Patent Publication Number: US-2021170654-A1

Title: Molding method and molding device

Description:
TECHNICAL FIELD 
     The present invention relates to a molding method and a molding device. 
     This application claims priority based on Japanese Patent Application No. 2018-026484 filed on Feb. 16, 2018, the entire disclosure of which is incorporated herein. 
     BACKGROUND ART 
     A molded resin article is manufactured by, for example, injection molding. When the molded resin article has a through-hole, the through-hole is formed by a perforation pin provided in a mold. The molten resin introduced into the mold is split into two by the perforation pin and joins on a back surface side of the perforation pin. At the junction, since a resin temperature is slightly decreased, the two resin flows cannot be completely merged, and a weld line may be formed (see, for example, PTL 1). The weld line may cause a decrease in strength of the molded resin article. In addition, the appearance of the molded resin article may be impaired by the weld line. 
     In the mold used in the molding method disclosed in PTL 1, the perforation pin can be made to protrude with respect to a cavity by a driving device. In this molding method, after filling the cavity, into which the perforation pin is not protruded, with the molten resin, the perforation pin is protruded into the uncured molten resin to form a through-hole. According to this molding method, in a case where the cavity is filled with the molten resin, the flow of the resin is not hindered by the perforation pin, and accordingly, no weld lines are formed. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Patent No. 2717896 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a case of manufacturing a thick molded article by using a high-strength resin such as a super engineering plastic (PEEK, PPS, or PI) or a fiber-containing resin (a resin containing a carbon fiber, a glass fiber, or the like), pressing weight of the perforation pin when forming the through-hole in the resin increases, in the molding method disclosed in PTL 1. Therefore, it may be difficult to form a through-hole. In addition, the installation of the driving device may be difficult, since a large-sized driving device is required to drive the perforation pin. 
     An object of the invention is to provide a molding method and a molding device which can easily produce a molded resin article having a hole and by which a weld line is hardly generated. 
     Solution to Problem 
     According to an aspect of the invention, there is provided a molding method including a first step of making a perforation pin protrude into a cavity of a mold, a second step of injecting a molten resin and filling the cavity with the molten resin so as to envelop a protruding part of the perforation pin, a third step of making the perforation pin further protrude, in a state where the resin is not cured, and a fourth step of obtaining a molded resin article having a hole by curing the resin and extracting the perforation pin. 
     According to the molding method, a movement distance of the perforation pin in the third step can be reduced, and the pressing weight in a case of pressing the perforation pin into the resin can be prevented. Accordingly, it is easy to manufacture a molded resin article having a hole. In addition, since the pressing weight can be reduced, a small-sized driving mechanism with a low output can be used, so that a problem hardly occurs in the installation of the driving mechanism. Therefore, a molded resin article can be easily manufactured. 
     According to the molding method, a weld line is difficult to be formed, since the protrusion length of the perforation pin in the second step is short. 
     In the first step, a protrusion length of the perforation pin may be 25% to 40% with respect to a dimension of the cavity in a protruding direction of the perforation pin. 
     Therefore, the pressing weight in a case of making the perforation pin protrude in the third step can be reduced, and the formation of the weld line can be prevented. 
     In the third step, the perforation pin may penetrate the resin. 
     Therefore, a molded resin article having a through-hole can be easily manufactured. 
     In the molding method, the mold includes a first mold and a second mold facing each other with the cavity interposed therebetween, and in the first step, a plurality of the perforation pins are used, and among the plurality of the perforation pins, a first perforation pin is made to protrude into the cavity from the first mold, and a second perforation pin is made to protrude into the cavity from the second mold. 
     According to the molding method, since the plurality of perforation pins are used, the movement distance per perforation pin in the third step can be reduced. Therefore, the pressing weight can be reduced. 
     According to another aspect of the invention, there is provided a molding device including a mold for injection molding, a perforation pin capable of protruding into a cavity of the mold, a driving mechanism for the perforation pin, and a control section which controls a protrusion length of the perforation pin in the cavity. 
     According to the molding device, since the control section is provided, the pressing weight of the perforation pin is prevented by making the perforation pin protrude in a plurality of stages, thereby facilitating the manufacturing of the molded resin article. The molding device can set the protrusion length of the perforation pin in the first step to be short, thereby preventing a weld line. 
     Advantageous Effects of Invention 
     According to one aspect of the invention, a molded resin article having a hole can be easily manufactured, and a weld line is hardly generated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a molding device used in a molding method according to a first embodiment. 
         FIG. 2  is a schematic view showing a first step of the molding method according to the first embodiment. 
         FIG. 3  is a schematic view showing a second step of the molding method according to the first embodiment. 
         FIG. 4  is a schematic view showing the second step of the molding method according to the first embodiment. 
         FIG. 5  is a schematic view showing a third step of the molding method according to the first embodiment. 
         FIG. 6  is a schematic view showing a fourth step of the molding method according to the first embodiment. 
         FIG. 7  is a process drawing showing details of the second step of the molding method according to the first embodiment. 
         FIG. 8  is a process drawing following the previous drawing. 
         FIG. 9  is a process drawing following the previous drawing. 
         FIG. 10  is a process drawing following the previous drawing. 
         FIG. 11  is a schematic view of a molding device used in a molding method according to a second embodiment. 
         FIG. 12  is a schematic view showing a first step of the molding method according to a second embodiment. 
         FIG. 13  is a schematic view showing a second step of the molding method according to the second embodiment. 
         FIG. 14  is a schematic view showing a third step of the molding method according to the second embodiment. 
         FIG. 15  is a diagram showing a relationship between a pressing weight ratio and a thickness ratio of a perforation pin and a relationship between a joining angle of a molten resin and the thickness ratio in an example and comparative examples. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments to which the invention is applied will be described in detail with reference to the drawings. The drawings used in the following description are for describing the configuration of the embodiments of the invention, and sizes, thicknesses, dimensions, and the like of each portion shown in the drawings may be different from dimensional relationships of the actual device. 
     [First Embodiment] (Molding Device) 
       FIG. 1  is a schematic view of a molding device  10  (a manufacturing device of a molded resin article) used in a molding method (a manufacturing method of a molded resin article) according to a first embodiment.  FIGS. 2 to 6  are schematic views showing each step of the molding method according to the first embodiment. 
     As shown in  FIG. 1 , the molding device  10  includes a mold  1 , a perforation pin  2 , a driving mechanism  3 , and a control section  4 . 
     The mold  1  is a mold for injection molding and includes a first mold  11  and a second mold  12 . A cavity  13  is provided between the first mold  11  and the second mold  12 . The cavity  13  has a shape corresponding to the molded resin article  20  to be manufactured (see  FIG. 6 ). An inner surface  11   a  of the first mold  11  and an inner surface  12   a  of the second mold  12  face each other with the cavity  13  interposed therebetween. A thickness direction of the cavity  13  (vertical direction in  FIG. 1 ) is also referred to as a Z direction. 
     The first mold  11  has an insertion hole  15  through which the perforation pin  2  is inserted. The inner surface  11   a  of the first mold  11  faces the cavity  13 . The inner surface  11   a  has a shape conforming to a first surface  20   a  of the molded resin article  20  (see  FIG. 6 ). 
     The inner surface  12   a  of the second mold  12  faces the cavity  13 . The inner surface  12   a  has a shape conforming to a second surface  20   b  of the molded resin article  20  (see  FIG. 6 ). The second surface  20   b  is a surface opposite to the first surface  20   a  of the molded resin article  20 . 
     The perforation pin  2  may have a columnar shape having a central axis along the thickness direction (Z direction) of the cavity  13 , for example, a columnar shape, a prismatic shape (a quadrangular prism shape, a triangular prism shape, or the like). A length direction of the perforation pin  2  (perforation member) faces the thickness direction (vertical direction in  FIG. 1 ) (Z direction) of the cavity  13 . The perforation pin  2  is inserted through the insertion hole  15 . The perforation pin  2  is configured such that a portion  2   b  including a leading end  2   a  can protrude with respect to the cavity  13  of the mold  1 . 
     The perforation pin  2  is movable in the length direction (vertical direction in  FIG. 1 ) (Z direction). Accordingly, the perforation pin  2  is configured to be able to protrude with respect to the cavity  13  of the mold  1 . The perforation pin  2  can be provided at a position (non-protruding position) where the perforation pin does not protrude from the inner surface  11   a  into the cavity  13  (see  FIG. 1 ), or can be provided at a position (protruding position) where the portion  2   b  including the leading end  2   a  protrudes from the inner surface  11   a  into the cavity  13  (see  FIGS. 2 to 5 ). At the most lowered position (most protruding position), the leading end  2   a  of the perforation pin  2  comes into contact with the inner surface  12   a  of the second mold  12  (see  FIG. 5 ). 
     As shown in  FIG. 2 , a distance of the cavity  13  in the thickness direction (vertical direction in  FIG. 2 ) (Z direction) is referred to as a “total thickness T”. The total thickness T is a dimension of the cavity  13  in a protruding direction of the perforation pin  2  (vertical direction in  FIG. 2 ). The thickness dimension of the cavity at the leading end  2   a  of the perforation pin  2 , that is, a distance between the leading end  2   a  and the inner surface  12   a  in the Z direction (vertical direction in  FIG. 2 ) is referred to as a “thickness t”. “Thickness t/total thickness T” is referred to as a “thickness ratio”. As shown in  FIG. 1 , when the perforation pin  2  is at the non-protruding position, the thickness t is equal to the total thickness T, and thus the thickness ratio is 1. As shown in  FIG. 5 , when the perforation pin  2  is at the most protruding position, the thickness t is zero, and thus the thickness ratio is zero. 
     The driving mechanism  3  is, for example, a motor or the like, and can move the perforation pin  2  in a protruding direction (downward in  FIG. 1 ) and in the opposite direction thereof. 
     The control section  4  can drive the driving mechanism  3  based on position information of the perforation pin  2  detected by a sensor (for example, an optical sensor) (not shown), and control a length of the perforation pin  2  in the protruding direction (the protrusion dimension from the inner surface  11   a ). 
     [First Embodiment] (Molding Method) 
     Next, a molding method according to the first embodiment will be described with reference to  FIGS. 1 to 6 . 
     (First Step) 
     In the molding device  10  shown in  FIG. 1 , the perforation pin  2  is at a non-protruding position (position not protruding from the inner surface  11   a  into the cavity  13 ). 
     As shown in  FIG. 2 , the driving mechanism  3  is operated by the control section  4 , and the portion  2   b  including the leading end  2   a  of the perforation pin  2  is protruded into the cavity  13 . The protrusion length of the perforation pin  2  is referred to as “L”. The protrusion length L is a dimension from the inner surface  11   a  of the first mold  11  to the leading end  2   a  of the perforation pin  2  in the Z direction (thickness direction of the cavity  13 ). The protrusion length L of the perforation pin  2  in the first step is “L 1 ”. 
     The protrusion length L 1  of the perforation pin  2  in the first step is smaller than the total thickness T of the cavity  13 . Therefore, the leading end  2   a  of the perforation pin  2  does not reach the inner surface  12   a  of the second mold  12 . 
     It is desirable that the protrusion length L 1  is 25% to 40% of the total thickness T. When the protrusion length L 1  is 25% or more of the total thickness T, the pressing weight can be reduced when making the perforation pin  2  further protrude in the third step which will be described later. When the protrusion length L 1  is 40% or less of the total thickness T, formation of a weld line in the molded resin article  20  (see  FIG. 6 ) can be prevented. 
     (Second Step) 
     As shown in  FIGS. 3 and 4 , a molten resin  16  is introduced (injected) into the cavity  13  of the mold  1  from a resin introduction hole  1   a . An introduction direction of the resin  16  is not particularly limited, and is, for example, a direction that intersects the Z direction (protruding direction of the perforation pin  2 ). For example, the introduction direction of the resin  16  is a direction orthogonal to the Z direction. 
     As the resin  16 , a thermoplastic resin is preferable. Examples of the thermoplastic resin include polyetheretherketone (PEEK), polyphenylenesulfide (PPS), polyimide (PI), polyethersulfone (PES), aromatic polyamide (PA), and polyamideimide (PAI). The resin  16  may be a fiber reinforcing resin. As the fiber reinforcing resin, for example, a carbon fiber reinforcing resin, a glass fiber reinforcing resin, or the like can be used. A tensile strength (for example, based on ASTM D638) of the molded resin article made of the resin  16  is, for example, 90 MPa or more (for example, 90 MPa to 262 MPa). 
       FIGS. 7 to 10  are process diagrams showing the details of the second step, and are schematic views showing a flow of the resin  16  seen from a direction parallel to the Z direction. As shown in  FIG. 7 , the resin  16  that has reached the perforation pin  2  is divided into a plurality of directions, goes around the perforation pin  2  and joins. As shown in  FIG. 8 , a joining angle in a case where a resin flow  17 A in a direction around one axis of the perforation pin  2  and a resin flow  17 B in a direction around the other axis of the perforation pin  2  joins on a side of a back surface  2   c  of the perforation pin  2  is referred to as “θ”. The joining angle θ is, for example, an angle formed by surfaces of the resin flows  17 A and  17 B that joins on the back surface  2   c  at the same height position as the inner surface  11   a  (see  FIGS. 3 and 4 ). 
     As shown in  FIGS. 9 and 10 , the resin  16  flows including the protruding part of the perforation pin  2 , and is filled in the cavity  13  as shown in  FIG. 4 . 
     As shown in  FIGS. 3 and 4 , since the protrusion length L 1  of the perforation pin  2  is short, a weld line is not easily formed. The reason that the weld line is not easily formed can be assumed as follows. Since the protrusion length L 1  of the perforation pin  2  is short, the resin  16  that has come into contact with the perforation pin  2  is not only easily divided in the direction around the axis of the perforation pin  2 , but also in other directions (for example, direction going around the back surface  2   c  from the leading end side of the perforation pin  2 ). For this reason, the resin flows in many directions join on the back surface  2   c  of the perforation pin  2 , and therefore, the joining angle θ shown in  FIG. 8  is easily increased. If the joining angle θ is large, a weld line is hardly formed. For example, if the joining angle θ is 135° or more, a weld line is hardly formed. 
     (Third Step) 
     As shown in  FIG. 5 , in a state where the resin  16  is not cured, the driving mechanism  3  is operated by the control section  4  to further protrude the perforation pin  2 . That is, the protrusion length L of the perforation pin  2  is set as a protrusion length L 2  longer than the protrusion length L 1  (see  FIG. 4 ). The protrusion length L 2  is equal to the total thickness T of the cavity  13 . The perforation pin  2  is positioned at the most lowered position (most protruding position), and the leading end  2   a  comes into contact with the inner surface  12   a  of the second mold  12 . Therefore, the perforation pin  2  penetrates the resin  16 . 
     In this step, a movement distance of the perforation pin  2  to the most protruding position when making the perforation pin  2  protrude is smaller than a movement distance of the perforation pin  2  from the non-protruding position (see  FIG. 1 ) to the most protruding position. Therefore, the pressing weight when the perforation pin  2  is pushed into the resin  16  can be suppressed. Therefore, it is easy to form the through-hole  18  (see  FIG. 6 ) by the perforation pin  2 . In addition, since the pressing weight can be reduced, a small-sized driving mechanism  3  with a low output can be used. Therefore, a problem hardly occurs in the installation of the driving mechanism  3 . 
     (Fourth Step) 
     As shown in  FIG. 6 , the resin  16  (see  FIG. 5 ) is cured by cooling or the like. The resin  16  may be cooled using a coolant such as water or air, or may be allowed to cool. The cured resin  16  becomes the molded resin article  20 . The molded resin article  20  is taken out of the mold  1 . The perforation pin  2  is extracted from the molded resin article  20 . In the molded resin article  20 , the portion where the perforation pin  2  was located becomes the through-hole  18 . 
     According to the molding method of the first embodiment, the cavity  13  is filled with the resin  16  in a state where the perforation pin  2  is protruded (see  FIGS. 3 and 4 ) in the second step, and the perforation pin  2  is further protruded in the third step (see  FIG. 5 ). Accordingly, the movement distance of the perforation pin  2  in the third step can be reduced, and the pressing weight when the perforation pin  2  is pushed into the resin  16  can be suppressed. Therefore, it is easy to manufacture the molded resin article  20  having the through-holes  18  (see  FIG. 6 ). In addition, since the pressing weight can be reduced, a small-sized driving mechanism  3  with a low output can be used, so that a problem hardly occurs in the installation of the driving mechanism  3 . Thus, the molded resin article  20  can be easily manufactured. 
     According to the molding method of the first embodiment, since the protrusion length L 1  (see  FIGS. 3 and 4 ) of the perforation pin  2  in the second step is short, a weld line is not easily formed as described above. 
     In the molding method of the first embodiment, the perforation pin  2  penetrates the resin  16  in the third step, so that the molded resin article  20  having the through-hole  18  can be easily manufactured. 
     Since the molding device  10  includes the control section  4 , the pressing weight of the perforation pin  2  is suppressed by making the perforation pin  2  protrude in two stages, and the molded resin article  20  is easily manufactured. The molding device  10  can set the protrusion length L 1  of the perforation pin  2  in the first step to be short by the control section  4 , so that the weld line can be prevented. 
     [Second Embodiment] (Molding Device) 
       FIG. 11  is a schematic view of a molding device  110  used in a molding method according to a second embodiment.  FIGS. 12 to 14  are schematic views showing each step of the molding method according to the second embodiment. 
     The molding device  110  includes a mold  101 , perforation pins  2 A and  2 B, driving mechanisms  3 A and  3 B, and control sections  4 A and  4 B. 
     The mold  101  is a mold for injection molding and includes a first mold  111  and a second mold  112 . A cavity  13  is provided between the first mold  111  and the second mold  112 . An inner surface  11   a  of the first mold  111  and an inner surface  112   a  of the second mold  112  face each other with the cavity  13  interposed therebetween. The first mold  111  has an insertion hole  15 A through which the first perforation pin  2 A is inserted. The second mold  112  has an insertion hole  15 B through which the second perforation pin  2 B is inserted. 
     The perforation pins  2 A and  2 B are movable in the length direction and can protrude with respect to the cavity  13 . 
     The driving mechanisms  3 A and  3 B are, for example, motors or the like, and can move the perforation pins  2 A and  2 B respectively in a protruding direction and in the opposite direction thereof. 
     The control sections  4 A and  4 B can drive the driving mechanism  3  based on position information of the perforation pins  2 A and  2 B detected by a sensor (not shown), and control a length of the perforation pins  2 A and  2 B in the protruding direction. 
     [Second Embodiment] (Molding Method) 
     Next, a molding method according to the second embodiment will be described with reference to  FIGS. 11 to 14 . 
     (First Step) 
     In the molding device  110  shown in  FIG. 11 , the perforation pins  2 A and  2 B are at the non-protruding position. 
     As shown in  FIG. 12 , the driving mechanisms  3 A and  3 B are operated by the control section  4 , and the portions including leading ends of the perforation pins  2 A and  2 B are protruded into the cavity  13 . 
     A total of protrusion lengths L 3 A and L 3 B of the perforation pins  2 A and  2 B in the first step is smaller than the total thickness T of the cavity  13 . Accordingly, the leading ends of the perforation pins  2 A and  2 B do not come into contact each other. It is desirable that the total of the protrusion lengths L 3 A and L 3 B is 25% to 40% of the total thickness T. Therefore, the pressing weight in a case of making the perforation pins  2 A and  2 B protrude in the third step can be reduced, and the formation of the weld line can be prevented. 
     (Second Step) 
     As shown in  FIG. 13 , the molten resin  16  is introduced (injected) into the cavity  13  of the mold  101  from the resin introduction hole  1   a . An introduction direction of the resin  16  is, for example, a direction that intersects the Z direction (protruding direction of the perforation pins  2 A and  2 B) (for example, direction orthogonal to the Z direction). The resin  16  includes the protruding parts of the perforation pins  2 A and  2 B, and is filled in the cavity  13 . In this case, since the protrusion lengths L 3 A and L 3 B of the perforation pins  2 A and  2 B are short, a weld line is not easily formed. 
     (Third Step) 
     As shown in  FIG. 14 , the driving mechanisms  3 A and  3 B are operated by the control sections  4 A and  4 B to further protrude the perforation pins  2 A and  2 B, in a state where the resin  16  is not cured. The leading ends of the perforation pins  2 A and  2 B come into contact with each other. Therefore, the perforation pins  2 A and  2 B penetrate the resin  16 . A total of protrusion lengths L 4 A and L 4 B of the perforation pins  2 A and  2 B in the third step is greater than the total of the protrusion lengths L 3 A and L 3 B. 
     (Fourth Step) 
     The resin  16  is cured by cooling or the like. The cured resin  16  becomes the molded resin article  20  (see  FIG. 6 ). The molded resin article  20  is taken out of the mold  101 . The perforation pins  2 A and  2 B are extracted from the molded resin article  20 . In the molded resin article  20 , the portion where the perforation pins  2 A and  2 B were located becomes the through-hole  18  (see  FIG. 6 ). 
     According to the molding method of the second embodiment, the cavity  13  is filled with the resin  16  in a state where the perforation pins  2 A and  2 B are protruded in the second step (see  FIG. 13 ), and the perforation pins  2 A and  2 B are further protruded in the third step (see  FIG. 14 ). Therefore, the pressing weight when the perforation pins  2 A and  2 B are pushed into the resin  16  can be suppressed. Therefore, it is easy to manufacture the molded resin article  20  having the through-holes  18  (see  FIG. 6 ). 
     In the molding method of the second embodiment, since two perforation pins  2 A and  2 B are used, the movement distance of the perforation pins  2 A and  2 B in the third step (movement distance per perforation pin) can be reduced, compared to that in the molding method of the first embodiment. Therefore, the pressing weight can be reduced. 
     According to the molding method of the second embodiment, since the protrusion lengths L 3 A and L 3 B of the perforation pins  2 A and  2 B in the second step are short, and accordingly, a weld line is not easily formed. In the molding method of the second embodiment, since two perforation pins  2 A and  2 B are used, the protrusion length of the perforation pins  2 A and  2 B in the second step (protrusion length per perforation pin) can be reduced, compared to that in the molding method of the first embodiment. Therefore, a weld line is not easily formed. 
     In the molding method of the second embodiment, the perforation pins  2 A and  2 B penetrate the resin  16  in the third step, so that the molded resin article  20  having the through-hole  18  can be easily manufactured. 
     Example 
     As shown below, the pressing weight and the joining angle when manufacturing the molded resin article  20  by the molding method of the first embodiment were evaluated by using the molding device  10  shown in  FIG. 1 . The perforation pin  2  has a circular shape (outer diameter of 3.6 mm) when seen from the length direction. 
     As shown in  FIG. 2 , the driving mechanism  3  made the perforation pin  2  protrude into the cavity  13  (first step) As shown in  FIGS. 3 and 4 , the molten resin  16  is introduced into the cavity  13  of the mold  1  (second step). As shown in  FIG. 5 , in a state where the resin  16  is not cured, the driving mechanism  3  made the perforation pin  2  further protrude (third step). As shown in  FIG. 6 , the resin  16  was cured, and the molded resin article  20  was taken out of the mold  1  (fourth step). 
     In the example, the thickness ratio (thickness t/total thickness T in  FIG. 2 ) is in a range of 0.25 to 0.75. 
     Comparative Examples 
     For comparison, the same evaluation test as in the example was performed, except that the perforation pin  2  was not protruded in the first step (that is, the thickness ratio was set to 1) (Comparative Example 1). In addition, the same evaluation test as in the example was performed, except that the perforation pin  2  was set at the most protruding position in the first step (that is, the thickness ratio was set to zero) (Comparative Example 2). In Comparative Example 2, since the perforation pin  2  is at the most protruding position in the first step, the perforation pin  2  does not move in the third step. 
       FIG. 15  is a diagram showing a relationship between a pressing weight ratio and a thickness ratio of a perforation pin and a relationship between a joining angle (see  FIG. 8 ) of a molten resin and the thickness ratio in an example and comparative examples. The “pressing weight ratio” is a ratio “W 1 /W 2 ” of a pressing weight W 1  in the third step and a pressing weight W 2  in the third step in the case of the thickness ratio 1 (Comparative Example 1). 
     From  FIG. 15 , it can be said that in the example (thickness ratio of 0.25 to 0.75), the pressing weight is lower than that in Comparative Example 1 (thickness ratio of 1), so that a molded resin article can be easily manufactured. In the example, the joining angle is larger than that in Comparative Example 2 (thickness ratio of zero). 
     In particular, in a case where the thickness ratio is 0.6 or more, it is considered that a weld line is hardly formed, since the joining angle is 135° or more. Therefore, at least in a range of the thickness ratio of 0.6 to 0.75, it can be said that good results were obtained for both the joining angle in the second step and the pressing weight in the third step. The thickness ratio of 0.6 corresponds to that a ratio of the protrusion length of the perforation pin  2  in the first step to the thickness dimension of the cavity  13  is 40%. The thickness ratio 0.75 corresponds to the ratio of 25%. 
     Hereinabove, the preferred embodiments of the invention have been described in detail, but the invention is not limited to such specific embodiments, and various modifications or changes may be made within the gist of the invention described in the appended claims. 
     For example, in the molding methods of the first embodiment and the second embodiment, the perforation pin penetrates the resin in the third step, but the perforation pin may not penetrate the resin. Therefore, the hole formed in the molded resin article may be not a through-hole. 
     In the molding methods of the first embodiment and the second embodiment, the perforation pin is protruded in two stages, but the number of stages in which the perforation pin is protruded may be any number of three or more. 
     The number of perforation pins used in the molding method of the first embodiment is 1, and the number of perforation pins used in the molding method of the second embodiment is 2, but the number of perforation pins used in resin molding may be any number of 3 or more. In addition, the number of holes formed in the molded resin article is not limited to one, and may be any number of 2 or more. 
     INDUSTRIAL APPLICABILITY 
     According to the molding method and the molding device described above, a molded resin article having a hole can be easily manufactured, and a weld line is hardly generated. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  101  mold 
               2 ,  2 A,  2 B perforation pin 
               3 ,  3 A,  3 B driving mechanism 
               4 ,  4 A,  4 B control section 
               10 ,  110  molding device 
               11 ,  111  first mold 
               12 ,  112  second mold 
               13  cavity 
               16  resin 
               18  through-hole (hole) 
               20  molded resin article 
             L, L 1 , L 2 , L 3 A, L 3 B, L 4 A, L 4 B protrusion length 
             T total thickness (dimension of cavity in the protruding direction)