Abstract:
Disclosed is a hydraulic fine blanking head for a mechanical press and [a] an infeeding method for same. The hydraulic fine blanking head includes an adjusting mechanism having an adjusting nut provided with an internal motion thread engaged with external motion threads on a main cylinder, the adjusting nut being turnable around a stroke axis, a sprocket wheel rotatable at a frontal surface of the adjusting nut, a hydraulic motor driving the sprocket wheel, and a brake for the motor shaft. Axial backlash between the respective 1 motion threads is prohibited by a pressure generated by a flow of pressurized hydraulic fluid which also generates a part forming force in the head. A conduit in communication with a hydraulic system and the interior of the head delivers the locking pressure, locking the threads against the backlash. Removal of pressure unlocks the threads. Infeed of the main cylinder with regard to the ram is adjustable by switching the motor and the brake on and off.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a hydraulic fine blanking head for a mechanical press, specifically a fine blanking press, which is supported by a head piece mounted on a press machine frame above a ram, which ram supports a table top and executes a stroke movement in axial alignment to its stroke axis, with a flange inserted into the head piece with a tube-like design, the shoulder of which fine blanking head is fixed by screwed connections at the side of the head piece facing the ram. The head piece includes a tube-like main cylinder with pistons and pins positioned inside thereof, with, the main cylinder being pressure tight and closed with a cover or a retaining plate, and a hydraulic system for feeding the main cylinder with a pressure fluid adjusted to a desired pressure. 
         [0002]    The invention further relates to a method for infeeding a high pressure hydraulic fluid to a hydraulic fine blanking head in a press, specifically a fine blanking press, wherein an adjustable pressure is applied through a hydraulic fluid fed to the fine blanking head from a high pressure source to pistons retained in the main cylinder, which produces a pressure and/or deformation force, which actuates the press ram mechanically or hydraulically. 
         [0003]    DE 1 279 622 A1 discloses a fine blanking press with a cutting piston, a plunger piston pressing a sheet metal workpiece onto the bedplate of the press and a pressure piston supporting the part of the workpiece that is to be cut out, wherein the head of the press is provided with an adjusting spindle for adjusting a stopping flange that limits the stroke of the movable yoke at the upper side. The limiting/stopping of the movable yoke is adjusted by turning threaded cylinders running one in another. The fine adjustment of the thread is carried out by means of a handwheel via a worm to a toothed wheel directly attached to the bottom of the outer threaded cylinder, whereas a quicker, less fine adjustment is provided by an electrical motor driving the worm via two bevel gears. 
         [0004]    Height adjustment of the cutting head due to the manual operation as described above does not permit a sufficient adjusting and infeed accuracy regarding the height position of the head. In addition it is of disadvantage that the repeating accuracy of the adjustment is low, such that the quality of the fine blanked parts suffers. 
         [0005]    A further disadvantage is that a spindle distortion due to the normally existing axial backlash between the cylinders can not be excluded. 
         [0006]    Other known solutions for adjusting the distance between a press upper tool fixed to a ram, working together with a press lower tool fixed to a bedplate, and the ram use arrangements of pressure wedges (DE 2 039 644 A1) or hydraulically actuated cylinders (DE 198 22 436 A1). However, these known solutions due to the cooperation of cutting piston, V-shaped projection piston and V-shaped projection pins are not suitable for fine blanking presses. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a hydraulic fine blanking head for presses and a method for feeding a fine blanking head of the above mentioned kind, or one that securely avoids the axial backlash between the adjustment elements during the fine blanking operations, to provide a high infeed, repeating accuracy, and simultaneous increase in operational reliability under conditions of continuous operation. 
         [0008]    With the present invention, the infeeding of the fine blanking head is integrated with existing functional elements of the head, providing an adjusting mechanism including an adjusting nut having an internal motion thread that is turnable around the stroke axis of the ram, a sprocket wheel fixed, but free to rotate, at a front surface of the adjusting nut and vertically arranged to the stroke axis, a hydraulic motor with motor shaft provided at the headpiece, a driving chain running around the motor shaft and the sprocket wheel, and a brake positioned to brake the motor shaft and an external motion thread provided at the head of the main cylinder. The external motion thread of the main cylinder is guided with axial backlash by the internal motion thread of the adjusting nut, wherein the motion threads are connected via a common conduit for feeding and draining fluid of the hydraulic system that alternates between supplying and draining hydraulic fluid to and from the head piece to thereby generate a locking pressure and subsequent relief of same, which prevents and then allows for axial backlash between the threads of the adjustment nut and main cylinder. The infeed of the main cylinder with regard to the ram is carried out by switching off the motor and switching on the brake when the pistons and pins are relieved from pressure. 
         [0009]    The adjusting nut is axially blocked at a wall region of the head piece on a side away from the ram having a shoulder and held by the tube-like part of the flange against the lifting movement of the ram. This makes it possible to reduce the quantity of parts and the mass of the fine blanking head. 
         [0010]    In a specific aspect of the fine blanking head according to the invention, the conduit for feeding the fluid to the motion threads is connected to a low-pressure hydraulic system by a pipe via a switchable directional control valve included in the system for opening and closing the pipe, which makes it possible to respectively lock the motion threads of the adjusting mechanism in dependence of the presence of pressure at the pistons and the pins and to unlock the motion threads when the pressure is released. Specifically, when the pressure is released, the hydraulic fluid is returned to the hydraulic motor, at a time when the backlash between the motion threads is permitted and infeed is desired by the fine blanking or forming operation. The blocking pressure acting on the adjusting mechanism for example can be adjusted by the pilot control of the directional control valve to a low pressure of for instance 65 bar. 
         [0011]    In another aspect, the head piece and the adjusting nut are provided with at least one common conduit opening into the motion thread, in order to supply the threads with lubricant that facilitates smooth operation of the adjusting nut. The tube-like part of the flange is provided with at least one further conduit for draining the lubricant from the motion threads, so that a continuous lubrication of the motion threads through a pipe, which is connected to a lubricant reservoir, is possible. 
         [0012]    According to a still further aspect of the invention the motion threads provided on the adjusting nut and main cylinder are configured as breech block threads tolerating a one-side static stress in the case of axial admission of hydraulic fluid under locking pressure, wherein the motion thread of the main cylinder presses against the motion thread of the adjusting nut, and the adjusting nut presses against the shoulder at the head piece. In this case backlashes, i.e., back threading is eliminated, and the adjusting mechanism is locked, when the device is pressurized with displacement or working pressure. 
         [0013]    In another specific aspect of the fine blanking head according to the invention, the hydraulic motor is connected to a high-pressure hydraulic system having a feeding pipe and a draining pipe via a pilot operated proportional valve. The rotation speed of the motor can be controlled by adjusting a predetermined actuating pressure. 
         [0014]    In a more specific aspect, the motor brake is connected to the high-pressure hydraulic system by a switchable directional control valve for switching the brake on and off, whereby accurate braking according to the position infeed of the fine blanking head according to the invention becomes possible. 
         [0015]    In a further preferred aspect of the invention the driving chain is a hollow pin chain, which advantageously engages with the sprocket wheel on the adjusting nut, wherein a second sprocket wheel is also provided, having a rotation axis arranged in parallel with respect to the sprocket wheel of the adjusting nut on a plate supported by the headpiece. The sprocket wheels lie on one plane in horizontal alignment, so that a torsion-free drive of the hollow pin chain is guaranteed. 
         [0016]    According to a further specific aspect of the fine blanking head according to the invention a touch table is provided at the retaining plate facing the ram, which is attached by safety pins inserted into holes in the tube-like part of the flange arranged parallel to the stroke axis of the ram. 
         [0017]    In a still further aspect, particularly adapted to a fine blanking operation, the main cylinder houses a V-shaped projection piston having a V-shaped projection that is pressed against a work piece to be processed, and projection pins that coaxially support the V-shaped projection piston, and a touch piston for detecting a lifting distance provided between the retaining plate and the touch table, in which the pistons lie on the stroke axis. 
         [0018]    According to a further aspect of the fine blanking head according to the invention, in the retaining plate is positioned a pressure plate supporting the V-shaped projection pins coaxially with regard to the stroke axis, wherein a central support is provided in alignment with the stroke axis, wherein the pressure plate is held by a retaining ring at the touch table. 
         [0019]    In yet another aspect, the invention is a method including the following steps: 
         [0020]    a Locking the motion threads of the adjusting nut and main cylinder in a position that prohibits axial backlash, i.e.,axial back threading, through admission of a fluid under pressure that also provides force necessary for fine blanking part formation, by feeding a pressurized hydraulic fluid to the fine blanking head through a conduit in the head, and attaining a predetermined locking pressure, 
         [0021]    b Unlocking both of the motion threads by relieving the pressure and forming force by switching off the locking pressure by shutting off the flow of hydraulic fluid in the conduit, 
         [0022]    c Feeding an actuating pressure fluid to a hydraulic motor at a predetermined pressure to operate the adjusting mechanism by turning the adjusting nut sprocket wheel via a drive chain driven by the motor until the main cylinder has reached a predetermined infeed position, 
         [0023]    d Switching off the motor by shutting of the flow of pressure fluid and connecting the brake pressure adjusted by the actuating pressure to a brake pressure fluid for fixing the adjusted position of the fine blanking head and 
         [0024]    e again switching on the locking pressure to the adjusting mechanism for locking the motion threads according to step a. 
         [0025]    The fine blanking head according to the invention is not only usable for mechanically driven presses, but also for hydraulic presses. Due to the integration of the adjusting means into the fine blanking head it is possible to prohibit the axial backlash between the adjusting elements during cutting operations, to reach a high infeed and repeating accuracy and to simultaneously increase the operational security during continuous operation. 
         [0026]    Further advantages and details of the invention accrue from the following description with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a perspective view of the press with mechanisms assembled in the head piece of the press fine blanking head according to the invention; 
           [0028]      FIG. 2  is a cross-section of the fine blanking head according to the invention in the retracted position; 
           [0029]      FIG. 3  is a cross-section of the fine blanking head according to the invention in the extended position; 
           [0030]      FIG. 4  is a top view of  FIG. 1  of the fine blanking head according to the invention in the extended position; 
           [0031]      FIG. 5  is a view of the conduit for feeding hydraulic fluid to the motion threads of the adjusting mechanism as cross-section along V-V of  FIG. 4 ; 
           [0032]      FIG. 6  is a perspective view of the adjusting mechanism with hydraulic motor and hollow pin chain; 
           [0033]      FIG. 7  is a top view of the hydraulic motor with sprocket wheels; and 
           [0034]      FIG. 8  is a hydraulic connection diagram of the head adjustment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]      FIG. 1  shows a perspective view of a mechanically driven toggle-type fine blanking press. The ram  1  supports a table top and can move upward along stroke axis HU, in the direction of the head piece  2  of the press. Fine blanking head  3  is positioned in the head piece  2  of the press in alignment with the stroke axis HU. 
         [0036]      FIG. 2  shows a cross-section of the fine blanking head  3 . As exemplified in  FIGS. 2 and 4 , fine blanking head  3  resides in a seating provided in the head piece  2  and is fixed in a form-fit arrangement. With reference to  FIG. 6  as well, it is shown that fine blanking head  3  is provided with a motor-driven adjustment mechanism  11  assembled of adjusting nut  6 , sprocket wheel  7 , hydraulic motor  8 , rotary encoder  4 , driving chain  9  and main cylinder  10 . Adjusting nut  6  can rotate around the stroke axis HU. Main cylinder  10  is positioned alongside the stroke axis HU, and is interior to the adjusting nut  6 . Adjusting nut  6  and main cylinder  10  are provided with interengaged motion threads  12  and  13  that are matched with regard to their flank angles, which threads  12  and  13  are breech block threads engaged coaxially with regard to the stroke axis HU, so that, when the adjusting nut  6  is turned, the main cylinder  10 , with respect to the ram  1 , can be transferred from a retracted position to an extended position, as shown in  FIG. 3 . In other words, the main cylinder  10  is adjustable to ram  1  with regard to its height. 
         [0037]    The head piece  2  has a step-like shoulder  15  that projects towards the head interior, that is, towards the stroke axis HU. Step-like shoulder  15  is located at the side directed to the head. Below the shoulder, the head piece  2  has a radial diameter greater than the radial diameter of the step-like shoulder  15 . Step-like shoulder  15  is supported axially by the adjusting nut  6 . The outer contour of the adjusting nut  6  complements the contour of the step-like shoulder. A lower side  16  of the adjusting nut  6  rests on upper side  17  of a tube-like part  18  of a flange  19  that is inserted into the head piece  2 , whereby the adjusting nut  6  is axially secured at its interior and exterior sides. Thus, the adjusting nut is axially supported. 
         [0038]    As shown in  FIGS. 2 and 3 , shoulder  20  of the flange  19  is fixed to the head piece  2  at the side facing the ram by threaded connectors  21  extending towards the head piece  2 . Shoulder  20  of flange  19  is provided with two oppositely positioned holes  22  positioned to parallel the stroke axis HU. Holes  22  extend into the tube-like part  18 , and receive pin-like antitwist protections  23  that axially guide a main plate  24  that closes the main cylinder  10 . The front side  25  of the antitwist protections  23  is secured by a screwed joint. 
         [0039]    Main cylinder  10  of fine blanking head  3  accommodates a V-shaped projection piston  27  and a touch piston  28  that are in axial alignment to each other. The V-shaped projection piston  27  is in mechanical stop with the main cylinder  10 . The touch piston  28  is hydraulically brought into positive locking with the V-shaped projection piston  27 . The V-shaped projection pins  29 , shown in  FIG. 3 , project through the main plate  24  and rest on a V-shaped projection pressure plate  30 , which is secured by a V-shaped projection retaining ring  31  fixed to the touch table  26 . Main plate  24  is held on the central support  32 , which supports the tool during the technology phase. 
         [0040]    The head of the main cylinder  10  is closed with a pressure tight seal by a V-shaped projection cover  33 . As seen in  FIGS. 2 and 6 , on the upper frontal side  34  of the adjusting nut  6 , sprocket wheel  7  can rotate, which via the driving chain  9 , for example a hollow pin chain, is driven by the hydraulic motor  8 , which turns the adjusting nut  6  around its axis, which is in coincidence with the stroke axis HU. The layout of this drive is further described later in this disclosure. 
         [0041]    The tube-like part  18  of flange  19 , at an inner wall  38  facing the stroke axis HU has a step-like upper shoulder  39  extending perpendicular to the stroke axis HU and a shoulder  40  positioned lower than shoulder  39  that also extends perpendicular to the stroke axis HU. Upper shoulder  39 , in comparison to lower shoulder  40 , has a significantly larger step height H. Shoulders  39  and  40  define axial support surfaces M 1  and M 2  on inner wall  38  of the tube-like part  18 , which axial support surfaces M 1  and M 2  are offset from each other. Axial support surfaces M 1  and M 2  glidingly support a respectively shaped main cylinder  10 . 
         [0042]    The external motion thread  13  on the head  41  of the main cylinder  10  is provided with a length such that it extends over the whole length of the internal motion thread  12  of the adjusting nut  6 . The external motion thread  13  on the head  41  of the main cylinder  10  has a lower end at an upper retracted shoulder  43 , which is positioned above an external wall  42  of the main cylinder  10 , with the external wall positioned radially inward of the external motion thread  13  (See FIG. 
         [0043]      3 ). The external wall  42  has a lower shoulder  44  that extends more inward radially, that is, closer to the stroke axis, relative to external wall  42  and motion thread  13 . Thus, shoulders  43  and  44  define height support surfaces M 3  and M 4  in external wall  42  that are axially offset from each other. Height support surfaces M 3  and M 4  glidingly support the lateral surfaces M 1  and M 2  provided on the inner wall  38  of the tube-like part  18 . 
         [0044]    As shown in  FIG. 2 , motion threads  12  and  13  of the adjusting mechanism  11  are retracted. In this state, a clearance  45  is provided below the motion threads  12  and  13 , which is defined by the upper shoulder  39  of the tube-like part  18  of the flange  19 , the upper retracted shoulder  43  on the head of main cylinder  10 , and at internal wall  38 . 
         [0045]    A conduit  46  is provided in the wall of the tube-like part  18  and extends into clearance  45 . Further, a conduit  47  is provided in the wall of the head piece  2 , which is connected to conduit  46  at one end and to a pipe  48  at its other end for draining lubricant into a reservoir of a lubricating system that is not further shown. Above the conduits  46  and  47 , a further conduit  49  is provided in the wall of the head piece  2  and a conduit  50  is provided in the wall of the adjusting nut  6 , wherein the conduit  50  opens into the motion thread  12  of the adjusting nut  6  for feeding lubricant. The conduit  49  is connected to a pipe  51 . Through a pump, lubricant can be fed to lubricate the motion threads  12  and  13 . 
         [0046]    Axial support surfaces M 3  and M 4  on external wall  42  of main cylinder  10  support axial support surfaces M 1  and M 2  on internal wall  38  of the tube-like part  18 . As shown in  FIG. 2 , a narrow, axially extending clearance  52  is provided between the lower shoulder  44  of the external wall  42  of the main cylinder  10  and the lower shoulder  40  of the internal wall  38  of the tube-like part  18 . As shown in  FIG. 5 , a feeding conduit  54  extends into the clearance  52 , which via a feeding pipe  61  is connected to a pressure pipe  53  of a low-pressure hydraulic system. See  FIG. 8 . The feeding conduit  54  herein penetrates the wall of flange  19  and the wall of the tube-like part  18 . The pressure pipe  53  via a directional control valve  55  (see  FIG. 8 ) is connected to a hydraulic system, that can reduce the pressure of the hydraulic system to a value sufficient to lock the motion threads  12  and  13 . 
         [0047]      FIG. 3  shows the fine blanking head  3  according to the invention in the extended state, in which the main cylinder  10  has moved due to the rotation of the adjusting nut  6 . In this position, the upper shoulder  43  of main cylinder  10  has moved to be in close proximity to the upper shoulder  39  of the tube-like part  18  of flange  19 , and is held at a determined distance to the shoulder  39 . The maximum infeed height of the fine blanking head  3  with regard to the ram  1  of the press is determined by means of a rotary encoder  4 , positioned at the hydraulic motor  8 . The main cylinder  10  then adjusts the fine blanking plate  24  together with the touch table  26  by a selected amount into the direction of the ram  1 . 
         [0048]      FIG. 4  and  FIG. 5  illustrate the position of the feeding conduit  56 . Via the clearance  52 , lower shoulder  40  provided on tube-like portion  18  of flange  19  and lower shoulder  44  provided on the main cylinder  10  are hydraulically moved in directions opposite each other, so that locking pressure of the hydraulic fluid can press the motion thread  13  of the main cylinder  10  against the motion thread  12  of the adjusting nut  6 , through action of a directional control valve  55  responding to a predetermined preset. See  FIG. 8 . This action results in the locking of the motion threads. 
         [0049]      FIGS. 6 and 7  show the adjusting mechanism at the head of the fine blanking head which, at the head piece  2 , includes: hydraulic motor  8 , driving chain  9 , for example a hollow pin chain, and the rotary encoder  4 . On a plate  57 , which is arranged in a plane on the frontal side  34  of the adjusting nut  6  (See  FIG. 3 ), sprocket wheel  7  which is in connection with adjusting nut  6  and, two sprocket wheels  35 , which are positioned side by side, are turnable around axes B, which axes are parallel to each other. The driving chain  9  free of torsion runs around the sprocket wheels  7  and  35 . 
         [0050]    Again, with reference to  FIG. 8 , the hydraulic motor  8  connects to the high-pressure hydraulic system through a feeding pipe  62  and a proportional valve  37 . A drain pipe  58  connects the hydraulic motor  8  via the proportional valve  37  with a reservoir pipe  53 . Brake  59  is provided on the axis of the sprocket wheel  35 , the brake  59  being connected to the hydraulic system by a feeding pipe  60  having a directional control valve  55 . 
         [0051]    The operation of the fine blanking head is explained in more detail with reference to  FIG. 8 , and other figures. 
         [0052]    The hydraulic system includes a pressure pipe  62  fed with a pressure of 65 bar from a pressure source and the reservoir pipe  53 . The pressure source is not shown in the figures. 
         [0053]    The pressure pipe  62 , via the proportional valve  37 , extends to the hydraulic motor  8 . The proportional valve  37  by a pilot control is adjusted to a predetermined nominal pressure, which adjusts the incoming pressure of the hydraulic fluid for the adjusting nut  6  to an actuating pressure in the range of 0 to 250 bar, preferably 220 bar. The proportional valve  37  may be a 4/3 directional control valve closed in the central position, so that the hydraulic motor  8  can be switched from the closed position to the open position, when the locked motion threads  12  and  13 , which will be described in more detail below, are unlocked, and a re-adjustment of the infeed of the fine blanking head  3  with respect to the ram  1  is carried out. 
         [0054]    When the pre-determined infeed position of the fine blanking head  3  has been reached, the proportional valve  37  switches to the closed position and brake  59  fixes the new position. This is realized by opening the directional control valve  55  that actuates the brake  59 . 
         [0055]    The hydraulic system branches off the feeding pipe  53  at pressure pipe  60 , which transports the hydraulic fluid via the directional control valve  55  through conduit  61  to conduit  54  in the wall of flange  19  of the tube-like part  18  via conduit  56  and into the clearance  52 , which feeds the hydraulic fluid to the adjusting mechanism  11 . See  FIG. 5 . The directional control valve  55  lets the hydraulic fluid pass, so that a secure locking of the motion threads  12  and  13  occurs. As long as the V-shaped projection piston  27  and/or forming pressure is coming in, the motion threads stay locked. Thus, it is not possible to alter the infeed height of the fine blanking head  3  with regard to the ram. 
         [0056]    The method according to the invention is executed as follows: 
         [0057]    The motion thread  12  of the adjusting nut  6  and the motion thread  13  of the main cylinder  10  are hydraulically locked in the axial direction when the pressure and forming force is produced by feeding a hydraulic fluid maintained at a locking pressure. After the production of the pressure and forming force is not needed, the motion threads  12  and  13  are unlocked by shutting off the hydraulic fluid, thus removing the pressure that had maintained the motion threads in a locked arrangement. Axial backlash along motion threads  12  and  13  is now possible. 
         [0058]    Freeing the motion threads to move frees the main cylinder to move as well. The hydraulic motor  8  starts operating, translating action through sprocket wheel  7  and driving chain  9 , turning the motion thread  12  of the adjusting nut  6  until the main cylinder  10  has reached its pre-determined position with regard to ram  1 , by action of the rotary encoder  4 . 
         [0059]    The hydraulic motor  8  is switched off by shutting off the hydraulic fluid. The driving shaft of the motor  8  is stopped by means of the brake  59 . The locking pressure for the motion threads  12  and  13  is switched on again, so that the motion threads have no backlash on the line of force, when the V-shaped projection and/or forming pressure is effective.