Patent Publication Number: US-2022227032-A1

Title: Injection mold

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-005301 filed on Jan. 15, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an injection mold for obtaining a molded article by filling a cavity with a molten resin. 
     Description of the Related Art 
     Resin molded articles are generally used for exterior parts or interior parts of automobile bodies. In the manufacturing process of the resin molded article, a cavity of an injection mold is filled with a molten resin. Thereafter, the molten resin is cooled and solidified in the cavity. Thus, the resin molded article is manufactured. 
     For example, there is a case where a large-sized resin molded article such as an automobile bumper is injection-molded. At this time, the side surface of the bumper, which is the lateral side of the vehicle, is deformed so as to open outward (outward in the vehicle width direction) by the pressure of the filled resin material. Along with the outward deformation of the side surface of the bumper, the fixed mold and the movable mold constituting the injection mold are deformed. As a result, a step occurs at a boundary portion between the fixed mold and the movable mold. There is a problem that a line is formed on an appearance design surface of the side surface of the bumper due to the occurrence of the step. 
     In order to solve the above-described problem, an injection mold disclosed in JP S61-015119 U includes a partial insert which is a part of a movable mold. When molding a bumper using the injection mold, an undercut portion is molded in a wheel arch portion between the partial insert and a fixed mold. The wheel arch portion constitutes the side surface of the bumper. The injection mold includes a convex portion on an outer side of the partial insert. The convex portion protrudes from a lower end of the fixed mold. When the movable mold and the fixed mold are closed to mold the bumper (molded article), the partial insert is pressed outward along with deformation of the side surface of the bumper. Outward movement of the partial insert is prevented by the convex portion. As a result, when the bumper is molded, the occurrence of a step on the side surface of the bumper that is an appearance design surface is suppressed. 
     In the injection mold disclosed in JP S61-015119 U, deformation of the movable mold and movement of the partial insert are suppressed by the convex portion of the fixed mold. Further, the fixed mold and the movable mold are separated in the mold closing direction of the injection mold. For this reason, when the wheel arch portion (undercut portion) is formed on a surface inclined with respect to the mold closing direction of the movable mold and the fixed mold, it is difficult to suppress the occurrence of a step in the entire region of the wheel arch portion (undercut portion). 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above-described problem. 
     According to an aspect of the present invention, provided is an injection mold comprising a fixed mold, and a movable mold configured to approach and separate from the fixed mold, the injection mold being configured to mold a molded article including a bottom surface portion perpendicular to a mold closing direction of the fixed mold and the movable mold, and a side surface portion inclined with respect to the bottom surface portion, the molded article being formed so as to have a substantially U-shaped cross section when viewed from a direction orthogonal to the mold closing direction, wherein the molded article includes, at an end portion of the side surface portion, an undercut portion inclined with respect to the mold closing direction, the injection mold further comprises an insert configured to mold the undercut portion in the side surface portion, and a cavity that is defined by the fixed mold, the movable mold, and the insert, and is filled with a molten resin, a first mold, which is one of the fixed mold or the movable mold, includes a convex portion protruding toward a second mold, which is another of the fixed mold and the movable mold, and a protruding end of the convex portion is located at a position shifted from the insert in a direction from the first mold toward the second mold. 
     According to the present invention, the injection mold includes the convex portion protruding toward the second mold, which is the other of the fixed mold and the movable mold. The protruding end of the convex portion is arranged at a position shifted from the insert in a direction from the first mold toward the second mold. When the cavity is filled with the molten resin to mold the molded article, the pressure of the molten resin is applied in a direction in which the molded article having a substantially U-shaped cross section opens. At this time, the convex portion is engaged with the second mold. Therefore, even when the undercut portion is inclined with respect to the side surface portion of the molded article, deformation of the second mold and movement of the insert can be suitably suppressed by the convex portion. 
     As a result, in the injection mold capable of molding a molded article having a substantially U-shaped cross section, deformation of the second mold, which is the other of the fixed mold and the movable mold, and movement of the insert during molding can be suppressed. Therefore, it is possible to suppress the occurrence of a step in the appearance in the vicinity of the undercut portion of the molded article. This makes it possible to improve the quality of the molded article. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall front view of an injection mold and a molded article according to an embodiment of the present invention, as viewed from a mold closing direction; 
         FIG. 2  is a cross-sectional view taken along line II-II of  FIG. 1 ; 
         FIG. 3  is an enlarged cross-sectional view of the vicinity of one end in the width direction of the injection mold in  FIG. 2 ; and 
         FIG. 4  is a side view of the injection mold and the molded article shown in  FIG. 1  as viewed from one side in the width direction. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1 and 2 , with an injection mold  10 , for example, a bumper (molded article S) for an automobile is molded. The injection mold  10  includes a fixed mold  12 , a movable mold  14 , and inserts  16 . The movable mold  14  is disposed above the fixed mold  12  (in an arrow A direction in  FIG. 2 ). The movable mold  14  can approach or separate from the fixed mold  12 . When a displacement mechanism (not shown) (for example, a hydraulic cylinder or the like) is driven, the movable mold  14  moves in a direction toward the fixed mold  12  (an arrow B direction in  FIG. 2 ) or a direction away from the fixed mold  12  (the arrow A direction in  FIG. 2 ). The inserts  16  are disposed between the fixed mold  12  and the movable mold  14 .  FIG. 1  is a front view of the movable mold  14  and the molded article S as viewed from the fixed mold  12 . 
     In the following description, in the injection mold  10 , a mold opening direction (upward) of the movable mold  14  is defined as the arrow A direction. A mold closing direction (downward) of the movable mold  14  is defined as the arrow B direction. A width direction orthogonal to the mold opening direction of the movable mold  14  is defined as an arrow C direction. A horizontal direction orthogonal to the width direction is defined as an arrow D direction (see  FIG. 1 ). 
     The fixed mold  12  is fixed to a work station or the like (not shown) via a fixed platen  18 . The fixed platen  18  has a plate shape and extends in the width direction. The fixed mold  12  has a recessed part  20 . The recessed part  20  is disposed on a dividing surface  12   a  of the fixed mold  12  that faces the movable mold  14 . The recessed part  20  is recessed in a direction (the arrow B direction) away from the movable mold  14 . When viewed from a direction (horizontal direction) orthogonal to the mold closing direction shown in  FIG. 2 , the center of the recessed part  20  in the width direction extends substantially in the horizontal direction (width direction). The cross-sectional shape of the recessed part  20  is a shape gently curved in a direction approaching the movable mold  14  (the arrow A direction), from the center in the width direction toward both ends in the width direction. 
     As shown in  FIGS. 2 and 3 , the fixed mold  12  includes two first groove portions (recessed portions)  22  and a second groove portion  24 . The two first groove portions  22  are recessed in the dividing surface  12   a  of the fixed mold  12  at both ends in the width direction. 
     The first groove portion  22  is disposed adjacent to the recessed part  20 . The first groove portion  22  includes a shallow groove portion  26  and a deep groove portion (recessed portion)  28 . The shallow groove portion  26  is disposed in the first groove portion  22  on the inner side in the width direction (at a position closer to the recessed part  20  than the deep groove portion  28 ). The deep groove portion (recessed portion)  28  is disposed in the first groove portion  22  on the outer side in the width direction (at a position farther from the recessed part  20  than the shallow groove portion  26 ). 
     The second groove portion  24  is disposed in the dividing surface  12   a  on the outer side in the width direction than the first groove portion  22 . The second groove portion  24  is more recessed than the first groove portion  22  in the dividing surface  12   a.    
     The depth of the deep groove portion  28  is a depth from the dividing surface  12   a . The depth of the shallow groove portion  26  is a depth from the dividing surface  12   a . The depth of the deep groove portion  28  is greater than the depth of the shallow groove portion  26 . 
     The cross-sectional shape of the second groove portion  24  is, for example, a substantially rectangular shape. The second groove portion  24  penetrates from one end to the other end of the fixed mold  12  in the width direction. 
     The movable mold  14  is coupled to the displacement mechanism (not shown) via a movable platen  30 . The movable platen  30  has a plate shape. The movable mold  14  includes a movable main body  32  and movable spacers  34 . The movable main body  32  is inserted into the recessed part  20  of the fixed mold  12 . The movable spacers  34  are engaged with both ends of the movable main body  32  in the width direction. The movable main body  32  includes a convex part  36 . The convex part  36  is disposed on a dividing surface facing the fixed mold  12 . The convex part  36  protrudes in a direction (the arrow B direction) from the movable mold  14  toward the fixed mold  12 . 
     The convex part  36  is disposed at a position facing the recessed part  20  of the fixed mold  12 . The cross-sectional shape of the convex part  36  is a shape corresponding to the shape of the bumper that is the molded article S. The center of the convex portion  36  in the width direction extends in a substantially horizontal direction (width direction). The cross-sectional shape of the convex part  36  is gently curved in a direction away from the fixed mold  12 , from the center in the width direction toward both ends in the width direction. In other words, the cross-sectional shape of the convex part  36  is a shape corresponding to the cross-sectional shape of the recessed part  20 . 
     The movable mold  14  approaches the fixed mold  12 , and the convex part  36  enters the recessed part  20 . Thus, a cavity  38  is formed between the movable mold  14  and the fixed mold  12 . The cavity  38  has a shape corresponding to the shape of the bumper that is the molded article S. The cavity  38  is a space having a predetermined width between the movable mold  14  and the fixed mold  12 . 
     When viewed from the horizontal direction of the injection mold  10  shown in  FIG. 2 , the cross-sectional shape of the cavity  38  is a substantially U-shape recessed toward the fixed mold  12 . The central portion of the cavity  38  in the width direction is the vehicle width center (a bottom surface portion S 1 ) of the bumper that is the molded article S. Both ends of the cavity  38  in the width direction are side surface portions S 2  that are outer sides of the bumper in the vehicle width direction. The side surface portions S 2  each include a wheel arch portion  40  inclined with respect to the bottom surface portion S 1  of the bumper. The wheel arch portion  40  surrounds an outer periphery of a tire (not shown) on the lateral side of a vehicle (not shown) with a predetermined distance therebetween. 
     In the cavity  38 , the direction toward the fixed mold  12  (the arrow B direction) is the direction toward the vehicle front side in the bumper. In the cavity  38 , the direction toward the movable mold  14  (the arrow A direction) is the direction toward the vehicle rear side in the bumper. In the cavity  38 , the horizontal direction (the arrow D direction) orthogonal to the width direction is the vehicle vertical direction in the bumper. 
     Both ends of the movable main body  32  in the width direction are each provided with a first step portion  42  and a second step portion  44 . The inserts  16  are engaged with the first step portions  42 . The second step portions  44  are disposed above the first step portions  42 . The movable spacers  34  are engaged with the second step portions  44 . 
     When viewed from a direction orthogonal to the mold closing direction of the injection mold  10  shown in  FIG. 2 , the cross-sectional shape of the first step portion  42  is rectangular. The first step portions  42  are recessed inward in the width direction by a predetermined distance from both ends of the movable main body  32  in the width direction. 
     When viewed from the horizontal direction of the injection mold  10  shown in  FIG. 2 , the cross-sectional shape of the second step portion  44  is, for example, a substantially rectangular shape. The second step portions  44  are recessed inward in the width direction by a predetermined distance from both ends of the movable main body  32  in the width direction. The second step portion  44  is recessed more inward in the width direction than the first step portion  42 . 
     Each of the first and second step portions  42  and  44  extends along the width direction (the arrow C direction) orthogonal to the mold opening direction of the movable mold  14 . Each of the first and second step portions  42  and  44  is horizontal along the width direction. The first step portion  42  and the second step portion  44  are stepped in the height direction (the directions of arrows A and B). 
     The movable spacers  34  are arranged in pairs on the outer side of the movable main body  32  in the width direction. Each of the movable spacers  34  includes a spacer main body  34   a  and a first protruding portion (convex portion)  46 . When viewed from the horizontal direction of the injection mold  10  shown in  FIG. 2 , the cross-sectional shape of the spacer main body  34   a  is substantially rectangular. The first protruding portion  46  is disposed at the outer end of the spacer main body  34   a  in the width direction. The first protruding portion  46  protrudes toward the fixed mold  12  (in the arrow B direction). 
     Each of the spacer main body  34   a  and the first protruding portion  46  is inclined at a predetermined angle with respect to the horizontal direction (the arrow D direction) orthogonal to the width direction of the injection mold  10 . 
     As shown in  FIG. 4 , the spacer main body  34   a  and the first protruding portion  46  are inclined in a direction (the arrow A direction) away from the fixed mold  12 , from one end in the horizontal direction, which is the lower side in the vehicle direction in the bumper (molded article S), toward the other side in the horizontal direction (in the arrow D 2  direction) orthogonal to the width direction. The inclination angle of the spacer main body  34   a  and the first protruding portion  46  is an angle along the wheel arch portion  40  of the bumper. That is, the first protruding portion  46  has a substantially constant height in the mold closing direction of the injection mold  10  (the arrow B direction). 
     The inner end of the spacer main body  34   a  in the width direction is engaged with the second step portion  44  of the movable main body  32 . The first protruding portion  46  is engaged with the second groove portion  24  of the fixed mold  12 . Thus, the movable spacers  34  are disposed across the movable main body  32  and the fixed mold  12 . Correspondingly to the movable spacer  34 , the second step portion  44  and the second groove portion  24  are inclined in a direction (the arrow A direction) away from the fixed mold  12 , from one side in the horizontal direction (the arrow D 1  side) toward the other side in the horizontal direction (the arrow D 2  side). 
     As shown in  FIGS. 1 to 4 , with the insert  16 , an end portion of the wheel arch portion  40  in the molded article S is molded. The end portion of the wheel arch portion  40  is an undercut portion. The insert  16  is a block body. The insert  16  includes a dented portion  52 . The dented portion  52  is a part of the cavity  38 . The inserts  16  are disposed as a pair on the outer side of the movable main body  32  in the width direction. 
     Each of the inserts  16  includes a main body portion  48  and a second protruding portion (protruding portion)  50 . When viewed from the horizontal direction orthogonal to the width direction of the injection mold  10  shown in  FIG. 2 , the cross-sectional shape of the main body portion  48  is substantially rectangular. The second protruding portion  50  protrudes toward the fixed mold  12  from the outer end of the main body portion  48  in the width direction. The insert  16  is disposed across the first step portion  42  of the movable main body  32  and the first groove portion  22  of the fixed mold  12 . 
     As shown in  FIG. 4 , the insert  16  includes a lower end directed toward the fixed mold  12  and the movable main body  32 . The lower end of the insert  16  has a cross-sectional shape corresponding to the wheel arch portion  40  of the bumper (molded article S). The lower end of the insert  16  has an arc-shaped cross section that curves away from the fixed mold  12 , from one end in the horizontal direction orthogonal to the width direction toward the other side in the horizontal direction (the arrow D 2  direction). An upper end  16   a  of the insert  16  abuts against the movable spacer  34 . The upper end  16   a  of the insert  16  is inclined at a predetermined angle correspondingly to the lower surface of the movable spacer  34  and is brought into surface contact with the lower surface of the movable spacer  34 . 
     As shown in  FIGS. 2 to 4 , the insert  16  is located at a position shifted in the mold opening direction (the arrow A direction) from the protruding end of the first protruding portion  46  over the entire region from one end in the horizontal direction orthogonal to the width direction toward the other side in the horizontal direction (the arrow D 2  direction). The height of the insert  16  is a height that allows the insert  16  to be housed in the movable mold  14 . The protruding end of the first protruding portion  46  is located at a position shifted in the mold closing direction from the insert  16 . 
     The main body portion  48  includes the dented portion  52 . The dented portion  52  is disposed on the lower surface of the inner end in the width direction engaged with the first step portion  42 . The dented portion  52  is dented upward (in the arrow A direction) from the lower surface of the main body portion  48 , to a predetermined depth. The cross-sectional shape of the dented portion  52  is, for example, a rectangular shape elongated in the width direction. The depth of the dented portion  52  is constant along the width direction. The inner end of the dented portion  52  in the width direction communicates with a gap between the recessed part  20  of the fixed mold  12  and the convex part  36  of the movable main body  32 . Thus, the dented portion  52  constitutes a part of the cavity  38 . That is, the dented portion  52  extends along the curved surface of the lower end of the insert  16 . 
     The second protruding portion  50  protrudes from the lower end of the main body portion  48  toward the fixed mold  12  by a predetermined height. When viewed from the width direction of the injection mold  10  shown in  FIG. 4 , the second protruding portion  50  is disposed on the outer side than the wheel arch portion  40  of the bumper. When viewed from the width direction of the injection mold  10  shown in  FIG. 4 , the cross-sectional shape of the second protruding portion  50  is an arc shape. 
     The outer side of the insert  16  in the width direction is engaged with the first groove portion  22  of the fixed mold  12 . The second protruding portion  50  of the insert  16  is inserted into and engaged with the deep groove portion  28 . The upper end  16   a  of the main body portion  48  of the insert  16  is brought into surface contact with the lower surface of the movable spacer  34  disposed thereabove. Similarly to the movable spacers  34 , the inserts  16  are disposed across the movable main body  32  of the movable mold  14  and the fixed mold  12 . 
     In addition, in the injection mold  10  described above, a case in which the movable mold  14  is provided with the first protruding portion (convex portion)  46  has been described, but the present invention is not limited to a configuration in which the movable mold  14  is provided with the first protruding portion  46 . The first protruding portion  46  may be provided on the fixed mold  12 . 
     Next, the operation and effects of the injection mold  10  will be described. 
     First, the displacement mechanism (not shown) is driven to lower the movable mold  14  of the injection mold  10 . The movable mold  14  approaches the fixed mold  12 . As shown in  FIG. 2 , the dividing surface of the movable mold  14  and the dividing surface  12   a  of the fixed mold  12  are brought into contact with each other. As the movable mold  14  is lowered, the convex part  36  enters the recessed part  20 . As the movable mold  14  is lowered, the first protruding portion  46  of the movable spacer  34  is inserted into the second groove portion  24 . As the movable mold  14  is lowered, the second protruding portion  50  of the insert  16  is inserted into the deep groove portion  28  of the fixed mold  12 . As a result, the injection mold  10  is closed to form the cavity  38  between the movable mold  14  and the fixed mold  12 . 
     Next, a molten resin is supplied to the cavity  38  from an injection machine (not shown). The molten resin is filled into the cavity  38 . The molten resin is filled into the dented portions  52  of the inserts  16  on both ends sides of the injection mold  10  in the width direction. In this manner, the cavity  38  is filled with the molten resin. 
     In the cavity  38 , the pressure of the molten resin (resin pressure) (see F in  FIG. 2 ) is applied toward the fixed mold  12  disposed outside the cavity  38 . At this time, the first protruding portions  46  of the movable spacers  34  and the second protruding portions  50  of the inserts  16  are inserted into the fixed mold  12  at both ends of the cavity  38  in the width direction. As a result, deformation of the fixed mold  12  is suitably suppressed by the first and second protruding portions  46  and  50  in the vicinity of both ends of the cavity  38  in the width direction. That is, the first and second protruding portions  46  and  50  serve as stoppers that suppress deformation of the fixed mold  12  outward in the width direction. 
     Then, the molten resin is cooled for a predetermined time period in a state where the cavity  38  is filled with the molten resin. As the molten resin is cooled, it solidifies in the cavity  38 . Thus, in the injection mold  10 , the molded article S (bumper for automobile) corresponding to the shape of the cavity  38  is obtained. At this time, on the side surface portion S 2  of the bumper, the inner end of the wheel arch portion  40  that is bent inward in the width direction is molded by the insert  16 . Deformation in the vicinity of both ends of the fixed mold  12  in the width direction is suppressed by the inserts  16 . Therefore, displacement in the width direction (the arrow C direction) between the lower end of the insert  16  and the fixed mold  12  is suppressed. As a result, displacement in the width direction between the insert  16  and the fixed mold  12  is suitably prevented. Accordingly, the occurrence of a step in the vicinity of the wheel arch portion  40  in the bumper is suitably prevented. 
     Finally, the displacement mechanism (not shown) is driven to raise the movable mold  14 . The movable mold  14  is separated upward from the fixed mold  12  by a predetermined distance and the injection mold  10  is opened. Thereafter, an ejector mechanism (not shown) is driven and the molded article S is pressed by the ejector mechanism. The pressing direction of the molded article S is a direction (downward, the arrow B direction) in which the molded article S is separated from the movable mold  14 . As a result, the bumper, which is the molded article S, is pressed by the ejector mechanism, released from the movable mold  14 , and taken out downward. 
     As described above, in the present embodiment, the molded article S having a substantially U-shaped cross section with a large size such as a bumper for an automobile is molded in the injection mold  10 . The side surface portion S 2  of the molded article S includes the undercut portion at the end portion of the wheel arch portion  40 . The undercut portion is inclined with respect to the mold closing direction of the fixed mold  12  and the movable mold  14 . The injection mold  10  is provided with the inserts  16  for molding the undercut portion. The movable spacers  34  of the movable mold  14  each include the first protruding portion  46 . The protruding end (lower end) of the first protruding portion  46  is located at a position shifted in the mold closing direction from the insert  16 . The first protruding portion  46  suppresses outward deformation of the fixed mold  12  due to the pressure F (resin pressure) of the molten resin filled in the cavity  38 . 
     When the molded article S is molded in the injection mold  10 , the pressure F of the molten resin is applied to the fixed mold  12  in a direction (outward) in which the molded article S having a substantially U-shaped cross section opens. At this time, the first protruding portion  46  protrudes further toward the fixed mold  12  than the insert  16  over the entire region from one end in the horizontal direction orthogonal to the width direction toward the other side in the horizontal direction (the arrow D 2  direction) in the injection mold  10 . Therefore, the first protruding portion  46  is inserted into and engaged with the fixed mold  12 . Accordingly, deformation of the fixed mold  12  in the vicinity of both sides in the width direction of the bumper having the undercut portions is suitably suppressed. 
     As a result, when the molded article S having a substantially U-shaped cross section such as a bumper for an automobile is molded, deformation of the fixed mold  12  can be suppressed. Accordingly, it is possible to suppress the occurrence of a step in the appearance in the vicinity of the undercut portion of the bumper. Therefore, the quality of the bumper can be improved. 
     The first protruding portion  46  of the movable spacer  34  has a substantially constant height in the mold closing direction of the injection mold  10 . Therefore, when the pressure F of the molten resin is applied to the first protruding portion  46  via the fixed mold  12  during molding of the molded article S, the amount of deformation (amount of inclination) of the first protruding portion  46  outward in the width direction can be made substantially constant in the horizontal direction (the arrow D direction). As a result, in the side surface portion S 2  of the bumper that is the molded article S, the undercut portion (the wheel arch portion  40 ) molded along the horizontal direction can be uniformly finished. 
     The movable spacer  34  of the movable mold  14  includes the first protruding portion  46 . The fixed mold  12  includes the insert  16 . The insert  16  includes the dented portion  52  that is a part of the cavity  38 . By arranging the insert  16  so as to face the movable mold  14 , deformation or movement of the insert  16  can be suppressed by the first protruding portion  46 . Therefore, when the molded article S is molded in the injection mold  10 , it is possible to more reliably suppress the occurrence of a step in the appearance of the bumper. 
     The insert  16  includes the second protruding portion  50  protruding toward the fixed mold  12 . The fixed mold  12  includes the first groove portion  22  (deep groove portion  28 ) into which the second protruding portion  50  is inserted. As a result, when the fixed mold  12  is pressed outward in the width direction by the pressure F of the molten resin during injection molding of the bumper, the insert  16  follows the fixed mold  12  and moves outward in the width direction integrally with the fixed mold  12 . Therefore, displacement in the width direction between the insert  16  and the fixed mold  12  is suppressed at a boundary portion between the insert  16  and the fixed mold  12 . As a result, at the boundary portion between the insert  16  and the fixed mold  12 , it is possible to suppress the occurrence of a step in the appearance of the bumper that is the molded article S. 
     The molded article S obtained by the injection mold  10  is a bumper for an automobile. The mold closing direction of the injection mold  10  is the front-rear direction of the automobile. The undercut portion of the bumper is the wheel arch portion  40  and is formed on the side surface portion S 2  of the molded article S. As a result, in the molding in the injection mold  10 , it is possible to prevent the occurrence of molding marks on the appearance design surface of the wheel arch portion  40 . 
     The above embodiment can be summarized as follows. 
     The above embodiment relates to an injection mold ( 10 ) comprising a fixed mold ( 12 ), and a movable mold ( 14 ) configured to approach and separate from the fixed mold, the injection mold being configured to mold a molded article (S) including a bottom surface portion (S 1 ) perpendicular to a mold closing direction of the fixed mold and the movable mold, and a side surface portion (S 2 ) inclined with respect to the bottom surface portion, the molded article being formed so as to have a substantially U-shaped cross section when viewed from a direction orthogonal to the mold closing direction, wherein the molded article includes, at an end portion of the side surface portion, an undercut portion inclined with respect to the mold closing direction, the injection mold further comprises an insert ( 16 ) configured to mold the undercut portion in the side surface portion, and a cavity ( 38 ) that is defined by the fixed mold, the movable mold, and the insert and is filled with a molten resin, a first mold, which is one of the fixed mold or the movable mold, includes a convex portion ( 46 ) protruding toward a second mold, which is another of the fixed mold and the movable mold, and a protruding end of the convex portion is located at a position shifted from the insert in a direction from the first mold toward the second mold. 
     In the above-described embodiment, the injection mold includes the convex portion protruding toward the second mold which is the other of the fixed mold and the movable mold. The protruding end of the convex portion is arranged at a position shifted from the insert in a direction from the first mold toward the second mold. When the cavity is filled with the molten resin to mold the molded article, the pressure of the molten resin is applied in a direction in which the molded article having a substantially U-shaped cross section opens. At this time, the convex portion is engaged with the second mold. Therefore, even when the undercut portion is inclined with respect to the side surface portion of the molded article, deformation of the second mold and movement of the insert can be suitably suppressed by the convex portion. 
     As a result, in the injection mold capable of molding the molded article having a substantially U-shaped cross section, deformation of the second mold, which is the other of the fixed mold and the movable mold, and movement of the insert during molding can be suppressed. Therefore, it is possible to suppress the occurrence of a step in the appearance in the vicinity of the undercut portion of the molded article. This makes it possible to improve the quality of the molded article. 
     The convex portion is formed at a constant height in the mold closing direction. Therefore, when the pressure of the molten resin is applied to the convex portion via the second mold during molding of the molded article, the amount of deformation (amount of inclination) of the convex portion outward in the width direction can be made substantially constant in the horizontal direction. As a result, in the molded article, the undercut portion formed along the horizontal direction can be finished uniformly. 
     The movable mold includes the convex portion, and the insert is disposed in the movable mold to form the cavity in the fixed mold. Accordingly, by disposing the insert in the movable mold, deformation or movement of the insert can be suppressed by the convex portion. Therefore, when the molded article is molded in the injection mold, a step occurring in the appearance of the molded article can be more reliably suppressed. 
     The insert includes a protruding portion protruding toward the fixed mold, and the fixed mold includes a recessed portion into which the protruding portion is inserted. Thus, when the fixed mold is pressed outward in the width direction by the pressure of the molten resin during injection molding of the molded article, the insert follows the fixed mold and moves outward in the width direction integrally with the fixed mold. Therefore, at the boundary portion between the insert and the fixed mold, displacement in the width direction between the insert and the fixed mold is suppressed. As a result, it is possible to suppress a step occurring in the appearance of the molded article at the boundary portion between the insert and the fixed mold. 
     The molded article is a bumper for an automobile, the mold closing direction is a front-rear direction of the automobile, and the undercut portion is formed on a surface to be a wheel arch portion ( 40 ) of the bumper. As a result, when the bumper is molded in the injection mold, it is possible to prevent the occurrence of molding marks on the appearance design surface of the wheel arch portion. 
     Note that the present invention is not limited to the embodiment described above, and various configurations can be adopted therein without departing from the gist of the present invention.