Patent Publication Number: US-2007113612-A1

Title: Manufacturing method for a press work product

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a manufacturing method for a press work product, more precisely, the manufacturing method for the press work product which has a tapped bore for a stem of a flat countersink head screw to penetrate therethrough and a countersink for a head of the flat countersink head screw to seat therein.  
      2. Description of the Related Arts  
      Various products can be the press work products, which were formed by the press work to be in desirable shapes. Among them, for example, FIGS.  4 (A) and  4 (B) illustrate the press work product  10  having the tapped bore  14  and the concave countersink  15  formed at periphery of the tapped bore  14 . Here, the press work product  10  is installed on an appropriate device (not shown in FIGS.) by the flat countersink head screw, wherein the countersink  14  is to have the stem of the flat countersink head screw penetrate therethrough and the countersink  15  allows the head of the flat countersink head screw to seat therein. Here, the press work is a forming means as plastic-deforming the material. More broadly, the press work is a forming means including forging.  
      With respect to this type of the press work product  10 , the outside diameter is formed as punching the plate material such as a rolled plate; the tapped bore  14  thereof is formed by punching; and the countersink  15  is formed by press form. That is, regarding this press work product  10 , generally, an individual press work product  10  is formed by a process of appropriate press forming as punching the plate material to be the work, punching the work to form the tapped bore  14 , and press forming the work to form the countersink  15 .  
      The above-described technology is a conventional type and the applicant did not take any written document describing the conventional technology into consideration at the time of this application.  
      According to the above-described conventional art, the countersink  15  is formed by press-forming. However, when the press-forming is being performed, the wall thickness of the countersink  15  is shifted toward outer direction of the countersink  15 . Therefore, as shown in  FIG. 4 (C), the outer diameter of the work is deformed, thereby making the countersink  15  distorted and preventing the same from being a complete round. Here, in the figure, for the sake of convenience of the explanation, the deformation of the outside diameter of the work and distortion of the countersink  15  may be exaggerated.  
      Especially, when the tapped bore  14  and the countersink  15  are provided around portions of the outside of the work, the outside diameter of the work tends to be easily deformed to a greater extent, thereby generating the above problem more significantly. Also, if the depth of the countersink  15  is equal or greater to 0.5 times the thickness of the work, the amount of the deformation/distortion relative to the wall thickness of the countersink  15  shifted as press forming the countersink  15  becomes larger, thereby generating the above problem more significantly.  
      As the deformation/distortion occurs to the countersink  15 , the head of the flat countersink head screw does not evenly abut against an entire surface area of the countersink  15 , which causes a half-abutment and makes the flat countersink head screw easily loosened. Therefore, for the countersink, the deformation/distortion should be minimized and more accurate complete round is desired.  
      In addition, when the countersink  15  is press-formed, the work may be placed in the press die in order to provide a stable press-forming and to avoid causing the deformation of the outside diameter of the work. However, more precisely, because the outside diameter of the work is formed as punching the plate material, generally, an outer end surface of the work has burr and gouge, which preventing the outside diameter of the work from being highly accurate. Therefore, even if the work is placed in the press die, the press die cannot retain the work as desired which causes backlash and deforms the outside diameter of the work to the extent of the backlash. Accordingly, a simple process of placing the work in the press die does not solve the problem of removing or minimizing the deformation/distortion of the countersink  15 .  
      This invention is made in consideration of the above facts and is to provide the manufacturing method for the press work product which minimizes the deformation/distortion of the countersink when forming the countersink by the press forming.  
     SUMMARY OF THE INVENTION  
      A primary method of this invention to resolve the above-described problem is the manufacturing method for the press work product which has the tapped bore for the stem of the flat countersink head screw to penetrate therethrough and the countersink for the head of the flat countersink head screw to seat therein, comprising steps of forming a work as the press work product by punching a plate material, trimming an outside diameter of the work, and forming the countersink by inserting the work after trimming the outside diameter into a press die to press form thereof.  
      Here, “trimming” is to cut an end surface of the work slightly and to remove the burr and gouge left on the end surface, which makes accurate outside diameter of the work. More concretely, the outside diameter formed by punching (hereinafter referred to as a first outside diameter) is cut about 0.1-0.5 mm to form slightly smaller outside diameter (hereinafter referred to as a second outside diameter). Here, the second outside diameter of the work after the trimming may, as it is, be treated as the outside diameter of the finished press work product or as may further be processed to lead the outside diameter to be the one of the finished press work product.  
      Under the above-described process of the method for manufacturing the press work product, the outside diameter of the work is trimmed to increase the accuracy and preciseness of the dimension, and then as the countersink is being formed thereon via press forming, the work is placed in the press die. Therefore, the outside diameter of the work is firmly retained by the press die. Furthermore, because the outside diameter of the work is firmly retained, no deformation/distortion occurs in the outside diameter of the work even if the wall thickness of the countersink  
      Accordingly, the above-structured manufacturing method for the press work product minimize the chance of causing the deformation/distortion of the countersink as the countersink is being formed by the press forming.  
      Also, regarding a formation of the tapped bore, no particular process is required, and the tapped bore may simultaneously be formed by punching during the work forming process, the trimming process, and the countersink forming process or may be formed prior to or after the countersink forming process or any appropriate stage.  
      In the above-described method, the press work product may be a disc-shape, and the tapped bores and countersink may be formed on plural positions around a stem center at outer side of the press work product.  
      Here, “at outer side portion” means a portion closer to an outer surface than a central region thereof between an inner side surface and an outer side surface defining the outside diameter, for example, when a center bore stands around the stem and the inner side surface exists at the inner side thereof. On the other hand, in the case that the press work product does not have the inner side surface, “at outer side portion” means a portion closer to the outer side surface than the central region between the center of the press work product and the outer side surface defining the outside diameter.  
      The above-described structure of the manufacturing method for the press work product is to define the shape of the press work product, and the above-manufacturing method for the press work product is employed for the press work product wherein the outside diameter of work can easily be deformed and the countersink can easily deformed/distorted when press-forming the countersink.  
      Hence, the above-described structure of the manufacturing method for the press work product surely reduces the chance of causing the deformation/distortion of the countersink as manufacturing the press work product having the countersink with tendency to be deformed/distorted.  
      In the above-described method, the depth of said countersink is equal or greater to 0.5 times the thickness of said work.  
      The above-described structure of the manufacturing method for the press work product also is to define the shape of the press work product, and the above-manufacturing method for the press work product is employed for the press work product wherein the outside diameter of work can easily be deformed and the countersink can easily deformed/distorted when press-forming the countersink.  
      Hence, the above-described structure of the manufacturing method for the press work product surely reduces the chance of causing the deformation/distortion of the countersink as manufacturing the press work product having the countersink with tendency to be deformed/distorted.  
      As above, this invention provides the manufacturing method for the press work product which surely reduces the chance of deforming/distorting the countersink as the countersink is being formed by press forming. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects of the present invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:  
       FIG. 1 (A) is a cross-section view of the press work product according to an example of the manufacturing method of this invention;  
       FIG. 1 (B) is a cross-section view of the press work product having the center hole with a partial enlarged view showing burr and gouge left on the end surface thereof according to an example of the manufacturing method of this invention;  
       FIG. 1 (C) is a cross-section view of the press work product having the center hole with a partial enlarged view showing the trimmed end thereof according to an example of the manufacturing method of this invention;  
       FIG. 1 (D) is a cross-section view of the press work product having the center hole with a tapered portion according to an example of the manufacturing method of this invention;  
       FIG. 1 (E) is a cross-section view of the press work product having the center hole with a tapped bore according to an example of the manufacturing method of this invention;  
       FIG. 1 (F) is a cross-section view of the press work product having the center hole with a countersink according to an example of the manufacturing method of this invention;  
       FIG. 2  is an enlarged cross-section view of a critical area at the tapped bore forming process;  
       FIG. 3  is an enlarged cross-section view of a critical area at the countersink forming process; and  
       FIG. 4 (A) is a plan view of an example of the press work product;  
       FIG. 4 (B) is a cross-section view taken along the line A-A of  FIG. 4 ( a ); and  
       FIG. 4 (C) is an enlarged partial plan view of the press work product. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION  
      One example of this invention relating a manufacturing method for a press work product will be explained with reference to the accompanying drawings.  FIG. 4 (A) and  FIG. 4 (B) are representative drawings of the manufacturing method of the press work product  10 ; however, the manufacturing method for the press work product according to this invention is not limited to this type. Therefore, the manufacturing method is applicable for a wide variety of range of the press work products  10  having a tapped bore  14 , through which a stem of a flat countersink head screw is penetrated, and a countersink  15 , which is formed around a circumferential line of the tapped bore  14  and in which a head of the flat countersink head screw is positioned.  
      The details of the press work product  10  will be explained next.  
      As shown in  FIG. 4 (A) and  FIG. 4 (B), the press work product  10  comprises a tubular main body  11 , a center bore  12  having a taper portion  13  and vertically formed around an axle of the main body  11 , tapped bores  14  vertically formed with an appropriate pitch around a circumferential line of the main body  11 , and a countersink  15  formed around a circumferential line of the tapped bore  14 .  
      Generally, the press work product  10  is installed in a various products using countersink. Although omitted in the figure, as a concrete example, the press work product  10  may be assembled in a synchronous pulley winding a timing belt for transmitting a drive of the engine crankshaft to a camshaft. More concretely, the press work product  10  is assembled in a synchronous pulley which, in order to control a timing of an opening-closing action of a valve for supplying and exhausting the air corresponding to the number of rotation of the engine, causes a phase shift with respect to the rotation between the peripheral teeth engaging with the timing belt and the axle rotating the camshaft. The synchronous pulley of this type is one type of fluid pressure devices operating to cause the rotation phase shifting or not to cause the rotation phase shifting. Furthermore, the above-press work product  10  is a cover for a housing of the fluid pressure devices sealing an internal fluid.  
      Also, the press work product  10  is manufactured by punching of the rolled plate as the plate material, more concretely “SPHE” and through various later described press forming processes.  
      Here, the countersink  15  is formed by press-forming and is positioned around outer side of the press work product  10 . Furthermore, the thickness thereof is equal or greater to 0.5 times the main body  11  and therefore the outer diameter of the press work product  10  can easily be deformed as press-forming the countersink  15 , thereby causing a larger distortion in the countersink  15 . Especially in this embodiment, the countersink  15  is formed around the peripheral surface of the press work product  10 , and the distance between the peripheral end of the countersink  15  and the outer diameter of the press work product  10  is shorter, thereby making it easy to cause the deformation of the outer diameter and larger distortion of the countersink  15 . Concretely, the distance between the peripheral surface of the press work product  10  and the peripheral end of the countersink  15  is short, about 0.5-5 mm, more concretely, 1-3 mm.  
      As employing the manufacturing method of this invention, the distortion of the countersink  15  can be minimized and the countersink  15  can accurately be in a circular shape.  
      Next, the manufacturing method of this invention will be explained with reference to  FIG. 1 .  
      A disc-shaped work  1  to be the work forming process is used to form the respective press work product  10  as punching the rolled plate of the plate material as shown in  FIG. 1 (A). A rough outside diameter of the finished press work product  10  is defined by the outside diameter of the work  1 .  
      Next, in the process of forming the center hole, a central region of the work  1  is punched to vertically form the center bore  12  as shown in  FIG. 1 (B). At this time, the outside diameter of the work  1  still is in the condition that the raw material is simply punched with low accuracy in its diameter because of burr and gouge left on the end surface as shown in the enlarged view.  
      Next, in the trimming process, the outside diameter of the work  1  is trimmed (c). That is, the burr and gouge are removed as smoothing the end surface of the periphery of the work  1  by cutting with a trimming die as appeared in the enlarged view. As such, the outside diameter of the work  1  becomes slightly smaller but the accuracy of the outside diameter is maintained. Also, at this time, using the center bore  12 , the position of the work  1  relative to the trimming die is determined.  
      Next, in the process of forming the tapered portion, the tapered portion  13  is press-formed at one side of the center bore  12 ( b ).  
      Next, in the forming process of the tapped bore, the tapped bore  14  is vertically formed by punching (e). At this time, as shown in  FIG. 2 , the tapped bore  14  is formed near the peripheral surface of the work  1 , and the wall thickness of the work  1  shifts (as shown in an arrow of the figure) to make it easy for the outside diameter of the work  1  to be deformed. However, the outside diameter of the work  1  with high accuracy in its outside diameter by trimming is placed in the press die K for the outside diameter of the work  1  to be firmly retained therein, thereby restricting the shifting generally occurring as punching the tapped bore  14  by a punch P and reducing the chance of causing the deformation of the work  1 . Also, the work  1  with high accuracy in its outside diameter  
      In the last process of forming the countersink, the countersink  15  is formed around the circumferential line of the tapped bore  14  by press-forming to complete the press work product  10 ( f ). At this time, the countersink  15  is formed around the peripheral surface of the work  1  and is shaped in a deep pocket like form, which tends to cause the deformation of the outside diameter of the work  1 . Especially, as shown in  FIG. 3 , the punch P press-forming the countersink  15  is tapered and as the tapered punch P is pressed against the work the wall thickness of the work  1  rather than the punching shifts larger (as appeared in the arrow in the figure), thereby tending to cause the deformation of the outside diameter of the work  1 .  
      However, because of the trimming process, the work with high accuracy outside diameter is placed in the press die K, and the outside diameter of the work  1  is firmly retained to restrict the large shifting of the wall thickness as the countersink  15  is press-formed by the punch P, thereby minimizing the chance of causing the deformation of the work  1 . Also, the work  1  with high accuracy of the outside diameter is placed in the press die K to be positioned, so that the positioning of the work  1  relative to the punch P is performed with high accuracy. Accordingly, the countersink  15  is vertically formed with high accuracy.  
      Also, in the case that one surface of the main body  11  of the press work product  10  closely contacts with other member, such as when the press work produce  10  may be used as a cover for a housing of the fluid pressure device, the contacting surface may be polished after the above-described press forming process so as to secure the highly accurate flatness thereon.  
      It is readily apparent that the above-described embodiments have the advantage of wide commercial utility. It should be understood that the specific form of the invention hereinabove described is intended to be representative only, as certain modifications within the scope of these teachings will be apparent to those skilled in the art. Accordingly, reference should be made to the following claims in determining the full scope of the invention.