Patent Publication Number: US-2017368592-A1

Title: Press machine

Description:
TECHNICAL FILED 
     The present invention relates to a press machine. More particularly, it relates to a press machine for use in progressive processing. 
     BACKGROUND TECHNIQUE 
     Progressive processing is a method of press-working a coiled material without cutting off the coiled material or coil strip up to the final step. Since it is the most effective method for producing a large number of parts, the progressive processing has been positively used to realize productivity improvement and labor saving. 
     Generally, in the progressive processing, a material is fed by a roll feeder, etc. In recent years, a system has been adopted in which, using a roll feeder, etc., controlled by CNC (Computer Numerical Control), a slide position of the press machine is detected with a rotary cam or an encoder installed on the press machine, and driving of the roll feeder is turned on/off in a suitable timing in accordance with the motion of the slide. In this system, in a state in which a punch and/or a guide pin of a die is engaged with the material, the material is released from the feeder. During which the punch and/or the guide pin is released from the material, the material is clamped, and feeding of the material is started and then stopped. 
     Although not for such progressive processing, Patent Document 1 discloses a reduction press in which a material to be rolled, which is to be fed by pinch rolls, is arranged between upper and lower sliders to perform a thickness reduction of the material. Upper and lower crankshafts which rotate with a phase difference of 180 degrees are slidably mounted on the upper and lower sliders of the reduction press, respectively. With this, the upper and lower sliders eccentrically rotate. With the eccentric rotational movements of the sliders, the material is moved in the flow direction while being pressed with the sliders. 
     Further, although not for the progressive processing, Patent Document 2 describes a press stamping device. This device is characterized in that the device has swinging clamping plates that move symmetrically and oppositely. The clamping plates move toward the outlet side of the device while moving toward each other to deform the work to be processed while advancing it. On the other hand, the clamping plates swing back to move away from the work while moving away from each other. 
     PRIOR ART 
     Patent Document 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 1999 (H11)-169901 
     Patent Document 2: Japanese Examined Patent Application Publication No. 1971 (S46)-5044 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the progressive processing, in addition to equipment of the entire system, a press machine, and dies, a roll feeder, a control panel for controlling the roll feeder, an operation panel, a rotary encoder, etc., are necessary. Therefore, there is a tendency that the facility installation area becomes large and the facility becomes expensive. 
     Further, a dedicated roll feeder, etc., are individually driven during the material feed time among the shape forming time and the material feed time of one press cycle. For this reason, the equipment/system is complicated. 
     Under the circumstance, an object of the present invention is to provide a press machine capable of performing progressive processing with a simple configuration. 
     Means for Solving the Problems 
     (1) A press machine according to the present invention is a press machine for use in progressive processing. The press machine includes upper and lower crankshafts having the same amount of eccentricity and driven in opposite directions with a phase difference of 180 degrees, a slide and a bolster rotatably connected to an eccentric part of the upper crankshaft and an eccentric part of the lower crankshaft, respectively, a parallel maintaining mechanism configured to maintain a parallelism between the slide and the bolster, and a clamp mechanism including an upper clamp attached to the slide and a lower clamp attached to the bolster. The slide and the bolster move toward/away from each other and advance/retreat together in a feed direction of the material in accordance with rotational driving of the upper and lower crankshafts. The clamp mechanism clamps the material to be processed when the slide and the bolster move toward each other and unclamps the material forwardly fed while being clamped when the slide and the bolster move away from each other. Here, the “parallelism between the slide and the bolster” denotes a parallelism between the lower surface of the slide which is an upper die mounting surface and the upper surface of the bolster which is a lower die mounting surface. 
     (2) In the above-described press machine, it is preferable that the parallel maintaining mechanism be composed of a guidepost or guideposts and that the guidepost connects the slide and the bolster, the guide post being attached to one of the slide and the bolster and slidable with respect to the other of the slide and the bolster. 
     (3) Further, in the above-described press machine, it is preferable that the clamp mechanism be provided with an upper spring and a lower spring to absorb relative vertical motion between the slide and the bolster, and to provide clamping force for the material. 
     (4) Further, it is preferable that the clamp mechanism be provided with an adjusting mechanism for adjusting a height position for clamping the material to be processed. 
     (5) In the above-described press machine, it is preferable to further include a temporary holding mechanism for temporarily holding the material which is unclamped. 
     Effects of the Invention 
     (1) In the press machine of the present invention, upper and lower crankshafts having the same amount of eccentricity and arranged with a phase difference of 180 degrees are provided, and the eccentric part of the upper crankshaft and the eccentric part of the lower crankshaft are rotatably connected to the slide and the bolster, respectively. Further, the slide and the bolster are constrained so as to be freely movable up and down by the parallel maintaining mechanism so that they are always maintained in parallel each other. 
     For this reason, the slide and the bolster make opposite parallel circular motion with keeping relative parallel state around each rotary center of the crankshaft. That is, in the vertical direction, the slide and bolster relatively move up and down in the opposite direction. However, in the horizontal direction, in the right-left direction in the figure, the slide and bolster move together with each other in the same direction. For example, in cases where the upper crankshaft rotates counterclockwise, the slide and the bolster synchronously move rightward during the crankshaft rotates from a point before the bottom death center by the crankshaft angle of 90 degrees (crankshaft angle 90 degrees) to a point after the bottom dead center by the crankshaft angle of 90 degrees (crankshaft angle: 270 degrees). Next, the slide and the bolster move synchronously leftward during the crankshaft rotates from the point after the bottom dead center by the crankshaft angle of 90 degrees (crankshaft angle: 270 degrees) to the point before the bottom dead center by the crankshaft angle of 90 degrees via the top dead center. This reciprocating motion is repeated. 
     By adopting the clamp mechanism utilizing the lateral movements synchronized with the vertical movements of the slide and the bolster for the press machine, it is possible to perform material clamping, material feeding, and material releasing during one press forming cycle with the press machine alone, which can eliminate the use of a dedicated feeder, a control therefore, rotary cams, etc. 
     Further, since the slide and the bolster are rotatably connected to the upper and lower crankshafts, it is not necessary to use connecting rods. For this reason, the height of the press machine can be reduced. 
     (2) In such a press machine, in cases where the parallel maintaining mechanism is composed of a guidepost, the guidepost connects the slide and the bolster and is attached to one of the slide and the bolster and is slidable with respect to the other of the slide and the bolster only in the direction perpendicular to a plane parallel to the slide and the bolster, the parallelism can be attained with a simple configuration. In addition, the relative position of the upper and lower dies can be secured. 
     (3) In cases where the clamp mechanism is provided with an upper spring and a lower spring to absorb relative vertical motion between the slide and the bolster, and to provide clamping force for the material, the timing of clamp and unclamp can be selected and the clamp force can be secured. 
     (4) In cases where an adjustment mechanism for adjusting the height position at which the material to be processed is clamped, by adjusting the height, the feed pitch of the material can be arbitrarily adjusted. 
     (5) Furthermore, in cases where a temporary holding mechanism for temporarily holding the unclamped material is further provided, even after unclamping, the material can be made to stand by at the position by the material holding mechanism. For this reason, it is possible to prevent an occurrence of pitch deviation in multi-step progressive dies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view showing a main part of an embodiment of a press machine according to the present invention. 
         FIG. 2  is a schematic partial cross-sectional view taken along the line A-A in  FIG. 1 . 
         FIG. 3A  is a schematic process diagram showing the operation of the slide and the bolster (phase: 0 to 90 degrees). 
         FIG. 3B  is a schematic process diagram showing the operation of the slide and the bolster (phase: 90 to 180 degrees). 
         FIG. 3C  is a schematic process diagram showing the operation of the slide and the bolster (phase: 180 to 270 degrees). 
         FIG. 3D  is a schematic process diagram showing the operation of the slide and the bolster (phase: 270 to 0 degrees). 
         FIG. 4  is a diagram showing motion curves of the slide and the bolster. 
         FIG. 5A  is a front view showing another embodiment, and  FIG. 5B  is a front view showing still another embodiment. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     1. Outline of Press Machine 
       FIG. 1  shows an example of a press machine according to the present invention. This figure shows a state in which dies are closed. Note that a front frame provided on the front side of the press machine is not illustrated. Also note that the front frame  4   a  is illustrated in  FIG. 2 . 
     The press machine  1  is for use in progressive processing, and is provided with a frame body composed of a frame member  2 . The frame member  2  includes, for example, a bed  3 , the front frame  4   a  (see  FIG. 2 ) provided on the bed  3 , a rear frame  4   b  (see  FIG. 2 ), right and left upper frames  4   c  and  4   c , right and left lower frames  4   d  and  4   d , and a crown or upper portion  5  provided at the upper ends of the frames  4   a ,  4   b  and  4   c . A window  2   a  (see  FIG. 2 ) is formed in the vicinity of the center of each of the front frame  4   a  and the rear frame  4   b , so that the pressing state can be visually recognized and the maintenance of the apparatus can be performed through each window  2   a.    
     Upper and lower die height adjustment mechanisms  6  and  7  are provided above and below the frame member  2 , respectively. Upper and lower bearing blocks  8  and  9  are attached to respective tip ends of the die height adjustment mechanisms  6  and  7 . 
     Returning to  FIG. 1 , opposite end portions (journal portions) of the upper and lower crankshafts  10  and  11  which are driven in opposite rotational directions with a phase difference of 180 degrees are pivotally supported by the respective bearing blocks  8  and  9 . Those crankshafts  10  and  11  are eccentric shafts each having an eccentric portion  10   a  and  11   a . The amounts of eccentricities of their eccentric portions (eccentric portions)  10   a  and  11   a  are the same. 
     The eccentric portion  10   a  of the upper crankshaft  10  and the eccentric portion  11   a  of the lower crankshaft  11  are rotatably connected to the slide  12  and a bolster  13 , respectively. An upper die  12   a  is attached to the lower surface of the slide  12 , and a lower die  13   a  is attached to the upper surface of the bolster  13 . 
     The above-described die height adjustment mechanisms  6  and  7  are configured to adjust the distance between the bearing blocks  8  and  9  and adjust the distance between the slide  12  and the bolster  13 . 
     The slide  12  and the bolster  13  are provided with guideposts (parallel maintaining mechanism)  14  for maintaining the parallel positional relationship thereof. The guideposts  14  regulate the rotational movements of the slide  12  and the bolster  13  around the respective axes of the upper and lower crankshafts  10  and  11 . 
     The slide  12  and the bolster  13  are provided with clamp mechanism  15 . The clamp mechanism  15  is composed of a pair of upper and lower members configured to hold a material W to be processed with biasing force of springs  15   e  between 90 degrees and 270 degrees in the phase of the upper crankshaft  10  (see  FIGS. 3A to 3D ). The clamp mechanism  15  is provided on both sides of the slide  12  and the bolster  13  (in the front-back direction along which the material W extends). 
     On the further outer sides of the clamp mechanisms  15 , temporary holding mechanisms  16  and  16  are provided on the right and left end faces of the front frame  4   a  and the rear frame  4   b . The temporary holding mechanisms  16  and  16  temporarily hold the material released (unclamped) by the clamp mechanisms  15  and  15  so as not to move. Each temporary holding mechanism  16  is composed of a pair of upper and lower members. 
     2. Details of Each Portion 
     The movements of the upper bearing block  8  in the right-left direction are restricted by the right and left upper frames  4   c  and  4   c . The upper bearing block  8  slides on the inner surfaces of the front frame  4   a , the rear frame  4   b , and the right and left upper frames  4   c  and  4   c , so that the vertical movements thereof are guided. 
     As the upper die height adjustment mechanism.  6 , for example, a screw-nut mechanism is used. The screw member  6   a  of the mechanism penetrates the crown  5  of the frame member  2 , and the vicinity of the lower end thereof is fixed to the upper bearing block  8 . Therefore, the screw member  6   a  cannot rotate. Further, an adjust nut  6   d  is screwed onto the screw member  6   a . The adjust nut  6   d  penetrates the crown  5 , and the outer threaded portion of the upper portion of the adjust nut is screwed into the nut member  6   b  and also screwed into a lock nut  6   c  fixing the nut member  6   b  to the adjust nut  6   d . The upper portion  5  is rotatably sandwiched between the lower flange of the adjust nut  6   d  having a diameter larger than that of the portion penetrating the upper portion  5  of the frame member  2 , the nut member  6   b , and the lock nut  6   c . As a result, the adjust nut  6   d , the nut member  6   b , and the lock nut  6   c  are integrated, and restrained in the vertical direction and rotatable with respect to the crown  5 . By rotating the nut member  6   b , the adjust nut  6   d  integrated with the nut member  6   b  can be rotated, so the screw member  6   a  can be moved up and down. This makes it possible to adjust the die height. After adjusting the height, another locknut  6   e  is screwed onto the screw member  6   a  from the above to lock the height position of the screw member  6   a.    
     Since the lower bearing block  9  and the lower die height adjustment mechanism  7  are the same in structure as the upper bearing block  8  and the upper die height adjustment mechanism  6 , the description thereof will be omitted. 
     As shown in  FIG. 2 , upper and lower servomotors  18  and  18  are connected to the upper and lower crankshafts  10  and  11  via couplings  17  and  17 , respectively. The upper and lower servomotors  18  and  18  are fixed to the upper bearing block  8  and the lower bearing block  9  via an upper bearing bracket  8   a  and a lower bearing bracket  9   a , respectively. Between the coupling  17  and the servomotor  18 , a decelerator  19  is provided. The decelerator  19  may be fixed using a bracket (not shown) as necessary. Further, even in cases where the servomotor  18  is directly connected to the crankshaft without providing the decelerator  19 , the servomotor may be fixed using a bracket. 
     Returning to  FIG. 1 , the clamp mechanism  15  is composed of an upper clamp  15   a  attached to the slide  12  and a lower clamp  15   b  attached to the bolster  13 , and is used as a pair of upper and lower clamps. For this reason, the upper clamp  15   a  will be described, and the description of the lower clamp  15   b  will be omitted. 
     The upper clamp  15   a  is composed of a rod-like member  15   c  penetrating the guide hole  15   g  formed in the slide  12  and slidable in the guide hole  15   g  in the axial direction, a presser foot  15   d  covered on the lower end of the rod-like member and the vicinity thereof, a spring  15   e  for urging the presser foot  15   d  toward the material side, a pair of nuts  15   f  screwed onto the male thread of the rod-like member  15   c  for fixing the height position of the rod-like member  15   c  with respect to the slide  12 . The upper clamp  15   a  and the lower clamp  15   b  can absorb vertical motion of the slide  12  and the bolster  13  by virtue of the elastic deformation of the spring  15   e , and the upper and the lower presser foots  15   d  can securely grip the material, i.e. coil strip, by virtue of the urging force of the spring  15   e . With the pair of nuts  15   f  loosened with each other, the rod-like member  15   c  is moved upward or downward with respect to the slide  12 . Then, the pair of nuts  15   f  are tightened each other. Thus, the position of the pair of nuts  15   f  with respect to the rod-like member  15   c  is fixed. This enables the adjustment of the maximum protrusion amount of the presser foot  15   d  from the slide  12  (height position of the lower surface of the presser foot  15   d ). As the material of the presser foot  15   d , for example, hardened steel of carbon steel material (SC material) or the like may be used. 
     The temporary holding mechanism  16  is composed of a pair of upper and lower members. The temporary holding mechanism  16  is composed of upper and lower support portions  16   a  and  16   a  provided on the right and left end faces of the front frame  4   a  and the rear frame  4   b  via brackets, and rollers  16   b  and  16   b  rotatably provided near the tip ends of the support portions  16   a  and  16   a  and the vicinity thereof. With these rollers  16   b  and  16   b , the material W is always sandwiched on the feed line L of the material W. The rollers sandwich the material W so as not to shift even when the clamp mechanism  15  releases the material W, and to guide the flow of the material W in the feed direction when the material is fed forward. 
     A flange-like portion  14   a  is provided on the circumferential surface of the guidepost  14  somewhat below the center in the longitudinal direction. The lower part of the guidepost  14  is driven into a fitting hole  13   b  formed in the bolster  13  and the lower surface of the flange-like portion  14   a  abuts against the upper surface of the bolster  13  and is fixed thereto. On the other hand, the upper part of the guidepost  14  is slidably fitted in the guide hole  12   b  formed in the slide  12  from the lower surface side in an upwardly protruded manner. 
     The slide  12  is suspended by the eccentric portion  10   a  of the upper crankshaft  10 , and the bolster  13  is supported by the eccentric portion  11   a  of the lower crankshaft  11 . The upper crankshaft  10  and the lower crankshaft  11  are rotatably connected to a connecting portion  12   c  of the slide  12  and a connection portion  13   c  of the bolster  13 , respectively. 
     3. Operation 
     Next, an example of the operation state of the press machine of the present invention will be described with reference to  FIG. 3A  (hereinafter, the operation state is simply referred to as “S”). 
     (S1): In this state, the phase of the upper crankshaft  10  is 0 degrees, i.e. the top dead center, and the lower crankshaft  11  is 180 degrees, i.e. the bottom dead center. The slide  12  and the bolster  13  are located at the middle position in the right-left direction. Further, the slide  12  and the bolster  13  are separated from each other, and are positioned farthest apart from each other from the feed line L of the material W. That is, the slide  12  and the bolster  13  are separated from each other by twice the amount of eccentricity of the crankshaft vertically from the feed line L of the material W. The upper and lower presser foots  15   d  and  15   d  of the clamp mechanism  15  are not clamping the material W. The temporary holding mechanism  16  is clamping the material W with the upper and lower rollers  16   b  and  16   b  at the feeding height position. 
     (S1 to S2): In this state, the phase of the upper crankshaft  10  shifts from 0 degrees to 90 degrees. Both the slide  12  and the bolster  13  move leftward in the figure (rearward in the traveling direction of the material W). Thus, the slide  12  and the bolster  13  move toward each other. 
     (S2): In this state, as shown in  FIG. 3B , the phase of the upper crankshaft  10  is 90 degrees. The slide  12  and the bolster  13  are positioned at the left movement end by being moved leftward from the intermediate position by the amount of eccentricity. Although the slide  12  and the bolster  13  have moved toward with each other, the upper and lower dies  12   a  and  13   a  have not yet being brought into contact with each other. On the other hand, the upper and lower presser foots  15   d  and  15   d  of the clamp mechanism  15  are clamping the material W. Since the phase is 90 degrees, the moving acceleration of the slide  12  and the bolster  13  in the right-left direction is 0 (zero). For this reason, the clamping of the material W can be performed assuredly. As will be described in detail later, the feed pitch can be changed depending on when clamping is performed. 
     (S2 to S3): In this state, the phase of the upper crankshaft  10  shifts from 90 degrees to 180 degrees. The material W is being clamped by the clamp mechanism  15 . Both the slide  12  and the bolster  13  move rightward in the figure (forward in the traveling direction of the material W). For this reason, the clamped material W also moves forward. Although the slide  12  and the bolster  13  further move toward each other, the upper and lower presser foots  15   d  and  15   d  of the clamp mechanism  15  do not further move toward each other since the upper and lower presser foots are clamping the material W. Therefore, the springs  15   e  and  15   e  are elastically deformed by the extent that the slide  12  and the bolster  13  further move toward each other. The clamp force is generated by the elastic deformation of the springs  15   e.    
     (S3): In this state, as shown in  FIG. 3C , the phase of the upper crankshaft  10  is 180 degrees. The slide  12  and the bolster  13  are located at the middle position in the right-left direction. In the vertical direction, the slide  12  and the bolster  13  are at the bottom dead center and the top dead center, respectively, and the upper and lower dies  12   a  and  13   a  are in contact with each other with the material W clamped therebetween. The upper and lower presser foots  15   d  and  15   d  of the clamp mechanism  15  is still clamping the material W by the urging force of the springs  15   e.    
     (S3 to S4): In this state, the phase of the upper crankshaft  10  shifts from. 180 degrees to 270 degrees. The material W is being clamped by the clamp mechanism  15 . Both the slide  12  and the bolster  13  move rightward in the figure (forward in the traveling direction of the material W). For this reason, the clamped material W moves forward. Thus, the slide  12  and the bolster  13  move away from each other. In the clamp mechanism  15 , the shrunk of the springs  15   e  and  15   e  gradually return to their original state, that is the natural length. 
     (S4): In this state, as shown in  FIG. 3D , the phase of the upper crankshaft  10  is 270 degrees. The slide  12  and the bolster  13  are positioned at the right movement end and moved rightward from the intermediate position by the amount of eccentricity. The slide  12  and the bolster  13  are further separated. The upper and lower presser foots  15   d  and  15   d  of the clamp mechanism  15  are just being unclamping the material W. Since the phase is 270 degrees, the moving acceleration of the slide  12  and the bolster  13  in the right-left direction is 0 (zero). For this reason, unclamping of the material W can be performed assuredly. 
     (S4 to S1): In this state, the phase of the upper crankshaft  10  shifts from 270 degrees to 0 degrees. The material W is not clamped by the clamp mechanism  15 . Both the slide  12  and the bolster  13  move leftward in the figure (rearward in the traveling direction of the material W) while moving away from each other. As the slide  12  and bolster  13  move away from each other, the presser foots  15   d  and  15   d  of the clamp mechanism  15  further move away from each other. The temporary holding mechanism  16  is sandwiching the material W during which the clamp mechanism  15  is in the unclamp state to prevent the material W from being moved. 
     In this embodiment, the material W is fed during which the phase of the upper crankshaft  10  is between 90 degrees and 270 degrees in which the presser foots  15   d  and  15   d  of the clamp mechanism  15  are clamping the material W. The feed amount can be changed by changing the height position of the rod-like member  15   c  of the clamp mechanism  15 , so that the phase of the crankshaft to start the clamping is changed. For example, if the distance between the upper and lower presser foots  15   d  and  15   d  relative to the material feed line L is increased, the phase of the upper crankshaft  10  clamping the material W by the presser foots  15   d  and  15   d  of the clamp mechanism  15  can be set to 135 degrees to 225 degrees. With this, the feed amount can be reduced. 
     In this embodiment, when the phase of the upper crankshaft  10  is 90 degrees, the clamp mechanism  15  is in contact with the material W. However, it may be configured such that the upper and lower presser foots  15   d  and  15   d  come into contact with the material W before the phase of the upper crankshaft  10  becomes 90 degrees so that the spring  15   e  is deformed in advance and the spring  15   e  is deformed sufficiently when the phase becomes 90 degrees so as to give a biasing force (clamping force) capable of assuredly holding the material W. Alternatively, it may be configured such that in order to give a large clamping force with a small deformation of the spring  15   e , a spring with a large urging force is used so that a sufficient clamping force can be exerted when the phase of the upper crankshaft  10  is around 90 degrees. 
     Example 
       FIG. 4  shows a motion of a slide and that of a bolster in the vertical direction according to an embodiment in which the amount of eccentricity of each of upper and lower crankshafts is set to 7.5 mm. The horizontal axis represents the phase (°: degrees) of the upper crankshaft  10  and the vertical axis represents strokes (mm) in the vertical direction. The circular symbol in the figure indicates the slide  12 , the square symbol indicates the bolster  13 , and the triangular symbol indicates the sum of strokes of the slide and the bolster (with opposite sign), i.e., the relative stroke of the slide to the bolster. 
     4. Other 
     Other Embodiments 
     In the above-described embodiment, separate upper and lower motors are used. However, in the press machine  20  shown in  FIG. 5A , the upper and lower crankshafts  10  and  11  are synchronously driven by a single motor. The motor  21  is provided on the upper surface of the crown  5  of the frame. The motor  21  is provided with a pulley  21   a . A flywheel (not illustrated) is provided at one end of the upper crankshaft  10 . A belt  22  is put on the flywheel and the pulley  21   a . On the other hand, the upper and lower crankshafts  10  and  11  are each provided with the same gear  23  and  23 . With these gears  23  and  23 , transmission and synchronization of driving forces of the upper and lower crankshafts  10  and  11  are obtained. These gears  23  and  23  rotate in opposite directions. Note that the reference numeral “14” denotes a guidepost. 
     In the press machine  24  shown in  FIG. 5B , the bolster  13  is driven by two lower crankshafts  11  and  11 . These crankshafts  11  and  11  rotate in the same direction. The upper and lower crankshafts  10 ,  11  and  11  are each provided with the same gear  23 ,  23 , and  23 . The gear  23  of the upper crankshaft  10  meshes with the respective gears  23  and  23  of the lower crankshafts  11  and  11 . Therefore, the upper and lower crankshafts  10 ,  11 , and  11  are driven synchronously. 
     The above-described die height adjustment mechanisms  6  and  7  may be provided on either the slide  12  or the bolster  13 . 
     As the above-described parallel maintaining mechanism  14 , the slide  12  or the bolster  13  may be driven by two crankshafts to restrict the rotation around the crankshaft. 
     In this embodiment, the coil spring  15   e  is used in the clamp mechanism  15 , but a leaf spring, an air damper, etc., may be used. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
           1 : press machine 
           2 : frame member 
           2   a : window 
           3 : bed 
           4   a : front frame 
           4   b : rear frame 
           4   c ,  4   c : right and left upper frame 
           4   d ,  4   d : right and left lower frame 
           5 : crown (upper portion) 
           6 : upper die height adjustment mechanism 
           6   a : screw member 
           6   b : nut member 
           6   c : locknut 
           6   d : adjust nut 
           6   e : locknut 
           7 : lower die height adjustment mechanism 
           7   a : screw member 
           7   b : nut member 
           7   c : locknut 
           7   d : adjust nut 
           7   e : locknut 
           8 : upper bearing block 
           8   a : upper bearing bracket 
           9 : lower bearing block 
           9   a : lower bearing bracket 
           10 : upper crankshaft 
           10   a : eccentric portion 
           11 : lower crankshaft 
           11   a : eccentric portion 
           12 : slide 
           12   a : upper die 
           12   b : guide hole 
           12   c : connecting portion 
           13 : bolster 
           13   a : lower die 
           13   b : fitting hole 
           13   c : connecting portion 
           13   d : scrap discharge port 
           14 : guidepost (parallel maintaining mechanism) 
           14   a : flange-like portion 
           15 : clamp mechanism 
           15   a : upper clamp 
           15   b : lower clamp 
           15   c : rod-like member 
           15   d : presser foot 
           15   e : spring 
           15   f : nut 
           15   g : guide hole 
           16 : temporary holding mechanism 
           17 : coupling 
           18 : servomotor 
           19 : decelerator 
           20 : press machine 
           21 : motor 
           21   a : pulley 
           22 : belt 
           23 : gear 
           24 : press machine 
         L: material feed line 
         W: material