Abstract:
A device and method are provided for preventing a tool from breaking during fine blanking and/or forming in a press. The device includes a fine blanking head positioned above a ram that carries out a stroke movement. The fine blanking head includes, among other things, a main cylinder retaining a V-shaped projection piston, a touch piston, several V-shaped projection pins, a main plate covering the main cylinder and a touch table to which the tool can be connected. Pressure provided by a hydraulic system is introduced to the device in distinct regions. Gaps between certain device components are maintained and monitored for purposes of determining the undesirable presence of foreign objects in the press operating path. If a sensor determines that the gaps are not maintained then the computer which operates valves that supply the pressure from the hydraulic system will shut the press down.

Description:
BACKGROUND OF THE INVENTION 
     A device for preventing a tool from breaking during fine blanking and/or forming in a press is disclosed. The tool includes an upper and a lower part with a fine blanking head positioned above a ram that carries out a stroke movement. The fine blanking head includes a main cylinder retaining a V-shaped projection piston lying on the stroke axis and several V-shaped projection pins arranged coaxial to the stroke axis, which are axially guided in a main plate covering the main cylinder and supported on a V-shaped projection pressure plate, wherein the main cylinder is held in the head piece of the press and closed by a V-shaped projection cover, and wherein valves connect the fine blanking head with a hydraulic system for producing pressure acting on and influencing the tool parts, which valves are triggered by a computer. 
     Further disclosed is a method for preventing a tool from breaking during fine blanking and/or forming in a press. The tool includes an upper and a lower part, wherein the main cylinder of the fine blanking head guides a V-shaped projection piston and a touch piston for producing a V-shaped projection force and a stripping force, which forces are pressure generated by a hydraulic system in communication with the fine blanking head, wherein piston pressure is adjusted by valves triggered by a computer. 
     DE 24 19 390 C2 discloses a device for the protection of a tool set of a hydraulic fine blanking press, the ram of which can be lifted by quick-elevating piston units and a working stroke pressure unit, wherein a detectable gap is present between the ram-driving element and a driven ram part. The detectable gap is maintained when pressure is low and closes when pressure is high. A sensor monitors the pressure conditions and a way switch until the ram has neared the tools to start the regular working stroke. The detectable gap is present between the ram and the frontal surfaces of the piston rods of the quick-elevating pistons and pressure is admitted to the detectable gap by touch cylinders in the ram, when the touch pistons rest against the frontal surfaces. 
     The detectable gap at the quick-elevating piston is positioned upstream of the ram. This protection device is continuously actuated when the detectable gap closes due to an elevated pressure load. This teaching is believed to not detect punchings, parts or foreign bodies in the tool and thus tool damage cannot be prevented. 
     DE 69 17 177 U discloses a tool protection apparatus in presses for processing a blank in which a first tool is moved by the working piston and a tool fixed to the frame, in which the press has two switches, which have to be actuated in a predetermined sequence, for interrupting the working stroke in case of an inverse actuating sequence. The first tool is axially movable with regard to the working piston element, which during the working stroke is held at a small distance before the working piston by elastic flexible means. A first limit stop switch, adjustable to the nominal height of the blank to be processed, is actuated by a limit stop, when the piston has moved for a part of its working stroke as predetermined by the adjustment of the first limit stop switch. A further limit stop switch is actuated by a further limit stop, when an element by the blank or a foreign body hitting the second tool is pushed back onto the piston. 
     The element is a lower tool mounting surface supported on a cylinder, which together with the working piston is enclosed within a ring-shaped pressure chamber, which is connected to a pressure fluid pipe having a shut off element, that makes it possible to let as much compressed air into the ring chamber to hold the mounting surface during the working stroke, in a practically suspended state before the piston. 
     Disadvantageous with this approach is the necessity of providing a second separate hydraulic system that requires compressed air and thus causes a considerable effort regarding circuitry and construction. Further, after the detection of a foreign body there is no possibility to compensate the kinetic energy of the drive. 
     Other known solutions for detecting punchings or other foreign bodies in the tool use optical sensors or ultrasonic sensors. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention is directed to a device that prevents a tool from breaking during fine blanking and/or forming in a relatively simple construction employing relatively fewer parts, thereby reducing costs. The device can absorb high tilting moments and compensate for the kinetic energy of the drive during a return stroke even before the press is switched off. 
     In one aspect of the present invention, punchings, parts or other foreign bodies are detected by the active elements of the fine blanking head, the head structure including the necessary components to perform that task. A touch piston is provided between a V-shaped projection piston and V-shaped projection pins, that with the V-shaped projection piston on the one hand and with the V-shaped projection pins and the V-shaped projection pressure plate on the other hand are present in an axially movable arrangement relative to each other, wherein the V-shaped projection piston has a first pressure room to which a preloading pressure of the hydraulic system can be admitted. Further, between the V-shaped projection piston and touch piston, there is a second pressure room to which a touch piston pressure can be admitted. Also, the touch piston has a further (third) pressure room to which can be admitted a differential pressure, wherein the first, second, and third pressure rooms, each through a connection in the V-shaped projection cover and by conduits in the main cylinder, are connected with the hydraulic system for admitting pressure to the V-shaped projection piston and the touch piston, with pressure admitted to the touch piston to apply force opposite to the effective direction of the preloading pressure. Further provided, as part of the device, is a touch table held suspendedly against a main plate by fixing means, described later herein, the touch table held at a determined detection distance that is weight compensated by the main plate. The touch table and main plate are positioned below the touch piston, at a head piece position in relative proximity to the ram. A sensor is provided to a gap between the touch table and main plate that in case of a change of the detection distance transmits a signal to the computer to immediately stop the press to protect the upper part of the tool. 
     The touch table, the main plate, the central support, the main cylinder and the adjusting nut non-positively and/or positively divert the pressing force into the head piece of the press depending on the motion of V-shaped projection piston, V-shaped projection pins and touch piston between upper and lower dead points. 
     In a specific aspect of the invention, the second pressure room of the V-shaped projection piston is located below a supporting shoulder at the wall of the main cylinder that projects in the direction of the stroke axis towards the lower piston surface of the V-shaped projection piston. Further, the touch piston has a pressure room located below the touch piston shoulder and above a supporting shoulder at the wall of the main cylinder that projects in the direction of the stroke axis. With this design, a touch piston pressure P 2  can act on the V-shaped projection piston in the opposite direction to the preloading pressure P 1  applied to the V-shaped projection piston, and a differential pressure P 3  acts on the touch piston, causing an axial shift of V-shaped projection piston, touch piston and V-shaped projection pins. 
     Further, the pressure room of the V-shaped projection piston, through a connection in the V-shaped projection cover, is connected to a pressure pipe of the hydraulic system that includes a proportional valve which supplies to the pressure room a preloading pressure for producing a V-shaped projection force or a stripping pressure for producing a stripping force or making the piston motionless. 
     Also, the second pressure room of the V-shaped projection piston and the pressure room for the touch piston, through a connection at the V-shaped projection cover with a directional control valve, provides pressure to the second pressure room through a feeding pipe in connection with a pressure pipe of the hydraulic system. 
     In a more specific aspect of the invention, the apparatus is provided with conduits supplying the pressure rooms that are axially aligned in the direction to the stroke axis in the wall of the main cylinder and open by bending into the respective pressure rooms. 
     Still more specifically, different quantities of hydraulic fluid can be fed into the individual pressure rooms. To realize this, the conduit for the V-shaped projection piston can be provided with a larger diameter than the conduit for the touch piston. 
     In one particular aspect, a fixing means is provided in the device which comprises a pressure spring and a straining screw and connects the main plate and touch table, which pressure spring and straining screw are positioned in a recess of the main plate, wherein the straining screw penetrates the main plate and the pressure spring provides compensation for the weight of the touch table and the upper part of the tool. 
     In another particular aspect, the device includes a sensor adjustably positionable in a seat of the main plate, the measuring point of which is determined by a switch flag arranged in the touch table, to provide for adjustment of the detection distance to the gap distance. 
     The gap distance, in the case of an immediate stop of the press, provides compensation for the kinetic energy, even before the press has stopped. 
     In another particular aspect, the main plate is attached at a frontal side of the main cylinder facing the ram with screwing means. 
     In a still further aspect, the touch table of the device is twist-proof and is axially movable with respect to the main plate through guidance provided by guiding pins arranged axially parallel to the stroke axis in holes provided for receiving the guiding pins. 
     Yet even further, there is an aspect of the invention in which the V-shaped projection pins and the V-shaped projection pressure plate are positioned coaxially with regard to the stroke axis, wherein the pressure plate is fixed at the touch table by a retaining ring and a central support is integrated in the main plate. 
     In operation, the force of pressure is diverted by means of a non-positive and/or positive connection by hydraulic locking and unlocking of a touch table, a main plate, a central support, a main cylinder and an adjusting nut into the head piece of the press, and by axially shifting the V-shaped projection piston and touch piston in alignment with the stroke axis (HU) prior to delivering the pressure force until the non-positive and/or positive connection between V-shaped projection pressure plate, V-shaped projection pins, touch piston and V-shaped projection piston is reached, wherein, between the touch piston and V-shaped projection pins, a gap distance between the main plate and the touch table is adjusted with hydraulic means and the gap distance weight compensated detection distance between the main plate and the touch table is adjusted with mechanical means, the change of which is scanned by the V-shaped pressure plate and/or the touch table in case of an inverse sequence of the stroke and detected by a sensor transmitting a signal to the computer, which will immediately stop the press. 
     The kinetic energy is compensated in the gap distance between touch table and V-shaped projection pins because the touch table can move in the direction of the V-shaped projection pins. 
     In yet another aspect, the present invention is a method for preventing the breaking during fine blanking and forming operations comprising the steps of:
     a Preloading a V-shaped projection piston and touch piston to a preloading pressure P 1  to realize the non-positive connection between them;   b Applying a differential pressure P 3  that differs from the preloading pressure P 1  to the touch piston to axially shift the touch piston;   c Maintaining a detection distance TA adjusted to a gap distance between the touch piston and V-shaped projection pins through the touch piston differential pressure P 3  and the preloading pressure P 1  acting against it for realizing a non-positive connection between the touch piston and V-shaped projection piston, wherein the preloading pressure P 1 , the touch piston pressure P 2  and the differential pressure P 3  are adjusted to the condition P 1 &gt;&gt;P 3  and P 2 =0;   d Superseding the hydraulic fluid under differential pressure P 3  in the touch piston pressure room through application of the upper pressure room preloading pressure P 1 ;   e Relieving the pressure on the V-shaped projection piston by switching off the preloading pressure P 1  when the upper dead point for the V-shaped projection piston and touch piston is reached;   f Stripping the V-shaped projection piston and touch piston by applying a constant stripping pressure P 4  and a constant touch piston pressure P 2  to the pressure rooms of V-shaped projection piston and touch piston, with the understanding that pressures P 2  and P 4  are not necessarily equal;   g Shifting the V-shaped projection piston and the touch piston until a sensor triggers a signal;   h Switching off the stripping pressure P 4  for the V-shaped projection piston and the touch piston and applying the preloading pressure P 1  to the upper pressure room of the V-shaped projection piston; and   i Repeating the step sequence a) to h) in case the sensor has not detected, depending on the ram stroke, a premature change of the detection distance TA.   

     In a specific aspect of the inventive method, the preloading pressure for the V-shaped projection piston is adjusted to a pressure of more than 110 bar. 
     In a more specific aspect of the inventive method:
         the touch piston pressure P 2  and the stripping pressure P 4  are adjusted to a low pressure below 110 bar, and   the differential pressure P 3  is adjusted to a low pressure below 110 bar or to zero.       

     Further advantages and details of the invention accrue from the following detailed description with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the press with the device according to the invention assembled in the head piece, 
         FIG. 2  is a cross-section of the device according to the invention in the extended state, 
         FIG. 3 . is a cross-section of the device according to the invention in the retracted state, 
         FIG. 4  is a cross-section of the main plate and the touch table with illustration of the mechanical weight compensation and 
         FIG. 5  is a cut out cross-section of the main plate and the touch table illustrating the arrangement of the sensor and the position of gap distance and detection distance. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a perspective view of a mechanically driven, toggle-type fine blanking press. Ram  1 , supporting a table top, of this press moves in an upward direction, along the stroke axis HU and towards the head piece  2  of the press. In the head piece  2  of the press, the device according to the invention is positioned in alignment with the stroke axis HU. 
       FIG. 2  shows the device according to the invention in cross-section. The device is assembled into the head piece  2  of the press and form-fit in place there. The device comprises a fine blanking head FSK, which includes a main cylinder  3 , an adjusting nut  4 , a flange  5  that is fixed to the head piece  2 , a main plate  6  and a touch table  7 . Main cylinder  3 , adjusting nut  4 , flange  5 , main plate  6  and touch table  7  in combination provide a non-positive arrangement that diverts the whole pressure force into the head piece  2  of the press. The non-positive connection is achieved by locking the motion threads BW 1  and BW 2  at the head of the main cylinder  3  and at the adjusting nut  4  by pressing the motion thread BW 1  of the main cylinder  3  against the motion thread BW 2  of the adjusting nut  4  in the direction of the upper dead point OT with hydraulic pressure PV. Conversely, the locked two motion threads BW 1  and BW 2  are unlocked by switching off the hydraulic pressure PV. 
     The non-positive connection is illustrated by the gray colored area in  FIG. 2 . 
     The head piece  2  is connected to the frame  8  of the press by straining screws SB (see  FIG. 1 ).
         Main cylinder  3  retains within its hollow interior a V-shaped projection piston  9  and a touch piston  10  in axial alignment to each other. The V-shaped projection pins  11  penetrate the main plate  6  and are supported by V-shaped projection pressure plate  12 , which is secured by a V-shaped projection retaining ring  13  fixed to the touch table  7 .       

     The main cylinder  3  is sealed pressure-tight at its head side by a V-shaped projection cover  15 . Above the V-shaped projection piston  9  a pressure room  16  is formed, which pressure room  16  is connected to a pressure pipe  56  through a connection  17  that is connected to pressure pipe  56  that is provided with an adjustable valve  18 . With this arrangement, the pressure room  16  is connected to the hydraulic system that supplies the pressure for producing a hydraulic preloading pressure P 1  that acts on the V-shaped projection piston  9  in the direction of the lower dead point UT. 
     As shown in  FIG. 3 , the main cylinder  3  is provided at is internal wall  20  with a first step-like shoulder  21  projecting in the direction of the stroke axis HU. The shoulder supports and limits the stroke of the V-shaped projection piston  9  in the direction of the lower dead point UT. Below first shoulder  21 , on the touch piston  10 , is positioned a second shoulder  22  projecting in the direction of the stroke axis HU, that borders the pressure room  31  of the touch piston  10 . An axially extending conduit  23  is provided in the wall  20  of the main cylinder  3 , which has about a 45° bend in the direction of the stroke axis HU at a location below the first shoulder  21 . The conduit  23  opens through the internal wall  20 . A pressure room  24  is formed below the V-shaped projection piston  9 , into which is fed the hydraulic fluid under touch piston pressure P 2 . The conduit  23  is in fluid connection to a low pressure pipe of the hydraulic system  56   a  through a feeding pipe  27  that is connected to connection  25  provided in V-shaped projection cover  15 . The feeding pipe  27  is provided with a control valve  26 . 
     Furthermore, the wall  20  of the main cylinder  3  is provided an axially extending conduit  29 , which conduit has about a 45° bend in the direction of the stroke axis HU. The conduit  29  opens from the internal wall  20  below the second shoulder  22  provided on the touch piston  10  and provides a pressure room  31  below a shoulder  30  of the touch piston  10 . The conduit  29  is in fluid connection with the hydraulic system  56   a  through feeding pipe  34  having reservoir  28  and control valve  33 . This arrangement connects with conduit  29  through connection  32  provided in the V-shaped projection cover  15 . Hydraulic fluid is admitted to the pressure room  31  in the direction of the upper dead point OT under a differential pressure P 3 , so that the touch piston  10  can be moved in the direction of the upper dead point OT. 
     The pressures P 2  and P 3  act against the preloading pressure P 1 , wherein the pressure P 3  causes the touch piston  10  to non-positively connect to the lower side  35  of the V-shaped projection piston  9 .
         Between the lower side  36  of the touch piston  10  and the frontal surface  37  of the V-shaped projection pins  11  is provided a gap having a predetermined gap distance SP of, for example, 4 to 10 mm, preferably 6 mm.       

     The gap distance SP provides a stopping distance of sufficient length that is employed where an immediate stop of the press to brake the kinetic energy or to retard same is needed. 
     The V-shaped projection pins  11  are supported on the V-shaped projection pressure plate  12 , so that a hydraulic displacement can be realized in dependence on the touch stroke, and the pressure P 3  applied counter to the pressure P 1 . The total V-shaped projection force produced by the preloading pressure is thus reduced by the force produced by the differential pressure P 3 .
         The head piece  2  at internal wall  42  that faces the stroke axis HU has step-like upper shoulder  43  that projects in the direction of the stroke axis HU, which upper shoulder  43  is supported by the adjusting nut  4 , an arrangement that provides axial stability against upward movement of the adjusting nut  4 , in the direction to the upper dead point OT. Also, the adjusting nut  4  is axially held in relation to the lower dead point UT by the tube-like part  39  of the flange  5 .   In tube-like part of the flange  5 , two holes  38  positioned diametrically opposite each other are provided, which are positioned in the tube-like part  39  parallel to the stroke axis HU. Holes  38  accommodate pin-like guiding pins  40  that axially guide the main plate  6  and provide antitwist protection for the main plate  6  and the main cylinder  3 .       

     As shown in  FIG. 4 , in the main plate  6  a recess  45  is provided for accommodating a fixing means  46  including a pressure spring  47  and an adjusting screw  48 . 
     The fixing means  46  makes it possible to compensate for the weight of the touch table  7  and the upper part of the tool  50  according to weight. In other words, the weights of the touch table  7  and the upper part of the tool  50  are compensated. At the lower side  49  of the touch table  7  are located standard fixing means for fixing the upper tool part  50 , so that it is not necessary to describe them in detail. 
       FIG. 5  shows in cross-section the main plate  6  and the touch table  7 . Vertical to the stroke axis HU, the main plate  6  is provided with a recess  51 , in which is positioned a sensor  52  for detecting the detection distance TA. The measuring point MP of the sensor  52  ends in a recess  54  arranged parallel to the stroke axis HU which is accessible from the lower side  53  of the main plate  6  for the measuring point MP of the sensor  52 . In this manner, the sensor  52  determines the distance to be detected TA, and permits for adjustment of same. 
       FIG. 5  also illustrates the position of the gap distance SP between the lower side of the touch piston  10  and the frontal surface of the V-shaped projection pins  11 , and the detection distance between the lower side  53  of the main plate  6  and the upper side of the touch table  7 . As shown in  FIG. 3 , the hydraulic system includes a pressure pipe  56 , which by a not shown pressure source is loaded to a pressure of 250 bar. To this pressure pipe  56  is connected feeding pipe  19  that extends through controllable proportional valve  18  to the pressure room  16  positioned above the V-shaped projection piston  9 . Through proportional valve  18 , the hydraulic preloading pressure P 1  is fed, acting in the direction of the lower dead point UT on the V-shaped projection piston  9 , to produce the V-shaped projection force. The preloading pressure P 1  can be adjusted to a pressure between 20 and 250 bar. 
     From a low-pressure pipe  56   a , a feeding pipe  27  via the controllable directional control valve  26  extends into the pressure room  24 , to provide stripping pressure P 4  for the touch piston  10 . The touch piston pressure P 2  is directly provided from the hydraulic system. A further feeding pipe  34  extends from the low-pressure pipe  56   a  via a reservoir  28  into the pressure room  31  below the touch piston  10 . The differential pressure P 3  acts against the preloading pressure P 1  and makes it possible to not-positively connect touch piston  10  and V-shaped projection piston  9 , in order to hold them connected. Also, it is possible to disconnect the non-positive connection between touch piston  10  and V-shaped projection piston  9  by again by switching on the valve  33 . In this way, the pressure potential of the reservoir  28  can be emptied. 
     The operation of the device according to the invention is described in detail below. The preloading pressure P 1  provides a projection force for the V-shaped piston  9 , which projection force is diverted by the non-positive and/or positive connection of touch piston  10 , V-shaped projection piston  9  and V-shaped projection pins  11 . Before the preloading pressure P 1  is admitted and until the non-positive connection of V-shaped projection piston  9  and touch piston  10  is reached, the V-shaped projection piston  9  and touch piston  10  are moving in alignment with the stroke axis HU, due to application of the applied differential pressure P 3 . This results in a non-positive connection between the lower side of the touch piston  10  and the frontal surface of the V-shaped projection piston  9 . As shown in  FIG. 5 , a fixed gap is present between the touch piston  10  and the V-shaped projection pins  11 , having a fix gap distance SP, which, for example, may be 6 mm. 
     The touch table  7  is suspendedly positioned at the main plate  6 , with compensation for weight, wherein for axial movement of touch table  7  are provided four guiding pins  40 , and for the weight compensation of same, four mechanical fixing means  46  in mechanical cooperation with high pressure spring  47  are provided, as aforedescribed. 
     A sensor  52 , provided to detect a distance TA between the main plate  6  and touch table  7 , can detect a too soon change of the detection distance TA that changes based on the ram stroke. The sensor  52  produces a signal sent to a computer  57  for processing the sensor signals. 
     In processing the signal, a differentiation occurs between two signal conditions. In a proper form-fit connection between V-shaped projection pressure plate  12 , V-shaped projection pin  11 , touch piston  10  and V-shaped projection piston  9 , a displacement against the preloading pressure P 1  is caused, that is carried out as a standard cancellation of the detection stroke. That is, the touch table  7  and the V-shaped projection pressure plate  12  touch the main plate  6  without detected change of the detection distance TA. The single process steps of the method according to the invention are carried out continuously. 
     However, where the detection distance TA is changed, for example, by the presence of punchings or other foreign bodies, the sensor  52  detects the change in detection distance and transmits this information to the computer  57 , where it is processed further. The change of the detection distance caused by the presence of punchings or other foreign bodies leads to a too early cancellation of the detection stroke, so that the computer  57  causes an immediate stop of the press. The kinetic energy during, an immediate stop due to the sufficient high detection distance can be halted by the action of a brake, or retarded by action of the drive. 
     A method employing the advantages offered by the aforedescribed apparatus is described as follows. In process step (a), the V-shaped projection piston  9  and the touch piston  10  are preloaded to a high pressure P 1 . 
     In process step (b), the detection distance TA is adjusted to the gap distance SP of touch piston  10  and V-shaped projection pins  11  through application of the resulting differential pressure P 3 , whereby a non-positive connection between touch piston  10  and V-shaped projection piston  9  is realized. The differential pressure P 3  is adjusted to 65 bar, for example. 
     In process step (c) it is provided that touch piston  10 , V-shaped projection pins  11 , V-shaped projection pressure plate  12 , which are under the influence of differential pressure P 3 , and V-shaped projection piston  9 , being under the influence of preloading pressure P 1 , are displaced by the ram  1 . 
     In process step (d), the preloading pressure P 1  is relieved when the V-shaped projection piston  9  is at the upper dead point OT, by turning off the preloading pressure source. 
     In process step (e), a differential pressure P 3  of, for example 65 bar, is applied the touch piston  10 , which makes it possible to realize or cancel the non-positive connection between touch piston  10  and V-shaped projection piston  9 , due to axial movement of the touch piston  10 . 
     In process step (f), the V-shaped projection piston  9  and the touch piston  10  are stripped at a desired stripping pressure P 4  of, for example, 70 bar, which is adjusted with the valve  18  for adjusting pressure in the V-shaped projection piston  9  pressure room  16 , with the differential pressure P 3  being applied. Simultaneously with the stripping pressure P 4  is applied the touch piston pressure P 2 , of for example 65 bar. 
     In process step (g), the stripping pressure P 4  is switched off and the pressure P 1  is applied to the upper pressure room  16  of the V-shaped projection piston  9 , when via touch piston  10 , V-shaped projection pins  11  and V-shaped projection pressure plate  12  was transmitted the signal for reaching the gap distance SP from the sensor  52 . 
     The sequence of process steps (a) to (g) then is repeated. 
     When this closing movement is actuated by a too early change of the detection distance TA, a quick stop of the machine is carried out, so the press is immediately stopped, A too early closing movement is always then actuated, when punchings, parts or other foreign parts are in the upper tool, because this leads to a too early change of the detection distance TA.