BACKGROUND OF THE INVENTION 
     The present invention relates to a hydroforming device which processes a raw material by hydraulic pressure. Preferably, the present invention relates to a hydroforming device which processes a steel pipe into a automobile component. Additionally, the present invention relates to a hydroforming method which uses the hydroforming device of the present invention. 
     A conventional method for achieving high pressure using a hydraulic intensifier is disclosed in “Pipe Working Method”, by Masanobu Nakamura, published by Nikkan Kogyo Shinbun Co. (Jan. 31, 1996). A further example of a conventional hydroforming device is disclosed in Japanese Laid-Open Patent Number 9-314240 (Japanese Patent Application Number 8-194175). 
     According to these conventional devices, when molding a steel pipe, the closing of the upper and the lower mold is conducted by a single closing cylinder disposed on the crown on the press machine. With this construction, in order to have the required closing force, the closing cylinder must have a large diameter and a large stroke length. As a result, the closing cylinder becomes a cylinder with a large volume. This type of construction is disadvantageous from the standpoint of high speed and responsiveness. In other words, the time needed for the closing motion is relatively long, thereby increasing production time. 
     Other conventional hydroforming devices process steel pipes by sending a high pressure fluid inside the pipe. In these hydroforming devices, by stroking a closing cylinder, an upper mold is raised and lowered, to supply the material inside the mold as well as to perform maintenance of the mold. As a result, it is necessary to manufacturer a press machine that is used exclusively for hydroforming. 
     For example, in Japanese Laid-Open Patent Publication Number 5-329693, a hydroforming press machine is disclosed that has a bed attached to a floor surface. Four columns pass through the bed in a freely vertically sliding manner. A crown is provided at the upper end of the columns. A lower frame is provided at the lower end of the columns. Four hydraulic cylinders drive the lower frame in a vertical direction. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a generic hydroforming device which is capable of hydroforming a raw material with a conventional press machine. 
     It is another object of the present invention to provide a hydroforming device which has high speed and high responsiveness, resulting in high productivity. 
     It is a further object of the present invention to provide a hydroforming method in which a raw material is molded at high speed and high responsiveness, resulting in a highly productive method of hyrdroforming. 
     Briefly stated, the present invention provides a plurality of closing cylinder devices disposed between a bolster of a press machine and a bed containing a lower mold of a hydroforming device. An upper mold is attached to a slide of the press machine. The upper mold and lower mold come together to form a cavity having the shape of the exterior of the desired molded product. A closing block, being movable between a first position which is between the slide and a crown of the press machine, and a second position, which avoids the slide, permitting free movement of the slide from the crown to the lower mold. When a material to be hydroformed is place in the lower mold, the upper mold is lowered. The closing block is fit into its first position, thereby restricting movement of the slide in the vertical direction. A inner work pressure is provided by a fluid inside the material to be molded. The closing cylinder devices provide a pressure, based upon the inner work pressure, to maintain the cavity at the desired shape, preventing the upper mold and the lower mold from being separated by the inner work pressure. 
     According to an embodiment of the present invention, the present invention provides a hydroforming method using a press machine, comprising: providing a closing block movable between a first position and a second position; the first position being between a crown of the press machine and a slide of the press machine, preventing movement of the slide above a predetermined maximum; the second position avoiding the slide, thereby allowing the slide to freely move to a lower surface of the crown of the press machine; providing a lower mold attached to a bolster of the press machine; providing an upper mold attached to the slide; the upper mold and the lower mold coming together to form a cavity having a shape of a molded product; providing a plurality of closing cylinder devices between a bed and the bolster; providing a material to be molded into the lower mold; lowering the slide so that the upper mold and the lower mold form the cavity; moving the closing block into the first position, thereby preventing raising of the slide; activating the closing cylinder devices to provide a closing force, maintaining the cavity during operation of the hydroforming method; and providing a work inner pressure from a liquid supplied to an interior of the material to be molded, whereby the work inner pressure shapes the material to the shape of the cavity while the closing cylinder devices maintain the cavity. 
     According to another embodiment of the present invention, the present invention provides a hydroforming device using a press machine, comprising: a closing block movable between a first position and a second position; the first position being between a crown of the press machine and a slide of the press machine, preventing movement of the slide above a predetermined maximum; the second position avoiding the slide, thereby allowing the slide to freely move to a lower surface of the crown of the press machine; a lower mold attached to a bolster of the press machine; an upper mold attached to the slide; the upper mold and the lower mold coming together to form a cavity having a shape of a molded product; a plurality of closing cylinder devices between a bed of the press machine and the bolster; means for providing a work inner pressure in a material to be molded by the hydroforming device; a closing force, generated by the plurality of closing cylinder devices, being controlled to rise with a rise in the work inner pressure, thereby maintaining the cavity at a desired shape during hydroforming operations. 
     According to a feature of the present invention, a hydroforming method includes providing a closing block, which is freely movable in a horizontal direction, on the crown of a press machine. The closing block moves between a position between the crown and a slide and a position which avoids the slide. A plurality of closing cylinder devices, raising and lowering the bolster, are disposed between the bed and the bolster of the press machine. A cavity is formed from the upper mold, which is anchored to the slide, and the lower mold, which is anchored to the bolster. An axial piston freely advances towards and retreats from an end surface of a work which is stored within the cavity. A closing force, controlled to rise with a rise in a work inner pressure, is generated by the closing cylinders. The work inner pressure being caused from a liquid supplied to the interior of the work by the shaft pushing piston. With such a method, the time needed for closing is shortened and a rational molding is anticipated. 
     According to a further feature of the present invention, the plurality of closing cylinders are suitably selected and operated, thereby optimizing the closing time and responsiveness. 
     According to a further embodiment of the present invention, a generic press machine, equipped with a clutch brake and a crank shaft, has a hydroforming device between its slide and its bolster. The hydroforming device includes a mold having a separated top and bottom, opposing shaft pushing cylinders, and a closing cylinder. 
     According to a feature of the present invention, a hydroforming device, for processing a tube material by hydraulic pressure, includes a base plate anchored to a bolster of a press machine. A closing cylinder is anchored to an upper surface of the base plate. A guide part is erected on the upper surface of the base plate. A middle plate, having a sliding part which joins with the guide part, allows for up and down movement. A lower mold is anchored to an upper surface of he middle plate. A die plate is anchored to a slide of the press machine. An upper mold is anchored to a lower surface of the die plate. An axial cylinder is equipped with a key which joins with a key groove provided on a lower surface of the die plate. 
     According to the previous embodiment and feature of the present invention, a hydroforming device is mounted on a generic press machine equipped with a clutch brake and a crank shaft. The upper mold is anchored to the slide via the die plate. The closing cylinder is anchored to the upper surface of the bolster via the base plate. When raising the upper mold in order to supply material to the mold or to conduct maintenance, the slide of the machine press is raised. When conducting hydroforming, the slide is held at the bottom dead center, and the upper mold and the lower mold are closed by the closing cylinder. In other words, by the hydroforming device of the present invention, a generic press machine, equipped with a clutch brake and a crank shaft, is used as the press machine for conducting hydroforming. Therefore, because existing press machines can be used, there is no need to manufacture an exclusive device for conducting hydroforming. Advanced hydroforming can be introduced into a manufacturing facility at a relatively low cost. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-section of a press machine having a hydroforming device according to an embodiment of the present invention. 
     FIG. 2 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG.  3 .is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 4 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 5 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 6 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 7 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 8 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 9 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 10 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 11 is a descriptive drawing of the hydroforming method according to the present invention. 
     FIG. 12 is a graph showing characteristic changes as a function of time. 
     FIG. 13 is a schematic diagram of a generic press machine. 
     FIG. 14 is a detailed drawing of a hydroforming device. 
     FIG. 15 is a detailed drawing of a hydroforming device according to an alternate embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a crown  1 , a column  2 , and a bed  3  are fastened together by a tie rod  6  and a nut  7 . These members construct a frame for a press machine. A slide cylinder  11  is provided on crown  1 . A slide piston  12  is built into slide cylinder  11 . Slide circuits  13   a  and  13   b  connect to slide cylinder  11 . 
     A slide  4  is linked to the lower end of slide piston  12 . Slide  4 , guided by a guiding device (not shown) provided on column  2 , freely rises and falls. Slide piston  12  rises and falls by the action of hydraulic pressure supplied from slide cylinder circuits  13   a  and  13   b . Slide  4  rises and falls by the action of slide piston  12 . 
     A closing block  14  is provided to allow for back and forth movement in the horizontal direction of FIG.  1 . Closing block  14  is constructed to freely advance and retreat between a first position in which it is inserted between the lower surface of crown  1  and the upper surface of slide  4 , to a second position, in which it avoids the upper surface of slide  4 . A cylinder device  15 , having a piston  16 , connects to circuits  17   a  and  17   b . Closing block  14  advances and retreats by the action of cylinder device  15 . 
     An axial cylinder  18  is provided on column  2 . An axial piston  19  is built into shaft pushing cylinder  18 . Shaft pushing piston circuits  20   a  and  20   b  connect to shaft pushing cylinder  18 . An axial piston circuit  21  connects to shaft pushing piston  19 . Due to hydraulic pressure supplied from shaft pushing cylinder circuits  20   a  and  20   b , shaft pushing piston  19  moves back and forth. In other words, shaft pushing piston  19  advances and retreats freely with respect to the upper and lower molds, which are later described. 
     A bolster  5 , freely rising and falling, is provided on the top part of bed  3 . In other words, bolster  5  is guided by a guiding device (not shown) provided on column  2 . A closing cylinder  22  is present between bed  3  and bolster  5 . In the present embodiment of the present invention, closing cylinder  22  is provided on top of bed  3 . A closing piston  23  is built into closing cylinder  22 . Closing circuits  24   a  and  24   b  connect to closing cylinder  22 . Closing cylinder  22 , closing piston  23 , and closing cylinder circuits  24   a  and  24   b  construct the closing cylinder device. 
     The upper end surface of closing piston  23  contacts the lower surface of bolster  5 . Closing piston  23  rises and falls by the liquid pressure supplied from cylinder circuits  24   a  and  24   b . Bolster  5  rises and falls in conjunction with the rising and falling of closing piston  23 . There are a plurality of closing cylinder devices placed at least at all corners underneath bolster  5 . The closing cylinder devices can be selected and used according to the work, which is described later. 
     An upper mold  8  is anchored to the lower surface of slide  4 . Opposite upper mold  8 , a lower mold  9  is anchored to the upper surface of bolster  5 . Upper mold  8  descends together with slide  4 . When upper mold  8  meets with lower mold  9 , they form the desired cavity  10 . Cavity  10  indicates the space having a shape which becomes the outer shape for the molded product. 
     Referring to FIG. 2, when slide  4  is raised, bolster  5  is lowered, shaft pushing piston is retreated, and closing block  14  is retreated. At this point, a steel pipe (hereinafter referred to as the work) is supplied to lower mold  19 . 
     Referring to FIG. 3, slide  4  is lowered. Together with slide  4  being lowered, upper mold  8  descends. Lower mold  9  and upper mold  8  meet, and the work is housed in cavity  10 . 
     Referring to FIG. 4, closing block  14  advances and enters between the upper surface of slide  4  and the lower surface of crown  1 . 
     Referring to FIG. 5, bolster  5  rises due to the action of closing piston  23 . The upper surface of slide  4  and the lower surface of closing  14  contact. With the closing force by closing piston  23 , upper mold  8  and lower mold  9  are initially pressurized and closed. 
     Referring to FIG. 6, shaft pushing piston  19  is advanced and positioned. When this occurs, the end part of shaft pushing piston  19  is inserted into the end inner diameter of the work. The end inner diameter part of the work becomes deformed a small amount. By this insertion motion, the outer part of shaft pushing piston  19  and the end inner diameter part of the work are in tight contact, acting to seal the hydraulic pressure within the work. 
     Referring to FIG. 7, when the molding (described below) is completed, the closing force from closing piston  19  is reduced. 
     Referring to FIG. 8, shaft pushing piston  19  is retreated. At this point, the end part of the work is separated from the end part of shaft pushing piston  19 . 
     Referring to FIG. 9, bolster  5  is lowered, causing the closing force to become zero. A space is created between the lower surface of closing block  14  and the upper surface of slide  4 . 
     Referring to FIG. 10, closing block  14  is retracted. 
     Referring to FIG. 11, slide  4  is raised. The molded product, which has been left in the lower mold upon raising slide  4 , is removed. With this final step, the molding operation of the work is complete. 
     Referring back to FIG. 6, molding is conducted when the press is in the state as shown in FIG.  6 . While closing by the action of closing piston  23 , liquid is sent into the work interior from holes opened on shaft pushing piston  19 . Synchronously with these motions, shaft pushing piston  19  is advanced. 
     Referring to FIG. 12, the changes in closing force, inner pressure of the work, displacement amount of shaft pushing piston  19 , and the hydraulic pressure of shaft pushing cylinder  18  are shown. 
     Closing force  101 , work inner pressure  102 , and displacement amount  103  of shaft pushing piston  19  are controlled based on time. Hydraulic pressure  104  of shaft pushing cylinder  18  is the result of controlling displacement amount  103  of shaft pushing piston  19 . Hydraulic pressure  104  of shaft pushing cylinder  18  is a monitor, so to speak. Displacement amount  103  of shaft pushing piston  19  is detected at a linear scale (not shown). 
     Closing force  101  rises with inner pressure  102  of the work. If the closing force is high from the start, upper mold  8  and lower mold  9  are deformed, and the frictional force between the mold and the work increases. There is seizing of the mold and the work, and the molding of the work is obstructed. In other words, it is necessary to change the closing force according to the rise of hydraulic pressure acting on the inner diameter part of the work. In other words, it is necessary to change the closing force according to the rise in inner pressure  102  of the work. 
     Closing force  101  at the initial step is P 1 . At this closing force P 1 , work inner pressure  102  is applied within the range where upper mold  8  and lower mold  9  do not open, and the work is molded by the work inner pressure  102 . In order to prevent the work from being thinned, or in order to prevent breaking of the work, shaft pushing piston  19  is advanced. Displacement amount  103  in this initial step is X 1 . Most of the molding work is completed in this initial step. 
     In the next step, closing force  101  is raised, and work inner pressure  102  is also raised. In this step, as described previously, because most of the molding work is completed, there is hardly any need to advance pushing piston  19 . In this step, molding of the corner parts, and the like, of the work is completed. 
     In the next step, closing force  101  is raised, and work inner pressure  102  is also raised. The outer shape of te work is accurately made into the shape of the cavity. Pressure is applied so that there is no deformation due to the so-called spring back phenomenon, occurring when the work is released from the upper and lower molds. 
     Following the above technical idea, closing force  101 , work inner pressure  102 , and displacement amount  103  of shaft pushing piston  19  are controlled. When molding is completed, the product is obtained following the series of motions in FIGS. 7-11, as previously described. 
     According to this embodiment of the present invention, by the action of closing block  14 , only a relatively short cylinder as with the closing cylinder is necessary. As a result, the hydroforming device of the present invention has the advantage of requiring a shortened time for closing, as well as good responsiveness. Furthermore, when operating by selecting from among a plurality of closing cylinder devices, the time needed for closing is further shortened, resulting is a further enhancement of the responsiveness of the hydroforming device. 
     Referring to FIG. 13, a generic press machine  31  vertically raises and lowers a slide  32  by a driving mechanism (not shown). A hydroforming device  35  is provided between a slide  32  and a bolster  33  of press machine  31 . 
     Referring to FIG. 14, slide  32  is shown at the bottom dead center. A base plate  34  is anchored to bolster  33 . A die plate  44  is anchored to slide  32 . A closing cylinder  37  is anchored on top of base place  34 . Furthermore, on the four corners on top of base plate  34 , a guide part  36 , which uses guide posts, is erected. Sliding parts  38  are provided on the four corners of a middle plate  39 . Sliding parts  38  join with guide part  36  in a condition where sliding parts  38  are freely mobile in the vertical direction. Sliding parts  38  support middle plate  39 . Furthermore, the upper surface of closing cylinder  37  contacts the lower surface of middle plate  39 . Middle plate  39  rises and falls along with the rise and fall of piston  37   a  of closing cylinder  37 . 
     Lower mold  40   b  is anchored to the upper surface center part of middle plate  39 . In addition, upper mold  40   a  is anchored to the lower surface center part of die plate  44 . Shaft pushing cylinders  41  are provided on right and left sides of mold  40 . The lower part of a block  42 , which is anchored to shaft pushing cylinder  41 , is anchored to middle plate  39 . Furthermore, a key  43   a , which is provided on the upper part of block  42 , joins with a key groove  45   a , which is provided on die plate  44 . A key  43   b , which is provided on the lower part of block  42 , joins with a key groove  45   b , which is provided on middle plate  39 . When slide  32  is at the bottom dead center, and piston  37   a  is at the lower limit position, there is a space between the bottom part of key groove  45   a  and the upper surface of key  43   a.    
     When hydroforming is to be conducted, slide  32  is at the bottom dead center, and the material is supplied to the inside of mold  40 . After supplying the material, slide  32  is at the bottom dead center, and piston  37   a  of closing cylinder  37  is raised. Thereupon, middle plate  39  is pushed up, and mold  10  is closed. At this time, there is a space between the bottom part of key groove  45   a  and the upper surface of key  43   a.    
     When the mold is closed, rod parts  41   a  of shaft pushing cylinders  41  advance to the inside of the mold from holes  46 , provided on the right and left side surfaces of mold  40 , and rod parts  41  a are inserted into the steel pipe end part of the material. High pressure fluid flows into the steel pipe, and the steel pipe is processed into the desired shape. At this time, shaft pushing cylinders  41  receive the reaction force of rods  41   a  in the lengthwise direction. However, because keys  43   a  and  43   b  are joined with key grooves  45   a  and  45   b , shaft pushing cylinders  41  do not shift from the reaction force. After completion of the precessing, rod parts  41   a  of shaft pushing cylinders  41  are retreated, and piston  37   a  of closing cylinder  37  is lowered, releasing the upper mold from the lower mold. Afterwards, with slide  32  in the bottom dead center, the product is removed from inside the mold, and the processing is completed. 
     Referring to FIG. 15, there is preferably a plurality of closing cylinders in the hydroforming device. 
     For the frame construction of press machine  31 , any known frame construction, such as a gate type or a C-frame, may be used, so long as it is a press machine having a suitable frame strength to withstand the closing force. Furthermore, with respect to the drive mechanism of slide  32 , any known drive mechanism may be used, such as a crank mechanism or a knuckle mechanism. 
     According to this embodiment of the present invention, hydroforming is conducted with a generic press machine which is equipped with a clutch brake and a crank shaft. As a result, it is not longer necessary to manufacture a machine exclusively for hydroforming, thereby allowing hydroforming to be introduced into a manufacturing facility at a relatively low cost. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.
A plurality of closing cylinder devices are provided between a bolster of a press machine and a bed containing a lower mold of a hydroforming device. An upper mold is attached to a slide of the press machine. The upper mold and lower mold come together to form a cavity having the shape of the exterior of the desired molded product. A closing block, being movable between a first position which is between the slide and a crown of the press machine, and a second position, which avoids the slide, permitting free movement of the slide from the crown to the lower mold. When a material to be hydroformed is place in the lower mold, the upper mold is lowered. The closing block is fit into its first position, thereby restricting movement of the slide in the vertical direction. A inner work pressure is provided by a fluid inside the material to be molded. The closing cylinder devices provide a pressure, based upon the inner work pressure, to maintain the cavity at the desired shape, preventing the upper mold and the lower mold from being separated by the inner work pressure.