be 980 MPa or more. In some embodiments, a high-strength steel sheet of 1180 MPa may be used, The thickness of the steel sheet is, for example, about 1 to 2 mm The single sheet of high-strength steel is press-formed by a room temperature pressing, a cold pressing, or a hot stamping. 
     Although not shown in  FIGS. 3 to 5 , but as shown in  FIG. 2 , the top wall  20 A of the hinge reinforcement  20  is joined by spot welding to the inner surface of the top wall  12 A of the outer panel  12  of the center pillar  10 . For this joining purpose, the top wall  20 A of the hinge reinforcement  20  includes welding projections  22 , each projecting from the top wall  20 A toward the outside of the vehicle by a height to form a raised welding surface  23 . The welding projections  22  are scattered along the vertical direction of the vehicle. 
     The outer surface of the welding projection  22 , i.e. the raised welding surface  23 , is flat, as shown in  FIG. 2 , in order to secure the strength of the spot welding joint with the top wall  12 A of the outer panel  12 . In some embodiments, the shape of each welding projection  22  may be semicircular or circular. However, in other embodiments, it may take various other shapes, such as a rectangle, triangle, ellipse, or hexagon. 
     The center pillar  10  and the hinge reinforcement  20  may also be welded between the lateral walls  12 B of the outer panel  12  and the lateral walls  20 B of the hinge reinforcement  20  at the spots indicated by crosses in  FIG. 2 . Accordingly, the lateral walls  20 B r,    20 B f  of the hinge reinforcement  20  shown in  FIGS. 4 and 5  each include a plurality of welding projections  25 , each forming a raised welding surface  26 . In  FIGS. 4 and 5 , however, the welding projections  25  of the lateral walls  20 B r,    205   f  are omitted. The welding projections  25  are raised toward the lateral walls  12 B of the outer panel  12 , and are scattered in the vertical direction of the vehicle. The raised welding surface  26  of each welding projection  25  is joined by spot welding to the inner surface of the lateral wall  12 B. 
       FIG. 7  schematically shows the welding projections  25  in the lateral wall  20 B of the hinge reinforcement  20 . Each welding projection  25  is raised outwardly from the lateral wall  20 B of the hinge reinforcement  20  by a height T 1 . As shown in  FIGS. 2 and 7 , each welding projection  25  is raised outward from the hinge reinforcement  20  in an area that extends over the entire width of the lateral wall  205 , from the ridge line L 1 , which is formed between the lateral wall  20 B and the top wall  20 A, to the edge of the lateral wall  20 B on the vehicle inner side. Each welding projection  25  has a sideways trapezoidal front shape, with a width W 1  at the edge adjacent the ridge line L 1  being narrower than a width W 2  at the edge on the vehicle inward side. The edge of each welding projection  25  adjacent the ridge line L 1  is beveled diagonally toward the ridge line L 1 . 
     The outer surface of each welding projection  25 , that is, the raised welding surface  26 , is flat, as shown in  FIGS. 2 and 7 , in order to secure the strength of the spot welding joint with each lateral wall  125  of the outer panel  12 . Accordingly, the raised welding surthce  26  has a flat surface which extends from the edge  27  of the lateral wall  20 B adjacent the ridge line L 1  to the edge of the lateral wall  2013  on the vehicle inward side, and which has a sideways trapezoidal front shape, with the length of the edge  27  adjacent the ridge line LI being smaller than the length of the edge  28  on the vehicle inward side. 
     As shown in  FIG. 5 , the lateral wall  2013 f of the hinge reinforcement  20  on the. vehicle front side includes, in an area near the lower end, a flat surthce portion  32  for attaching the lock striker  30  that locks the front door to the closed. position. The shaded area in  FIG. 5  indicates the striker mounting flat surface portion  32 . The same area is shown enlarged in  FIG. 6 , in which the position where the lock striker  30  is to be arranged is shown by two-dot chain lines. The lock striker  30  is secured to the lateral wall  12 B of the outer panel  12  and to the lateral wall  20 B of the hinge reinforcement  20  via a planar lock striker base  31  supporting the body of the lock striker  30 . The striker mounting flat surface portion  32  is therefbre required to be formed flat without wrinkles and wrinkles. 
     The flat surface portion  32  shown in  FIG. 6  has an end edge  32 A on the vehicle inward side which is formed convex toward the inside of the vehicle (downward as seen in  FIG. 6 ) in the press forming process. The convex edge may be, for example, smoothly and gently curved. The fiat surface portion  32  is formed in the process of press forming the hinge reinforcement  20 . 
     A method of manufacturing the hinge reinforcement  20  by press forming will now be described with reference to  FIGS. 8 and 9 . The present method includes a drawing process as a first step, and an unbending process as a second step.  FIG. 8  shows the arrangement of forming dies in the drawing process, and  FIG. 9  shows the arrangement of forming dies in the unbending process.  FIGS. 8 and 9  both illustrate the press forming of the flat surface portion  32  in the cross section taken along the line VII-Vii of  FIG. 5 . The direction of pressing the hinge reinforcement  20  is indicated in  FIGS. 4 and 5  by white arrow P. 
       FIG. 8  illustrates the drawing process of the first step. The drawing die includes a fixed lower die  40 , a movable upper die  42 , and cushioning dies  44  arranged on opposite sides of the lower die  40 . The upper die  42  integrally includes a first portion  42 A for drawing the lateral wall  20 B f  on the forward side and a second portion  42 B for drawing the lateral wall  20 Br on the rearward side. The cushioning die  44  follows the movement of the upper drawing die  42 . 
     The die face form of the portion  42 A of the upper die  42  for forming the lateral wall  20 B f  of the hinge reinforcement  20  will now be described. As shown in  FIGS. 5 and 6  at D 1  by a solid line, the portion of the die face that forms the striker mounting flat surface portion  32  has a convex surface, similar to the above-mentioned convex edge  32 A of the fiat surface portion  32  on the forward side in the pressing direction. That is, the convex surface of that portion of the die face is a smoothly and gently curved surface that swells forward in the pressing direction with reference to the die face forming the portions of the lateral wall  20 B f  adjacent to the flat surface portion  32 . A conventional, non-convex die face that forms the flat surface portion  32  is shown by a broken line D 1   a.  The conventional die face position is also shown in  FIG. 8 , with broken lines, The die face being convex means that the depth of drawing at the flat surface portion  32  is larger than that at the adjacent portions. 
       FIG. 9  illustrates an unbending process of the second step, The unbending die includes a fixed lower die  50 , a movable upper die  52 , and a pad  54  for holding the workpiece being pressed. The upper die  52  includes, separately, a first upper die  52 A for unbending the lateral wall  20 B f  and a second upper die  52 B for unbending the lateral wall  20 Br. The pad  54  holds the drawn product (workpiece) of the first step against the lower die  50 . The unbending process is performed with the workpiece held by the pad  54 . 
     As described above, the die face form of the upper die  52 A for unbending the lateral wall  20 B f  is similar to that of the portion  42 A of the upper die  42  forming the lateral wall  20 B f  in the above-mentioned drawing process. Specifically, the die face fbrm of the upper die  52 A is as shown in  FIGS. 5 and 6  by solid line D 2 . In the unbending process of the second step, the portion of the die face of the upper die  52 A forming the striker mounting flat surface portion  32  has a convex surface, similar to the convex edge  32 A of the flat surface portion  32  on the forward side in the pressing direction, That is, the convex surface of that portion of the die face is a smoothly and gently curved surface that swells forward in the pressing direction with reference to the die face forming the portions of the lateral wall  20 B f  adjacent to the flat surface portion  32 . The conventional die face position is indicated by a broken line D 2   a,  as in the ease of drawing process in the first step. 
     As mentioned above, the press forming of the hinge reinforcement  20  includes the drawing process of the first step and the unbending process of the second step described above. The form of the hinge reinforcement  20  in the middle of the forming process after—the drawing of the first step is shown in  FIGS. 11 to 13 . The final form of the hinge reinforcement  20  after the unbending of the second step is shown in  FIGS. 3 to 5  mentioned above.  FIG. 11  showing the form in the middle of the forming process is a view of the top wall  20 A of the hinge reinforcement  20  as seen from the outside of the vehicle.  FIG. 12  shows the lateral wall  20 B r  on the vehicle rearward side of the hinge reinforcement  20  of FIG. II as viewed from the direction of arrow XII.  FIG. 13  shows a lateral wall  20 B f  on the vehicle forward side of the hinge reinforcement  20  of  FIG. 11  as viewed from the direction of arrow XIII The pressing direction is indicated by white arrow P in each of these drawings as well. The press forming of the hinge reinforcement  20  is performed by pressurizing in the direction of arrow P. Note that in  FIGS. 11 to 13 , the welding projections  22  and  25  are not shown, as with  FIGS. 3 to 5 . 
     In  FIG. 9  showing the unbending process of the second step, the two-dot chain lines indicates the cross-sectional form of the lateral wall  20 B of the hinge reinforcement  20  ( FIGS. 11 to 13 ) after the drawing process of the first step shown in  FIG. 8 . The hinge reinforcement  20  of this form is pressed by the upper unbending die  52 , as shown by arrows in  FIG. 9 , into the form indicated by solid lines. 
     The striker mounting flat surface portion  32  of the lateral wall  20 B f  on the vehicle forward side is formed during the press forming of the hinge reinforcement  20 , For the purpose of forming the flat surface portion  32 , the die face forming the flat surface portion  32  of each of the drawing and unbending upper dies  42 A,  52 A for the first and second steps is convex in the pressing direction at the forward edge. As a result, in the press forming process of either step, the forward edge pushes material from the center of the convex surface to both sides so that excess material due to the forming is moved aside without staying within the flat surface portion  32  and thus leveled off. This process prevents surface undulation from being formed in the area for the flat surface portion in the press fbrming of the flat surface portion  32 . That is, the process prevents or suppress formation of wrinkles due to surface undulation. 
     When high-strength steel is used as the material for the press forming, wrinkles or surface undulation once formed in the area for the fiat surface portion during the press forming process are difficult to be flattened. Since the die face forming the striker mounting flat surface portion  32  is convex from the first, drawing step onward, as described above, wrinkles are prevented or suppressed even during press forming. This allows the flat surface portion  32  to be formed flat with high accuracy, As a result, the lock striker  30  can be accurately and reliably attached to the flat surthce portion  32 . 
     In the present embodiment, press forming is performed in the two steps of drawing and unbending process. Therefore, the product (workpiece) of the drawing step may have a series of shock lines caused by the drawing. Such shock lines are not so much as to affect the flatness, although they will not be removed by the subsequent unbending process. 
     In the above embodiments, the vehicle structural member is a center pillar and the reinforcement is a hinge reinforcement that reinforces the center pillar. However, in another embodiment, they may be another kind of pillar and reinforcement. Alternatively, they may be a vehicle structural member other than a pillar and a vehicle structural member for it. 
     The additional part attached to the lateral wall of the hinge reinforcement has been described as a lock striker for locking the vehicle door. However, in another embodiment, it may be a part other than a lock striker. 
     The additionally attached part has been described as being mounted to one of the lateral walls of the hinge reinforcement. However, in another embodiment, such parts may be attached to both lateral walls. 
     The press forming of the hinge reinforcement has been described as performed in two steps i.e. the drawing and unbending processes. However, in other embodiments, it may be performed in one step or in three or more steps. 
     In the embodiments described above, one of the lateral walls of the reinforcement includes a flat surface portion for mounting an additional vehicle part, and the flat surface portion has an edge forward in the direction of pressing the reinforcement, the forward edge being curved and convex in the press direction. As a result, during the process of press forming the flat surface portion, material in the forward edge in the pressing direction is pushed from the center of the convex shape to both sides so that the excess material due to the forming is moved aside without staying within the flat surface portion and thus leveled off. This effect of the pressing continues from the beginning to the end of the press forming process. This prevents or suppresses formation of wrinkles in the flat surface portion, and allows to form a highly accurate flat surface shape. As a result, the additional part can be attached with high accuracy. 
     In the above embodiments, the structural member for the vehicle is a pillar in a side of the vehicle, and the reinthrcement is a hinge reinforcement reinforcing the pillar. In this case, the flat surface portion for attaching additional parts to the hinge reinforcement can be formed. flat while preventing or suppressing formation of wrinkles. Therefore, the form of the pillar member reinforced by the hinge reinforcement can be made accurate. 
     In the above embodiments, the additional vehicle part is a striker for locking the vehicle door, and the striker—is attached to the flat surface portion. This configuration allows the striker mounting flat surface portion to be formed flat with no or reduced wrinkles, resulting in the lock striker being mounted with high accuracy. 
     In the above embodiments, the reinforcement is manufactured by press forming with a press forming die, wherein the press forming die includes a first die face corresponding to the flat surface portion of the lateral wall and a second die face corresponding to a portion adjacent to the flat surface portion of the lateral wall, and the first die face is curved and convex in the pressing direction relative to the second die face. The use of press forming die having such a die face in press forming a reinforcement such as a hinge reinforcement allows the flat surface portion to be formed flat while preventing or suppressing wrinkles. 
     In the above embodiments, the step of press forming includes drawing the reinforcement with a drawing die and unbending the drawn reinforcement with an unbending die, wherein the drawing and unbending dies each have the above-mentioned curved and convex first die face. The use of these drawing and unbending dies in the press forming prevent or suppress formation of wrinkles in the flat surface portion in a more reliable way. 
     While described above referring to specific embodiments, the present disclosure is not limited to these examples, and those skilled in the art can make various substitutions, improvements, and/or modifications without departing from the objective of the present disclosure.