Abstract:
A stamping device includes a base body; an elongated punch having a longitudinal axis; a supporting arrangement for holding the punch in the base body and for guiding the punch for axial displacements between an advanced position and a retracted position; a driving unit releasably held in the base body and including a driving device for axially displacing the punch; a coupling device having a first state in which the coupling device operatively connects the driving device with the punch and a second state in which the driving device is disconnected from the punch; and a receiving arrangement for holding the punch in a desired axial position when the coupling device is in its second state.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of German Application No. 198 55 578.4 filed Dec. 2, 1998, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a stamping device particularly for providing holes in unfired ceramic substrates, also referred to hereafter as “green sheets”. 
     In the manufacture of, for example, multilayer ceramic substrates used as circuit boards for supporting and electrically contacting electrical and electronic components, it is often required to provide a predetermined hole pattern in flat green sheets. The holes which may serve, for example, for a throughgoing contacting of printed circuit conductors, are provided by hole-stamping devices which, to ensure the required accuracy of the circuit board construction, are made with a tolerance of a few microns. 
     U.S. Pat. No. 5,233,895 discloses a stamping apparatus for stamping green sheets. The apparatus comprises an essentially stationary table on which the green sheet is positioned and on which it may be shifted as required. Above the table a base or carrier body is arranged which has a guiding device for an axially movable punch. The free end of the punch which serves as the stamping tool is axially displaceably supported in a throughgoing opening of an otherwise cup-shaped guide. In the table, facing the punch, an opening is provided into which the punch end may penetrate. 
     The punch is connected at its upper end with a cylindrical coil positioned in the annular gap of a permanent magnet arrangement in which a radial magnetic field is produced. An electrical energization of the coil thus results in an axial motion of the coil and the punch so that the latter may be moved into an advanced position and back into a retracted position. 
     The repeated stamping operations cause wear of the punches requiring their periodic replacement, either individually or as a group. 
     For performing such a replacement, U.S. Pat. No. 5,024,127 discloses the provision of a coupling device to releasably connect the electric drive arrangement and the stamping device formed by a punch. The punch is guided in a guiding device for axial displacements. The driving device has a plunger aligned with the punch and is movable by means of an electric drive connected with one end of the plunger. That end of the plunger which is oriented towards the punch and oriented away from the drive carries a coupling element which accommodates a head provided on the punch. For this purpose the coupling element defines a socket which, in the axial direction, is bordered by an engagement face for the frontal end of the punch and a second, split surface which is defined by a fork and which serves as an engagement face for the punch head. In case the driving device, the plunger and the coupling element are separated from the punch, the position of the punch is undefined. It may therefore move, for example, under its own weight, into a position which does not correspond to the position of disengagement. Such an occurrence may render the handling of the apparatus more difficult and may lead to problems particularly in case the punch has to be periodically replaced, for example, because of wear. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved stamping device of the above-outlined type whose handling is rendered better compared to conventional devices, particularly in case of punch replacement. 
     This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the stamping device includes a base body; an elongated punch having a longitudinal axis, a supporting arrangement for holding the punch in the base body and for guiding the punch for axial displacements between an advanced position and a retracted position; a driving unit releasably held in the base body and including a driving device for axially displacing the punch; a coupling device having a first state in which the coupling device operatively connects the driving device with the punch and a second state in which the driving device is disconnected from the punch; and a receiving arrangement for holding the punch in a desired axial position when the coupling device is in its second state. 
     Thus, the stamping device according to the invention has a base body on which one or a plurality of punches are axially shiftably supported between an advanced (stamping) position and a retracted position. The shifting of the punch is effected by a driving unit which has preferably a separate driving device for each punch. The driving devices are controlled by a control unit in such a manner that the punches may be shifted briefly into the stamping position to thus perform the stamping step. The transmission of the axial motion from the respective driving device to the associated punch is effected by a coupling device which may be disengaged when required. The coupling device provides for a fixed connection between the driving device and the respective punch in the axial direction and thus makes possible the axial transmission of motion, whereby the driving device determines the axial position of the punch. In case the driving device is separated (disconnected) from its associated punch, the axial position of the punch is no longer set by the driving device. For such a case, according to the invention, the receiving device serves to hold the punch in a desired axial position. The purpose of such a positioning is, for example, to prevent the punch from assuming unintentionally its advanced position in which its free end (stamping end) would project from its guide and from the base body and thus would be exposed to risks of being damaged. The receiving device sets the position of the respective punch at least to such an extent that its range of motion is significantly limited at least in one direction, while it may move freely in the opposite direction. Such an arrangement has, for example, the advantage that, after the driving unit has been removed, the punches may be taken out of their guide and may be replaced. 
     The receiving device which takes over the punch as long as the driving unit is disengaged, holds the punch in a predetermined position even when the driving unit is re-positioned or reconnected. Such steps may be particularly easily performed and thus a significantly simplified handling is achieved. 
     Preferably a plurality of identically structured punches are supported by the base body or, more precisely, by a guiding device supported on the base body, in such a manner that the punches are displaceable axially independently from and parallel to one another, provided they are released by the receiving device. In case the punches are received by the receiving device, they are all held in a predetermined position, preferably in the retracted position. 
     According to a preferred embodiment of the invention, the punches are each formed by a cylindrical shank adjoined, as the stamping tool, by a cylindrical stamping portion, whose diameter is significantly less than the diameter of the shank. The shank is supported in a guide, such as a guide sleeve. The stamping portion passes through an opening of a cup-shaped guiding or stripping element. In the withdrawn position the stamping portion does not project beyond the guiding and stripping element; the frontal end of the stamping portion is positioned within an opening provided in the guiding and stripping element. The shank and the stamping portion are preferably in a coaxial alignment with one another. The guide sleeve guides the shank during introduction of the punch with such an accuracy that the stamping portion penetrates into the opening of the guiding and stripping element without contacting or colliding with the latter. 
     At its end remote from the stamping element, the punch preferably has a head which, together with the coupling element associated therewith, forms the coupling device for coupling the punch to the driving device. The coupling element connects the punch in a form-fitting (form-locking) manner; for this purpose the coupling element has a laterally open socket for the punch head. The socket is bordered by two facing surfaces between which the head of the punch passes with a very small clearance or with practically no clearance. For uncoupling the driving device from the punch, the punch is laterally displaced relative to the driving device, so that the punch head may move out laterally from the socket. The coupling elements of all the driving devices or at least of one group of the driving devices are identically oriented so that the coupling and uncoupling of the coupling devices may be effected by a lateral displacement of the entire driving unit or a determined group of driving devices. As a result, it is, for example, feasible to remove a driving unit from the stamping device, whereby the punches separately driven by the respective driving unit are individually accessible and replaceable, if required. 
     As a receiving device for the punch heads a head plate is provided which is positioned between the driving unit and the guiding devices for the punches. The guiding devices are provided on the base body and are formed, for example, by guide sleeves. The head plate is thus situated in the vicinity of that end of the respective punch which is oriented towards the respective driving device and is thus in the vicinity of the coupling device. In such a position the head plate may take over the punches and/or their heads when they are released by the coupling elements. As the driving unit is disconnected from the punches, the latter are received by the head plate so that the punches may not move in an uncontrolled manner into an undesired position, for example, into an advanced (stamping) position. 
     For receiving the punch heads, a special engagement zone (punch head supporting surface region) is provided on the head plate preferably for each punch. The engagement zone is shifted underneath the punch head before the latter may entirely move out of the coupling element. Advantageously, the engagement zone formed on the head plate lies at the same level as the corresponding engagement face on the coupling element, that is, it is situated coplanar therewith, when the coupling element is in the retracted position. 
     In order to hold the coupling element positively in the retracted position during uncoupling, the coupling element preferably has an end face which, when the coupling element is in the retracted position, is situated at the same level as a supporting surface provided at the underside of the head plate. As result, during uncoupling, the coupling element is in a firm engagement, for example, with the base body or a counter support and is thus positively maintained in a position in which a transfer of the punch head from the socket to the head plate is feasible. 
     On the coupling element a positioning surface may be provided which adjoins the lower end face of the coupling element and which serves to guide the coupling element into a replacement position in which the punch head may be transferred to the head plate. Such a replacement position is preferably the position which determines the retracted position of the punch. The positioning surface may be formed, for example, by an oblique run-on face which may cooperate with a stationary edge (counter support) formed, for example, on the base body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view of the stamping device according to the invention. 
     FIG. 2 is a schematic, partially sectional side elevational view of a preferred embodiment of the stamping device according to the invention. 
     FIG. 3 is a top plan view of the stamping device shown in FIGS. 1 and 2. 
     FIG. 4 is a fragmentary sectional side elevational view of the stamping device shown in FIGS. 1-3, shown at an enlarged scale. 
     FIGS. 5 a ,   5   b  and  5   c  are views similar to FIG. 4, illustrating three different operational positions of the stamping device. 
     FIG. 6 is a schematic sectional top plan view of the driving devices with coupled punches. 
     FIG. 7 is a view similar to FIG. 6 illustrating the driving devices separated from the punches. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a stamping device  1  by means of which a predetermined or selectable hole pattern is to be provided in a flat substrate, particularly unfired ceramic layers (green sheets) which find application in the manufacture of ceramic substrates for electronic components or component groups. The stamping device includes a table  2  which has an essentially planar upper side  3  on which a green sheet to be provided with holes is positioned. Means for positioning the green sheet on the table  2  and for moving (shifting) the same are not illustrated in further detail. 
     Above the table  2  a stamping head  4  is disposed which comprises an essentially flat base body  5  which defines a clearance  6  with the table  2  for the introduction and passage of the green sheet. The base body  5  is, by means not illustrated in detail, disposed in a predetermined position relative to the table  2 . If required, the base body  5  may be moved in such a manner towards or away from the table  2  that the clearance  6  is widened or narrowed. During operation, particularly for performing the stamping steps, the stamping head  4 , however, remains stationary, as may be seen in FIG.  2 . As further illustrated in FIG. 2, underneath the table  2  a receiving space  7  for the stamping waste and a corresponding removal device are arranged. The table  2  is surrounded by a frame  8  provided at its upper side with an opening  9  into which one part of the base body  5  of the stamping head  4  may penetrate. 
     For stamping the green sheet or other flat material introduced into the clearance  6 , individual punches, of which only two are shown at  10  and  11 , are mounted on the stamping head  4 . The punches may be displaced in such a manner that their free ends move out of the base body  5 , they traverse the clearance  6  and penetrate into a respective aligned opening provided in the table  2 . The punches  10  and  11  may be operated independently and separately from one another. For driving the punches, a driving unit  12  is provided which is composed of a plurality of individual electric driving devices, of which two are shown at  13  and  14 . Preferably each punch  10  and  11  has its own, independently operable driving device as shown in FIG. 2 symbolically at  14  for the punch  11 . 
     The driving device  14  is formed of a separately controlled magnetic or electromagnetic drive not illustrated in detail. Upon actuation of the driving device  14 , a shank or plunger  16  projecting from its underside  15  is moved downwardly through a predetermined distance. The driving device  14  is, similarly to the other driving devices, connected with the base body  5  by a respective carrier element  17  and supported in such a manner that the plunger  16  is in alignment with the punch  11 . 
     Turning to FIG. 4, a coupling device  18  which connects the plunger  16  with the punch  11 , includes a coupling element  19  and a head  20  mounted on the punch  11 . The head  20  of the punch  11  is formed by a cylindrical part which has a greater diameter than that of a cylindrical shank portion  21  of the punch  11  adjoining directly the head  20 . The lower end of the shank portion  21  has a transitional region  22  which is adjoined by a cylindrical stamping portion  23 . The shank portion  21  serves for supporting and guiding the punch  11  in the base body  5 . For this purpose the base body  5  has a throughgoing bore  24  which is arranged coaxially with the punch  11  and in which a guide sleeve  25  is arranged to cooperate with the punch  11  by axially guiding the shank portion  21  and thus the punch  11  with a minimum clearance. 
     The stamping portion  23  projects into a throughgoing opening  26  of a guiding and stripping element  27  which is seated in the bore  24  at the underside of the base body  5 . The punch  11  is in a retracted position A if the stamping portion  23  does not project from the opening  26 . For performing a stamping operation, the punch  11 , as shown for the punch  10  in FIG. 4, is axially displaced so that the stamping portion  23  moves out of the throughgoing opening  26  and, after traversing the clearance  6 , penetrates into a corresponding bore provided in the table  2 , whereby the punch  10  assumes an advanced position B (stamping position). 
     The coupling element  19  forming part of the coupling device  18  and carried by the plunger  16  has a socket  28  for receiving the cylindrical head  20  formed on or soldered to the shank portion  21  of the punch  11 . The socket  28  is open transversely to the punch  11 , that is, in a lateral direction X. Further, relative to the longitudinal direction of the punch  11  which coincides with its direction of motion Y, the socket  28  is bordered by a planar face  29  and a planar supporting face  30  which is parallel to the face  29 . The distance between the two faces  29  and  30  is only slightly larger than the axial length of the punch head  20 , whereby the latter is received with a minimal clearance in the socket  28 . 
     That portion of the coupling element  19  which reaches underneath the punch head  20  and on which the supporting face  30  is formed, is of forked construction, that is, it is provided, in the X direction, with a laterally-oriented opening  31  through which the shank portion  21  of the punch  11  may extend. The width of the opening  31  is less than the diameter of the punch head  20  so that the latter may not slip through the opening  31 . 
     To facilitate an introduction of the punch head  20  into the socket  28 , its faces  29  and  30  are provided with a respective lead-in chamfer at their end oriented away from the head  20  as viewed in the transverse direction X. 
     As it may also be observed in FIG. 4, the coupling element  19  is provided with a chamfered surface  32  at its end oriented away from the driving device  14 . The chamfered surface  32  serves as a positioning face which, in cooperation with a stationary edge  33  provided on the base body  5 , constitutes a positioning device for axially guiding the coupling element  19  into an upper position in which the punch  11  is in its retracted position A. The edge  33  acts as a counter support for the inclined (chamfered) surface  32 . Thus the cooperation between the two components  32  and  33  result in a camming action causing the coupling element  19  to move axially together with the punch  11 . 
     All the punches (of which only punches  10  and  11  are described and shown in FIGS.  2  and  4 ), are of identical construction. The guide sleeves  25  for guiding and supporting the punches, the guiding and stripping devices  27 , the coupling devices  18  and the driving devices (of which only the driving device  14  is shown in FIGS. 2 and 4) are likewise of identical structure, so that the foregoing description of the punch  11  and the components cooperating therewith apply equally to all other punches and the components as well as elements cooperating therewith. The punches and the driving devices may be arranged in groups as shown in FIG.  3 . The entire driving unit  12  composed of all the driving devices is supported such that it may be shifted in the X direction so that all coupling elements  19  may be moved into and out of engagement with the respective punch heads  20 . All the punches are preferably moved back into their retracted position A and maintained there when they are situated in that position. In particular, an unintentional shifting of the punches into their stamping position B has to be prevented in case the driving unit is disconnected from the punches. 
     For preventing such an unintentional shift of the punches, a movable head plate  34  is provided as shown in FIG.  4 . The movable head plate is mounted on a slide face  35  of the base body  5  to be shiftable in the X direction. On its upper face  36  the head plate  34  has for each punch a respective supporting region  37  which lies in a common plane with the supporting face  30  of the socket  28  of the coupling elements  19  when the latter are in a position which defines the retracted position A of the punches. The head plate  34  has for each punch an aperture  38  through which the respective coupling element  19  may pass and which adjoins the supporting region  37 . 
     On its side oriented towards the coupling element  19 , the supporting region  37  changes into a lead-in chamfer. At the edge of the aperture  38  an enlargement (bay)  38   a  is provided which is adapted to receive the shank portion  21  of the respective punch when the head plate  34  is shifted underneath the respective punch head  20 . The bay  38   a  faces the open end of the opening  31  of the coupling element  19  and is disposed essentially as a linear continuation thereof. For receiving the punch heads  20 , the head plate  34  is shiftable in the X direction and the length of the displacement path of the head plate  34  is so dimensioned that the punch heads  20  are transferred from the coupling elements  19  to the head plate  34  when the driving unit  12 , together with the head plate  34 , is shifted in the X direction for disconnecting the driving unit  12  from the punches. The head plate  34  is preferably connected with an arresting device which allows a displacement thereof only together with the driving unit  12 . Therefore, when the driving unit  12  is removed, the head plate  34  is immobilized. 
     The thickness of the head plate  34  preferably equals the thickness of that part of the coupling element  19  which extends underneath the respective punch head  20 . Such a thickness is the distance between the supporting face  30  of the socket  28  and that end face of the forked part of the coupling element  19  which lies on the opposite side from the supporting face  30 . Such an arrangement ensures that the supporting face  30  and the supporting surface region  37  of the head plate  34  lie in a common plane when the driving unit  12  is disconnected from the punches (such as the punches  10  and  11 ) by a lateral displacement of the driving unit  12  from the punches. During this occurrence the coupling elements  19  arrive in engagement with that region of the slide face  35  which immediately adjoins the respective edge  33  of the base body  5 , thus fixing the position of the coupling elements  19 . 
     In the description which follows, the punch replacement in the above-described stamping apparatus  1  will be set forth. 
     It is initially assumed that the stamping device  1  is in a state illustrated in FIGS. 4 and 6. All driving devices are connected with the respective associated punches. The punch heads  20  are situated completely in the respective sockets  28  of the coupling elements  19 . 
     It is now assumed that a punch replacement is to be performed. 
     As illustrated in FIG. 5 a  for the punch  11 , for a punch replacement the driving unit  12  with the associated coupling element  19  and the head plate  34  are displaced in such a manner that the punch head  20  begins to laterally move out of the socket  28 . In case the coupling element  19  is not in the position which corresponds to the retracted position A, the chamfered face  32  of the coupling element  19  runs up on the edge  33  of the base body  5 . Upon further displacement of the coupling element  19  in the X direction as seen, for example, in FIG. 5 b,  the coupling element  19  is axially pressed progressively toward the driving device until the punch  11  arrives in its retracted position A. During this occurrence the punch head  20  slides out of the socket  28 . Because of the small distance between the free ends of that part of the coupling element  19  which reaches underneath the head  20  and the adjoining edge of the aperture  38  which surrounds the coupling element  19 , the punch head  20  glides on the supporting surface region  37  before it entirely leaves the coupling element  19 . The distance between the edge of the aperture  38  and the end of the supporting face  30  is less than the diameter of the punch head  20 . When the coupling element  19  has entirely released the punch head  20 , the head plate  34  is shifted underneath the punch head  20  so that the shank portion  21  of the punch  11  enters the bay  38   a.  Such a position is shown in the side view of FIG. 5 c  and in the top plan view of FIG.  7 . The heads  20  of all punches are now carried by the head plate  34 . The driving.devices may be removed individually or in groups to thus gain access to the punches which may be replaced individually or in groups. 
     During the re-connection of the driving devices which takes place in a reverse order, all coupling elements  19  find the punch heads  20  in the correct position. The punch heads  20  are situated immediately next to the respective socket  28  without a height offset. A re-connection may be carried out with ease and without exposing the punch heads  20  to lateral forces. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.