Abstract:
A punch assembly for a turret punch press having a two piece reciprocally movable punch member that has a punch point insert removably attached to a punch driver that allows replacement of the punch point insert without the need to extract the punch member from its punch guide. A locking assembly having four vertical guideways containing slider strips for coupling the punch point insert to the punch driver ensures precision registration of the punch point insert with its driver.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     This invention relates generally to high speed metal punching equipment suited for installation in a turret-style punch press and more particularly to the design of a punch assembly used in such equipment that allows for quick removal of a worn punch insert from the punch guide for refurbishment and return or replacement. 
     II. Discussion of the Prior Art 
     To provide increased mean-time-to-repair of punch assemblies used in high-speed CNC controlled turret punch presses, it has proved expedient to employ a high-grade high speed steel insert such as American National Standards Institute M2 steel punch point insert affixed to the end of a lower cost steel punch driver to reduce cost of the punch press assembly. Notwithstanding the use of such a high-grade and relatively expensive punch point insert, after a period of use in punching holes through sheet steel and other metals, it becomes necessary to replace the punch point insert with a new or resharpened one. To reduce the downtime of the turret punch press for such punch point insert replacement, it is desirable that an operator be able to perform this task in a minimum amount of time and most preferably without the need for special hand tools. 
     In prior art punch assemblies having a two-piece driver/insert combination, it has generally been necessary to first remove the punch driver and insert from the upper end of the punch guide and subsequently remove the punch insert from the punch driver so that the punch point insert can be replaced with a new or refurbished unit. The present invention makes possible reduced manufacturing costs, such as machining expenses e.g. through the use of stamped components while at the same time simplifying punch point replacement by providing a way to releasably clamp the stripper member to the end of the punch guide and the punch point insert to the punch driver. The clamping mechanism employed is most preferably actuated by hand and in most cases without the need for any special tools or without the need to remove the punch driver and insert from the punch guide. 
     SUMMARY OF THE INVENTION 
     The present invention provides a punch assembly for a turret punch press comprising an outer, generally cylindrical punch guide having a cylindrical bore extending longitudinally therethrough from an upper end to a lower end. Contained within the bore of the guide or housing is a punch driver that is reciprocally movable within the bore. Releasably affixed to the lower end of the punch driver, preferably by one or more flexible stamping elements, is a punch insert having a punch point of a predetermined shape at a lower end thereof. 
     Affixed to the upper end of the punch driver is a canister assembly which includes a cylindrical, tubular housing containing a compression spring for normally biasing the punch driver to a retracted disposition within the bore. 
     Formed inward from a peripheral surface of the generally cylindrical punch driver and extending longitudinally are a plurality of guideways in which are fitted a corresponding plurality of locking sliders which can be stampings shaped to engage the punch insert and lock same to the punch driver when the locking sliders are in a first disposition within the guideways and to disengage from the punch insert when in a second disposition within the guideways. Cooperating with the plurality of locking sliders is a lock collar that is concentrically disposed on the punch driver and rotatable through a predetermined arc between a locked disposition and an unlocked disposition relative to the locking sliders. 
     The stripper member for the punch assembly, which itself can be a metal stamping of substantially uniform thickness throughout, is releasably clamped to the punch guide at a lower end thereof most preferably by leaf spring elements, and it includes an aperture conforming in shape to the punch point of the punch insert allowing the punch point to extend through the aperture in the stripper member upon application of a force to the canister assembly that exceeds the return force offered by the compression spring. The clamping structure holding the stripper member to the bottom of the punch press guide is also manually actuatable without the need for any special tools to unclamp and reclamp the stripper member from and onto the punch guide. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts. 
         FIG. 1  is an isometric view of a preferred embodiment of a punch assembly from a high speed turret punch constructed in accordance with the present invention; 
         FIG. 2  is an isometric view as in  FIG. 1  but with the outer punch guide removed; 
         FIG. 3  is an exploded perspective view showing the manner of attachment of the punch canister to the punch driver; 
         FIG. 4  is a perspective view shown with the canister cover and return spring removed to better illustrate the mode of attachment of the canister assembly with a punch driver. 
         FIG. 5  is a detailed perspective view of the structure releasably securing the punch insert to the punch driver; 
         FIG. 5A  is a horizontal cross-section taken on line  5 A- 5 A of  FIG. 5 ; 
         FIG. 6  is a view like that of  FIG. 5 , but with the lock collar, retaining ring and centering collar removed to show underlying parts; 
         FIG. 6A  is a rear perspective view of a vertical slider strip component; 
         FIGS. 7A-7D , respectively, show a perspective view, a side view, a top view and a bottom view of the punch insert with  FIG. 7C  also showing the position of alignment strap  48 ; 
         FIG. 8  is a cross sectional view of the embodiment of  FIG. 1  taken along the XY plane; 
         FIG. 9  is a cross sectional view of the embodiment of  FIG. 1  taken along the YZ plane; 
         FIG. 10  is an enlarged detail view of the lower end of  FIG. 9 ; 
         FIG. 11  is a detailed view showing the placement of the cone collar; and 
         FIG. 12  is a perspective view of the cone collar component. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This description of the preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. In the description, relative terms such as “lower”, “upper”, “horizontal”, “vertical”, “above”, “below”, “up”, “down”, “top” and “bottom” as well as derivatives thereof (e.g., “horizontally”, “downwardly”, “upwardly”, etc.) should be construed to refer to the orientation as then described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “connected”, “connecting”, “attached”, “attaching”, “join” and “joining” are used interchangeably and refer to one structure or surface being secured to another structure or surface or integrally fabricated in one piece, unless expressively described otherwise. 
     As shown in  FIG. 1 , the punch assembly is indicated generally by numeral  10 . It comprises an outer, generally cylindrical punch guide  12  which, as shown in the cross-sectional views of  FIGS. 8-10 , includes a cylindrical bore  14  that extends longitudinally therethrough from the guide&#39;s upper end  16  toward, but short of its lower end  18 . A counter bore  19  of a slightly greater diameter than that of bore  14  extends inward from the lower end  18  as can be seen in  FIG. 9 . 
     Releasably secured to the lower end  18  of the punch guide  12  is a stripper member  20  in the form of a generally circular plate which can be a metal stamping of substantially uniform thickness throughout that requires minimal machining and has a central aperture  22  conforming in shape to that of a punch point  24 , as can be best seen in the enlarged cross-sectional view of  FIG. 10 . 
     As seen in  FIG. 2 , the stripper member  20  has an annular sidewall provided with a plurality of regularly spaced upwardly extending tabs  26  formed around the periphery thereof that are adapted to fit into a corresponding pattern of recesses formed in the bottom end  18  of the guide  12  and to be engaged by a pair of leaf spring retainer clips  28  which can be metal stampings that fit into recesses  30  that are machined into the sidewall of the guide  12 . Only one such recess is visible in the view of  FIG. 1 , the other being on a diametrically opposed location as depicted in the cross-sectional view of  FIG. 8 . The configuration of the leaf spring retainer clip is such that depression of a pad portion thereof, identified by numeral  32  in  FIG. 1 , further into the recess  30  will cause the lower end thereof that engages the tabs  26  to deflect radially outward so as to no longer engage the tabs and allows the stripper member  20  to be removed from the bottom end  18  of the punch guide  12 . 
     Referring again to the cross-sectional views of  FIGS. 8-10 , there is disposed within the longitudinal bore  14  and counter bore  19  of the punch guide a two-piece, reciprocally movable combination of a punch driver  34  in its cooperative relationship with the punch point insert  24 . The punch driver  34  is preferably formed from relatively low-cost steel while the punch point insert  24 , preferably fabricated from high grade steel such as powdered metal or tungsten carbide that is pressed, formed or machined into a desired shape. While a tungsten carbide insert increases the cost, because it is approximately three times stiffer than steel and is much denser than steel or titanium, it makes for a longer wearing tool that is highly abrasion resistant and capable of withstanding higher temperatures than standard high speed steel tools. It is also well recognized that tungsten carbide is capable of maintaining a sharp cutting edge in a way that is superior to other tools. 
     The shape configuration of the punch point insert can be discerned from the views of  FIGS. 7A-7D . Here, the punch point insert is illustrated as a rectangular edge and will produce a rectangular slug upon being made to descend through a sheet metal workpiece. Of course, other shapes are achievable by modifying the shape of the downwardly depending portion  38  of the punch point insert  24 . 
     In  FIGS. 7B and 7C , the punch point insert is shown to have a generally rectangular head portion  40 , but with radiused corners, and projecting upwardly therefrom is a somewhat diamond-shaped protuberance  42  that is designed to fit within a recess  44  formed in the bottom surface of the punch driver as best seen in the enlarged cross-sectional view of  FIG. 10 . If desired, the protuberance can be on the punch driver and the recess in the insert. To maintain a desired angular orientation between the punch point insert  24  and the punch driver  34 , a longitudinally extending groove  46  is formed inward from the peripheral surface of the punch driver as seen in  FIG. 3 , and fitted into this groove is a leaf spring alignment strap  48  having a notch  50  that is arranged to straddle the tapered protuberance  42  ( FIG. 7C ) and apply a centrally directed bending force for yieldably engaging punch point ramp surfaces  42   a  and  42   b  which are slanted relative to one another so as to maintain the desired exact rotative registration of the insert about a vertical axis with no clearance unlike an ordinary pin or key which require clearance. 
     With continued reference to the exploded view of  FIG. 3 , the punch driver  34  has opposed flat abutment surfaces  52  and  54  machined therein on which a canister assembly, indicated generally by numeral  56 , is adapted to be secured. With reference to  FIGS. 2-4 , the canister assembly is seen to comprise a cylindrical, tubular housing  58  having an inside diameter that is sized to fit over the outer diameter of a relatively stiff compression spring  60 . Fitted atop the cylindrical housing  58  is a punch head  62  that has a pair of spaced-apart, downwardly depending legs  64 ,  66  where the legs terminate in transversely extending feet  68  as shown. The canister assembly further includes a spring retainer plate  70  consisting of a circular plate having a central aperture  72 . Fitted through the aperture  72  is a pair of couplers  74  and  76  that are generally U-shaped, with the legs of the “U” extending upwardly as seen in  FIG. 4  and also having feet that are designed to engage the feet  68  on the legs  64  and  66  that are integrally formed with and project downward from the punch head  62 . The spring retainer plate  70  is designed to rest upon the upper end of the punch guide  12 , as seen in  FIG. 1 . Couplers  74  and  76  slide in and out radially in retainer plate  70  aperture to allow for assembly with punch head  62 . When so positioned, the flattened portions  52  and  54  of the punch driver  34  above the shoulder  78  fit between the couplers  74  and  76  thereby locking them radially outward to maintain engagement with punch head  62  feet  68 . A flathead cap screw  80  fits through an aperture in the punch head  62  and is screwed into a threaded bore  82  formed inward from the top surface of the punch driver  34 . 
     From what is described, it can be recognized that a mechanical or electro mechanical ram forming part of the turret punch imparts a downward force on the punch head  62 , it will drive the punch driver  34  downward through the aperture in the spring retainer plate  70  of the canister by a distance, D, shown in  FIG. 4  and which is sufficient to penetrate through a sheet metal workpiece positioned adjacent the stripper member  20 . When this driving force is removed, the return spring  60  acting between the spring retainer plate  70  and the punch head  62  will function to move the punch driver  34  in the upwards direction such that the punch point insert will no longer extend through the aperture  22  in the stripper member  20 . 
     Without limitation, the return spring  60  follows Hook&#39;s Law for springs. 
     Next to be described is the structure for releasably securing the punch point insert  24  to the punch point driver  34  and, in this regard, reference will be made primarily to  FIGS. 5 ,  6  and  8 - 10  of the drawings. 
     Referring now to the enlarged partial view of  FIG. 5  and cross-sectional view of  FIG. 5A , there are formed inward from the cylindrical surface of the punch driver  34  four guideways, as at  84 , milled or ground at 90° radial spacings thereabout. These four grooved guideways are adapted to receive four vertical slider strips which can be metal stampings that require little machining, two of which are visible in the view of  FIG. 6  and are identified by numerals  86 . The exposed surface thereof as seen in  FIG. 6  is slightly rounded so as to conform to the cylindrical profile of the punch driver  34  and includes a flat facing zone  88  that extends about half of the distance across the width dimension of the vertical slider strip and a raised zone  90  extending across the remaining half of the strip&#39;s width dimension. Formed in the raised zone  90  is a notched-out portion  92 .  FIG. 6A  is a rear perspective view of the vertical slider strip  86  and it is configured to exhibit a notched-out region  94  adapted to fit about the head portion  40  of the punch point insert  24  in the manner shown in  FIG. 6 . 
     Each of the slider strips  86  has associated with it a cylindrical pin as at  96 . The inner ends of these pins are adapted to contact either the flat portion  88  of the slider strip or the notched-out portion  92  thereof. As seen in  FIGS. 5 and 5A , the pins  96  fit into apertures formed radially through a toroidal lock collar  98  that is supported by an annular, C-shaped retaining ring  100  designed to reside in the annular groove  102  formed in the punch driver  34  as seen in  FIG. 6 . The retaining ring  100  prevents the lock collar  98  from moving longitudinally downward along the punch driver. 
     From the drawings of  FIGS. 5 ,  5 A and  6 , it can be appreciated that when the locking collar is rotated about a vertical axis, the pins  96  may be repositioned so as to either reside on the flat surface  88  or have its end disposed in the notched-out portion  92  of the vertical slider strip. With the pins  96  residing on the flat portion  88 , as the punch point insert  24  is manually pulled downward, the vertical slide strip is able to move with it to the point where the notched-out region  94  on the back surface of the strip  86  no longer locks to the insert and it can be pulled free of the punch point driver  34 . However, when the locking collar is rotated manually, e.g. through a port  99  in the guide  12  ( FIG. 1 ) so as to reside in the notched-out portion  92 , the vertical slider strip is unable to be displaced within its slot  84  and the notched-out portion  94  continues to lock the punch point insert  24  to the bottom surface of the driver  34 . 
     Hidden from view in  FIG. 5  by a centering collar  104 , but visible in the partial view of  FIG. 11 , is a cone collar  106  that is shown by itself in  FIG. 12 . As seen in  FIGS. 11 and 12 , the cone collar  106  is machined so as to have an upper ring portion  108  with four downwardly projecting and inwardly tapered teeth  110  and when assembled onto the punch driver  34  in surrounding relationship with respect to the four slider strips  86 , the teeth are seen to fall between adjacent ones of the strips  86  and rest upon the inside conical surface of the centering collar  104 . The cone collar  106  and the centering collar  104  work together to create a high precision centering feature. The centering collar  104  has a precision cylindrical fit with respect to the cone collar  106  and the cone collar itself has a precision cylindrical fit with the punch driver  34  which, in turn, has a precision cylindrical fit with the ID of the bore  14  of the punch guide  12 . In addition, the slide strips  86  are forced outward on the bottom end due to the ramping action caused by the sliders  86  notched-out portion  94  against angled ramps # 95  ( FIG. 10 ) on insert  24  as collar  98  is rotated such that pins  96  enter area  92  against ramping edge # 97  ( FIG. 6 ) on sliders  86  to securely hold punch insert and sliders in the up position. To provide extremely precise centering, the outward force of the ramps is further advantaged, by pressing outwardly against the centering collar  104 . The circular area on the perimeter of the centering collar not being pushed against by the sliders then react equally and opposite thus sway inwardly against the cone collar. This provides a precise centering mechanism not achievable with normal bore and shaft connections. 
     In that the stripper  20  is stamped with curled-up fingers  26  for positioning into the punch guide, it is designed such that the operator can remove the stripper before the punch insert is removed, thus obviating the need for the operator to pull the canister assembly  56  off the punch guide as required by known prior art designs just to change the punch insert. 
     This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.