PRESS FORMING METHOD AND PRESS FORMING APPARATUS FOR EXTERNAL AUTOMOTIVE PANELS

Abstract

A press forming method for an external automotive panel according to the present invention is a method for press forming a sheet metal 51 into an external automotive panel 61 having a character line 63 and panel surface portions 65a and 65b using a punch 3, a die 5, and a workpiece holder 7.The press forming method includes: a step of providing an elastic body 9 that protrudes towards the punch side 3 over the forming surface portion of the die side 5b, forming the panel surface portion 65a and bringing the elastic body 9 into contact with a sheet metal 51 before the die 5; and a press forming step while the elastic body 9 is being crushed and pressure from the sheet metal 51 causes the elastic body 9 to protrude from the forming surface portion of the die side 5b such that a frictional force between the crushed elastic body 9 and the sheet metal 51 is equal to or greater than an absolute value of the difference between the stresses acting on both sides of a portion 53 corresponding to the character line 63.

Description

PRESS FORMING METHOD AND PRESS FORMING APPARATUS FOR EXTERNAL AUTOMOTIVE PANEL FIELD OF INVENTION The present invention relates to a press forming method and press forming apparatus for an automotive exterior panel, wherein a character line is formed by press forming. In the present invention, a metal sheet refers to a hot-rolled sheet, a cold-rolled sheet, or a steel sheet surface-treated with a surface treatment (electrogalvanizing, hot-dip galvanizing, or organic coating treatment and the like) applied to a steel sheet, as well as a sheet made of various metals such as stainless steel, aluminum, and magnesium. BACKGROUND OF THE INVENTION External automotive panels used for the exterior of doors, front bumpers, rear bumpers, and similar components are frequently marked with a character line on their outer surface to improve the design capabilities and tensile rigidity of automobiles. The character line is usually created by pressing a (smooth) sheet of metal against a ridge formed on a punch in a press mold and sandwiching this ridge with valley lines from a die. Especially in recent years, to further enhance the design capabilities of automobiles, it has become necessary to provide a character line that is shaped (i.e., the curvature of the ridge is large, with a small radius of curvature). Incidentally, in this type of press forming, when the stress generated in the sheet metal during forming is unbalanced, the sheet metal can slip in a direction of high stress. The punch ridge can then contact a portion other than the portion intended to be given the character line, resulting in a linear pattern. This linear pattern remains even after coating, and it is a cosmetic defect called an external panel offset line. The offset line is a hindrance to improving automotive design capabilities because it is especially noticeable when press forming is performed to provide a shape character line using a punch in which the tip of the ridge is formed by an arc with a small section radius. So far, several techniques have been proposed to restrict the generation of that linear pattern and provide a character line. For example, Patent Literature 1 describes a press forming method for providing a die and a workpiece holder in the form of an auxiliary cross-section of a design cavity to sandwich a peripheral edge of a flat part, such that a central portion of the flat part is pre-bent and deformed along a punch forming surface and then forms a design surface by punch forming. Patent Literature 2 describes a method for preventing line displacement using a suction device, in which a suction hole is formed on a press surface provided with a linear projection to form the line of character, effecting suction from the suction hole via a gas flow path and adsorbing the sheet metal onto the press surface and forming this press, thereby restricting the movement of the sheet metal.Patent Literature 3 «ηορηη / ζζηζ / Β / γίΛΐ» describes a technique for performing primary press forming on a material by means of a punching angle and a cushioning pad and then effecting deep stretching and bulging as the punch descends, thereby preventing the displacement line from being generated in a portion of a metal material with which the punching angle is in contact. Patent Literature 4 describes a technique for removing the displacement line to obtain a high-quality press-formed product by means of a first press-forming step to form a preformed shape and a second press-forming step to further form the preformed shape, when producing the press-formed product having a ridge portion. Patent Literature 5 describes a technique for forming the character line on the smooth workpiece by means of a die pad made of an elastic body and a punch tip, and forming a portion other than the character line by means of the die and punch while the formed character line is constrained by the die pad and punch.Patent Literature 6 describes a technique for restricting the sliding of the smooth piece by pressing a plate-shaped smooth piece against a lower press-forming tool having a convex R portion to form the character line and putting a pressing pad in contact with the smooth piece in the vicinity of the convex R portion after the smooth piece is attached to the convex R portion. List Quote Patent Literature Patent Literature 1: Japanese Patent No. 5876786 Patent Literature 2: Japanese Patent Application Open to the Public No. 2015-199102 Patent Literature 3: Japanese Patent No. S63-58652 Patent Literature 4: Japanese Patent No. 5959702 Patent Literature 5: Japanese Patent Open to the Public No. 2018-158351 Patent Literature 6: Japanese Patent Open to the Public No. 2018-183786 BRIEF DESCRIPTION OF THE INVENTION Technical problem However, the techniques described in Patent Literatures 1 to 6 have the following problems. In the technique described in Patent Literature 1, the deformation by the die and the workpiece holder provided with the auxiliary cross-section forming is not restricted by the punch, and only the two ends of the smooth workpiece corresponding to the design cavity can be restricted, thus limiting this bending deformation to a linear shape. In the technique described in Patent Literature 2, a suction device is required, which is not used in ordinary press forming, and there is a concern that the shape of the suction hole will be transferred to a surface of the formed product. In the technique described in Patent Literature 3, since the shape of a final product is partially formed during forming, there is a concern that surface distortion may occur between a fully formed portion and an incompletely formed portion. In the technique described in Patent Literature 4, since the press forming tool for creating the preformed shape and the press forming tool for creating a target shape are different, the number of steps, such as replacing the press forming tool, has increased. In the technique described in Patent Literature 5, since the character line is formed by the elastic body, there is a concern that when a plurality of character lines are close to each other, the character line cannot be formed according to the target shape. In the technique described in Patent Literature 6, when the surface formation is complex, there is a concern that it may not be possible to establish an appropriate time for the pressure pad to come into contact with the smooth part, and the pressure pad may cause the smooth part to bend or flex. The present invention has been produced to solve the problems mentioned above, and an objective of the present invention is to provide the press forming method and press forming apparatus for the external automotive panel, in which the displacement line is prevented without increasing man-hours for press forming and the objective line is formed. Solution to the problem To solve the problem and achieve the object, a press-forming method for an external automotive panel, according to the present invention, press-forms a sheet metal in the external automotive panel having a character line and continuous panel surface portions on both sides of the character line using a punch, a die oriented towards the punch, and a workpiece holder oriented towards one end of the die, wherein the die includes an elastic body projecting towards the punch instead of a forming surface portion on the die side so that the elastic body can make contact with and press a portion away from the portion corresponding to the character line in the sheet metal.along the portion corresponding to the character line and is supported so that it can contract until a portion of the contact surface in contact with the sheet metal is level with the forming surface portion on the die side. The press forming method includes: a spring body contact step of moving the die relative to the punch side while both ends of the sheet metal are sandwiched between the die and the blank holder, to bring the spring body's contact surface portion into contact with the sheet metal before a portion of the sheet metal in contact with the punch elastically deforms; and a press forming step of further moving the die relative to the punch side upward to a bottom dead center while pressing the sheet metal by the spring body's contact surface portion to contract the spring body.where a protruding quantity of the elastic body from the forming surface portion of the die side is adjusted so that a frictional force provided by a product of a load from the elastic body pressing the sheet metal in the press forming step and a coefficient of friction between the elastic body and the sheet metal, is equal to or greater than an absolute value of a difference between the stresses acting on both sides sandwiching the portion corresponding to the character line. Furthermore, in the press forming method for the external automotive panel according to the present invention, the elastic body is supported on the die side by means of a movable device configured to press the elastic body towards the punch and press the sheet metal. «ηορηη / ζζηζ / Β / γίΛΐ Furthermore, in the press forming method for the external automotive panel according to the present invention, the elastic body presses a portion on one side that has low tension between portions on both sides that sandwich the portion corresponding to the character line. Furthermore, in the press forming method for the external automotive panel according to the present invention, the elastic body presses a portion on one side that has high tension between portions on both sides that sandwich the portion corresponding to the character line. Furthermore, a press forming apparatus for an external automotive panel, according to the present invention, includes: a punch; a die oriented towards the punch; and a workpiece holder oriented towards an end of the die, wherein the press forming apparatus forms a sheet of metal in the external automotive panel having a character line and continuous panel surface portions on both sides of the character line, wherein the die includes die-side forming surface portions that respectively form the panel surface portions on both sides of the character line, one of the die-side forming surface portions including a spring body projecting towards the punch as opposed to the die-side forming surface portion so that the spring body can come into contact with and press a position away from a portion corresponding to the character line in the sheet metal,along the portion corresponding to the character line and is supported to be contractile until a portion of the contact surface in contact with the sheet metal is level with the forming surface portion on the die side and a projecting amount of the elastic body is established from the forming surface portion on the die side so that a frictional force provided by a product of a load of the elastic body pressing the sheet metal in the press forming process and a coefficient of friction of the elastic body and the sheet metal, is equal to or greater than an absolute value of a difference between the stresses acting on the sides sandwiching the portion corresponding to the character line. Furthermore, in the press forming apparatus for the external automotive panel according to the present invention, the elastic body is supported on the die side by means of a movable device configured to press the elastic body towards the punch and press the sheet metal. Furthermore, in the press forming apparatus for the external automotive panel according to the present invention, the elastic body is provided over the die to press a portion onto a side that has low tension between portions or both sides that sandwich the portion corresponding to the character line. Furthermore, in the press forming apparatus for the external automotive panel according to the present invention, the elastic body is provided over the die to press a portion on one side that has high tension between portions on both sides that sandwich the portion corresponding to the character line. Advantageous Effects of the Invention According to the present invention, by projecting the elastic body from the forming surface portion of the die side and forming the sheet metal in a press while the elastic body is pressed against the sheet metal, a frictional force between the elastic body protruding from the forming surface portion of the die side and being crushed and the sheet metal can be greater than a difference between the stresses acting on both sides sandwiching the portion corresponding to the character line in the sheet metal and it is possible to form in a press the outer panel in which the displacement line generated by the difference between the stresses is prevented and the character line is formed. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a diagram illustrating a press forming apparatus for an external automotive panel according to a first embodiment of the present invention. Figures 2a to 2e are diagrams illustrating a press forming method for the external automotive panel according to the first embodiment of the present invention. Figure 3 is a diagram illustrating a load P that presses a sheet of metal by means of a flattened elastic body and the stresses F1 and F2 generated in the sheet of metal in a press forming process, in the press forming method for the external automotive panel according to the first embodiment of the present invention. Figures 4a to 4e are diagrams that illustrate another aspect of the press forming apparatus and the press forming method for the external automotive panel according to the first embodiment of the present invention. Figure 5 is a diagram illustrating a press forming apparatus for an external automotive panel according to a second embodiment of the present invention. Figures 6a to 6e are diagrams illustrating a press forming method for the external automotive panel according to the second embodiment of the present invention. Figures 7a to 7e are diagrams that illustrate another aspect of the press forming apparatus and the press forming method for the external automotive panel according to the second embodiment of the present invention. Figures 8a to 8d are diagrams illustrating a press forming apparatus and a conventional press forming method for the external automotive panel and a displacement line generated in the press forming process. Figure 9 is a diagram that illustrates a cross-sectional shape result of the outer panel obtained by press forming analysis in an example. Figure 10 is a diagram illustrating a result of an evaluation value As of the surface distortion of the outer panel obtained by press formation analysis in the example. DETAILED DESCRIPTION OF THE INVENTION Before explaining a press forming method and a press forming apparatus for an external automotive panel according to the first and second embodiments of the present invention, a displacement line generated in the press forming of the external automotive panel having a character line will be described. Reason why the displacement line is generated For example, as illustrated in Figure 8d, an external automotive panel 61, which is an object of the present invention, is deeply stretched as follows, using a press forming apparatus 41 that includes a punch 43 having a ridge 43a extending in a front and rear direction from a paper surface, a die 45 having a valley line «ηορηη / ζζηζ / Β / γίΛΐ 45a extending in the front and rear direction of the paper surface and parts holders 47 oriented towards both ends of the die 45. First, as illustrated in Figure 8a, one end 51a and one end 51b of the sheet metal 51 are sandwiched respectively between the die 45 and the toolholders 47. Then, while the ends of the sheet metal are sandwiched, as illustrated in Figures 8b to 8d, the die 45 is moved relative to the side of the punch 43 upward to a bottom dead center, for press forming of the external automotive panel 61 by forming a character line 63 by means of the ridge 43a of the punch 43 and the valley line 45a of the die 45. When the die 45 moves relative to the side of the punch 43 in this press forming process, the ridge 43a of the punch 43 first comes into contact with the sheet metal 51 and the initial bend or flex in the sheet metal 51 (Figure 8b). Then, in a process of deep drawing progress by the die 45 and the punch 43, stresses are generated in the sheet metal 51 in the respective directions from an initial bend towards the ends 51a and 51b sandwiched by the smooth workpiece holders 47 (Figures 8b and 8c). The stresses generated in the sheet metal 51 differ from each other with the initial bending as the limit due to a difference between the respective distances from the initial bending to end 51a and end 51b, a difference between the angles of a portion of panel surface 65a and a panel surface 65b (Figure 8d) with respect to a press forming direction and the like. For example, as in the press forming of the external automotive panel 61 illustrated in Figure 8d, when the forming depths of end 51a and end 51b are almost the same and an angle 6b on the side of end 51b from the initial bend bend with respect to the press forming direction is smaller than an angle 0a on the side of end 51a, the stress generated on the side of end 51b is greater than the stress generated on the side of end 51a (Figure 8b). When a tension difference is generated in the sheet metal 51 as described above, the sheet metal 51 slides from a side with low tension to a side with high tension, and the initial bend slides to the side of end 51b that has high tension (Figure 8c). Then, the initial bend is crushed by die 45 and punch 43 at the bottom dead center, and a linear pattern, i.e., the displacement line, is generated (Figure 8d). Thus, in the external automotive panel 61, where the character line 63 is formed, the stress imbalance generated in the sheet metal 51 during a deep drawing process is a factor that causes the displacement line. Examples of factors causing stress imbalance include the difference in the respective distances and angles of the portion with which the punch ridge 43a makes contact, up to end 51a and end 51b, and a difference in the forming depths at both ends of the sheet metal 51 due to these factors. When the formation depths at both ends 51a and 51b of the metal sheet 51 are different from each other, the stress generated on the side of end 51b that has a larger formation depth in the process of deeper stretching and the displacement line is generated by the difference in stress with the end that has the smaller formation depth. Therefore, in employing the press forming method of the present invention, as illustrated in Figures 8a to 8c, it is preferred that the metal sheet 51 be pre-positioned in a direction (horizontal direction on the paper surface) perpendicular to the press forming direction, so that the press forming and the stresses acting respectively on the regions (on the end side 51a and the end side 51b) divided by the portion by which the crest 43a of the punch 43 makes contact are actually measured or the stresses are calculated by press forming analysis by the finite element method (FEM) or similar, so that the magnitude and value of the stresses generated in the metal sheet 51 in the press forming process are obtained in advance. The press forming method and press forming apparatus for external automotive panel parts will now be described according to the first and second embodiments of the present invention. Note that in the following description, components having the same function are denoted by the same reference numbers as those described above, and duplicate explanations will be omitted. First modality Press training apparatus A press forming apparatus 1 for external automotive panel parts according to the first embodiment (hereafter simply referred to as “press forming apparatus 1”) is an apparatus for press forming sheet metal 51 into the external automotive panel 61 having character line 63 and continuous panel surface portions 65a and 65b on both sides of character line 63 and as illustrated in Figures 1 and 2, includes a punch 3, a die 5, a workpiece holder 7 and an elastic body 9. As illustrated in Figure 8d described above, it is assumed that the external automotive panel 61 (Figure 2e) can be formed in the first mode having the stress generated on the end side 51b greater than the stress generated on the end side 51a from the initial bending in the press forming process (Figures 2a to 2e). As illustrated in Figures 1 and 2a to 2e, punch 3 has a ridge 3a and punch-side forming surface portions 3b and 3c located on both sides that sandwich ridge 3a. Ridge 3a forms character line 63 (Figure 2e). Punch-side forming surface portions 3b and 3c respectively form panel surface portions 65a and 65b (Figure 2e). Die 5 has a valley line 5a, die-side forming surface portions 5b and 5c continuous on both sides sandwiching valley line 5a, and a groove 5d formed in a concave shape in die-side forming surface portion 5b. Valley line 5a cooperates with ridge 3a of punch 3 to form character line 63 (Figure 2e). Die-side forming surface portions 5b and 5c cooperate respectively with punch-side forming surface portions 3b and 3c to form panel surface portions 65a and 65b (Figure 2e). Here, the forming surface portion on the punch side 3b and the forming surface portion on the die side 5b form a portion 55a on a side that has low stress acting on the sheet metal 51 in the press forming process, in the panel surface portion 65a. On the other hand, the forming surface portion on the punch side 3c and the forming surface portion on the die side 5c form a portion 55b, which is on a side that has high stress acting on the sheet metal 51 in the press forming process, in the panel surface portion 65b. The groove 5d is formed in a concave shape on the forming surface portion of the die side 5b and the elastic body 9 is provided there. The workpiece holders 7 are arranged to face both ends of the die 5 and cooperate with the die 5 to sandwich the ends 51 a and 51 b of the sheet metal 51. The elastic body 9 is provided in the groove 5d of the die-side forming surface portion 5b, so that the elastic body 9 can make contact at a position away from a portion 53 corresponding to the character line 63 on the sheet metal 51, along portion 53 and press the sheet metal 51, protruding towards the punch 3 unlike the die-side forming portion 5b and is supported by a lower part of the groove 5d so that it is contractile in the press-forming direction until a contact surface portion 9a in contact with the sheet metal 51 is level with the die-side surface portion 5b. The elastic body 9 has a hardness and a shape that can be deformed along a form of a press forming tool at the bottom dead center and is preferably a rubber material or a urethane material that has, for example, a Shore hardness of 40 to 100 HS. Then, as illustrated in the following equation (1), a protruding quantity of the elastic body 9 from the forming surface portion of the die side 5b is adjusted so that a frictional force between the elastic body 9 and the sheet metal 51 provided by a product of a load P pressing the sheet metal 51 by contraction of the compressed elastic body 9 in the forming process in the press and a coefficient of friction pe of the elastic body 9 and the sheet metal 51 is equal to or greater than a value of a difference between the stresses F1 and F2 acting on both sides sandwiching the portion 53 corresponding to the character line 63. |F1 - F2| < P χ pe (1) Here, it is assumed that the protruding amount of the elastic body 9 is equal to the amount of contraction of the elastic body 9 in the press forming direction when the die 5 moves relative to the punch side 3 to bottom dead center. Therefore, it is preferred that the load P pressing the sheet metal 51 due to the contraction of the elastic body 9 be calculated from the amount of contraction of the compressed elastic body 9. Furthermore, the coefficient of friction pe of the elastic body 9 and the metal sheet 51 is measured beforehand by means of a slip test or similar method. Alternatively, when rubber or urethane material is used as the elastic body 9, the coefficient of friction pe with the metal sheet 51 is generally pe = 0.1 to 0.3 (lubricated), pe = 0.5 to 0.6 (dry), and these values ​​can thus be used. The difference between the stresses acting on both sides sandwiching portion 53 corresponding to character line 63 in the press forming process is obtained beforehand by means of an experiment using a strain gauge or similar to measure the stress acting on sheet metal 51 when actually press forming the automotive panel Rnopnn / zznz / B / YiAi external 61 or the press formation analysis of the external automotive panel 61 by the finite element method (FEM) or similar. Press training method The press forming method for the external automotive panel 61 according to the first modality will be described by taking as an example a use case of the press forming apparatus 1 where the external automotive panel 61 in which the character line 63 illustrated in Figure 2e is formed using the press forming apparatus 1 which includes the punch 3, the die 5, the workpiece holder 7 and the elastic body 9 illustrated in Figure 1. As illustrated in Figures 2a to 2e, the press forming method for the external automotive panel according to the first embodiment is a method in which the sheet metal 51 disposed between the punch 3 and the die 5 and having both ends 51a and 51b sandwiched between the die 5 and the workpiece holders 7 is press formed into the external automotive panel 61 having the character line 63 and the panel surface portions 65a and 65b continuous on both sides of the character line 63 and includes a spring body contact step of moving the die 5 relative to the side of the punch 3, to bring the spring body 9 into contact with the sheet metal 51 before the die 5 and a press forming step of further moving the die 5 relative to the side of the punch 3 to the bottom dead center while crushing the spring body 9 and pressing the sheet metal 51. Elastic body contact point The elastic body contact step is a step in which the die 5 moves relative to the side of the punch 3 while the ends 51a and 51b of the sheet metal 51 are sandwiched respectively between the die 5 and the workpiece holders 7 and the elastic body 9 is made contact with the sheet metal 51 before the die 5 before a portion of the sheet metal 51 in contact with the crest 3a of the punch 3 is plastically deformed to generate the initial bend by flexing. It can be determined that plastic deformation of the metal sheet 51 by the crest 3a occurs, for example, when the stress of the portion of the metal sheet 51 in contact with the crest 3a exceeds a stress εθ calculated by the following equation (2). εθ = t / 2R (2) Here, R is a bend radius of the character line 63 and t is a plate thickness of the sheet metal 51. Press training step The press forming step is a step of further moving the die 5 relative to the punch side 3 to the bottom dead center while pressing the sheet metal 51 by means of the contact surface portion 9a of the elastic body 9 to contract the elastic body 9. As illustrated in equation (1) mentioned above, the overhanging amount of the elastic body 9 provided over the forming surface portion of the die side 5b is set so that the frictional force provided by the product of the load P due to the contraction (deformation) in the press forming direction of the elastic body 9 crushed in the press forming step and the coefficient of friction pe of the elastic body 9 and the sheet metal 51 is equal to or greater than the absolute value of the difference between the stresses (F1 and F2) in the «ηορηη / ζζηζ / B / γίΛΐ Figure 3) acting respectively on the ends 51a and 51b that sandwich the portion 53 corresponding to the character line 63 on the metal sheet 51. Here, the load P by the elastic body 9, the coefficient of friction pe of the elastic body 9 and the metal sheet 51, and the difference between the stresses (F1-F2) acting on both sides sandwiching portion 53 of the metal sheet 51 are provided as described above. Reason why the displacement line is prevented The reason why the external automotive panel 61 can be press-formed by preventing the displacement line by the press-forming method and the press-forming apparatus 1 for the external automotive panel 61 according to the first modality will be described below with reference to Figures 2e and 3. First, die 5 moves relative to the punch side 3, and the elastic body 9 provided on the forming surface portion of die side 5b comes into contact with portion 55a of sheet metal 51 before die 5 and presses sheet metal 51 against the forming surface portion of punch side 3b (Figures 2a and 2b). Subsequently, the portion of sheet metal 51 in contact with the ridge 3a of punch 3 is plastically deformed to generate the initial bend (Figure 2d). Subsequently, when die 5 is moved further relative to the side of punch 3 (Figure 2d), stresses F1 and F2 are generated in the sheet metal 51 in the respective directions towards ends 51a and 51b, with the initial bend as the limit (Figure 3). Thus, as in the conventional press forming method described above, there is a difference between the stress F1 on the side of end 51b and the stress F2 on the side of end 51a. Due to this difference in tension, the sheet metal 51 can slide from the low-tension side of end 51a to the high-tension side of end 51b, and the initial bend can slide toward the high-tension side of end 51b. However, by friction with the elastic body 9 in contact and by pressing portion 55b onto the low-tension side of the sheet metal 51, it is possible to prevent the sheet metal 51 from sliding toward the high-tension end 51b and to move the die 5 relatively close to bottom dead center without sliding the initial bend (Figures 2d and 2e). As a result, it is possible to press-form the external automotive panel 61 in which the displacement line is prevented and the character line 63 is formed. Note that in the first mode, a position where the metal sheet 51 is pressed by the elastic body 9 is established in a position far from the portion 53 corresponding to the character line 63. When the external automotive panel 61 illustrated in Figure 2e is formed in press, the far position of the portion 53 corresponding to the character line 63 in the portion 55a corresponding to the panel surface portion 65a comes into contact with the elastic body 9 along the portion 53. The width of the groove 5d needs to be wider than that of the elastic body 9 to accommodate the deformation of the elastic body 9 being pressed. As described in Patent Literature 6, when the elastic body 9 is placed in the vicinity of portion 53 corresponding to character line 63, because the vicinity is a position where the forming stress of character line 63 is high, a corner of the enlarged groove 5d comes into contact with the vicinity of portion 53 corresponding to character line 63 and a linear failure is likely to occur. In the present invention, the groove 5d is located away from the portion 53 corresponding to the character line 63 and is located on the forming surface portion of the die side 5b, which is relatively flat and does not have high stress, and thus there is no problem of causing the linear failure mentioned above as described in Patent Literature 6. Note that in the groove 5d to accommodate the elastic body 9, the corner of the groove 5d on the character line side 63 is preferably separated from the portion 53 corresponding to the character line 63 by 10% or more of the length of the forming surface portion of the die side 5b. Other aspects In the press forming method and press forming apparatus 1 mentioned above, the elastic body 9 is brought into contact with portion 55a on the side having low tension between portions 55a and 55b on both sides sandwiching portion 53 corresponding to character line 63 on sheet metal 51 and the external automotive panel 61 having character line 63 is press formed while the elastic body 9 was crushed to press the sheet metal 51. However, as another aspect of the first embodiment of the present invention, as illustrated in Figures 4a to 4e, a press forming apparatus 11 may be employed in which an elastic body 15 has been brought into contact with and presses the portion 55b on the side having high tension between the portions 55a and 55b on both sides sandwiching the portion 53 corresponding to the character line 63 in the sheet metal 51. As illustrated in Figures 4a to 4e, the press forming apparatus 11 includes the punch 3, a die 13, the workpiece holders 7, and the elastic body 15. Since the punch 3 and the workpiece holders 7 are the same as those of the press forming apparatus 1 described above, the die 13 and the elastic body 15 will be described below. Die 13 has a valley line 13a, die-side forming surface portions 13b and 13c continuous on both sides sandwiching the valley line 13a, and a groove 13d formed in a concave shape on the die-side forming surface portion 13c. The valley line 13a cooperates with the ridge 3a of punch 3 to form the character line 63 (Figure 4e). The forming surface portion of the die side 13b forms portion 55a on the side that has low tension acting on the sheet metal 51 in the press forming process on the panel surface portion 65a. On the other hand, the forming surface portion of the die side 13c forms portion 55b on the side that has high tension acting on the sheet metal 51 in the press forming process on the panel surface portion 65b. The groove 13d is formed in a concave shape on the forming surface portion of the die side 13c and the elastic body 15 is provided there. The elastic body 15 is provided in the groove 13d formed in the forming surface portion of the die side 13c so that the elastic body 15 can make contact in a position away from the portion 53 corresponding to the character line 63 on the sheet metal 51, along the portion 53 and press the sheet metal 51, protruding towards the punch 3 a «ηορηη / ζζηζ / Β / γίΛΐ unlike the forming surface portion of the die side 13c and is supported by a bottom of the groove 13d to be contractile in the forming direction until a portion of the contact surface 15a in contact with the sheet metal 51 is level with the forming surface portion of the die side 13c. In the press forming of the external automotive panel 61 using that press forming apparatus 11, first, the die 13 is moved relative to the side of the punch 3 and the elastic body 15 is brought into contact with the sheet metal 51 before the die 13 before the portion of the sheet metal 51 in contact with the crest 3a of the punch 3 is plastically deformed to generate the initial bend by flexure (Figures 4a and 4b). Subsequently, the elastic body in contact 15 is crushed and the die 13 is moved further relative to the side of the punch 3 to the bottom dead center while pressing the sheet metal 51, to press form the external automotive panel 61 having the character line 63 (Figures 4c to 4e). Here, as illustrated in equation (1) mentioned above, a protruding amount of the elastic body 15 is set so that the frictional force between the protruding elastic body 15 towards the punch 3, as opposed to the forming surface portion of the die side 13c, and the sheet metal 51 is equal to or greater than the absolute value of the difference between the stresses F1 and F2 respectively acting on the ends 51a and 51b sandwiching the portion 53 corresponding to the character line 63. Thus, even when forming the metal sheet 51 in a press, when the elastic body 15 is brought into contact with and presses the portion 55b on the side with high tension, the metal sheet 51 does not slide to the side of the end 51b that has high tension, and it is possible to move the die 13 relative to the lower dead center without slipping the initial bend (Figures 4c to 4e). From the above, it is possible to form the external automotive panel 61 in a press, in which the displacement line is prevented and the character line 63 is formed. Second modality In explaining the press forming method and the press forming apparatus 21 of the external automotive panel 61 according to the second embodiment of the present invention, first, the press forming apparatus 21 according to the second embodiment will be described. Press training apparatus The press forming apparatus 21 for the external automotive panel 61 according to the second modality (hereafter simply referred to as the “press forming apparatus 21”) is an apparatus for press forming the sheet metal 51 onto the external automotive panel 61 having the character line 63 and the panel surface portions 65a and 65b continuous on both sides of the character line 63 and as illustrated in Figures 5 and 6a to 6e, includes the punch 3, a die 23, the workpiece holders 7, an elastic body 25 and a movable device 27. Since the punch 3 and the workpiece holders 7 are the same as those of the press forming apparatus 1 according to the first modality described above, the die 23, the elastic body 25 and the movable device 27 will be described below. Similar to die 5 of the press forming apparatus 1 according to the first embodiment described above, die 23 has a valley line 23a, die-side forming surface portions 23b and 23c continuous on both sides sandwiching the valley line 23a and a groove 23d formed in the concave shape in the die-side forming surface portion 23b. The valley line 23a cooperates with the ridge 3a of punch 3 to form the character line 63 (Figure 6e). The die-side forming surface portions 23b and 23c cooperate respectively with the punch-side forming surface portions 3b and 3c to form the panel surface portions 65a and 65b (Figure 6e). The forming surface portion on the die side 23b forms portion 55a on the side that has low stress acting on the sheet metal 51 in the press forming process in the panel surface portion 65a. On the other hand, the forming surface portion on the die side 23c forms portion 55b on the side that has high stress acting on the sheet metal 51 in the press forming process in the panel surface portion 65b. The groove 23d is formed in a concave shape on the forming surface portion of the die side 23b and is provided with the elastic body 25 and the movable device 27. The elastic body 25 is provided in the groove 23d of the forming surface portion of the die side 23b so that the elastic body 25 can make contact in a position away from the portion 53 corresponding to the character line 63 on the sheet metal 51, along the portion 53 and press the sheet metal 51, protruding towards the punch 3 unlike the forming surface portion of the die side 23b and is provided in the groove 23d so that it is contractile in the forming direction until a portion of the contact surface 25a in contact with the sheet metal 51 is level with the forming surface portion of the die side 23b. The elastic body 25 has the hardness and shape that allows it to deform along the shape of the press forming tool at the bottom dead center and is preferably rubber material or urethane material that has, for example, a Shore hardness of 40 to 100 HS. Furthermore, the elastic body 25 is supported by the bottom of the groove 23d through the movable device 27 capable of pressing the elastic body 25 towards the punch 3 to press the sheet metal 51. The movable device 27 presses the elastic body 25 towards the punch 3 so that the elastic body 25 protrudes towards the punch 3, unlike the forming surface portion of the die side 23b. In the press forming process, the contact surface portion 25a of the elastic body 25 is in contact with the sheet metal 51, and the crushing occurs at the same level as the forming surface portion of the die side 23b. The elastic body 25 contracts and includes a pad 27a to which the elastic body 25 is attached, and a pressure source 27b to apply pressure to the pad 27a. Here, examples of the pressure source 27b include air pressure and oil pressure. In the press forming apparatus 21 according to the second modality, the protruding quantity of the elastic body 25 is set so that the frictional force between the elastic body 25 and the metal sheet 51, which is provided by the product of the load P that presses the metal sheet 51 by the elastic body 25 crushed in the press forming process and the movable device 27 and the coefficient of friction pe of the elastic body 25 and the metal sheet 51, is equal to or greater than the absolute value of the difference between the stresses F1 and F2 acting on both sides that sandwich the portion corresponding to the character line 63 (see equation «ηορηη / ζζηζ / Β / γίΛΐ (1) above). Here, the load that presses the metal sheet 51 by means of the elastic body 25 is a load due to the contraction of the flattened elastic body 25 and the movable device 27 presses the elastic body 25 with a pressure acting on the pad 27a by means of the pressure source 27b. Furthermore, the value of the coefficient of friction pe of the elastic body 25 and the metal sheet 51 is provided as in the first modality described above. Furthermore, the difference between the stresses acting on the sheet metal 51 in the press forming process using the press forming apparatus 21 according to the second modality is obtained beforehand by experiment using the strain gauge or similar to measure the stress acting on the sheet metal 51 when the external automotive panel 61 is actually press formed or by press forming analysis of the external automotive panel 61 by the finite element method (FEM) or similar. Press training method The press forming method for the external automotive panel 61 according to the second modality will be described by taking as an example a case where the external automotive panel 61 in which the character line 63 illustrated in Figure 6e is formed by press forming using the press forming apparatus 21 which includes the punch 3, the die 23, the workpiece holders 7, the elastic body 25 and the movable device 27 illustrated in Figure 5. As illustrated in Figure 6e, the press-forming method for the external automotive panel 61 according to the second embodiment is a method in which the sheet metal 51 disposed between the punch 3 and the die 23 and having both ends 51a and 51b sandwiched between the die 23 and the workpiece holders 7 is press-formed into the external automotive panel 61 having the character line 63 and the panel surface portions 65a and 65b continuous on both sides of the character line 63 and includes a spring-body contact step of moving the die 23 relative to the punch side 3, to bring the spring body 25 into contact with the sheet metal 51 before the die 23 and a press-forming step of further moving the die 23 relative to the punch side 3 to the bottom dead center while crushing the spring body 25 and pressing the sheet metal 51. Elastic body contact point The elastic body contact step is a step in which the die 23 moves relative to the side of the punch 3 while the ends 51a and 51b of the sheet metal 51 are sandwiched respectively between the die 23 and the workpiece holders 7 and the elastic body 25 is made contact with the sheet metal 51 before the die 23 before the portion of the sheet metal 51 in contact with the crest 3a of the punch 3 is plastically deformed to generate the initial bend by flexing. It was determined that the plastic deformation of the metal sheet 51 by the crest 3a occurs, for example, when the stress of the portion of the metal sheet 51 in contact with the crest 3a exceeds the stress εθ calculated by equation (2) above. Press training step The press forming step is a step of further moving the die 23 relative to the punch side 3 to the bottom dead center while crushing the elastic body 25 «ηορηη / ζζηζ / Β / γίΛΐ» until the elastic body 25 is level with the forming surface portion of the die side 23b and pressing the sheet metal 51. In the press forming method according to the second modality, as illustrated in equation (1) mentioned above, in the elastic body 25 provided on the forming surface portion of the die side 23b, the protruding amount of the forming surface portion of the die side 23b and a pressure from the pressure source 27b acting on the pad 27a are adjusted so that the frictional force provided by the product of the load P (P in Figure 1) that presses the sheet metal 51 by means of the elastic body 25 supported through the movable device 27 in the press forming step and the coefficient of friction pe of the elastic body 25 and the sheet metal 51 is equal to or greater than the absolute value of the difference between the stresses F1 and F2 acting respectively on the ends 51a and 51b that sandwich the portion 53 corresponding to the character line 63 in the sheet metal 51. Here, the coefficient of friction pe of the elastic body 25 and the metal sheet 51 and the difference between the stresses (F1-F2) acting on both sides sandwiching portion 53 of the metal sheet 51 are provided as described above. Effects of operation The operating effects of the press forming method and the press forming apparatus 21 according to the second modality are as follows. As illustrated in Figures 6a to 6d, when the sheet metal 51 is press formed while the elastic body 25 supported by the groove 23d of the forming surface portion of the die side 23b through the movable device 27 is brought into contact with and presses the sheet metal 51, it is possible to apply a load due to the contraction of the elastic body 25 crushed by a load acting on the pad 27a by the pressure source 27b to the sheet metal 51. Then, the load that presses the sheet metal 51 by the spring body 25 can be adjusted by the amount of the spring body 25 protruding from the forming surface portion of the die side 23b and the load acting on the pad 27a by the pressure source 27b. Here, it is assumed that the amount of the spring body 25 protruding is equal to the amount of shrinkage in the press forming direction of the spring body 25 when the die 23 moves relative to the punch side 3 to bottom dead center. For example, even if a sufficient frictional force cannot be obtained with the metal sheet 51 or the difference between the stresses (F1 - F2) in the metal sheet 51 is large before the load pressing the metal sheet 51 is sufficiently large due to the contraction of the elastic body 25, by further applying a load to the pad 27a to which the elastic body 25 is attached by means of the pressure source 27b, the degree of freedom to adjust the load of the elastic body 25 pressing the metal sheet 51 is increased. This is preferable because it is possible to press form the external automotive panel 61 in which the displacement line is more effectively prevented and the character line 63 is formed. Other aspects In the press forming method and press forming apparatus 21 mentioned above for the external automotive panel 61, the external automotive panel 61 having the character line 63 is press formed while the elastic body 25 supported by the movable device «ηορηη / ζζηζ / Β / γίΛΐ» comes into contact with and presses the portion 55a on the side having low tension in the sheet metal 51. However, as another aspect of the second embodiment of the present invention, as illustrated in Figures 7a to 7e, a press forming apparatus 31 can be employed in which an elastic body 35 supported by a movable device 37 is brought into contact with and presses the portion 55b on the side having high tension in the sheet metal 51. As illustrated in Figures 7a to 7e, the press forming apparatus 31 includes the punch 3, a die 33, the workpiece holders 7, the elastic body 35, and the movable device 37. Since the punch 3 and the workpiece holders 7 are the same as those of the press forming apparatus 1 described above, the die 33, the elastic body 35, and the movable device 37 will be described below. Die 33 has a valley line 33a, die-side forming surface portions 33b and 33c continuous on both sides sandwiching valley line 33a, and groove 33d formed in a concave shape on die-side forming surface portion 33c. The valley line 33a cooperates with the ridge 3a of punch 3 to form the character line 63 (Figure 7e). The forming surface portion of the die side 33b forms portion 55a on the side that has low tension acting on the sheet metal 51 in the press forming process on the panel surface portion 65a. On the other hand, the forming surface portion of the die side 33c forms portion 55b on the side that has high tension acting on the sheet metal 51 in the press forming process on the panel surface portion 65b. The groove 33d is formed in a concave shape in the forming surface portion of the die side 33c and the elastic body 35 and the movable device 37 are provided there. The elastic body 35 is provided in the groove 33d of the forming surface portion of the die side 33c so that the elastic body 35 can make contact in a position away from portion 53 corresponding to character line 63 on the sheet metal 51, along portion 53 and presses the sheet metal 51, protrudes towards the punch 3 unlike the forming surface portion of the die side 33c and is provided in the groove 33d so that it is contractile in the press forming direction until a portion of the contact surface 35a in contact with the sheet metal 51 is level with the forming surface portion of the die side 33c. The elastic body 35 has the hardness and shape that allows it to deform along the shape of the press forming tool at the bottom dead center and is preferably rubber material or urethane material that has, for example, a Shore hardness of 40 to 100 HS. Furthermore, the elastic body 35 is supported by the bottom of the groove 33d through the movable device 37 capable of pressing the elastic body 35 towards the punch 3 to press the sheet metal 51. The movable device 37 presses the elastic body 35 towards the punch 3 so that the elastic body 35 protrudes towards the punch 3 from the forming surface portion of the die side 33c and in the press forming process, the contact surface portion 35a of the elastic body 35 comes into contact with the sheet metal 51 and the flattening is carried out level with the forming surface portion of the die side 33c and the elastic body 35 contracts and includes a pad 37a to which the elastic body 35 is attached and a pressure source 37b to apply pressure to the pad 37a. Here, examples of the pressure source 37b include air pressure and oil pressure. In the press forming of the external automotive panel 61 using a press forming apparatus 31, first, the die 33 is moved relative to the side of the punch 3 and the elastic body 35 is brought into contact with the sheet metal 51 before the die 33 before the portion of the sheet metal 51 in contact with the crest 3a of the punch 3 is plastically deformed to generate the initial bend by flexure (Figures 7a and 7b). Subsequently, the die 33 is moved further relative to the punch side 3 to the bottom dead center while the elastic body 35 is crushed and the sheet metal 51 is pressed, to press form the external automotive panel 61 in which the character line 63 is formed (Figures 7c to 7e). When the sheet metal 51 is formed in a press while the elastic body 35 supported by the groove 33d of the forming surface portion of the die side 33c through the movable device 37 is brought into contact with and presses the sheet metal 51, it is possible to apply a load due to the contraction of the elastic body 35 crushed by a load acting on the pad 37a by the pressure source 37b to the sheet metal 51. In this way, even when the metal sheet 51 is formed in the press while the elastic body 35 is brought into contact with and presses the portion 55b on the side with high tension, the metal sheet 51 does not slip to the side of the end 51b that has high tension, and it is possible to move the die 33 relative to the lower dead center without slippage of the initial bend (Figures 7c to 7e). Thus, it is possible to press form the external automotive panel 61 in which the displacement line is prevented and the character line 63 is formed. Note that the load that presses the sheet metal 51 by the elastic body 35 can be adjusted by the protruding amount of the elastic body 35 from the forming surface portion of the die side 33c and the load acting on the pad 37a by the pressure source 37b. Therefore, for example, even if sufficient frictional force cannot be obtained with the metal sheet 51 or the difference between the stresses (F1-F2) in the metal sheet 51 is large before the load pressing the metal sheet 51 is large enough due to the contraction of the elastic body 35, the degree of freedom to adjust the load of the elastic body 35 pressing the metal sheet 51 is increased. This is preferable because it is possible to press form the external automotive panel 61 in which the displacement line is more effectively prevented and the character line 63 is formed. Example An example was carried out to verify a displacement line prevention effect when the external automotive panel is press formed and the character line is formed by the press forming method and the press forming apparatus for the external automotive panel according to the present invention and thus will be described below. In the present modality, the press forming analysis was carried out in which an external panel model simulating the external automotive panel having the character line was formed in a press by means of the press forming method according to the present invention and the presence or absence of the displacement line in the press-formed external panel model was evaluated. In the press forming analysis, a 0.7 mm thick SGCC-F steel plate was used as the sheet metal and the external panel model (not illustrated) was analyzed, which has the character line and continuous panel surface portions on both sides of the character line. Here, the radius of curvature R of the character line was 3 mm and the width of the panel surface portions was 50 mm. The angles of the panel surface with respect to the press forming direction were 0a = 85° and 0b = 65°. In the present modality, as a conventional example, the press forming analysis of a deep stretching process of the sheet metal in the outer panel was carried out by means of a press forming apparatus that includes the punch, the die and the workpiece holders (see Figures 8a to 8d). Then, in the press forming process, the stress on the side of the panel surface portion that has a small angle (6b = 65°) is greater than on the side of the panel surface portion and the difference obtained between the stresses acting on both sides of the portion corresponding to the character line was 202 kN. Next, as an example of the invention, the press forming apparatus, including the punch, die, workpiece holder, and elastic body, was used, and the press forming analysis was performed in the deep drawing process of the sheet metal. (See Figures 2a to 2e) while the elastic body was in contact with and pressed into the position away from the portion corresponding to the character line on the sheet metal (position in which a corner of the character side of the groove is at 10% of the length of the forming surface portion of the die side). The elastic body was provided in the groove of the forming surface portion on the die side to project 12 mm from the forming surface portion on the die side to the punch side so that the elastic body can make contact with the away position of the portion corresponding to the character line on the sheet metal, along the portion and can press the sheet metal. Here, the protruding amount of the elastic body from the forming surface portion on the die side was fixed or established based on the difference between the stresses (= 202 kN) acting on both sides sandwiching the portion corresponding to the character line in the press forming process according to the conventional example. Note that in the press analysis, the material of the elastic body was liquid urethane, the coefficient of friction between the elastic body and the sheet metal was 0.6, and the elastic modulus of the elastic body was 253 N / mm². Figure 9 illustrates a cross-sectional shape result of the outer panel obtained by press forming analysis. Here, Figure 9 illustrates an elongated state of a portion of the press-formed outer panel centered on the character line and rotating the cross-sectional shape result so that the panel surface portion on the side that has a small angle with respect to the press forming direction is substantially horizontal. From Figure 9, in comparison with the example, in the conventional example, a concave shape was observed (a portion surrounded by a dotted ellipse in Figure 9) due to the displacement line over the panel surface portion on the side that has high tension. Figure 10 illustrates a result of the surface distortion evaluation of the outer panel obtained by press forming analysis. An evaluation value As of the surface distortion illustrated in Figure 10 is expressed by the maximum-minimum difference in height measured by the three-point gauge (fixed tension L) as described in the following well-known reference. (Reference Literature) The Japan Sheet Metal Forming Research Group, Press Forming Difficulty Handbook 4th Edition, Chapter 5 Poor Surface Shape Accuracy and Evaluation for Forming Difficulty, pp. 218-221, Nikkan Kogyo Shimbun, Ltd. (2017) From Figure 10, the difference between the maximum and minimum values ​​of the surface distortion As evaluation value was 0.0102 in the conventional example, while it was 0.0046 in the example. Thus, it can be understood that the surface distortion in the panel surface portion was reduced by press forming while being pressed by the elastic body. As described above, according to the present invention, it has been illustrated that it is possible to press form the external automotive panel in which the displacement line is prevented and the character line is formed. Industrial Applicability According to the present invention, it is possible to provide a press forming method and a press forming apparatus for an external automotive panel, in which a displacement line is prevented without increasing man-hours to press forming and forming a line of objective character. List of Reference Signs PRESS TRAINING APPARATUS AWL 3rd CREST 3b, 3c PORTION OF FORMING SURFACE ON THE PUNCH SIDE DIE 5th VALLEY LINE 5b, 5c DIE SIDE FORMING SURFACE PORTION 5d SLOT PLAIN PARTS CARRIERS ELASTIC BODY PRESS TRAINING APPARATUS DIE 13th VALLEY LINE 13b, 13c DIE SIDE FORMING SURFACE PORTION 13d SLOT ELASTIC BODY PRESS TRAINING APPARATUS DIE 23rd VALLEY LINE βηορηη / ζζηζ / Β / γίΛΐ 23b, 23c DIE SIDE FORMING SURFACE PORTION 23d SLOT ELASTIC BODY MOBILE DEVICE 27a PAD 27b PRESSURE SOURCE PRESS TRAINING APPARATUS DIE 33rd VALLEY LINE 33b, 33c DIE SIDE FORMING SURFACE PORTION 33d SLOT ELASTIC BODY MOBILE DEVICE 37a PAD 37b PRESSURE SOURCE PRESS TRAINING APPARATUS AWL 43rd CREST DIE 45th VALLEY LINE PLAIN PARTS CARRIERS SHEET METAL PORTION CORRESPONDING TO THE CHARACTER LINE 55a, 55b PORTION CORRESPONDING TO THE PANEL SURFACE PORTION EXTERNAL AUTOMOTIVE PANEL CHARACTER LINE 65a, 65b PORTION OF PANEL SURFACE

Claims

1. A press forming method for an external automotive panel, press forming a sheet metal in the external automotive panel having a character line and continuous panel surface portions on both sides of the character line using a punch, a die facing the punch, and a workpiece holder facing one end of the die, wherein the die includes a spring body projecting towards the punch as opposed to the forming surface portion on the die side, such that the spring body is able to make contact and press on a position away from a corresponding portion on the character line in the sheet metal, along the portion corresponding to the character line, and is supported so that it can contract until a portion in contact with the sheet metal is level with the forming surface portion on the die side.The press forming method is characterized in that it comprises: an elastic body contact step consisting of moving the die relative to the punch side while both ends of the sheet metal are sandwiched between the die and the workpiece holder, to bring the contact surface portion of the elastic body into contact with the sheet metal before a portion of the sheet metal in contact with the punch is elastically deformed; and a press forming step of further moving the die relative to the punch side to a bottom dead center while pressing the sheet metal by means of the contact surface portion of the elastic body to contract the elastic body.where a projecting amount of the elastic body of the forming surface portion of the die side is fixed so that a frictional force provided by a product of a load of the elastic body pressing the sheet metal in the press forming step and a coefficient of friction of the elastic body and the sheet metal, is equal to or greater than an absolute value of a difference between the stresses on both sides sandwiching the portion corresponding to the character line.

2. The press forming method for the external automotive panel according to claim 1, further characterized in that the elastic body is supported on the die side by means of a movable device configured to press the elastic body towards the punch and press the sheet metal.

3. The press forming method for the external automotive panel according to claim 1 or 2, further characterized in that the elastic body presses a portion on one side having low tension between portions on both sides that sandwich the portion corresponding to the character line.

4. The press forming method for the external automotive panel according to claim 1 or 2, further characterized in that the elastic body presses a portion on one side having high tension between portions on both sides that sandwich the portion corresponding to the character line.

5. A press forming apparatus for an automotive exterior panel, characterized in that it comprises: a punch; a die oriented towards the punch; and a workpiece holder oriented towards an end of the die, wherein the pressing apparatus forms a sheet of metal in the automotive exterior panel having a character line and continuous panel surface portions on both sides of the character line, wherein the die includes die-side forming surface portions that respectively form the panel surface portions on both sides of the character line, one of the die-side forming surface portions includes an elastic body projecting towards the punch as opposed to the surface portion forming the die side, such that the elastic body is capable of making contact and pressing in a position away from the portion corresponding to the character line in the sheet of metal,along the portion corresponding to the character line, and is supported to be contractile until a portion of the contact surface in contact with the sheet metal is level with the forming surface portion of the die side, and a protruding amount of the elastic body from the forming surface portion of the die side is fixed so that a frictional force provided by a product of a load of the elastic body pressing the sheet metal in the press forming process and a coefficient of friction of the elastic body and the sheet metal, is equal to or no greater than an absolute value than the difference between the stresses acting on both sides sandwiching the portion corresponding to the character line.

6. The press forming apparatus for the external automotive panel according to claim 5, further characterized in that the elastic body is supported on the punch side by means of a movable device configured to press the elastic body towards the punch and press the sheet metal.

7. The press forming apparatus for the external automotive panel according to claim 5 or 6, further characterized in that the elastic body is provided over the die so as to press a portion on one side having low tension between portions on both sides that sandwich the portion corresponding to the character line.

8. The press forming apparatus for the external automotive panel according to claim 5 or 6, further characterized in that the elastic body is provided over the die to press a portion on the side having high tension between portions on both sides that sandwich the portion corresponding to the character line.

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