Abstract:
A hose coupling fitting is furnished with a coupling head portion having a connecting hole, and a nipple portion having a nipple hole, and is fabricated through sequential cold forging steps carried out on a rod material. Specifically, a first pilot hole is formed along the center axis from a first end of the rod material, and a second pilot hole is formed along the center axis from the other end of the rod material. The second pilot hole is connected to the first pilot hole, and is formed with smaller diameter than the first pilot hole and larger diameter than the nipple hole. The surrounding area of the second pilot hole is then worked to form the nipple portion.

Description:
This application claims the benefit of and priority from Japanese Application No. 2007-175728 filed Jul. 4, 2007, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of manufacturing a hose coupling fitting for connecting various kinds of hoses for fluids, such as automotive brake hoses. 
     2. Description of the Related Art 
     Conventional hose coupling fittings of this kind are furnished with a coupling head portion having a connection opening and a coupling body which has a nipple portion; a line on the brake cylinder side is connected to the connection opening, and a hose on the master cylinder side is inserted into and connected with the nipple portion to connect the master cylinder with the brake cylinder. In a hose coupling fitting of this design, the nipple portion is a thin elongated pipe which inserts into the path of the hose and which must be worked to high dimensional accuracy. For this reason the part is typically manufactured by a cutting operation, or by producing a separate component and unifying this with the coupling body by welding. 
     In this regard, with a view to manufacturing a hose coupling fitting of simpler design composed of single component without the need for a cutting process, methods which simply entail a series of cold forging steps have been considered; one such known technique is disclosed in JP 2002-361359 A. In this conventional technique, a large-diameter bore is formed in a thick, short rod-shaped material which then undergoes several cold forging steps to produce the connection opening and the nipple portion. However, in a conventional hose coupling fitting of ferrule shape having a socket portion and a nipple portion, appreciable deformation is necessary in order to transform the large-diameter through-bore into a narrow and elongated nipple hole, and it is difficult in practice for uniform shaping to take place between the upper end face and the lower end face of the nipple hole, thus creating the problem of appreciable deviation in the inside diameter dimension due to inside diameter taper or rippling, and making it difficult to achieve the desired shape. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a hose coupling fitting whose nipple portion can be produced with a high degree of accuracy through a series of cold forging steps. 
     In order to achieve the stated object at least in part, it is possible for the present invention to be reduced to practice as the embodiments shown below. 
     According to an aspect of the invention is provided with a method of manufacturing a hose coupling fitting comprising: a coupling head portion having a connecting hole for connection to a pipe; and a nipple portion having a nipple hole for connection to a hose. The method comprises: a plurality of sequentially performed cold forging steps carried out on a column-shaped rod material. The plurality of steps include: forming a first pilot hole which extends along a center axis of the rod material from an end of the rod material to form the connecting hole, and forming a second pilot hole which extends along the center axis of the rod material from the other end of the rod material to form the nipple hole; and forming the coupling head portion by forging a portion surrounding the first pilot hole, and the nipple portion by forging a portion surrounding the second pilot hole. The second pilot hole is connected to the first pilot hole, and is formed with smaller diameter than the first pilot hole and larger diameter than the nipple hole. 
     In a preferred embodiment, the coupling head portion having the connecting hole and the nipple portion having the nipple hole are formed through cold forging of the rod material of circular cylinder shape. Specifically, through cold forging, a first pilot hole for forming the connecting hole is formed along the center axis of the rod material from a first end of the rod material, and a second pilot hole is formed along the center axis of the rod material from the other end of the rod material. The second pilot hole is formed with smaller diameter than the first pilot hole and larger diameter than the nipple hole. At this point the second pilot hole may be formed so as to connect to the first pilot hole at one time, or to connect with it multiple stages. Next, a working process is carried out to make the portion surrounding the first pilot hole into the coupling head portion, and to make the portion surrounding the second pilot hole into the nipple portion. 
     According to another embodiment, the hose coupling fitting can be formed simply through a series of steps involving cold forging of the rod material, and thus no cutting step is required, thereby affording a simpler working process and excellent productivity. Moreover, since it suffices for the second pilot hole to be bored through a solid section of the rod material equal in length to the total length of the rod material minus the depth of the first pilot hole, its passage length can be shorter, the load on the punch and pin can be reduced, and the desired shape can be produced easily with high accuracy. Additionally, since the second pilot hole is formed prior to working of the nipple portion, due the absence of work hardening in the surrounding area, a long narrow nipple hole can be formed easily in the rod material with reduced load on the punch and pin. 
     In the method of manufacturing a hose coupling fitting of another embodiment, there can be employed a step wherein, where the inside diameter of the second pilot hole is denoted as d 5  and the inside diameter of the nipple hole is denoted as d 3 , d 5 /d 3  is set to between 1.1 and 3, preferably between 1.2 and 2. The reason is that if d 5 /d 3  exceeds 3, a high degree of working will be needed to reduce the diameter of the second pilot hole to that of the nipple hole, making it difficult to work the material into the desired shape. 
     As another embodiment, there can be employed a step wherein the second pilot hole is formed by forming a recess along the center axis, then punching through the center portion along the center axis to connect with the first pilot hole. 
     Best Mode for Carrying Out the Invention 
     These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a hose coupling fitting pertaining to an embodiment of the present invention, connecting a pipe to a hose. 
         FIG. 2  is a sectional view showing the hose coupling fitting prior to connection of the pipe and the hose in  FIG. 1 . 
         FIG. 3  shows the dimensions of a hose coupling fitting. 
         FIGS. 4A through 4D  show the manufacturing process of a hose coupling fitting. 
         FIGS. 5A through 5C  show the manufacturing process continued from  FIG. 4 . 
         FIGS. 6A through 6B  show the cold forging process. 
         FIGS. 7A through 7B  show the cold forging process continued from  FIG. 6B . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     (1) General Configuration of Hose Coupling Fitting  10   
       FIG. 1  is a sectional view of a hose coupling fitting  10  used to connect a pipe H 1  to a hose H 2  pertaining to an embodiment of the present invention. The hose coupling fitting  10  is used for connection of an automotive brake hose or the like; the pipe H 1  is connected through threadable attachment of a fastening member  30 , while at the other side of the hose coupling fitting  10 , the hose H 2  is connected through swaging with the hose H 2  pressure-fit therein. The hose coupling fitting  10  is mounted onto a mounting member VM via a mounting fitting AP by positioning a mounting hole VMa of the mounting member VM on a mounting shoulder portion  10   a  which has been disposed in the outside peripheral edge part of the hose coupling fitting  10 . 
     (2) Configuration of Hose Coupling Fitting  10   
     The configuration of the various parts of the hose coupling fitting  10  will be described in detail.  FIG. 2  is a sectional view showing the hose coupling fitting  10  prior to connection of the pipe H 1  and the hose H 2  in  FIG. 1 . The hose coupling fitting  10  includes a coupling head portion  14 , a dividing wall  16 , a socket portion  18 , and a nipple portion  20  which are integrally formed from metal material. In the interior of the hose coupling fitting  10  there are formed holes which extend in the axial direction for attachment of the pipe H 1  and the hose H 2  shown in  FIG. 1 ; the holes are separated by the dividing wall  16 , that is, a connecting hole  14   a  for attachment of the pipe H 1  is formed in the coupling head portion  14 , while a socket hole  18   a  for attachment of the hose H 2  is formed in the socket portion  18  and the nipple portion  20 . The socket portion  18  is the part in which the hose H 2  is connected through swaging diametrically inward from the outside peripheral portion thereof with the hose H 2  ( FIG. 1 ) inserted into the socket hole  18   a . The nipple portion  20  has a pipe body  22  which projects from the dividing wall  16  for pressure-fitting the hose H 2 . A nipple hole  22   a  for connecting the pipe H 1  and the hose H 2  is formed through the center of the pipe body  22  and the dividing wall  16 . The pipe body  22  is pressure-fit into the hose H 2 , and the hose H 2  is then connected by swaging the socket portion  18  from the outside peripheral side. 
     As shown in  FIG. 3 , exemplary dimensions for the various parts are, in the coupling head portion  14 , length L 1  of 11.5 mm, outside diameter D 1  of 15 mm, and connecting hole  14   a  inside diameter d 1  of 9.5 mm. In the socket portion, length L 2  may be 17 mm, outside diameter D 2  may be 13.5 mm, and inside diameter d 2  may be 11.3 mm; while in the nipple portion  20 , length L 3  may be the same as the socket portion  18 , while outside diameter D 3  may be 3.6 mm, and inside diameter d 3  may be 2.2 mm. 
     (3) Manufacturing Process of Hose Coupling Fitting  10   
     The process for manufacturing the hose coupling fitting  10  through a cold forging process will now be described.  FIGS. 4 and 5  show the cold forging process of the hose coupling fitting  10 . The hose coupling fitting  10  is manufactured from a single rod material through a plurality of cold forging steps. First, a rod material  12 A of metal material shown in  FIG. 4A  is set in a die (not shown), and recesses which will ultimately serve as a first pilot hole  14 Aa and a second pilot hole  22 Aa are formed in the rod material  12 A as shown in  FIG. 4B , producing a workpiece  12 B. The first pilot hole  14 Aa is a hole used to form the connecting hole  14   a  ( FIG. 2 ); its inside diameter d 4  is substantially identical to the inside diameter d 1  of the connecting hole  14   a . The second pilot hole  22 Aa is a hole used to form the nipple hole  22   a ; its inside diameter d 5  is smaller than the inside diameter d 4  of the first pilot hole  14 Aa, and larger than the inside diameter d 3  of the nipple hole  22   a , e.g. 3 mm. Next, as shown in  FIG. 4C , a recess  14 Ab is formed in the center of the first pilot hole  14 Aa and the second pilot hole  22 Aa is increased in depth to produce a workpiece  12 C; then, as shown in  FIG. 4D , the second pilot hole  22 Aa is extended and punched through to connect with the first pilot hole  14 Aa to produce a workpiece  12 D. 
     Next, the workpiece  12 D of  FIG. 4D  is worked to produce a workpiece  12 E shown in  FIG. 5A .  FIG. 6A  depicts the cold forging process; the workpiece  12 D is arranged in a die  41  and punch  43 . At this point, since the pin  43   a  of the punch  43  is formed with diameter substantially the same as the inside diameter d 3  of the nipple hole  22   a  but smaller than the inside diameter d 5  of the second pilot hole  22 Aa, there will be gap between it and the second pilot hole  22 Aa. Then, the workpiece  12 D is extruded forward by the punch  43  as shown in  FIG. 6B . By so doing, the workpiece  12 D is cold-forged into the shape of the workpiece  12 E, that is, the section shown at right in the drawing is reduced in diameter until it equals the outside diameter of the socket portion  18 , and the second pilot hole  22 Aa equals that of the pin  43   a.    
     Subsequently, the workpiece  12 E of  FIG. 5A  is worked to produce a workpiece  12 F shown in  FIG. 5B .  FIG. 7A  depicts the cold forging process with the workpiece  12 E having been set in dies  45 ,  46 . The die  46  has a pin  46   a . The pin  46   a  is a rod shaped member of outside diameter equal to the inside diameter d 3  of the nipple hole  22   a . Meanwhile, the punch  47  is provided with a circular pipe portion  47   a  which is positioned concentric to the pin  46   a . The pipe portion  47   a  is the section in which the socket hole  18   a  is formed, and is defined by a tubular body of outside diameter equal to the inside diameter d 2  of the socket hole  18   a . The workpiece  12 E is then extruded forward by the punch  47  as shown in  FIG. 7B . The workpiece  12 E is thereby worked into the workpiece  12 F. The workpiece  12 F is then worked with a die and punch (not shown) into the workpiece  12 G ( FIG. 5C ), that is, to the length of the socket portion  18  and the length of the nipple portion  20  shown in  FIG. 2 . Then, by way of an after-treatment, a screw thread or the like is formed in the workpiece  12 G, to obtain the hose coupling fitting  10 . 
     (4) Working Effects of the Hose Coupling Fitting  10   
     The hose coupling fitting  10  described above affords the following working effects. 
     (4)-1 The hose coupling fitting  10  can be formed from the rod material  12 A simply by a series of cold forging steps with no cutting step required, thus affording a simple working process and excellent productivity. 
     (4)-2 As shown in  FIG. 3  and  FIG. 4B , since the nipple hole  22   a  in inner diameter d 3  is worked through reduction in diameter from the second pilot hole  22 Aa having inside diameter d 5  slightly larger than its original inside diameter d 3 , the forging ratio is low. Therefore, even a long narrow nipple hole  22   a  can be formed easily to the desired shape with a high degree of accuracy. 
     (4)-3 Since the second pilot hole  22 Aa is subjected to working with the pin  43   a  shown in  FIG. 6  inserted leaving a gap, the load bearing on the pin  43   a  can be reduced, facilitating the forging process. 
     (4)-4 Since the second pilot hole  22 Aa is formed prior to working of the nipple portion  20  and so on in subsequent steps, the hole can be formed easily in the rod material in the absence of work hardening in the area, under conditions of reduced load on the punch and pin. 
     (4)-5 Since the second pilot hole  22 Aa is formed so as to connect to the first pilot hole  14 Aa subsequent to formation of the first pilot hole  14 Aa, it can be shorter by the equivalent of the length of the first pilot hole  14 Aa, and the load on the punch and pin can be reduced. 
     (4)-6 As shown in  FIGS. 6 and 7 , since the socket portion  18  and the nipple portion  20  are fabricated through expansion by forward extrusion of the workpieces  12 D,  12 E, the initial second pilot hole  22 Aa can be shorter and formed easily. 
     The foregoing detailed description of the invention has been provided for the purpose of explaining the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. The foregoing detailed description is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Modifications and equivalents will be apparent to practitioners skilled in this art and are encompassed within the spirit and scope of the appended claims.